Ultrastructure of Irritant and Allergic Contact Dermatitis Chapter 8 119

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Chapter 8 Ultrastructure of Irritant 8 and Allergic Contact Dermatitis

Carolyn M. Willis

Contents In the sections which follow, ultrastructural 8.1 Introduction ...... 117 changes seen in skin exposed to irritants and allergens are described.With the exception of the last sec- 8.2 Ultrastructural Changes in the Epidermis . . 117 tion, which deals specifically with a recent study of 8.2.1 Stratum Corneum ...... 117 chronic chromate hand dermatitis, the data refer to 8.2.2 Viable Keratinocytes ...... 118 the effects of acute exposure. 8.2.2.1 Irritant Contact Dermatitis ...... 118 8.2.2.2 Allergic Contact Dermatitis ...... 121 8.2.3 Langerhans Cells ...... 121 8.2 Ultrastructural Changes 8.2.3.1 Allergic Contact Dermatitis ...... 122 in the Epidermis 8.2.3.2 Irritant Contact Dermatitis ...... 122 8.3 Ultrastructural Changes in the Dermis . . . 124 The stratified nature of the epidermis, and the pres- 8.4 Ultrastructural Changes ence of Langerhans cells and melanocytes in addi- in Chronic Contact Dermatitis ...... 124 tion to keratinocytes, presents a wide variety of bio- 8.5 Summary ...... 125 chemical and immunological targets for topically ap- References ...... 125 plied irritants and allergens. Primary contact occurs at the outermost stratum corneum,which,depending on the chemical characteristics of the substance, may show ultrastructural evidence of damage. Diffusion into and penetration of the viable epidermal regions then take place. Again depending upon the chemical 8.1 Introduction nature of the agent, as well as the severity of response and time of examination post-exposure, morpholog- Electron microscopy has provided us with a valuable ical indications of metabolic interruption may be tool to investigate the cellular and subcellular effects seen. of topical exposure to irritants and allergens, com- plementing histological examination at the light mi- croscope level. Most reported data are based on the 8.2.1 Stratum Corneum use of conventional preparative techniques, but de- velopments such as post-fixation in ruthenium te- The outermost diffusion barrier of the skin, the stra- troxide to visualize intercellular lipids and the par- tum corneum, is a 20- to 30-cell-thick layer of flat, allel examination of semi-thin and ultra-thin resin- hexagonal, protein-rich corneocytes surrounded by embedded samples have enhanced our understand- intercellular lipids.Generally speaking,chemical irri- ing of the cellular changes that take place. It is impor- tants rather than allergens produce marked changes tant to remember, however, that electron microscopy to its structure and behavior, as evidenced, biophysi- gives us only a snapshot of a minute fraction of a skin cally, by increased transepidermal water loss. Recent biopsy. Therefore, studies employing small sample ultrastructural studies utilizing ruthenium tetroxide numbers, with limited scrutiny of each specimen, as a post-fixative have greatly increased our under- should be viewed with a degree of caution. This is standing of the manner in which some irritant chem- particularly true for irritant contact dermatitis in- icals interact with this region of the epidermis and vestigations, where considerable inter-individual contribute to the development of irritant contact der- variation in the intensity of the response to chemicals matitis (ICD). The application of low concentrations occurs, and where the cellular damage inflicted is of the anionic surfactant sodium lauryl sulfate (SLS) rarely uniform across the application site. to normal human skin was found by Fartasch to re- 08_117_126 04.11.2005 15:39 Uhr Seite 118

