Chapter 1∗ 1. Introduction Fungi are among the most common foreign aerobiological particles that we inhale. Personal exposure to airborne microorganisms, particularly fungi both in indoor, outdoor, residential and occupational environments, is widely recognized as exacerbating agents of non-infectious respiratory diseases such as allergic rhinitis, asthma, bronchitis, organic dust toxic syndrome and hypersensitivity pneumonitis. However, the role of fungi in mediating allergic reactions remains unclear. Although many species are known to produce allergens inducing an Immunoglobulin E (IgE) and IgG response, the importance of many other additional species remains unrecognised. This is partly because of the vast number of fungi that occur naturally and the diversity of allergens within different species, which is further confounded by the poor quality of commercial extracts available for diagnosis and the methods of analysis used to quantify airborne counts. In addition, the interaction of fungi with the airways is complex and involves a number of innate and acquired mechanisms, including allergic responses. This introduction will discuss the current understanding of allergy, the biology of fungi, the nature and location where people may come into contact with fungal allergens and review the methods available to measure exposure to airborne fungi and diagnose fungal allergic sensitisation. 1.1 Respiratory allergy – a brief history of the problem The first documented report of an allergic reaction occurred to King Menes of Egypt around 2, 600 B.C., who supposedly died from anaphylaxis following a wasp sting. ∗ Chapter 1, Section 1.6 was published as “Measuring environmental fungal exposure” in Medical Mycology in 2005. 1 Other reports from ancient history include, Britannicus, the son of the Roman emperor Claudius, who was described to develop swelling around his eyes following horse riding and King Richard III of England, who was reported to get urticaria from strawberries (Cohen and Evans, 1991). Adverse health effects related to microbial growth in the indoor environment were documented as far back as Leviticus, in the 3rd book of the Old Testament, in which home occupants were warned against the growth and spread of red or green-like depressions on the walls, which was most likely mould growth (Schoental, 1980; Leviticus, 14th Chapter, versus 34-45). The most comprehensive early clinical description of hay-fever was published by Dr. Charles Blackley in 1873, who observed that the inhalation of grass pollen during winter induced hay-fever (Blackley, 1873). The term allergy (from the Greek word “allos” meaning changed or altered state and “ergon” meaning reaction or reactivity) was later coined by the Venetian paediatrician, Clemons von Pirquet in 1906 (von Pirquet, 1907). Further development of the field occurred during 1911, when Noon and Freeman injected allergen solutions into subjects to build up immunotolerance, in addition to performing provocation tests by putting drops of allergen extracts in the eyes of subjects (Noon, 1911). In 1918, Robert Crooke opened the first clinic in a New York hospital to treat allergic symptoms and along with colleague Arthur Cocoa, were the first to use the term “atopy” and the serum factors called “reagins”. These were further characterised throughout the 1960’s and were later termed “IgE antibodies” by Ishizaka and colleagues (Roitt et al., 1998). This breakthrough enabled further progress into the understanding of the mechanisms of atopy and sensitisation to allergen sources (Bennich et al., 1968). Allergy is currently defined as the hypersensitive response of the immune system to ingested or inhaled foreign proteins and allergens (Bierman and Van Arsdel, 1999; Blumenthal and Rosenberg, 1999; Chiu and Fink, 2002). The clinical manifestation of symptoms, including wheeze, coughing, shortness of breath, sneezing, nasal discharge, urticaria, angioedema and anaphylaxis are conditions associated with allergic rhinitis, conjunctivitis and bronchial asthma. Environmental exposure to allergens is an important step in the aetiology and exacerbation of allergic conditions, in 2 particular allergic rhinitis, conjunctivitis and bronchial asthma (Blumenthal and Rosenberg, 1999). However, even after extensive environmental exposure to certain aeroallergen sources, it has been shown that not all individuals develop allergic disease, which is strong evidence for genetic predisposition (Marsh et al., 1981; Howard et al., 1997; Cookson, 1999; Holloway et al., 1999; Ong and Hirsch, 1999). 