Cat IgA, representative of new carbohydrate cross-reactive allergens

Background: Allergens from cat are among the most potent elicitors of allergic disease. Four cat allergens have been identified; however, evidence indicates the existence of additional allergens. Objective: In this study, we evaluated IgE sensitization to IgA from cat. Methods: Sera from cat-sensitized patients (n = 81) were analyzed for IgE antibodies to purified cat IgA in the Pharmacia CAP System. Indirect ELISA was performed with cat IgA, cat IgM, and deglycosylated cat IgA. Competitive inhibition ELISA was performed with cat IgA, cat IgM, calf intestine alkaline phosphatase (CIP), and cat serum albumin on solid phase bound cat IgA. IgE reactivity was also evaluated on membrane blotted cat IgA. Results: Thirty-eight percent (31/81) of the cat-sensitized sera were ImmunoCAP-positive to cat IgA. Indirect ELISA demonstrated a high correlation between IgE reactivity to cat IgA and cat IgM (r = 0.94; P < .001). Very low responses were observed to deglycosylated IgA. Strong inhibition of cat IgA was observed in all sera after preincubation with cat IgA and cat IgM. Inhibition was also observed in most sera after preincubation with CIP. Immunoblotting demonstrated that the IgE reactivity was mainly directed to the heavy chain of IgA. Conclusion: This study has revealed a new allergen, cat IgA, containing a novel group of cross-reactive epitopes depending on carbohydrates also present on IgM and partially on CIP. Clinical implications: This new group of cross-reactive carbohydrate IgE epitopes should be taken into consideration when diagnosing patients with suspected animal allergy.