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While both induce varying degrees of spongiosis, sult not so much in an alteration of the existing lipid clearly visible by both light and electron microscopy, structure, but rather an alteration in the synthesis of chemical irritants also give rise to a heterogeneity of new lipids [1]. Hence, disturbance of lamellar body forms of intracellular damage that are time, dose lipid extrusion and transformation into lipid bilayers and, in some cases, irritant dependent. occurred, in the absence of any disruption to the intercellular lipid layers of the upper stratum corneum. By way of contrast, acetone produced a different 8.2.2.1 Irritant Contact Dermatitis pattern of change.Epidermal lipid lamellae displayed disruption and loss of cohesion throughout the stra- Two early studies provided some of the first evidence tum corneum – the transformed, more nonpolar, la- that irritants can damage the skin by different mech- mellar lipids showing greater disruption than the anisms. A comparison between the effects of an acid more polar lamellar body sheets [1]. A similar dis- and an alkali on human epidermis found that sodium ruption of stratum corneum intercellular bilayers hydroxide dissolved the contents of horny cells and was also seen in human skin patch-tested with water disrupted tonofilament–desmosome complexes, alone [2], which would have the effect, as pointed out while hydrochloric acid did not [3]. Similarly, in a by the investigators, of enhancing skin permeability comparative study of two lipid solvents, the response and susceptibility to irritants. to acetone, which was characterized by intracellular 8 edema of keratinized cells and vacuolation of spi- Core Message nous cells, was conspicuously different to that to kerosene, in which the formation of large lacunae and í cytolysis of spinous cells were seen [4]. In our own Chemical irritants generally have a greater study, designed to systematically compare the mor- impact than allergens on the ultrastructure phological effects of six structurally unrelated irri- of the stratum corneum. tants on normal human skin, electron microscopy also revealed significant differences in the nature of the cellular damage induced by different chemicals after 48 h of exposure [5]. Patch test reactions to SLS 8.2.2 Viable Keratinocytes were characterized by parakeratotic cells in the upper epidermis, containing dense osmiophilic cyto- The greatest diversity of ultrastructural effects on vi- plasm with numerous lipid droplets and vesicles, but able keratinocytes within the epidermis is undoubt- an absence of keratohyalin granules (Figs. 1, 2). In edly exerted by irritants, rather than by allergens. contrast, the cationic detergent benzalkonium chlo-

Fig. 1. The interface between dark, osmiophilic, vesiculated, parakeratotic cells in the upper epidermis and paler cells of the stratum spinosum in a 48-h patch test reaction to sodium lauryl sulfate (SLS) (4%) 08_117_126 04.11.2005 15:39 Uhr Seite 119

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ride produced distinct areas of necrosis (Fig. 3). Ap- plication of the 12-C-long chain fatty acid nonanoic acid resulted in the formation of tongues of dyskeratotic cells, largely composed of dense, wavy aggregates of osmiophilic keratin filaments associated with prominent intercellular desmosomes, and containing shrunken nuclei with condensed, marginated heterochromatin (Fig. 4). Exposure to dithranol produced different changes again, namely markedly enlarged upper epidermal keratinocytes, containing finely dispersed filaments and ribosomes, and, in keeping with previous findings [6, 7], disrupted mitochondria (Fig. 5). The concept of ultrastructural changes being irritant-dependent was further supported by a recent study of the effects of a wide variety of irritant chemicals on the skin of hairless guinea pigs [8].Although the skin changes described were not identical to those seen in human skin, partly perhaps as a result of concentration differences, it was clear, that again the nature of the epidermal damage elicited by SLS differed markedly from that of benzalkonium chloride.

Fig. 2. Basal keratinocytes in a 48-h SLS (4%) patch test reaction, illustrating lipid droplet accumulation and prominent intracytoplasmic vesiculation

Table 1. Ultrastructural changes induced in the viable epidermis by acute exposure to selected irritants.Changes depend on the irritant, its concentration, and time

Irritant Ultrastructural changes

Sodium lauryl Spongiosis, vesiculation, nuclear/intra- sulfate cytoplasmic/mitochondrial vacuolation, lipid droplet accumulation, hydropic swelling, decreased desmosomes with aggregation of tonofilaments Benzalkonium Nuclear/intracytoplasmic vacuolation, chloride nuclear pyknosis, mitochondrial swelling, organelle disruption, hydropic swelling, spongiosis Dithranol Hydropic swelling, mitochondrial membrane disruption, spongiosis, intracytoplasmic vacuolation, dyskeratosis, apoptosis, colloid bodies Croton oil Marked spongiosis, intracytoplasmic vacuolation, pyknotic/enlarged nuclei Nonanoic acid Dyskeratosis, nuclear/intracytoplasmic vacuolation, vesiculation, lipid droplet accumulation, pyknotic nuclei Acetone Acantholysis, spongiosis, nuclear/intracytoplasmic edema and vacuolation Sodium Disrupted tonofilament–desmosome Fig. 3. An area of necrosis induced in the mid epidermis by hydroxide complexes 48-h patch testing with benzalkonium chloride (0.5%). Kerati- nocytes show extensive vacuolation, pyknotic nuclei, and dis- Combined human and animal data [3–12] rupted organelles and membranes 08_117_126 04.11.2005 15:39 Uhr Seite 120

