Copyright #ERS Journals Ltd 2001 Eur Respir J 2001; 17: 733±746 European Respiratory Journal Printed in UK ± all rights reserved ISSN 0903-1936

Health effects of diesel exhaust emissions

A. Sydbom*, A. Blomberg#, S. Parnia#,}, N. Stenfors#, T. SandstroÈm#, S-E. DahleÂn*

Health effects of diesel exhaust emissions. A. Sydbom, A. Blomberg, S. Parnia, N. *Unit for Experimental Asthma & Stenfors, T. SandstroÈm, S-E. DahleÂn. #ERS Journals Ltd 2001. Allergy Research, The National Insti- ABSTRACT: Epidemiological studies have demonstrated an association between tute of Environmental Medicine, Kar- different levels of air pollution and various health outcomes including mortality, olinska Institutet, Stockholm, Sweden. #Dept of Respiratory Medicine and exacerbation of asthma, chronic bronchitis, respiratory tract infections, ischaemic heart Allergy, University Hospital, UmeaÊ, disease and stroke. Of the motor vehicle generated air pollutants, diesel exhaust Sweden. }Respiratory Cell andMole- particles account for a highly signi®cant percentage of the particles emitted in many cular Biology Research Division, towns and cities. This review is therefore focused on the health effects of diesel exhaust, Southampton General Hospital, Tre- and especially the particular matter components. mona Road, Southampton, UK. Acute effects of diesel exhaust exposure include irritation of the nose and eyes, lung function changes, respiratory changes, headache, fatigue and nausea. Chronic exposures Correspondence: S-E. DahleÂn, Unit for are associated with cough, sputum production and lung function decrements. In addition Experimental Asthma & Allergy Research, The National Institute of to symptoms, exposure studies in healthy humans have documented a number of Environmental Medicine, Karolinska profound in¯ammatory changes in the airways, notably, before changes in pulmonary Institutet, SE-171 77 Stockholm, function can be detected. It is likely that such effects may be even more detrimental in Sweden. asthmatics and other subjects with compromised pulmonary function. Fax: 46 8300619 There are also observations supporting the hypothesis that diesel exhaust is one important factor contributing to the allergy pandemic. For example, in many Keywords: Air pollution, allergy incid- experimental systems, diesel exhaust particles can be shown to act as adjuvants to ence, animal studies, asthma exacerba- allergen and hence increase the sensitization response. tion, diesel, human exposure Much of the research on adverse effects of diesel exhaust, both in vivo and in vitro, has Received: October 5 2000 however been conducted in animals. Questions remain concerning the relevance of Acceptedafter revision October 20 2000 exposure levels and whether ®ndings in such models can be extrapolated into humans. It is therefore imperative to further assess acute and chronic effects of diesel exhaust in The authors were supportedby the mechanistic studies with careful consideration of exposure levels. Whenever possible and Swedish Heart and Lung Foundation, ethically justi®ed, studies should be carried out in humans. The Medical Research Council =project Eur Respir J 2001; 17: 733±746. No 9071), the Swedish National Road Administration =VaÈgverket) andThe Foundation for Health Care and Allergy Research =VaÊrdal).

There is growing international concern regarding standthe relevance of associations foundin the the adverse health effects of air pollution. Pollution is epidemiological studies. This overview is based on a becoming an important public health problem and literature search including papers published up to the political issue, due to the rapid growth in world ®rst quarter of the year 2000. Much of the research on population andthe increasing world-widemigration the adverse effects of diesel exhaust, both in vivo and in from rural to urban areas [1]. Recent UnitedNations vitro, has been conducted in animals. Such experimental estimates have indicated that 47% of the global studies are reviewed critically and the ®ndings are population is living in urban areas. This urbanization comparedwith those in human studies. has brought with it an increasedneedfor transporta- tion andhence an increase in motor vehicle generated air pollutants. However, a large number of epidemio- Diesel emission logical studies from different parts of the world have consistently identi®ed an association between ambient Of the motor vehicle generatedair pollutants, diesel levels of air particles andvarious health outcomes, exhaust particles =DEPs) account for a highly signi®- including mortality, exacerbation of asthma, chronic cant percentage of the particles emittedin many towns bronchitis, respiratory tract infections, ischaemic heart andcities [3, 4]. Complete combustion of diesel fuel disease and stroke [2]. Indeed, the United Nations En- produces water and carbon dioxide, but use of diesel in vironment Programme has identi®ed particulate matter motor vehicles normally results in incomplete combus- pollution as the most serious air pollution problem tion andthe formation of various gases, liquidsand facedby many cities [3]. It is therefore important to solidparticles. Comparedwith petrol engines, diesel evaluate the health effects of motor vehicle generated engines produce far less carbon monoxide, but give rise pollutants in mechanistic studies, in order to under- to a greater amount of nitrogen oxides and aldehydes, 734 A. SYDBOM ET AL. which are particularly prone to cause irritation of the sensitizedindividuals in urban areas, patients with upper respiratory tract. Diesel engines also produce airway diseases such as asthma have been found more submicron soot particles that are believedto mediate adversely affected than the normal population to several of the observedadverse effects. It has been inhalation of air pollution components [17, 18] andin estimatedthat the particulate emission from diesel particular acidaerosols [19]. Various studies have engines per travelleddistance is over 10 times higher shown that overall lung deposition is increased in than the emission from petrol engines of equivalent patients with obstructedairways [20±22]. For example, power running on unleaded petrol, and over 100 times a 30% reduction in airway cross-sectional area results higher than that from petrol engines ®ttedwith catalytic in a deposition increase in the bifurcating airways of converters [5, 6]. w100% [2, 23]. There is also an interesting case-report The dose of particle deposited in the lung depends on of DEPs alone causing asthma [24]; three nonsmok- their concentration in the inhaledair andtheir size. ing railroadworkers, without any previous history of Particles with a diameter <5 mm [7, 8] reach the alveoli asthma, developed persistent asthma after acute expo- andare depositedthere, whereas particles larger than 5 sure to excessive levels of DE. This was registeredin a mm only reach the proximal airways andare eliminated situation where two locomotive units were coupled by mucociliary clearance. Previous human studies using together andthe crew riding in the secondlocomotive radioactive particles have demonstrated that 83% of unit were exposedfor 2±5 h to signi®cant levels of DE. particles with a mass median diameter of 2.5 mmare All three subjects developed asthma, which persisted deposited in the lung, whereas only 31% of particles of 1±3 yrs after exposure. Although the actual levels were 11.5 mm are deposited [9]. Recent electron microscopy never measured, it is likely that such excessive exposure studies suggest that over 80% of DEPs have a size ¡0.1 rarely occurs even in occupational situations. mm; DEPs consist of a carbonaceous core similar to carbon black, onto which an estimated18,000 different high-molecular-weight organic compounds are adsor- Experimental studies of diesel emissions bed[2]. Diesel exhaust =DE), in addition to DEPs, contains a complex mixture of gases such as carbon Human subjects monoxide =CO), nitric oxides =NO, NO2), sulphur dioxide =SO2), hydrocarbons, formaldehyde, transition Exposure challenge studies. Experimental human expo- metals andcarbon particles [10]. Regarding the health sure studies have mainly been carried out using expo- effects, recent focus has been on ultra®ne particles sure chamber set-ups with controlledDE challenges. =diameter <0.05±0.10 mm). They are highly reactive and It is critical to ensure that the methodis designedso are present in large numbers in the urban environment. as to maintain a certain relationship between the parti- They are able to penetrate the epithelium andvascular culate andgaseous components andto obtain particles walls andenter the bloodstream. It has been hypothe- of the same size andchemical properties throughout sizedthat ultra®ne particles account for the systemic the exposure series. A unique andcarefully validated effects of DEPs, such as increasedcarcinogenicity [11], system for exposures has been particularly useful [25, potentiation of autoimmune disorders [12], alterations 26]. The effects of such diesel exposures have been in bloodcoagulability andincreasedcardiovascular evaluatedin humans using symptom questionnaires, disorders [13, 14]. lung function measurements andbronchoscopy with biopsy sampling andairway lavage. Air pollution as a cause of increased In one study, healthy volunteers were exposed to DE, asthma and allergy? with a NO2 concentration of 1.5 parts per million =ppm). Bronchoalveolar lavage =BAL) 18 h after DE Parallel to the increase in air pollution, there has also exposure revealeda signi®cant decrease in the total been a rapidincrease in the global incidence of allergic number of metachromatic cells =mast cells) in the diseases such as asthma and rhinitis in the last two bronchial portion anda signi®cant increase in neu- decades, which cannot be attributed to genetic changes, trophils in the bronchoalveolar portion. An increase in andis assumedto be relatedto changes in environ- the CD4+/CD8+-ratio was foundin the bronchoalveo- mental factors [15]. Observations in Japan have sug- lar portion, along with a reduced phagocytosis rate by gestedthat children living close to roadswith heavy alveolar macrophages in vitro [26]. traf®c are more likely to develop allergies [15]. Recent In another study on healthy volunteers, symptoms epidemiological data support the theory that atopic andlung function responses to DE were assessed.All children may constitute a group of individuals that run the exposedsubjects reportedan unpleasant smell and a heightenedrisk of developing negative health effects eye irritation but there was no alteration in the lung following exposure to airborne particles [16]. The function tests measuredas forcedexpiratory volume in existence of such sensitive subgroups amongst the one second=FEV 1) [25]. Two other studies [21, 26], general population wouldseem to deserve particular investigatedwhether the use of a particle trap on the tail attention for risk assessment. This review has identi®ed pipe of an idling diesel engine would reduce the DE- several effects of DEPs on immunological or in¯am- induced effects on symptoms, lung function and airway matory systems that