Abstract
Incidence of fungal infections has increased alarmingly in past few decades. Of the fungal pathogens, the Aspergillus fumigatus has been a major cause of allergic bronchopulmonary aspergillosis (ABPA) which has five main stages--the acute, remission, exacerbation, glucocorticoid dependent and fibrotic stage. The diagnosis of ABPA remains difficult due to its overlapping clinical and radiological features with tuberculosis and cystic fibrosis. From past few decades, the crude fractions of A. fumigatus have been used for immunodiagnosis of ABPA. Most of the detection kits based on crude fractions of A. fumigatus are quite sensitive but have low specificity. Till date 21 known and 25 predicted allergens of A. fumigatus have been identified. Of these allergens, only five recombinants (rAsp f1-f4 and f6) are commercially used for diagnosis of allergic aspergillosis. Remaining allergens of A. fumigatus have been restricted for use in specific diagnosis of ABPA, due to sharing of common antigenic epitopes with other allergens. Complete sequencing of A. fumigatus genome identified 9926 genes and the reports on the proteome of A. fumigatus have shown the presence of large number of their corresponding proteins in the pathogen. The analysis of immunoproteomes developed from crude fractions of A. fumigatus by IgG/IgE reactivity with ABPA patients and animal sera have identified the panel of new antigens. A brief description on the current status of A. fumigatus antigens is provided in this review. The implementation of advance recombinant expression and peptidomic approaches on the A. fumigatus antigens may help in the selection of appropriate molecules for the development of tools for more specific early diagnosis of ABPA, and desensitization therapies for patients of allergic disorders.
Highlights
Among the pathogenic species of Aspergillus, A. fumigatus is the most common cause of aspergillosis which includes a spectrum of diseases
It was demonstrated by Fukahori et al (2010) that A. fumigatus conidia could regulate the functions of airway dendritic cells in the development of mite allergen-induced allergic airway inflammation [58]
To overcome the limitations associated with A. fumigatus recombinant molecules or crude antigens based assays, the identification of new and specific allergens has become essential for the development of more specific diagnostic assays to detect allergic aspergillosis in the suspected patients at an early stage of infection
Summary
Among the pathogenic species of Aspergillus, A. fumigatus is the most common cause of aspergillosis which includes a spectrum of diseases. The conidial production of A. fumigatus has been highly prolific and, the human respiratory tract always remains at risk of acquiring Aspergillus infection [1]. The germination of conidia in the respiratory tract and the extent of mycelial colonization in lungs has been shown to be influenced by the competence of the host immune system [2]. It has been suggested that the immunogenic responses may get induced after the release of cellular proteins including virulence factors and allergens from metabolically active germinating conidia. Such initial allergic reactions have been accountable for development of different forms of allergic aspergillosis. Detailed knowledge of allergenic and antigenic molecules of A. fumigatus is required for the selection of molecules for application in specific diagnosis and immunotherapy of aspergillosis
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