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Fig. 4. Dyskeratotic upper epidermal cells, containing dense, wavy aggregates of osmiophilic keratin filaments, produced by 48-h patch testing with nonanoic acid (80%)

Fig. 5. Enlarged upper epidermal keratinocyte, with cytoplasm containing finely dispersed filaments and ribosomes and perinuclearly clustered mitochondria, in a 48-h patch test reaction to dithranol (0.2%) 08_117_126 04.11.2005 15:39 Uhr Seite 121

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The ultrastructural changes to the viable cells in tion of tonofilaments into short bundles, is a consis- the epidermis variously described by investigators tent feature of the viable epidermal layers in allergic during the last three decades [3–10] (Table 1) are, in contact dermatitis (ACD) (Fig. 6), and one that is de- the main, indicative of autolysis or cytolysis, which tectable in sensitized individuals by electron micros- would eventually lead to disintegration of the cell. In copy as early as 3 h after exposure to hapten [14]. some cases, however, certain alterations, such as con- Intracellular changes to keratinocytes, such as vac- densation of chromatin and cytosol, clumping of uolation and endoplasmic reticulum dilatation, also tonofilaments and budding of membrane-bound cell occur, but since the majority of allergens are also in- fragments, may be suggestive of another form of cell trinsically irritant in nature, ascribing such changes death, that of apoptosis. Often ultrastructurally in- with any degree of certainty to the process of sensiti- distinguishable from dyskeratotic cells in the early zation itself is very difficult. Indeed, in a study of stages, apoptotic keratinocytes have been described chromium reactions in humans and guinea pig, the in reactions to a number of well-studied irritants authors concluded that keratinocyte intracellular re- [11–13]. action patterns were nonspecific and could not be distinguished from those of vehicle or occlusion Core Message alone [15].

í Structurally unrelated chemical irritants Core Message damage the skin by different mechanisms, which is reflected in the varying ultrastruc- í The predominant ultrastructural change in tural changes seen in the epidermis. These the epidermis of acute allergic contact der- changes also depend on concentration, matitis lesions is spongiosis. time, intensity of reaction, and species.

8.2.3 Langerhans Cells 8.2.2.2 Allergic Contact Dermatitis Much of the ultrastructural data relating to Langer- Intercellular edema or spongiosis, characterized by hans cell (LC) behavior in contact dermatitis focuses, dilated intercellular spaces, stretched or absent tono- not surprisingly, on ACD rather than ICD. Contradic- filament–desmosome complexes and the aggrega- tory electron microscopy findings have emerged over

Fig. 6. Low-power micrograph of the lower region of the epidermis of a 48-h patch test reaction to nickel sulfate (5%). Spongiosis and exocy- tosis are the predominant features 08_117_126 04.11.2005 15:39 Uhr Seite 122

