Analytical bias of cross-reactive polyclonal antibodies for environmental immunoassays of Alternaria alternata

Background Alternaria alternata is recognized as an important aeroallergen indoors and outdoors, and exposure to the fungus has been identified as a risk factor for asthma. Two recent publications concluded that 95% to 99% of American homes contained detectable amounts of Alternaria antigens when analyzed with a polyclonal antibody (pAb)–based ELISA. Objectives We investigated the cross-reactivity of the commercially available pAbs that were used in those studies. Methods Reactivity to 24 fungal species commonly found in indoor environments was analyzed by inhibition ELISA by using solid-phase A alternata antigen. The pAbs were also tested by immunoblotting and halogen immunoassay for a subgroup of fungi. Results Spores of 7 fungi including species of Alternaria , Ulocladium , Stemphylium , Epicoccum , Drechslera , and Exserohilum strongly inhibited the binding of the pAbs when tested by ELISA. Six other fungi reacted in the ELISA at a lower level, and 11 fungal species including several Penicillium , Aspergillus , Fusarium , and Cladosporium species failed to show inhibition. The immunoblots and the halogen immunoassay staining confirmed the cross-reactivity patterns of the ELISA. Conclusion The pAbs against A alternata were found to cross-react broadly with related and nonrelated fungi. The prevalence data previously reported for A alternata should be considered to be fungal-reactive rather than A alternata –specific.