may potentially have particular in¯ammation, comparedto effects inducedby un®l- relevance for a role of chronic diesel exhaust exposure teredDE. Exposure to DE without a ®lter caused in the pandemic of allergic disease. increases in symptoms andairway resistance as well as Irrespective of whether or not vehicle generated airway in¯ammation with BAL neutrophilia. Macro- pollutants contribute to the increasednumbers of phage phagocytosis was reduced. The particle trap HEALTH EFFECTS OF DIESEL EXHAUST EMISSIONS 735 reduced the number of particles by 46% but there was of DE. In order to evaluate if exposure to a lower no signi®cant difference in symptoms, lung function or concentration =more similar to relevant exposure con- in BAL neutrophil numbers after DE with or without centrations in ambient air), wouldinduce a similar the trap [26]. Therefore, for these effects, the relative response, healthy andasthmatic subjects have been importance of DEPs andother components of DE has exposedto DE with a PM 10 concentration of 100 yet to be established. mg.m-3 for 2 h. Bronchoscopy with biopsy sampling, In a recent study [27], ®lters intended for use in the air bronchial wash andBAL was performed6 h after the intake into the passenger compartment of vehicles were endof the exposure. Data from this studyare forth- testedfor their ability to prevent DE effects. Thirty-two coming. healthy nonsmoking subjects were exposedfor 1 h in a Studies of inducedsputum have also been usedto specially designed exposure chamber, once to air and evaluate DE effects on the human airways [32]. Sixteen once to un®lteredDE andsubsequently to DE ®ltered healthy nonsmoking subjects were exposedto air and with four different air intake ®lters. The exposure level DE at a particle concentration of 300 mg.m-3 for 1 h. was 300 mg of particles with a 50% cut-off aerodynamic Sputum induction was performed 6 and 24 h after diameter of 10 mm per cubic metre =PM10 300 mg.m-3). each exposure. Six hours after exposure to DE, a sig- The study included measurements of lung function, ni®cant increase was foundin neutrophil percentage symptoms andnasal responses. It provedpossible to of total cells in sputum, together with an increase in the distinguish differences in ef®cacy between the ®lters, all concentration of IL-6 andmethyl-histamine, compared of which gave air quality superior to the un®ltered to control air exposures. exhaust. While no acute effects were seen on nasal In summary, these data con®rm that the acute lavage, rhinometry andlung function =measuredas mediator and cytokine responses, together with the FEV1 andFVC), there were major effects on symp- enhancedexpression of the vascular adhesion mole- toms. The use of a particle ®lter in combination with cules in the airway mucosa, may represent an early an active charcoal ®lter was demonstrated to give sig- stage in the in¯ammatory response following exposure ni®cantly better results than the other ®lters. to DE, andbe of importance in the development of the The effect of a high ambient concentration of DE DE induced airway in¯ammation. The results further =300 mg.m-3) on various airway parameters including suggest that the DE concentration is an important cells andsoluble components was assessed[28]. The factor to take into account when evaluating the time results showedan increase in neutrophils, mast cells, course of DEPs-induced airway in¯ammation. CD3+, CD4+ andCD8+ T-lymphocytes in the airway mucosa, along with upregulation of adhesion molecules Nasal challenge studies. DEPs have been shown to intracellular adhesion molecule =ICAM)-1 and vascular potentiate immunoglobulin-E =IgE) production in hu- cell adhesion molecule =VCAM)-1 in the vascular endo- man respiratory mucosal membranes. DIAZ-SANCHEZ thelium 6 h after exposure to DE. In addition, increased [33] performeda studyin which nasal DEP challenges numbers of cells expressing leukocyte function asso- at various doses were used to investigate the effect on ciatedantigen =LFA)-1 =the ligandfor ICAM-1) were localized immunoglobulin production. Four days found. This in¯ammatory response was an order of after challenge with 0.3 mg DEPs a signi®cant in- magnitude greater than the effects documented after crease in nasal IgE, but not in other immunoglobulin allergen challenge in atopic asthmatics [29, 30] indicat- classes, was detected. There was also an increase in ing a pronouncedsignal for in¯ammatory cell recruit- the number of IgE secreting cells in nasal lavage, but ment as a response to DE exposure. This upregulation no increase in immunoglobulin-A =IgA) secreting cells. of endothelial and leukocyte adhesion molecules pro- Human nasal provocation studies have shown that vides a mechanism for the in¯ux of in¯ammatory cells DEPs can act as an adjuvant to allergen. Nasal chal- into the airways. Furthermore, immunohistochemical lenge was performedwith DEPs =0.3 mg), the ragweed staining for cytokines has shown enhancedexpression allergen Amb a I, or both, in a group of ragweed- of interleukin =IL)-8 andgrowth relatedoncogene sensitive subjects [34]. Ragweedchallenge alone demon- =GRO)-a in the airway epithelium, which can also play stratedan increase in IgE andimmunoglobulin-G 4 a role in the recruitment of in¯ammatory cells after =IgG4) as well as ragweed-speci®c IgE in the lavage exposure to DE [31]. The increase in neutrophils in the ¯uid. However, after challenge with allergen and DEPs airway mucosa following exposure to DE was also there was a sixteen-foldincrease in ragweed-speci®c evident in the bronchial wash, whereas the increase in IgE. DEPs alone increasedtotal IgE, but in combina- the number of submucosal mast cells did not corre- tion with allergen there was an increase in antigen- spondto any changes in the number of metachromatic speci®c IgE andin expression of Th0 andTh2-type cells =mast cells) in the lavages. However, an elevated cytokines =IL-4, IL-5, IL-6, IL-10 andIL-13). It is concentration of methyl-histamine detected in the BAL currently believedthat such deviations of the immune after exposure to DE supports increaseddegranulation system may have a crucial role for the development of of mast cells [28]. In contrast to the pronounced an atopic response [35]. These studies suggest that in¯ammatory response detected in the airways, lung DEPs can enhance B-cell differentiation. By initiating function parameters were foundunaffectedfollowing andelevating IgE production, DEPs may theoretically exposure to DE [28]. Consequently, lung function play a role in the increasedprevalence of allergic measurements alone cannot be usedto excludeadverse disease. air-pollution-associatedairway responses. Nasal challenge with a combination of DEP and These pronouncedairway in¯ammatory responses allergen has been shown to induce larger ragweed- were detected at a fairly high =300 mg.m-3) concentration speci®c IgE andIgG 4 responses comparedwith DEP 736 A. SYDBOM ET AL. alone but with similar total IgE levels [36]. There was Exposure studies in rats. Long-term studies looking also a change in the cytokine pattern, favouring allergic at the effects of DE exposure in rats have demon- sensitization. The authors propose that synergism be- stratedincreasedaccumulation of particles andaggre- tween DEP andnatural allergens is a key feature in gates of particle laden macrophages in the alveoli increasing allergen induced respiratory allergic disease. andperibronchial interstitial tissues, as well as local There is also evidence of DEPs inducing IgE isotype in¯ammation, epithelial proliferation, ®brosis and switching. FUJIEDA et al. [37] exposedhuman volunteers, emphysematous lesions. by nasal challenge, to DEPs together with ragweed For example, rats were exposedto DE for 30 months allergen. There was a local increase in IgE production, [41] andexaminedat 6 month intervals by electron cytokine production and an even greater increase in microscopy. Changes consistent with anthracosis were mucosa-speci®c ragweedIgE production. The isotype seen after 6 months exposure at a concentration of switching occurredonly when DEPs andallergen ex- 1,000 mg.m-3. There were foci of diesel particle laden posure was combined. The ®ndings suggest that increa- alveolar macrophages. DEPs were foundin type 1 sing environmental DEPs with the same environmental epithelial cells andthere was also hypertrophy and loadof allergen couldbe a factor behindthe increasing proliferation of type 2 cells. An in®ltration of particle sensitization andprevalence of allergic asthma. laden macrophages, neutrophils, mast cells and plasma Healthy, nonsmoking human volunteers have been cells in the interstitium of the alveolar septa was also exposedto DEPs by intranasal instillation andcyto- seen. The most prominent changes, however, were focal kines in nasal lavage were estimatedafter 18 h by shortening of cilia andthe protrusion of nonciliated an indirect approach =messenger riboneucleic acids cells. mRNA) [38]. Before challenge, most subjects hadde- MOHR et al. [42] comparedthe effects of inhaled tectable mRNA levels of only a few cytokines =Inter- DE with those of coal oven gas mixedwith pyrolyzed feron IFN-c, IL-2 andIL-13), while after challenge pitch. Three groups of rats were exposedto clean with 0.3 mg DEPs, these three anda number of air, ®lteredDEPs or un®lteredDEPs =4,000 mg.m-3). additional cytokines =IL-4, IL-5, IL-6 and IL-10) were Another group was exposedto coal oven ¯ue gas seen in increasing levels. Increase in such nasal cytokine mixedwith pitch fumes pyrolyzedundernitrogen. expression after DEP exposure couldagain contribute Most of the DEP-exposedanimals haddeposits to enhancedlocal IgE production. consisting of large amounts of carbonaceous particles Taken together, these studies suggest that DEPs phagocytozedby alveolar macrophages andthis was have the ability to induce IgE responses directly by associatedwith severe chronic in¯ammation, alveolar acting on B-cells andindirectly by enhancing the septal thickening, bronchiolo-alveolar hyperplasia and opportunity for cytokine production. DEPs in combi- alveolar lipoproteinosis. Rats exposedto coal oven ¯ue nation with allergens are able to generate a Th2-type gas hadmuch less severe in¯ammatory changes. cytokine response andthus favour the production of Inastudyexposingratstoincreasingconcentrations allergen-speci®c IgE. It has therefore been proposed of DEPs =350±7,000 mg.m-3), for up to 24 months [43], that DEPs can enhance B-cell differentiation and, by a progressive increase in the lung burden of particles initiating andenhancing IgE production, they may be was seen at the higher DEP concentrations. Tracheal of importance in the increasedincidence of allergic mucociliary transport was not affected, but there was a airway diseases [34]. signi®cant prolongation of long-term pulmonary clea- rance half-times in the two groups that were exposed Animals to the highest concentrations of DEPs. DEPs cause dust overloading and impairs pulmonary Some general points must be raisedregarding animal clearance at high doses in both rat and man. There studies. Apart from the possibility that mechanisms appears to be a thresholdabove which particle