Role of recombinant Aspergillus fumigatus antigens in diagnosing Aspergillus sensitisation among asthmatics

BACKGROUND The diagnosis of Aspergillus-sensitised asthma (ASA) and allergic bronchopulmonary aspergillosis (ABPA) is made using IgE against crude antigens of A fumigatus (cAsp). However, the IgE against cAsp has limitations due to cross-reactivity with other fungi. OBJECTIVE To evaluate the utility of recombinant A fumigatus (rAsp) antigens in detecting ASA and their role in differentiating true from cross-sensitisation. METHODS We performed IgE against rAsp (f 1, f 2, f 3, f 4 and f 6), cAsp and other fungal (Alternaria, Candida, Cladosporium, Malassezia and Trichophyton) antigens in subjects with A fumigatus-unsensitised asthma (Af-UA [n = 51]), ASA (n = 71) and ABPA (n = 123). The diagnoses were made using cAsp-IgE and compared using rAsp-IgE. Subjects with elevated cAsp-IgE, but negative rAsp f 1 and f 2, were presumed to lack true A fumigatus sensitisation. RESULTS The prevalence of any rAsp antigen positivity (cut-off, 0.35 kUA/L) varied from 2%-22%, 32%-73% and 84%-98% for Af-UA, ASA and ABPA, respectively. The prevalence of sensitisation to other fungi ranged from 29%-65%, 59%-85% and 87%-95%, respectively, among subjects with Af-UA, ASA and ABPA. Nineteen subjects of ASA and one subject with ABPA were positive with cAsp-IgE but negative for rAsp f 1 and f 2 and were also cross-sensitised to at least one of the other fungi. Five subjects of Af-UA (cAsp-IgE negative) were rAsp f 1 or f 2 positive. CONCLUSIONS Crude Aspergillus antigens may misclassify Aspergillus sensitisation among asthmatics. IgE against rAsp antigens (f 1 and f 2) potentially detect true Aspergillus sensitisation and could be used for this purpose.