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the years, however, stimulating debate on a number have been conducted,some of which are summarized of issues, including whether overt cellular damage to in Table 2. From these, it would appear that there is LC is an inherent feature of allergic contact reactions, early metabolic activation, as indicated by prominent and the extent to which the changes seen are specific rough endoplasmic reticulum and Golgi apparatus, to ACD. Nevertheless, there is now no doubting the during the early stages of induction and elicitation, central role that this antigen-presenting, mononucle- followed later by degenerative changes, such as ar cell occupies from an immunologic point of view membrane disruption and condensation of nuclear [16]. As to whether LCs have a functional role in ICD chromatin (Fig. 7). In a rare ultrastructural study also remains a matter of speculation, but, here, there linking LC function and morphology more closely, is certainly a great deal of evidence of cellular dam- Rizova et al. described an alteration in the pattern of age to LC, most of which is likely to be nonspecific in endocytosis of major histocompatibility complex origin. class II (HLA-DR) molecules specific to allergens. Sensitizer-treated LCs internalized HLA-DR prefe- rentially in lysosomes collected near the nucleus, 8.2.3.1 Allergic Contact Dermatitis whereas irritant-treated and nontreated LCs internalized the molecules in prelysosomes located near As early as 1973, ultrastructural observations led to the cell membrane [27]. speculation that Langerhans cells might play a role in 8 allergic contact reactions [17]. Close apposition to mononuclear cells was described as being an exclu- 8.2.3.2 Irritant Contact Dermatitis sive feature of ACD, and a variety of cellular changes suggestive of targeted physiological activity were Current immunological evidence does not support seen. In the intervening years, numerous ultrastruc- the concept of any specific functional activities for tural studies designed to elucidate the behavior of LC LC during the evolution of ICD, other than perhaps

Table 2. A summary of the major ultrastructural changes induced in Langerhans cells by selected chemical allergens.(DNCB Din- itrochlorobenzene, DNFB dinitrofluorobenzene)

Allergen(s) Langerhans cell changes Ref.

Various Apposition to mononuclear cells. Prominent rough endoplasmic reticulum and [17] (human, 4–72 h) Golgi complexes, glycogen accumulation, presence of polyribosomes, lysosome-like projections, ruffled cell membranes. Disruption to membranes DNCB (guinea pig, 2–48 h) Early cellular vacuolar and granular changes, with apposition to mononuclear cells. [18] Later migration to/loss from the horny layer Nickel, thiuram mix, Apposition to other cells, marked endocytosis with greatly increased cytoplasmic [19] epoxy resin, neomycin content of vesicles, the latter having trilaminar membranes and specific granules. (man, 72 h) Dark cytoplasmic vesicles (nickel). No evidence of cell damage DNCB (guinea pig, Early activation (6 h), with prominent rough endoplasmic reticulum and Golgi, [20] 2 h to 14 days) and numerous lysosomes and vacuoles. After 12 h, cell damage, evidenced by disruption of cell membranes, etc. Various (human, 3–168 h) Increased metabolic activity in some cells, with distended endoplasmic reticulum, [21] pronounced microtubules and increased numbers of Birbeck granules. Also occasional necrotic cells, with condensed chromatin and shrunken cytoplasm Various (human, 3–72 h) No morphological changes indicative of damage [22] Picryl chloride, DNFB 1–24 h, activation with enlargement of cell and nucleus and increase in [23] (mouse, 1–96 h) mitochondria, Golgi and endoplasmic reticulum. After 48 h, degenerative changes DNFB (induction) Activation from 15 min, with LC showing intense endocytotic activity – numerous [24] (guinea pig, 15 min to 24 h) coated vesicles and Birbeck granules Various (human, 72 h) Increased numbers of LC, increased synthesis and cell surface expression of HLA [25] class II molecules DNFB (mouse, 1–96 h) During induction phase, cellular and endocytotic activation. Degenerative changes, [26] including membrane rupture, cytoplasmic edema and irregular condensation of nuclear chromatin, in the late elicitation phase 08_117_126 04.11.2005 15:39 Uhr Seite 123

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Fig. 7. Degenerative changes, including disrupted organelles and membranes, in a Lange- rhans cell within the epidermis of a 48-h patch test reaction to nickel sulfate (5%). Activated Langerhans cells were also present in the same biopsy sample

as a contributor to the milieu of inflammatory medi- the chemical nature of the irritant applied [29]. Ta- ators, through their production and release of cyto- ble 3 provides a summary of some of the ultrastruc- kines such as interleukin-1 (IL-1) [28]. Morphological tural studies in this area, which provide evidence for evidence, however, certainly points to their partici- LC being both activated (Fig. 8) and in a state of de- pation in ICD, which, within the epidermis, shows generation during the evolution of ICD. Earlier be- variability with respect to time, severity of insult, and liefs that apposition of LC to mononuclear cells with-

Table 3. A summary of the predominant ultrastructural changes induced in Langerhans cells by acute exposure to selected chemical irritants.These are irritant-,dose-,time- and species-dependent. (BC Benzalkonium chloride, CO croton oil, SLS sodium lauryl sulfate)

Irritant(s) Langerhans cell changes Ref.