reten- may be very different from those in man, studies using tion andin¯ammation occurs. It has been calculated, radioactive particles have also demonstrated that there mostly on the basis of evidence from animal studies, is a large difference in the dosimetry of the small that the thresholdis y500 mg.g-1 lung tissue [44]. airways of rodents compared to humans. Therefore, However, it is dif®cult to assess how this correlates to care must be taken when extrapolating animal data levels in the inhaledair, andthere may be important to humans. Certainly, for ozone at least, it has been interactions between the actual concentration andthe shown that in order to elicit the same response in duration of the exposure. After acute exposure to a high rodents as in humans, several times higher concentra- concentration of DEPs =5,700 mg.m-3 for 3 days) the tions are required [39]. In addition, in many studies on particles were foundto be eliminatedef®ciently [45]. animals, the doses of DE are much higher than those There was a rapidinitial increase in the elimination humans are exposedto in daily life. Measurements in followedby a decline in macrophage burden. A chronic the Scandinavian countries have shown that the average low dose =50 mg.m-3 of DEPs; exposure for 52 weeks) 24-h particulate matter concentration variedfrom 30± was also clearedrelatively ef®ciently. More than 80% 150 mg.m-3 total suspended particles =TSP). However, in of the inhaledDEPs hadbeen eliminated1 yr after the certain industrial areas, concentrations of up to 1,500 exposure. However, comparison showedthat animals mg.m-3 have been measured. In Stockholm for example, exposedto the higher concentrations clearedmore of 1-h mean values 300±500 mg.m-3 have been foundat the total lung burden than those exposed chronically to kerbsides and maximum levels of almost 600 mg.m-3 low concentrations. At the longer low concentration have been reachedin a tunnel in the centre of the city exposure, the macrophage burden was relatively greater [40]. andassociatedwith a steadydevelopment of lung HEALTH EFFECTS OF DIESEL EXHAUST EMISSIONS 737 maculae, suggesting that continuous low dose exposure exposed®rst in utero =by exposing the mother from may be more detrimental than acute high dose ex- conception andthroughout gestation) andthen from posure. birth up to 6 months of age. Another group, repre- Taking these experimental ®ndings into account, a senting an adult model, was exposed between the mathematical model for the prediction of lung burden ages of 6 and12 months. It was foundthat DEPs andalveolar clearance in rats has been constructed[46]. alteredthe airway ¯uidconstituents andtissue At low lung burdens, the alveolar clearance rate of collagen in both groups. Interestingly, in the adult diesel soot was calculated to be constant and due to group, there was a six-foldincrease in neutrophils as macrophage elimination via the mucociliary transport well as increasedcellularity in the lung-associated system, whereas at high lung burden, the alveolar lymph nodes, delayed clearance of particles and an in- clearance appears to be determined principally by the crease in lung weight. However, none of these chan- capacity for transport to the lymphatic system. It ges were seen in rats exposedduring development. In shouldbe recognizedhowever that the elimination of adult rats there was also a focal aggregation of soot- particles from central andperipheral airways may be laden alveolar macrophages, but only scattered indivi- vastly different and partly dependent upon the tidal dual macrophages were found in the young rats. The air¯ow during the exposure. Recent data in humans authors concluded that there was no evidence for suggest that elimination from the peripheral airways developing rats being more susceptible to the toxic may be considerably slowerthan previously thought [47]. effects of NO2 or DE; if anything, the data would indicate that developing rats may be less sensitive. Exposure studies in cats. A group of cats was exposedto DEPs for >2 yrs [48]. Their exposure was divided into Studies in animals with experimental lung dis- two periods. During the ®rst period, which lasted 61 ease. Epidemiological studies have indicated that weeks, 6,000 mg.m-3of DEPs was used. At this point, subjects with pre-existing lung disease may be more no changes in the lungs were evident. During the susceptible to episodic high levels of airborne pollu- following 62 weeks, a higher concentration of 12,000 tants than normal subjects [52]. This has been studied mg.m-3 DEPs was usedandafter the 2 yrs, a pattern in a rat model [53], in which pulmonary emphysema of restrictive lung disease had developed. was induced in rats by intratracheal instillation of the In another similar study, cats were exposed to DEPs proteolytic enzyme elastase, andmanifestedas enlar- andNO 2 for over 2 yrs. After 62 weeks, the concentra- gedalveoli, alveolar ducts andrupturedalveolar tion of DEPs hadincreasedfrom 6,340±11,700 mg.m-3 septa. These structural changes were not by them- andthe concentration of NO 2 from 2.68±4.37 ppm selves associatedwith in¯ammation or alterations of [49]. Morphological changes were seen, mainly in the bronchioles. The emphysematous rats anda group of proximal acinar regions of lungs, with peribronchial control rats were then exposedfor 24 months to DE . -3 ®brosis, bronchiolar metaplasia, increasednumbers of =3,500 mg m ), NO2 =9.5 ppm), or air as control. Diffe- lymphocytes, ®broblasts andinterstitial macrophages rent parameters were measuredsuch as lung burdenof containing DEPs. The study indicated a persistent diesel soot particles, respiratory function, BAL ¯uid ®brogenic effect on the proximal acinar region of the composition, clearance of radiolabelled particles, pul- lungs following long-term DE. monary immune response, lung collagen, excisedlung weight andvolume, andhistopathology. The hypo- Intratracheal exposure studies of diesel exhaust parti- thesis was that the effects of pre-existing emphysema cles in mice. In a study of in vivo toxicity of DEPs in andlong-term DE exposure on lung function and the ICR mouse strain [50], an acute intratracheal instil- morphology were additive. The results, however, sho- lation of DEPs =400±1,000 mg.mouse-1) was foundto wedthat rats with experimentally inducedemphy- cause severe lung injury andhigh mortality. The sema were no more susceptible to inhalation of NO2 cause of death was pulmonary oedema mediated by or DE than control rats. In fact, fewer soot particles endothelial cell damage. The toxicological effect and accumulatedin the emphysematous lungs [53, 54]. the increasedmortality were to a great extent pre- ventedby pretreatment with the oxygen radical sca- Intraspecies comparative studies. Morphological chan- venger superoxide dismutase =SOD), supporting the ges have also been examinedin a comparative studyof hypothesis that DEP toxicity is connectedto pro- Cynomolgus monkeys andrats. Both animal species -1 duction of the radical superoxide O2 leading to receivedfour different exposures for 24 months: DEPs endothelial cell damage. =2,000 mg.m-3), coal dust =2,000 mg.m-3), a combina- tion of DEPs andcoal dust =1,000 mg.m-3 +1,000 Studies of developing lung in the rat. Studies on humans mg.m-3) or ambient air [55]. It was foundthat mon- in different geographical areas have raised the con- keys retainedrelatively more particulate matter than cern that children and the elderly may be particularly rats. The sites of particle retention were the same for susceptible to the harmful effects of air pollution. In DEPs, coal dust and the DEPs/coal dust combina- support of this, there have also been studies indica- tion. Rats retainedmore material in the lumen of ting the possibility of impairedlung development in alveolar ducts and alveoli, whereas monkeys retained animals exposedto oxidant gases or inhaledtoxicants more in the interstitium. Rats showedsigni®cant early in life. In one study which aimed to investigate alveolar epithelial hyperplasia, in¯ammation andsep- . -3 this, rats were exposedto DE =3,500 mg m ), NO2 tal ®brosis. In contrast, such morphological changes =9.5 ppm), or to air as a control [51]. One group, were not seen in the monkeys. The results indicate which representeda developing lung model, was that particle retention patterns andtissue reactions in 738 A. SYDBOM ET AL. rats exposedto DEPs may not be predictive of the reac- in the airway corresponded to speci®c IgG1 production. tions in primates [56]; primates may retain more DEPs, In another study, the combination of sensitization to but may also be less sensitive to the harmful effects. allergen together with diesel exposure, led to enhanced in®ltration of eosinophils andneutrophils andalso an increment of goblet cells, together with enhanced Immunology and allergy airway resistance andIL-5 andIgG 1 production, but not IgE production. DE alone did not induce patho- In vivo studies logical changes [64]. Other studies carried out with higher doses of DEPs =300 mg) under similar conditions To study the effect of DEP on the accumulation of have demonstrated an increase in speci®c IgE [65]. particles in lung-associatedlymph nodesandthe effect Together with the aforementionedstudies, this suggests on antibody responses after immunization, rats and that this response may be dose and time dependent. In mice [57] were exposedto varying doses of DEPs =350± ICR mice exposedto DEPs by intratracheal instillation, 7,000 mg.m-3) for 24 months. Control andexposed an increase in epithelial eosinophils, lymphocytes and animals were immunized, by intratracheal instillation of goblet cells was seen, together with increasedproduc- sheep redbloodcells, after exposure at 6, 12, 18, and24 tion of IgG andIgE andthe proallergic cytokines IL-2, months. Pathological changes were maximal after 18± IL-4, IL-5 andgranulocyte macrophage colocny stimu- 24 months at 3,500 or 7,000 mg.m-3 exposure levels. lating factor =GM-CSF), but not interferon =IFN)-c Microscopic ®ndings were: increase in particle content [62]. The combination of DEPs andOA has also been of alveolar macrophages; concentration of macro- shown to increase the bronchoconstriction response to phages closer to terminal bronchioles; wall ®brosis; inhaledacetylcholine [66]. Furthermore, daily inhala- bronchial metaplasia; and, in some cases, squamous tion of DEPs may enhance the allergen response, metaplasia. There were cholesterol clefts andincreased possibly by increasedlocal expression of proin¯amma- numbers of interstitial neutrophils andintra-alveolar tory cytokines such as IL-5 andGM-CSF [67]. In one granular eosinophilic material with entrappedfree study, increased IgE production was also seen in particles. Lung-associatedlymph nodeswere blackened mice after intranasal administration of suspended par- andenlargeddue to clusters of DEPs. There was ticulate matter =SPM) together with OA at 3-week increasedcellularity in rats exposedto the highest dose. intervals for a periodof 21 weeks [68]. However, the levels of speci®c antibodies were not To study the effect of DEPs on allergen-induced signi®cantly changed. bronchial hyperresponsiveness, mice