Impact of Aspergillus fumigatus in allergic airway diseases

Fungi are ubiquitous and responsible for causing a broad spectrum of type I-IV hypersensitivity diseases [1]. Recent epidemiologic studies clearly outline the link between fungal sensitization and exacerbations of allergic asthma, leading to increased morbidity and mortality [2-4]. The major respiratory manifestations caused by fungi include allergic bronchopulmonary mycoses (ABPM), severe asthma with fungal sensitization (SAFS), hypersensitivity pneumonitis, fungal sinusitis and allergic rhinitis [1]. In contrast to other allergens (e.g. pollen), fungi also pose a life-threatening risk for invasive pneumonia in immunocompromised patients; further emphasizing their significant impact on human health. It is now understood that the pathogenesis of diseases like asthma and allergy is determined by the interactions between host, genes and environment [5,6]. In this review, we focus on the role of filamentous fungi in respiratory allergic diseases, and discuss how fungi mediate T helper (Th) 2 -mediated allergic diseases as a result of host-pathogen interactions that lead in ineffective clearance of spores, and how predisposing factors like host genetics determine outcomes for respiratory diseases.Amongst the filamentous fungi, Aspergillus species have been strongly linked with exacerbations of asthma and other respiratory allergic diseases [2,7]. Over 80% of Aspergillus-related conditions, such as extrinsic allergic alveolitis, asthma, allergic sinusitis, chronic eosinophilic pneumonia, hypersensitivity pneumonitis, SAFS, and allergic bronchopulmonary aspergillosis (ABPA) are most frequently caused by A. fumigatus [8]. ABPA is the most complex allergic manifestation caused by A. fumigatus, and was first reported in the United Kingdom by Hinson et al. in 1952 [9]. Other fungi such as Cryptococcus neoformans and Scedosporium apiospermum are also associated with similar clinical manifestations broadly referred to as ABPM.Improved diagnostic methods and awareness have led t