Mercuric chloride, soap, No apposition to mononuclear cells. Glycogen accumulation [17] SLS (human, 24–48 h) Dithranol, nonanoic acid Apposition to mononuclear cells. Ultrastructural evidence of both stimulation and [30] (human, 6–72 h) degeneration Dithranol (human, 24–48 h) Fine structural changes in the mitochondria [31] BC (human, 3–168 h) Evidence of both increased metabolic activity (distended endoplasmic reticulum [21] and increased numbers of mitochondria and Birbeck granules) and necrosis (condensed chromatin and shrunken cytoplasm) CO, BC, SLS (mice, 1–96 h) Degenerative changes, with mitochondrial swelling and irregular cytoplasmic [23] vacuolization, followed by membrane disruption and disorganization of the cellular components. With low concentration of CO, prior activation of LC, with increased numbers of mitochondria and enlargement of nuclei Six irritants of varying Varying numbers of damaged cells displaying vesiculation, loss of integrity of [29] chemical structure organelles and membranes, condensed nuclear heterochromatin and lipid (human, 48 h) accumulation. Frequent activated LC, with numerous Birbeck granules in reactions to benzalkonium chloride 08_117_126 04.11.2005 15:39 Uhr Seite 124

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Fig. 8. An activated Langerhans cell containing numerous Birbeck granules and wid- ened rough endoplasmic reticulum, induced by patch testing with benzalkonium chloride (0.5%). Within the same biopsy sample, Lange- rhans cells displaying degenerative changes were also seen

in the epidermis was unique to ACD [17] have now An earlier light and electron microscopy study of been set aside, following numerous reports of its oc- hairless mice revealed that many irritant chemicals currence also in ICD [31]. cause, in addition to the above changes, enlargement or hyperplasia of sebaceous glands, with basal cells displaying morphological signs of enhanced meta- Core Message bolic activity,such as increases in rough endoplasmic reticulum and sebum droplets [33]. Ultrastructural í Langerhans cells within both allergic evidence has also led to the belief that platelets lining and irritant patch test reactions show the dermal venular endothelium during irritant reac- ultrastructural evidence of both activation tions contribute significantly to the pathogenesis of and degeneration. the overall response, at least in mice, being closely linked to the formation of edema [34].

Core Message 8.3 Ultrastructural Changes in the Dermis í Edema and capillary dilatation are com- Commonly seen changes within the dermis of both monly described ultrastructural features ACD and ICD lesions include edema and capillary within the dermis of allergic and irritant dilatation,with disruption and degeneration of colla- patch test reactions. gen being an additional feature of some irritant reactions [32]. In their recent light- and electron-microscopic investigation of the effects of a range of chemical irritants on the skin of hairless guinea pigs, Sue- ki and Kligman [8] observed variations in the dermis 8.4 Ultrastructural Changes that were, to a degree, irritant-dependent. Exposure in Chronic Contact Dermatitis to SLS and to organic solvents affected the dermis relatively little. In contrast, benzalkonium chloride Little information is available regarding the ultra- and various urticariogens and comedogenic agents structural changes associated with chronic contact induced marked dilation of lymphatic vessels, as well dermatitis. This is largely because of the difficulty of as capillaries. Increased numbers of granules within accurately characterizing the disorder. Most clinical dermal mast cells were also described for the latter cases of chronic contact dermatitis are attributable to irritants, although this was not quantified in any a complex admix of endogenously and exogenously way. derived provocation factors. Atopy often plays a role 08_117_126 04.11.2005 15:39 Uhr Seite 125