were sensitizedto DEPs showedan adjuvant activity on IgE produc- OA andthen exposedto DE =3,000 mg.m-3)[69].Three tion in mice. Mice injectedintraperitoneally with weeks after DEPs exposure, they were challengedwith ovalbumin =OA) mixedwith DEP showedhigher IgE OA. DE exposure, combinedwith antigen challenge, levels than mice immunizedwith OA alone. In addition, inducedairway hyperresponsiveness andairway in¯am- Japanese cedar pollen =JCPA) speci®c IgE production mation, including increased numbers of eosinophils and couldbe seen in mice immunizedwith JCPA mixedwith mast cells in the lung tissue. DEP exposure alone also DEPs, but not in animals immunizedwith JCPA alone increasedairway hyperresponsiveness, but there was no [58]. In another study [59], DEPs and carbon black were eosinophil in®ltration. In a similar set-up, diesel inha- instilledintranasally in mice andthe animals were then lations =3,000 mg.m-3) in combination with OA sen- exposedto JCPA. There was a signi®cant adjuvant sitization increasedthe number of goblet cells in lung effect of the particles on JCPA speci®c IgE andIgG tissue, causedincreasedrespiratory resistance and production. increasedimmune response measuredas speci®c IgE, In order to elucidate whether the carbon core of the IgG1 andIL-5 in the lung tissue [70]. DEPs or the adsorbed organic substance is responsible A rhinitis model in guinea pigs was used to study for the effect [60], mice were immunizedfour times with short-term effects of DE =3 h exposure at 1,000 and either OA, OA with DEPs or OA with carbon black 3,200 mg.m-3) [71]. Following diesel exposure alone, =carbon black). Speci®c IgE for OA was then analysed. there was no induction of sneezing, nasal secretion or Both DEPs andcarbon black showedan adjuvant congestion. However, DEPs augmentedthe sneezing activity for speci®c IgE production after intranasal andnasal secretion inducedby histamine, but hadno instillation, indicating that they were both responsible signi®cant effect on histamine-induced nasal conges- for the effect. There have also been other studies which tion, suggesting that acute exposure to high levels of have demonstrated this effect in mice [61]. DE may cause nasal mucosal hyperresponsiveness, but A difference in antibody response between acute and no overt symptoms of rhinitis. HIRUMA et al. [72] also chronic exposure to DEP was suggestedin a studyusing reportedeffects of DEPs on the nasal mucosa of guinea combinedintratracheal inoculations of DEPs and pigs consistent with the development of nasal hyper- antigen in mice. Increasedairway in¯ammation, and reactivity. It was foundthat diesel exposure ledto a antigen speci®c IgG1, were seen after 6 weeks [62], dose dependent increase in histamine-induced vascular whereas a longer exposure =9 weeks) was required permeability, an increasedeosinophilic in®ltration into before there was a detectable increase in antigen speci®c the epithelial layer andalso enhancednasal reactivity to IgE. histamine. When mice were injectedintratracheally with OA The mechanisms involvedin asthma andallergy alone or together with DEPs [63], there was no signi- development after DEPs exposure may include incre- ®cant adjuvant activity of IgE production by DEPs =50 asedpenetration of allergen across the respiratory mg). However, the degree of eosinophilic in¯ammation mucosa or direct modulation of the immunological HEALTH EFFECTS OF DIESEL EXHAUST EMISSIONS 739 response [73]. Particulate air pollution includes particles that exposure of nasal or bronchial epithelial cells to from diesel andgasoline engine exhaust andbiological DEP results in increasedsynthesis andrelease of materials such as plant debris and tyre debris e.g. latex, proin¯ammatory mediators, cytokines such as IL-6, IL- that may be allergens [74]. Some allergens, such as the 8 or GM-CSF, andadhesion molecules [80]. major grass pollen Lolium perenne -1 =Lol p1) allergen, In line with the observations during nasal challenge are also shown to speci®cally bindto DEPs. This might in vivo [36, 38], studies on isolated human B-lympho- be a possible mechanism for the triggering of asthma cytes have demonstrated enhanced IgE synthesis follo- attacks anda theoretical contributing factor to the wing exposure to DEPs [81]. In a study of puri®ed increase in asthma prevalence [75]. human B-cells stimulatedby IL-4, the ability of DEPs ORMSTAD et al. [76] have studied the allergen car- to induce IgE production could be mimicked by poly- rying effect of DEP. This was an in vitro study of aromatic hydrocarbons =PAH) extracted from DEPs. allergen adsorption to particles such as indoor-sus- However, DEP-PAH did not induce IgE production in pended particles matter =SPM) and DEPs. They unstimulatedB-cells, indicating that it only enhances reportedthat the cat allergen = Fel d1), dog allergen ongoing IgE production. Phenanthrene, a major poly- =Can f1) andbirch pollen allergen = Bet v1) couldall aromatic hydrocarbon and an important component of be foundon the surface of SPM, whereas house dust DEPs, has shown the same enhancing effect on IgE mite allergen =Der p1) was not. However, all four production in a human B cell line [82]. allergens were foundto be absorbedto DEPs. A The effect of DEP-PAH on the release andmRNA chemical characterization of the coating of Birch pollen expression of IL-8, monocyte chemotactic peptide-1 grains collectedduring pollen season in the north of =MCP-1) andRANTES =Regulatedon activation Stockholm has been published[77]. The greatest por- normal T cell expressedandsecreted)was investigated tion =80%) consistedof n-alkanes andn-alkenes, but by paripteral bloodmononuclear cells =PBMCs) methylketones, ethers, alcohols andamino alcohols obtainedfrom healthy subjects. The production of were also identi®ed. protein in supernatants was assessedby enzyme linked immunoabsorbent assay =ELISA), andmRNA produc- In vitro studies. Some in vitro studies have been tion by semiquantitative reverse transcriptase poly- performedon animal cells, but most of the work has merase chain reaction =RT-PCR). There was a dose been conducted on cells derived from humans. The dependent increase in the secretion of IL-8 and eosinophil is a major effector cell in allergic in¯am- RANTES in response to increasing concentrations of matory disorders. In one study, the effects of DEPs DEP-PAH =range 0.5±50 ng.mL-1). However, there andDEP extract on eosinophil adhesion, survival rate was a signi®cant dose dependent inhibition of MCP-1 anddegranulation were assessed[78]. Eosinophils, secretion. The expression of mRNA coding for IL-8, human mucosal microvascular endothelial cells RANTES andMCP-1 showedvariations that paral- =HMMECs) andhuman nasal epithelial cells lelled the production of the corresponding proteins. =HNECs) were preincubatedwith andwithout DEP These results suggestedthat DEP-PAH can modulate extract. Radiolabelledeosinophils were allowedto chemokine pathways at the transcriptional level [83]. adhere to monolayers of HMMECs and HNECs with Other studies have been performed using cultured the degree of reactivity being determined after wash- human bronchial epithelial cells =HBEC) exposedto ing, andthe numbers of adherent eosinophils were DEPs [84]. Exposure of these cells to DEP at 50 calculated. There was a signi®cant increase in the adhe- mg.mL-1, ®lteredDEPs solution or DEP at 100 mg.mL-1 siveness of eosinophils to HNECs, but not HMMECs. attenuatedthe ciliary beat frequency =CBF) dose DEP also induced eosinophil degranulation without dependently and increased the release of IL-8, GM- changing the eosinophil survival rate. These results CSF andsoluble ICAM-1 =s/CAM-1). The observa- wouldindicate that DEPs play a signi®cant role in tions support the hypothesis that DEPs exposure may the promotion of nasal hypersensitivity induced by leadto functional changes andthe release of pro- enhancedeosinophil in®ltration anddegranulation. in¯ammatory mediators with the potential to in¯uence The cytotoxicity of DEP-induced phagocytosis and the development of airway disease. Speci®cally, in®ltra- the resulting immune response were studied in human tion of neutrophils andother in¯ammatory cells would bronchial andnasal epithelial cell cultures [79]. DEPs be promotedby the observedchanges. exposure induced a time and dose-dependent mem- In another report, the effect of DEPs on the CBF, brane damage. Transmission electron microscopy andproduction of IL-8, GM-CSF, RANTES and showedthat DEPs underwent endocytosis by epithelial sICAM-1 by culturedhuman bronchial cells was com- cells andtranslocatedthrough the epithelial cell sheet. paredbetween nonatopic, nonasthmatic subjects and Flow cytometric measurements allowedestablishment atopic patients with mildasthma. Bronchial cells from of the time and dose dependency of this phagocytosis these two groups were exposedto 10±100 mg.mL-1 DEP andits lack of speci®city for different particles =DEPs, for 24 h. The baseline CBF was the same in both carbon black andlatex were tested).DEPs ledto a time- groups. There was a signi®cant attenuation in the CBF, dependent increase in IL-8, GM-CSF and IL-1 beta in response to increasing DEP levels in both groups, release. This in¯ammatory response occurredlater than with the largest changes at 100 mg.mL-1. The cell cul- phagocytosis andit appearedto dependon the types tures from asthmatics constitutively releasedsigni®c- of adsorbed compounds, as in this study carbon black antly greater amounts of IL-8, GM-CSF andsICAM-1 hadno effect on cytokine release. andwere the only cultures to release RANTES. In Airway epithelial cells play a prominent role in the response to 10 mg.mL-1 of DEP, there was a signi®cant pathogenesis of respiratory disease. Studies have shown increase in the release of IL-8, GM-CSF andsICAM-1 740 A. SYDBOM ET AL. in cells from asthmatics. However, exposure to doses of YANG et al. [90] studied the possible role of cyto- 50 and100 mg.mL-1 ledto a decrease in the release of kines in the toxic effect of DEPs on rat alveolar IL-8 andRANTES. In contrast, only these higher macrophages =AM). The macrophages were incubated concentrations of DEPs causeda signi®cant increase with DEPs in different concentrations as well as with in the release of IL-8 andGM-CSF in cells from methanol, washedDEPs or DEP methanol extracts. nonasthmatics. These results suggest that the bronchial High concentrations of DEPs andmethanol extracts epithelial cells of asthmatics are more sensitive than increasedIL-1 secretion by AM, while there was no cells from normal subjects to DEPs, andthat they are effect on TNF-a. DEPs inhibitedproduction of IL-1 also different with regard to the amounts of proin- andTNF- a stimulatedby endotoxin =lipopolysacchar- ¯ammatory mediators released [85]. ide). The results suggest that the pro-in¯ammatory The effect of DEPs has also been studied in three cytokine IL-1 may play a role in the pulmonary different in vitro systems of human airway epithelial response to DEP inhalation. The suppressive response cells: nasal polyps, bronchial cells obtainedat lung of AM pretreatedwith DEPs, to endotoxin stimulation tumour resection or at autopsy, andthe bronchial may be a