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

Summary 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.