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and even where sensitization to a relevant hapten is 4. Lupulescu AP, Birmingham DJ, Pinkus H (1973) An elec- proven, the influence of concomitant irritant expo- tron microscopic study of human epidermis after acetone and kerosene administration. J Invest Dermatol 60 : 33–45 sure is difficult to disentangle. However, recently, 5. Willis CM, Stephens CJM, Wilkinson JD (1989) Epidermal Shah and Palmer [35] attempted to document the damage induced by irritants in man. A light and electron variations in ultrastructural appearance of chronic microscopy study. J Invest Dermatol 93 : 695–700 occupational hand dermatitis linked to chromate al- 6. Swanbeck G, Lundquist PG (1972) Ultrastructural changes lergy. Examination of a broad spectrum of clinical of mitochondria in dithranol treated psoriatic epidermis. Acta Derm Venereol (Stockh) 52 : 94–98 disease, in terms of intensity and duration, revealed 7. Molière P, Dubertret L, Sa E, Melo MT, Salet C, Fosse M, cellular features within the epidermis common to Santus R (1985) The effect of anthralin (dithranol) on mi- other inflammatory dermatoses. These included tochondria. Br J Dermatol 112 : 509–515 marked spongiosis and intracellular vacuolation, 8. Sueki H, Kligman AM (2003) Cutaneous toxicity of chemi- particularly within the basal layers. However, the au- cal irritants on hairless guinea pigs. J Dermatol 30:859–870 9. Metz J (1972) Elecktronenmikroskopische Untersuchun- thors also described, for the first time in relation to gen an allergischen und toxischen Epicutantestreaktionen chromate dermatitis, the presence of spindle-shaped des Menschen. Arch Derm Forsch 245 : 125–146 granular cells, possibly mast cells, in the upper der- 10. Tovell PWA,Weaver AC, Hope J, Sprott WE (1974) The ac- mis, closely opposed to the dermo-epidermal junc- tion of sodium lauryl sulphate on rat skin – an ultrastruc- tion. tural study. Br J Dermatol 90 : 501–506 11. Lindberg M, Forslind B, Wahlberg JE (1982) Reactions of epidermal keratinocytes in sensitized and non-sensitized guinea pigs after dichromate exposure: an electron micro- Core Message scopic study.Acta Derm Venereol (Stockh) 62:389–396 12. Kanerva L (1990) Electron microscopic observations of í dyskeratosis, apoptosis, colloid bodies and fibrillar degen- More studies of chronic contact dermatitis eration after skin irritation with dithranol. J Cutan Pathol are required to appreciate more fully the 17 : 37–44 ultrastructural changes which take place. 13. Forsey RJ, Shahidullah H, Sands C, McVittie E, Aldridge RD, Hunter JA, Howie SE (1998) Epidermal Langerhans cell apoptosis is induced in vivo by nonanoic acid but not by sodium lauryl sulphate. Br J Dermatol 139 : 453–461 14. Komura J, Ofuji S (1980) Ultrastructural studies of allergic 8.5 Summary contact dermatitis in man. Arch Dermatol Res 267 : 275–282 The past two or three decades have seen the publica- 15. Forslind B, Wahlberg JE (1978) The morphology of chromium allergic skin reactions at electron microscopic reso- tion of a wealth of information on the ultrastructural lution: studies in man and guinea pig.Acta Derm Venereol morphology of acute allergic and irritant contact Suppl (Stockh) 79 : 43–51 dermatitis. Much still needs to be learnt, however, 16. Cumberbatch M, Dearman RJ, Griffiths CE, Kimber I about the cellular features of the chronic forms of (2003) Epidermal Langerhans cell migration and sensit- contact dermatitis. The introduction of modified tis- isation to chemical allergens. APMIS 111 : 797–804 17. Silberberg I (1973) Apposition of mononuclear cells to sue preparation techniques has greatly improved vis- Langerhans cells in contact allergic reactions. An ultra- ualization of the stratum corneum and increased our structural study. Acta Derm Venereol (Stockh) 53 : 1–12 understanding of the damage caused by topical ex- 18. Hunziker N, Winkelman RK (1978) Langerhans cells in posure to chemicals. However, the continued paucity contact dermatitis of the guinea pig. Arch Dermatol 114 : 1309–1313 of studies utilizing correlative functional and mor- 19. Falck B, Andersson A, Elofsson R, Sjöborg S (1981) New phological techniques still limits the extent to which views on epidermis and its Langerhans cells in the normal purely electron microscopic findings can be mean- state and in contact dermatitis. Acta Derm Venereol Suppl ingfully translated into pathophysiological events. (Stockh) 99 : 3–27 20. Bian Z, Bing-He W (1985) Cytochemical and ultrastructural studies of the Langerhans cells. Int J Dermatol 24 : 653–659 References 21. Willis CM,Young E, Brandon DR,Wilkinson JD (1986) Im- munopathological and ultrastructural findings in human 1. Fartasch M (1997) Ultrastructure of the epidermal barrier allergic and irritant contact dermatitis. Br J Dermatol 115 : after irritation. Microsc Res Tech 37 : 193–199 305–316 2. Warner RR, Boissy YL, Lilly NA, Spears MJ, McKillop K, 22. Giannotti B, de Panfilis G, Manara GC (1986) Langerhans Marshall JL,Stone KJ (1999) Water disrupts stratum corne- cells are not damaged in contact allergic reactions in hu- um lipid lamellae: damage is similar to surfactants.J Invest mans. Am J Dermatopathol 8 : 220–226 Dematol 113 : 960–966 23. Kolde G, Knop J (1987) Different cellular reaction patterns 3. Nagao S, Stroud JD, Hamada T, Pinkus H, Birmingham DJ of epidermal Langerhans cells after application of contact (1972) The effect of sodium hydroxide and hydrochloric sensitizing,toxic,and tolerogenic compounds.A compara- acid on human epidermis. Acta Derm Venereol (Stockh) tive ultrastructural and morphometric time-course analy- 52 : 11–23 sis. 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24. Hanau D, Fabre M, Schmitt DA (1989) ATPase and mor- 30. Kanerva L, Ranki A, Mustakallio K, Lauharanta J (1983) phologic changes in Langerhans cells induced by epicut- Langerhans cell-mononuclear cell contacts are not specif- aneous application of a sensitizing dose of DNFB. J Invest ic for allergy in patch tests. Br J Dermatol 109 [Suppl 25] : Dermatol 92(5) : 689–694 64–67 25. Mommaas AM, Wijsman MC, Mulder AA, van Praag MC, 31. Kanerva L, Ranki A, Lauharanta J (1984) Lymphocytes and Vermeer BJ, Koning F (1992) HLA class II expression on Langerhans cells in patch tests. Contact Dermatitis 11 : human epidermal Langerhans cells in situ: upregulation 150–155 during elicitation of allergic contact dermatitis. Hum Im- 32. Willis CM (1995) The histopathology of irritant contact munol 34 : 99–106 dermatitis.In:Van der Valk PGM,Maibach HI (eds) The ir- 26. Kolde G (1996) Turnover and kinetics of epidermal Lange- ritant contact dermatitis syndrome. CRC, Boca Raton, Fla., rhans cells and their dendritic precursor cells in experi- pp 297–298 mental contact dermatitis. Arch Dermatol Res 288 : 33. Lesnik RH, Kligman LH, Kligman AM (1992) Agents that 197–202 cause enlargement of sebaceous glands in hairless mice. I. 27. Rizova H, Carayon P, Barbier A, Lacheretz F, Dubertret L, Topical substances. Arch Dermatol 284 : 100–105 Michel L (1999) Contact allergens, but not irritants, alter 34. Senaldi G, Piguet P-F (1997) Platelets play a role in the receptor-mediated endocytosis by human epidermal pathogenesis of the irritant reaction in mice. J Invest Der- Langerhans cells. Br J Dermatol 140 : 200–209 matol 108 : 248–252 28. Kimber I (1999) Contact sensitisation mechanisms. In: 35. Shuh M, Palmer IR (2002) An ultrastructural study of Basketter DA (ed) Toxicology of contact dermatitis; aller- chronic chromate hand dermatitis. Acta Derm Venereol gy, irritancy and urticaria. Wiley, Chichester, chap 5 (Stockh) 82 : 254–259 29. Willis CM, Stephens CJM,Wilkinson JD (1990) Differential effects of structurally-unrelated chemical irritants on the 8 density and morphology of epidermal CD1a+ cells. J In- vest Dermatol 95 : 711–716