factor contributing to the impairment of epithelial cell line BEAS-2B [86]. DEP =10±100 mg.mL-1) pulmonary defence systems after prolonged DEPs induced a dose- and time-dependent stimulation of IL-8 exposure. andGM-CSF production by all three kindsof epithelial In one study, the effect of DEPs on isolated tissues cells. Using double chamber plates, it was shown that andculturedcells from the respiratory tract of guinea the cells couldonly be stimulatedfrom the apical side. pigs was examined [91]. DEPs induced a dose depen- As a control, neither coal nor graphite showedany dent relaxation of tracheal smooth muscle and time stimulatory effect, whereas benzpyrene, a constituent of dependent cytotoxicity on tracheal smooth muscle cells DEPs, did. Thus it appears that human epithelial cell andlung ®broblasts. On the basis of pharmacological exposure to DEP might stimulate cytokine production, interventions, it was suggestedthat the cytotoxicity of with possible relevance for the allergic in¯ammation. DEPs may be mediated via generation of oxygen In another investigation, the effect of DEPs in doses radicals. DEPs have also been shown to produce 40±330 mg.mL-1 was recorded using the human bron- aggressive oxygen radicals in a cell-free in vitro system chial epithelial cell line, BEAS-2B [87]. DEP diameter in the presence of appropriate electron donors [92], ranged25±35 nm andthe particles were phagocytized which in part may explain the potential toxicity and by these cells. There was an increase in IL-6 andIL-8 mutagenicity of DEPs. production =11-fold and 4-fold, respectively). Exposure of these cells to tumour necrosis factor =TNF)-a also stimulateda strong increase in IL-6 andIL-8 produc- The role of endogenous nitric oxide tion. There was an additive effect on the production of IL-6 andIL-8 after TNF- a priming andsubsequent Nitric oxide =NO) is found in the exhaled air of exposure to DEPs, seen only at low doses of DEPs animals andhumans. Increasedlevels of NO in exhal- =10±70 mg.mL-1)andTNF-a =0.05±0.2 ng.mL-1). edair are associatedwith asthma andairway disease To elucidate the molecular mechanism of action of andNO has been observedto suppress Th1 cells DEPs, IL-8 gene expression was studied by northern leading to a Th2 type response that is associated with blot analysis, andrun-on transcription assay in human allergy [93]. The role of NO in asthma-like symptoms bronchial epithelial cells. Suspended DEPs =1±50 inducedby DEPs has been studiedin mice [94]. mg.mL-1) increasedthe steadystate levels of IL-8 Repeatedintratracheal instillation of DEPs in mice mRNA. Electrophoretic mobility shift assay =EMSA) induced a four-fold increase in macrophages, neutro- demonstrated that DEPs induced increased binding phils, eosinophils andlymphocytes in BAL ¯uid.DEPs to the speci®c motif of the nuclear transciption factor induced a two-fold increase of NO in exhaled air and kB=NF-kB), but not of transcription factor AP-1. NF- an increase in staining for the enzyme nitric oxide kB is known to stimulate the trancription of genes synthetase =NOS) in the airway epithelium. The in- coding for in¯ammatory molecules like TNF-a andIL- crease in respiratory resistance induced by the DEP 8. The luciferase reporter gene assay using wildtype instillation was suppressedby the NOS inhibitor NG- andmutatedNF- kB binding sequences showed that methyl-L-arginine =L-NMA). These ®ndings in mice DEP-induced NF-kB activation was involvedin IL-8 suggest that some effects of DEPs may be mediated by transcription. These results indicate that DEPs activate endogenous NO. In contrast, MUTO et al. [95] found NF-kB, which may act as an important mechanism for that DEP, like L-NMA, abolishedthe acetylcholine the increasedin¯ammatory cytokine release [88]. =Ach)-induced relaxation of aortic rings preconstricted The effects of DEP extract on the expression of with phenylephrine. NO release from aortic rings in histamine H1 receptor =H1R) mRNA andthe produc- response to Ach was inhibitedby DEPs =100 mg.mL-1, tion of IL-8 andGM-CSF in human nasal andmucosal 60 min). NO releasedby the bronchial epithelium in microvascular endothelial cells have also been investi- rabbit bronchial strips attenuatedthe bronchoconstric- gated. The change in expression of H1R mRNA was tion inducedby Ach andthis attenuation was abolished evaluatedby RT-PCR andsouthern blot analysis. The by 60 min preincubation with DEPs =100 mg.mL-1)or amount of IL-8 andGM-CSF was measuredby L-NMA. Their conclusion was that inhibition of NO ELISA. It was foundthat DEP ledto a signi®cant release by DEPs may be a part of the observed upregulation of the H1R gene expression as well as an respiratory effects of DEPs. Clearly further studies are increase in histamine-inducedIL-8 andGM-CSF requiredto establish the signi®cance of these opposite production [89]. results in two different animal models. HEALTH EFFECTS OF DIESEL EXHAUST EMISSIONS 741

Cardiovascular effects toxicity contributes to the lung oedema that is known to be one prominent cause of death in DEPs exposed Epidemiological studies have associated increased animals. It appears unlikely, however, that inhalation mortality in cardiovascular diseases with episodes of of DEPs by humans couldproduce the concentrations heavy air pollution [96, 97]. SEATON et al. [14] suggested employedin these particular experiments. The experi- that the ultra ®ne particles wouldinduce airway in- ments indicating effects of DE on the NO system and ¯ammation in susceptible individuals, release of media- oxygen radical formation have been discussed above. tors andan increase in bloodcoagulability. A literature All in all, the possible mechanisms involvedin the survey has provided some support for the hypothesis allegedrole of DE on various cardiovascular events of possible association between occupational exposure remain unknown. to dust and increased risk of ischaemic heart disease [98±100]. For example, coal miners showedmanifesta- tions of pneumoconiosis andincreasedincidence of Discussion ischaemic heart disease. There were also increased levels of ®brinogen in the bloodof coal miners with pneu- The epidemiological support for particle effects on moconiosis, and®brinogen is a risk factor for ischaemic asthma andrespiratory health is very evident. The heart disease. A hypothesis has been put forward that experimental studies of DEPs include in vitro models, long-term inhalation of particles retainedin the lung animal in vivo models, studies of healthy humans and induces an in¯ammation which is accompanied by an occasional observations in patients. Respiratory, im- increase of plasma ®brinogen, leading to elevated risk munological andsystemic effects have indeedbeen for bloodclotting andischaemic heart disease [100]. documented. The main effects on the respiratory system In a recent study combining measurement of air are summarizedin table 1. pollution exposure with personal meters andof hae- The acute effects include irritation of the nose and matological markers in collectedblood,it was found eye, lung function changes, airway in¯ammation, that there was a relationship between exposure to headache, fatigue and nausea. In addition to symp- particulate matter, measuredas PM 10, andchanges in toms, exposure studies in healthy humans have docu- haemoglobin concentration, haematocrit =packedcell menteda number of profoundin¯ammatory changes volume) andredbloodcell count [101]. There were in the airways, notably, before changes in pulmonary concomitant decreases in platelet number and ®brino- function can be detected. It is likely that such effects gen levels. By also measuring plasma albumin, the may be even more detrimental in asthmatics and other authors concluded that the decrease in haemoglobin subjects with compromisedpulmonary function. was causedby increasedperipheral sequestration of red Chronic exposure to DE induces cough, sputum bloodcells, rather that generalizedhaemodilution. The production and lung function decrements. Pathological study supports particulate air pollution, or a very andhistological ®ndings in the lung after DEPs closely associatedconfounding factor, having the exposure have mostly been studied in rats and include potential to affect important cardiovascular phenom- increases in lung weight, increasednumbers of par- ena. Studies of acute episodes of increased air pollution ticles in the lung andan increasedburdenof soot, have documented effects on plasma viscosity [102], and associatedwith alveolar in®ltration of macrophages, acute exposure to DE has effects on in¯ammatory cells macrophage aggregation, chronic in¯ammatory res- in the blood[28]. In a time series panel studyof par- ponses, proliferation andhyperplasia of alveolar epi- ticulate air pollution, there was an association between thelium andtype 2 cells, thickening of alveolar septa particle levels andpulse, but not with oxygen satura- andwall ®brosis. tion [103]. There was a time lag between exposure and Due to the complexity of DE, it is likely that some the effect on pulse that the authors interpretedas an effects are causedby the gaseous components whereas indication of lung in¯ammation with consequent other effects relate to the particle content. The sug- release of mediators and cytokines being the primary gestedmechanisms of detrimental actions of parti- event. Some recent studies in the elderly [104±106] have culate matter include oxidative stress and actions of impliedan association between increasedparticulate particulate matter content such as metals, hydrocar- matter =PM2.5) in ambient air pollution anddecreased bons, acids and carbon core. The ultra®ne particles heart rate variability, suggesting a possible contribution are currently suspectedof being the most aggressive to increasedcardiovascular mortality anddecreased particulate component of DE. Comparison of DEPs autonomic control. andcarbon black in animal inhalation studies show The studies of the direct in¯uence of DE on various that both induce a reduction in lung function and cardiovascular responses, however, remain very few. accumulation of macrophages, suggesting that the Pretreatment of human serum with DEP extracts =500± toxic effect of DEPs is, in part, coupledto the carbon 2,500 mg.mL-1) gave a dose-dependent reduction in core. However, much more work is needed to pinpoint complement haemolytic activity of up to 20% [107], and the relative role of different components of DE, as well activation of the alternative complement pathway. A as the interaction between the different components, direct toxic action of DEPs was examined in a model andother environmental factors. of isolatedatria from guinea pigs [108]. DEPs in lower There are several observations that support the hy- doses =10±500 mg.mL-1) induced a transient but dose- pothesis that DE is one important factor contributing dependent increase in contractile force. DEPs in doses to the allergy pandemic. For example, DEPs introduced >500 mg.mL-1, only decreased contractile force and by different routes, intraperitoneally, intranasally or induced cardiac arrest. It was concluded that cardiac intratracheally, may act as adjuvant to allergen and 742 A. SYDBOM ET AL.

