Allergenic cross-reactivities in flea-reactive canine serum samples

Abstract

Objectives - To determine whether flea extract could be determined (via ELISA) to share allergenic epitopes with other insects, and to determine whether sera with different reactivities to insect extracts have different cross-reactivity patterns. Sample Population - 69 canine serum samples that were selected from samples submitted for routine ELISA allergy testing and had previously been found to have high reactivities to flea. Procedure - Each serum sample was assessed by means of a direct ELISA for IgE binding to 11 common insects. Samples that were reactive primarily to flea extract alone were designated pool 1, samples that were reactive to small numbers of insects were designated pool 2, and samples that were reactive to all or almost all insects were designated pool 3. Samples that did not have any apparent patterns of cross-reactivity were not included in the rest of the study. Inhibition ELISA techniques were used with the 3 serum pools to determine whether multiple insect extracts inhibited reactivity on flea-coated ELISA plates. Those extracts were used to coat ELISA plates, and reciprocal inhibition studies were then performed. Results - Black fly, black ant, and cockroach extracts were capable of > 50% inhibition of flea solid-phase IgE binding with all 3 serum pools. In the ELISA inhibition studies, flea extract was able to inhibit IgE binding to each extract with all pools, confirming reciprocal inhibition. Conclusions - Inhibition of IgE binding to solid-phase flea antigen by black ant, black fly, and cockroach extracts suggested sharing of allergenic epitopes among these species. Reciprocal inhibition studies further confirmed these findings. These results indicated in vitro cross-reactivity between flea, black ant, black fly, and cockroach extracts. These results need to be further investigated in vivo. Clinical Relevance - It is possible that dogs may become sensitized to fleas via exposure to other insects, and that flea allergenic dogs may have signs of pruritus, in the absence of fleas, if exposed to cross-reactive insects.