1.2 Prevalence of allergic respiratory disease The prevalence of “allergy” affects approximately 20-30% of the population, although this figure has been shown to be highly variable between countries in the recent International Study of Asthma and Allergies in Childhood (ISAAC, 1998). In the questionnaire-based survey, which included 155 centres in 56 countries, the highest prevalence (>20%) of allergic rhinitis and asthma among children aged 13-14 years were found in Australia, New Zealand, The United Kingdom and Ireland. Other studies have identified similar prevalence rates (~10-20%) (Hagy and Settipane, 1969; Gergen et al., 1987; Wuthrich, 1989; Ogino et al., 1990), although recent evidence suggests that allergic diseases may be increasing for reasons that remain to be identified. Epidemiologic studies have hypothesised that the rise in allergic diseases, particularly in industrialised countries, can be attributed to a number of societal and environmental variables. Increasing levels of atmospheric pollutants, including cigarette smoke (Wuthrich, 1989; Davies et al., 1998), suspended particulate matter (Takafuji and Nakagawa, 2000), diesel exhaust particulate (D'Amato et al., 2000), ozone and sulphur dioxide (D'Amato, 2000) have been shown to damage the mucosal membrane and promote IgE mediated immune responses. However, these factors alone may not necessarily account for the increased prevalence of disease. Societal changes, including shifts towards single parent families, childhood vaccinations, parental control, children spending more time indoors and cleaner home environments are factors believed to have changed the incidence of common childhood diseases, which have resulted in differences of allergen exposure (Erwin and Platts-Mills, 2005). In addition, factors associated with the lifestyle of populations or families, such as socio-economic status, 3 sibship size, early childhood infection, dietary habits, growing up in anthroposophic families or a farming environment are important parameters that are often neglected in epidemiologic studies and might prove to be of greater relevance in the study of allergic disease (Kitch et al., 2000; von Mutius, 2000). Thus, anthropogenic change has lead to the creation of what is known as the “Hygiene hypothesis”. This is currently the subject of much research. The Hygiene hypothesis refers to a paradox, whereby the greater hygiene of modern lifestyles reduces microbial exposure, but also modulates immune responses, such that the likelihood of developing allergic diseases is increased. Within the atopic population, the prevalence of mould allergy has been estimated to range from 2 to 90% (Hasnain et al., 1985; Santilli et al., 1985; Lehrer et al., 1986; Portnoy et al., 1987; Sprenger et al., 1988; Brunekreef et al., 1989; Santilli et al., 1990; O'Hollaren et al., 1991; Szantho et al., 1992; Helbling et al., 1994; Horner et al., 1995; Vijay et al., 1998; Black et al., 2000; Zureik et al., 2002). The heterogeneity between the prevalence of reactivity can be accounted for by variations in airborne fungal concentrations in different sampling environments, the selection criteria for test subjects and the source and batch of commercial fungal extracts. Previous studies have shown that reactions to commercial extracts vary anywhere from 6-70% in the same population (Aas et al., 1980; Portnoy et al., 1987). Using recently available assays for individual fungal allergens, the allergenic content of commercial extracts of Aspergillus fumigatus may vary by up to 400 fold (Vailes et al., 2001). Given the ubiquitous nature of fungi, the number and diversity of species, their composition and the vast numbers of tiny, buoyant spores they frequently produce, it is not surprising that variations in allergen extracts exist and thus the true prevalence of fungal allergy will remain unknown until standardized extracts are made available and tested on well-defined populations. 1.3 Innate and adaptive immunity The host response against fungal pathogens, foreign bodies and infection requires an integrated response between innate immunity, adaptive immunity and fungal virulence 4 factors. Innate immunity is the first line of defence against pathogen invasion until adaptive immunity develops and is driven by the mediation of specific cell types, including macrophages, eosinophils, basophils and T-lymphocytes, such as γδ T-cells or natural killer cells (Nicod and Spiteri, 2001). This arm of immunity initially senses the incoming pathogens via complex interactions between secreted pathogenic macromolecules and a family of host Toll-like receptors (TLRs), which then initiate a range of host defensive mechanisms. To date, at least 10 members of TLRs and their associated ligands including lipopolysaccharides, lipoproteins, bacterial peptidoglycans and bacterial deoxyribonucleic acid have been identified (Krutzik et al., 2001; Nicod and Spiteri, 2001; Takeda and Kaisho, 2003). Further recent findings