Table 1. ± Some effects of diesel emission with relevance to the respiratory system System Effects Reference

Human volunteers F airway resistance andin¯ammation [21, 26] Exposure chamber F neutrophils in BAL andsputum [26, 28, 31, 32] challenge E mast cells in BAL, F mast cells in airway mucosa [26, 28] F in ICAM-1, VCAM-1 [28, 29, 30] F in IL-8 in airway epithelium [31] F in IL-6 in sputum [32] Humans F in local IgE [33, 37] Nasal provocations F in IgE secreting cells [33] FF spec IgE =DEP + antigen) A allergic sensitization [36, 37] F in IL-4, IL-5, IL-6, IL-10 Rat Increasedlung weight, chronic in¯ammation with increased [41±43, 51, 55, 57] Chronic exposure number of in¯ammatory cells, chronic degenerative changes Bronchiolo-alveolar hyperplasia [42, 55, 57] Prolongation of clearance [43, 51] Cat Pattern of restrictive lung disease, in¯ammatory reactions, [48, 49] Chronic exposure bronchiolo metaplasia Mice Severe lung injury, high mortality, cause of death: pulmonary [50] Acute high exposure oedema =intratracheally) Mice Airway in¯ammation with increasednumber of in¯ammatory [62, 63, 65, 94] Chronic exposure cells F goblet cells [65, 70] F respiratory resistance [70] Mice F IgE levels [58, 59] DEP + allergen F spec IgE levels [58, 59, 65, 70] Exposure F spec IgG1 levels [62, 63, 70] F IL-2, IL-4, IL-5 [62, 70] F GM-CSF [62] Human nasal epithelial cells F adhesion and degranulation of eosinophils [78] =HNEC) F IL-1b, IL-6, IL-8 [79, 80] In vitro exposure F GM-CSF [79, 80] F adhesion molecules [80] Human bronchial cell culture F IL-1b, IL-6, IL-8 [79, 80] In vitro exposure F GM-CSF [79, 80, 85] F adhesion molecules [80, 85] Human bronchial epethelial cell F IL-6, IL-8 [84, 87] =HBEC) F IL-8 mRNA [88] In vitro exposure F GM-CSF [84] F sICAM-1 [84] Human B-cell line F IgE production [82] In vitro exposure Human peripheral blood F IL-8 [83] mononuclear cells =PBMC) F RANTES [83] In vitro exposure E MCP-1 secretion [83] Rat alveolar macrophages F IL-1 [90] In vitro exposure E IL-1, TNF-a - stimulatedby endotoxin [90] BAL: bronchoalveolar lavage; DEP: diesel exhaust particles; GM-CSF: granulocyte macrophage colony stimulating factor; ICAM-1: intracellular cell adhesion molecule; IL: interleukin; MCP-1: monocyte chemotactic peptide 1; MRNA: messenger ribonucleic acid; RANTES: regulated on activation normal T-cell expressed and secreted; ICAM-1: soluble intracelluler adhesion molecule; TNF-a: tumour necrosis factor alpha; VCAM-1: vascular cell adhesion molecule-1; F: increase; E: decrease. hence increase the sensitization response. This has been trigger asthma attacks andDEP-binding may facilitate observedboth in human andanimal studies. IgE penetration of allergen through the airway mucosa. production in response to allergen has been shown to be It is often believedthat atopic children are a spe- enhancedby DE. DEPs affect human B-cells andmay cially sensitive group, but the few animal studies that enhance IgE production by several mechanisms. In have been carriedout have not supportedthe hypoth- addition, DEPs show effects on the allergic response esis that the developing lung [51] or lungs with induced that involve in¯ammatory cells in the respiratory mu- emphysema [53] are more prone to lung injury due to cosa, such as T cells, mast cells andepithelial cells, and particulate matter. On the basis of publisheddata, there also on local production of various pro-in¯ammatory is no single mechanism of action, that can explain the cytokines. Another possible mechanism of action of various public health effects of particulate air pollution DEPs on allergic responses is to act as a carrier of shown in epidemiological studies. One major short- pollen allergens, allowing enhanceddeposition of pol- coming of many experimental studies relates to their len in the lower airways. Allergens boundto DEPs may inability to establish whether or not the exposures HEALTH EFFECTS OF DIESEL EXHAUST EMISSIONS 743 usedfor the studies are relevant to the backgroundor 13. Schwartz J, Dockery DW, Neas LM. Is daily mortality peak exposures which may occur in real life, acutely associatedspeci®cally with ®ne particles? J Air Waste or chronically. In addition, theoretically, both acute Manag Assoc 1996; 46: 927±939. exposure to high levels of diesel exhaust particles and 14. Seaton A, MacNee W, Donaldson K, Godden D. chronic exposure to low levels may impair respiratory Particulate air pollution andacute health effects . functions andhave various other detrimental effects, Lancet 1995; 345: 176±178. but the mechanisms may be different. Such a situ- 15. D9Amato G, Liccardi G, D9Amato M. Environment ation exists in the case of a classical trigger of asthma and development of respiratory allergy: I. Outdoors. such as allergen: acute exposure to high allergen doses Monaldi Arch Chest Dis 1998; 49: 406±411. produces effects that differ from those caused by 16. Boezen HM, van der Zee SC, Postma DS, et al. Effect repeatedlow dose exposure [109±111]. As reviewed, of ambient air pollution on upper andlower respi- ratory symptoms andpeak expiratory ¯ow in children . some of the studies of chronic exposure of rats to diesel Lancet 1999; 353: 874±878. exhaust particles =vide supra) also highlight such dif- 17. Hobbs CH, Mauderly JL. Risk assessment for diesel ferences between high andlow dose exposures. It is exhaust andozone: The datafrom people andanimals . therefore imperative to further assess acute andchronic Clin Toxicol 1991; 29: 375±384. effects of diesel exhaust in mechanistic studies with 18. Rusznak C, Devalia JL, Davies RJ. The impact of careful consideration of exposure levels. Whenever pollution on allergic disease. Allergy 1994; 49: 21±27. possible andethically justi®ed,such studies shouldbe 19. US Environmental Protection Agency. Toxicological performedin humans, but animal andcell culture studies of particulate matter. 1996. Triangle Park, NC, models that are suf®ciently predictive and sensitive, USA. US Environmental Protection Agency. Air may also provide important information on these Quality criteria for particulate matter; vol II, chapter matters. 11, pp. 1±231. 20. Morgan WKC, Reger RB, Tucker DM. Health effects of diesel emissions. Ann Occup Hyg 1997; 41: 643±658. References 21. Rudell B, Ledin M-C, HammarstroÈm U, Stjernberg N, LundbaÈck B, SandstroÈm T. Effects on symptoms and 1. Salvi S, Frew A, Holgate S. Is diesel exhaust a cause lung function in humans experimentally exposedto for increasing allergies? Clin Exp Allergy 1999; 29: 4±8. diesel exhaust. Occup Environment Med 1996; 53: 658± 2. Salvi S, Holgate S. Mechanisms of particulate matter 662. toxicity. Clin Exp Allergy 1999; 29: 1187±1194. 22. Scheepers PTJ, Bos RP. Combustion of diesel fuel 3. UnitedNations Environment Program. Air pollution from a toxicological perspective. II. Toxicity. Int Arch in the worlds megacities. Environment 1994; 36: 5±37. Occup Environ Health 1992; 64: 163±177. 4. Department of Health. Particle dosimetry. Nonbio- 23. Kim CS, Hu SC. Regional deposition of inhaled logical particles andhealth. COMPEAP =Committee particles in human lungs: comparison between men on the Medical Effects of Air Pollutants). 1995; 29±42. andwomen . Am J Physiol 1998; 84: 1834±1844. 5. Nauss KM, Busby WF Jr, Cohen AJ, et al. Critical 24. Wade JF, Newman LS. Diesel asthma. Reactive issues in assessing the carcinogenicity of diesel exhaust: airways disease following overexposure to locomo- A synthesis of current knowledge. In: Health Effects tive exhaust. JOM 1993; 35: 149±154. InstituteÂs Diesel working group, eds. Diesel exhaust ± 25. Rudell B, SandstroÈm T, HammarstroÈm U, Ledin M-L, A critical analysis of emission, exposure andhealth HoÈrstedt P, Stjernberg N. Evaluation of an exposure effects. Cambridge, MA., Health Effects In- setup for studying effects of diesel exhaust in humans. stitute, 1995; pp. 13±18. Int Arch Occup Environ Health 1994; 66: 77±83. 6. Zweidinger RL, Garland D, Oliver CN, et al. The 26. Rudell B, Sandstrom T, Stjernberg N, Kolmodin- determination of carbonyl content in oxidatively Hedman B. Controlled diesel exhaust exposure in an modi®ed proteins. In: Packer L, Glazier AN, eds. exposure chamber: Pulmonary effects investigated London, Academic Press, 1990; 464±477. with bronchoalveolar lavage. J Aerosol Sci 1990; 21: 7. Brain JD, Valberg PA. Deposition of aerosol in the 411±414. respiratory tract. Am Rev Respir Dis 1979; 120: 1325± 27. Rudell B, Wass U, HoÈrstedt P, et al. Ef®ciency of 1373. automotive cabin air ®lters to reduce acute health 8. Chow JC. Measurement methods to determine com- effects of diesel exhaust in human subjects. Occup pliance with ambient air quality standards for sus- Environ Med 1999; 56: 222±231. pended particles. J Air Waste Manag Assoc 1995; 45: 28. Salvi S, Blomberg A, Rudell B, et al. Acute in¯am- 320±382. matory responses in the airways andperipheral blood 9. Anderson M, Svartengren M, Philipson K, Camner P. after short-term exposure to diesel exhaust in healthy Regional human lung deposition studied by repeated human volunteers. Am J Respir Crit Care Med 1999; investigations. J Aerosol Sci 1994; 25: 567±581. 159: 702±709. 10. Scheepers PT, Bos RP. Combustion of diesel fuel from 29. Montefort S, Lai CK, Kapahi P, et al. Circulating a toxicological perspective. I. Origin of incomplete adhesion molecules in asthma. Am J Respir Crit Care combustion products. Int Arch Occup Environ Health Med 1994; 149: 1149±1152. 1992; 64: 149±161. 30. Montefort S, Gratziou C, Goulding D, et al. Bron- 11. Cammer P, Perschagen G, Ahlborg U, Ljungvist S, chial biopsy evidence for leukocyte in®ltration and Victorin K. Health effects of diesel exhaust emissions. upregulation of leukocyte-endothelial cell adhesion =1988) Stockholm, Nordic Council of Ministers. molecules 6 hours after local allergen challenge of 12. Yoshino S, Sagai M. Enhancement of collagen- sensitizedasthmatic airways . J Clin Invest 1994; 93: induced arthritis in mice by diesel exhaust particles. 1411±1421. J Pharmacol Exp Ther 1999; 290: 524±529. 31. Salvi SS, Nordenhall C, Blomberg A, et al. Acute short 744 A. SYDBOM ET AL.

term exposure to diesel exhaust increases IL-8 and of long-term bronchiolar clearance of particles from GRO-a production in healthy human airways.Am measurements of lung retention andtheoretical esti- J Respir Crit Care Med 2000; 161: 550±557. mates of regional deposition. Exp Lung Res 1999; 25: 32. NordenhaÈll C, Pourazar J, Blomberg A, Levin J-O, 495±516. Sandstrom T, AÈ delroth E. Airway in¯ammation fol- 48. Moorman WJ, Clark JC, Pepelko WE, Mattox J. lowing exposure to diesel exhaust: A study of time Pulmonary function responses in cats following long- kinetics using induced sputum. Eur Respir J 2000; 15: term exposure to diesel exhaust. J Appl Toxicol 1985; 1046±1051. 5: 301±305. 33. Diaz-Sanchez D, Dotson AR, Takenaka H, Saxon A. 49. Hyde DM, Plopper CG, Weir AJ. Peribronchial Diesel exhaust particles induce local IgE production ®brosis in lungs of cats chronically exposedto diesel in vivo andalter the pattern of messenger RNA exhaust. Lab Invest 1985; 52: 195±206. isoforms. J Clin Invest 1994; 94: 1417±1425. 50. Sagai M, Saito H, Ichinose T, Kodama M, Mori Y. 34. Diaz-Sanchez D. The role of diesel exhaust particles Biological effects of diesel exhaust particles. I. In vitro andtheir associatedpolyaromatic hydrocarbonsin the production of superoxide and in vivo toxicity in mouse. induction of allergic airway disease. Allergy 1997; 52: Free Rad Biol Med 1993; 14: 37±47. 52±56. 51. Mauderly JL, Bice DE, Carpenter RL, et al. Effects of 35. Prescott SL, Macaubas C, Smallacombe T, Holt BJ, inhaled nitrogen dioxide and diesel exhaust on deve- Sly PD, Holt PG. Development of allergen-speci®c T- loping lung. Research Report - Health Effects Institute cell memory in atopic andnormal children . Lancet 1987; 8: 3±37. 1999; 353: 196±200. 52. Motley HL. Environmental air pollution effect on 36. Diaz-Sanchez D, Tsien A, Fleming J, Saxon A. pulmonary function. Aerospace Med1971; October: Combineddieselexhaust particulate andragweed 1108±1110. allergen challenge markedly enhances human in vivo 53. Mauderly JL, Bice DE, Cheng YS, et al. In¯uence of nasal ragweed-speci®c IgE and skews cytokine pro- preexisting pulmonary emphysema on susceptibility of duction to a T helper cell 2-type pattern. J Immunol rats to inhaleddieselexhaust . Am Rev Respir Dis 1990; 1997; 158: 2406±2413. 141: 1333±1341. 37. Fujieda S, Diaz-Sanchez D, Saxon A. Combined nasal 54. Mauderly JL, Bice DE, Cheng YS, et al. In¯uence of challenge with diesel exhaust particles and allergen experimental pulmonary emphysema on the toxico- induces in vivo IgE isotype switching. Am J Respir Cell logical effects from inhaled nitrogen dioxide and diesel Mol Biol 1998; 19: 507±512. exhaust. Research Report - Health Effects Institute 38. Diaz-Sanchez D, Tsien A, Casillas A, Dotson AR, 1989; 30: 1±47. Saxon A. Enhancednasal cytokine productionin hu- 55. Nikula KJ, Avila KJ, Grif®th WC, Mauderly JL. Sites man beings after in vivo challenge with diesel exhaust of particle retention andlung tissue responses to particles. J Allergy Clin Immunol 1996; 98: 114±123. chronically inhaled diesel exhaust and coal dust in rats 39. Sandstrom T, Blomberg A, Helleday R, Rudell B. Air andCynomolgus monkeys . Environ Health Perspect pollution allergy interaction: experiences from animal 1997; 105: 1231±1234. studies. Eur Respir Rev 1998; 8: 168±174. 56. Nikula KJ, Avila KJ, Grif®th WC, Mauderly JL. Lung 40. Olander L. LuftfoÈroreningar i fordon =Contaminants inside cars - concentrations and measures). Arbet- tissue responses andsites of particle retention differ slivsinstitutet =The Swedish National Institute for between rats andCynomolgus monkeys exposed Working Life) 1996. Stockholm. chronically to diesel exhaust and coal dust. Fundam 41. Kato A, Kyono H, Kuwabara N. Electron-micro- Appl Toxicol 1997; 37: 37±53. scopic observations on rat lungs after long term 57. Bice DE, Mauderly JL, Jones RK, McClellan RO. inhalation of diesel emissions -- non-neoplastic lesions. Effects of inhaleddieselexhaust on immune responses Japanese J Thoracic Dis 1992; 30: 238±247. after lung immunization. Fundam Appl Toxicol 1985; 42. Mohr U, Takenaka S, Dungworth DL. Morphological 5: 1075±1086. effects of inhaleddieselengine exhaust on lungs of rats: 58. Muranaka M, Suzuki S, Koizumi K, et al. Adjuvant Comparison with effects of coal oven ¯ue gas mixed activity of diesel-exhaust particulates for the pro- with pyrolyzedpitch. In: Ishinishi N, Koizumi A, duction of IgE antibody in mice. J Allergy Clin McClellan RO, StoÈber W, Eds. Carcinogenic and Immunol 1986; 77: 616±623. mutagenic effects of diesel engine exhaust. Amster- 59. Maejima K, Tamura K, Taniguchi Y, Nagase S, dam, Elsevier Science Publishers B.V., 1986; 459±470. Tanaka H. Comparison of effects of various ®ne 43. Wolff RK, Henderson RF, Snipes MB. Alterations in particles on IgE antibody production in mice inhaling particle accumulation andclearance in lungs of rats Japanese Cedar pollen allergens. J Toxicol Environ chronically exposedto dieselexhaust . Fundam Appl Health 1997; 52: 231±248. Toxicol 1987; 9: 154±166. 60. Nilsen A, Hagemann R, Eide I. The adjuvant activity 44. PritchardJN. Dust overloadingcauses impairment of of diesel exhaust particles and carbon black on pulmonary clearance: Evidence from rats and humans. systemic IgE production to ovalbumin in mice after Exp Pathol 1989; 37: 39±42. intranasal instillation. Toxicology 1997; 124: 225±232. 45. Strom KA, Garg BD, Johnson JT, D9Arcy JB, Smiler 61. Lovik M, Hogseth A-K, Gaarder PI, Hagemann R, KL. Inhaledparticle retention in rats receiving low Eide I. Diesel exhaust particles and carbon black exposures of diesel exhaust. J Toxicol Environ Health have adjuvant activity on the local lymph node 1990; 29: 377±398. response andsystemic IgE productionto ovalbumin . 46. Yu CP, Yoon KJ. Retention modeling of diesel ex- Toxicology 1997; 121: 165±178. haust particles in rats andhumans . Research Report - 62. Takano H, Yoshikawa T, Ichinose T, Miyabara Y, Health Effects Institute 1991; 40: 1±24. Imaoka K, Sagai M. Diesel exhaust particles en- 47. Falk R, Philipson K, Svartengren M, et al. Assessment hance antigen±induced airway in¯ammation and local HEALTH EFFECTS OF DIESEL EXHAUST EMISSIONS 745

cytokine expression in mice. Am J Respir Crit Care epithelial cells in vitro andalter cytokine production . Med 1997; 156: 36±42. Am J Physiol 1999; 276: L604±L613. 63. Ichinose T, Takano H, Miyabara Y, Yanagisawa R, 80. Devalia JL, Bayram H, Rusznak C, et al. Mechanisms Sagai M. Murine strain differences in allergic airway of pollution-induced airway disease: In vitro studies in¯ammation andimmunoglobulin productionby a in the upper andlower airways . Allergy 1997; 52: 45± combination of antigen anddieselexhaust particles . 51. Toxicology 1997; 122: 183±192. 81. Takenaka H, Zhang K, Diaz-Sanchez D, Tsien A, 64. Miyabara Y, Ichinose T, Takano H, Lim HB, Sagai Saxon A. Enhancedhuman IgE productionresults M. Effects of diesel exhaust on allergic airway in- from exposure to the aromatic hydrocarbons from ¯ammation in mice. J Allergy Clin Immunol 1998; 102: diesel exhaust: Direct effects on B-cell IgE production. 805±812. J Allergy Clin Immunol 1995; 95: 103±115. 65. Fujimaki H, Nohara O, Ichinose T, Watanabe N, 82. Tsien A, Diaz-Sanchez D, Ma J, Saxon A. The organic Saito S. IL-4 production in mediastinal lymph node component of diesel exhaust particles and phenan- cells in mice intratracheally instilledwith dieselex- threne, a major polyaromatic hydrocarbon consti- haust particulates andantigen . Toxicology 1994; 92: tuent, enhances IgE production by IgE-secreting 261±268. EBV-transformedhuman B cells in vitro. Toxicol 66. Takano H, Ichinose T, Miyabara Y, Yoshikawa T, Appl Pharmacol 1997; 142: 256±263. Sagai M. Diesel exhaust particles enhance airway 83. Fahy O, Tsicopoulos A, HammadH, Pestel J, Tonnel responsiveness following allergen exposure in mice. AB, Wallaert B. Effects of diesel organic extracts on Immunopharm Immunotoxicol 1998; 20: 329±336. chemokine production by peripheral blood mono- 67. Takano H, Ichinose T, Miyabara Y, et al. Inhalation nuclear cells. J Allergy Clin Immunol 1999; 103: 1115± of diesel exhaust enhances allergen-related eosinophil 1124. recruitment andairway hyperresponsiveness in mice . 84. Bayram H, Devalia JL, SapsfordRJ, et al. The effect Toxicol Appl Pharmacol 1998; 150: 328±337. of diesel exhaust particles on cell function and release 68. Takafuji S, Suzuki S, Koizumi K, et al. Enhancing of in¯ammatory mediators from human bronchial effect of suspended particulate matter on the IgE epithelial cells in vitro. Am J Respir Cell Mol Biol 1998; antibody production in mice. Int Arch Allergy Appl 18: 441±448. Immunol 1989; 90: 1±7. 85. Bayram H, Devalia JL, Khair OA, et al. Comparison 69. Miyabara Y, Ichinose T, Takano H, Sagai M. Diesel of ciliary activity andin¯ammatory mediatorrelease from bronchial epithelial cells of nonatopic non- exhaust inhalation enhances airway hyperresponsive- asthmatic subjects andatopic asthmatic patients and ness in mice. Int Arch Allergy Immunol 1998; 116: 124± the effect of diesel exhaust particles in vitro. J Allergy 131. Clin Immunol 1998; 102: 771±782. 70. Miyabara Y, Takano H, Ichinose T, Lim H-B, Sagai 86. Ohtoshi T, Takizawa H, Okazaki H, et al. Diesel M. Diesel exhaust enhances allergic airway in¯am- exhaust particles stimulate human airway epithelial mation andhyperresponsiveness in mice . Am J Respir cells to produce cytokines relevant to airway in¯am- Crit Care Med 1998; 157: 1138±1144. mation in vitro. J Allergy Clin Immunol 1998; 101: 778± 71. Kobayashi T, Ikeue T, Ito K, et al. Short-term 785. exposure to diesel exhaust induces nasal mucosal 87. Steerenberg PA, Zonnenberg JAJ, Dormans JAMA, hyperresponsiveness to histamine in guinea pigs. et al. Diesel exhaust particles induced release of Fundam Appl Toxicol 1997; 38: 166±172. interleukin 6 and8 by =primed)human bronchial 72. Hiruma K, Terada N, Hanazawa T, et al. Effect of epithelial cells =BEAS 2B) in vitro. Exp Lung Res 1998; diesel exhaust on guinea pig nasal mucosa. Ann Otol 24: 85±100. Rhinol Laryngol 1999; 108: 582±588. 88. Takizawa H, Ohtoshi T, Kawasaki S, et al. Diesel 73. Gorski P, Tarkowski M, et al. Non speci®c en- exhaust particles induce NF-kappa B activation in vironmental factors andasthma development . Polish human bronchial epithelial cells in vitro: importance in J Occup Med Environ Health 1992; 5: 227±236. cytokine transcription. J Immunol 1999; 162: 4705± 74. Glovsky MM, Miguel AG, Cass GR. Particulate air 4711. pollution: Possible relevance in asthma. Allergy 89. Terada N, Hamano N, Maesako KI, et al. Diesel Asthma Proc 1997; 18: 163±166. exhaust particulates upregulate histamine receptor 75. Knox RB, Suphioglu C, Taylor P, et al. Major grass mRNA andincrease histamine-inducedIL-8 and pollen allergen Lol p 1 binds to diesel exhaust parti- GM-CSF production in nasal epithelial cells and cles: implications for asthma andair pollution . Clin endothelial cells. Clin Exp Allergy 1999; 29: 52±59. Exp Allergy 1997; 27: 246±251. 90. Yang H-M, Ma JYC, Castranova V, Ma JKH, et al. 76. OrmstadH, Johansen BV, GaarderPI. Airborne Effects of diesel exhaust particles on the release of house dust particles and diesel exhaust particles as interleukin-1 andtumor necrosis factor-alpha from allergen carriers. Clin Exp Allergy 1998; 28: 702±708. rat alveolar macrophages. Exp Lung Res 1997; 23: 77. Henricsson S, Westerholm R, Nilsson S, Berggren B. 269±284. Chemical characterisation of extractable compounds 91. Hirafuji M, Sakakibara M, Endo T, et al. Biological foundin the coating of birch =Betula) pollen . Grana effects of diesel exhaust particles =DEP) on tissues 1996; 35: 179±184. andcells isolatedfrom respiratory tracts of guinea 78. Terada N, Maesako K, Hiruma K. Diesel exhaust pigs. Res Comm Mol Pathol Pharmacol 1995; 90: 221± particulates enhance eosinophil adhesion to nasal 233. epithelial cells andcause degranulation . Int Arch 92. Vogl G, Elstner EF. Diesel soot particles catalyze the Allergy Appl Immunol 1997; 114: 167±174. production of oxy-radicals. Toxicol Lett 1989; 47: 17± 79. BolandS, Baeza-Squiban A, Fournier T, et al. Diesel 23. exhaust particles are taken up by human airway 93. Bingisser RM, Tilbrook PA, Holt PG, Kees UR. 746 A. SYDBOM ET AL.

Macrophage-derived nitric oxide regulates T cell acti- 103. Pope CA, III, Dockery DW, Kanner RE, Villegas vation via reversible disruption of the Jak3/STAT5 GM, Schwartz J. Oxygen saturation, pulse rate, and signaling pathway. J Immunol 1998; 160: 5729±5734. particulate air pollution. Am J Respir Crit Care Med 94. Sagai M, Ichinose T. Role of nitric oxide in asthma- 1999; 159: 365±372. like symptoms induced by diesel exhaust particles in 104. GoldDR, Litonjua A, Schwartz J, et al. Ambient mice. Japanese J Thoracic Dis 1995; 33: 212±217. pollution andheart rate variability . Circulation 2000; 95. Muto E, Hayashi T, Yamada K, Esaki T, Sagai M, 101: 1267±1273. Iguchi A. Endothelial-constitutive nitric oxide syn- 105. Liao D, Creason J, Shy C, Williams R, Watts R, thase exists in airways anddieselexhaust particles Zweidinger R. Daily variation of particulate air inhibit the effect of nitric oxide. Life Sci 1996; 59: pollution andpoor cardiacautonomic control in the 1563±1570. elderly. Environ Health Perspect 1999; 107: 521±525. 96. Dockery DW, Pope CA. Acute respiratory effects of 106. Pope III CA, Verrier RL, Lovett EG, et al. Heart rate particulate air pollution. Ann Rev Publ Health 1994; variability associatedwith particulate air pollution . 15: 107±132. Am Heart J 1999; 138: 890±899. 97. Schwartz J. Air pollution anddailymortality: a review 107. Kanemitsu H, Nagasawa S, Sagai M, Mori Y. andmeta analysis . Environ Res 1994; 64: 36±52. Complement activation by diesel exhaust particles 98. SjoÈgren B. Occupational exposure to dust: In¯am- =DEP). Biol Pharm Bull 1998; 21: 129±132. mation andischaemic heart disease . Occup Environ- 108. Sakakibara M, Minami M, Endo T, et al. Biological ment Med 1997; 54: 466±469. effects of diesel exhaust particles =DEP) on isolated 99. SjoÈgren B. Mortality of Dutch coal miners in relation cardiac muscle of guinea pigs. Res Comm Mol Pathol to pneumoconiosis, chronic obstructive pulmonary Pharmacol 1994; 86: 99±110. disease, and lung function. Occup Environment Med 109. Ihre E, Zetterstrom O. Increase in non-speci®c bron- 1998; 55: 503±503. chial responsiveness after repeatedinhalation of low 100. SjoÈgren B. A possible connection between furnace dust doses of allergen. Clin Exp Allergy 1993; 23: 298±305. exposure, plasma ®brinogen levels andcardiovascular 110. Sulakvelidze I, Inman MD, Rerecich T, O'Byrne PM. disease.Scand JWork Environ Health1998; 24:236±237. Increases in airway eosinophils andinterleukin-5 with 101. Seaton A, Soutar A, CrawfordV, Stout R, et al. minimal bronchoconstriction during repeated low- Particulate air pollution andthe blood . Thorax 1999; dose allergen challenge in atopic asthmatics. Eur 54: 1027±1032. Respir J 1998; 11: 821±827. 102. Peters A, Doring A, Wichmann HE, Koenig W. In- 111. ArshadSH, Hamilton RG, AdkinsonNF, Jr. Repe- creasedplasma viscosity duringthe 1985 air pollution atedaerosol exposure to small dosesof allergen. A episode: a link to mortality? Lancet 1997; 349: 1582± model for chronic allergic asthma. Am J Respir Crit 1587. Care Med 1998; 157: 1900±1906.