Transfer of passive cutaneous anaphylaxis to Malassezia pachydermatis by the serum of atopic dogs with Malassezia dermatitis

Abstract

In atopic dogs with Malassezia dermatitis (MD), type 1 hypersensitivity reactions and circulating serum IgE reactive to M. pachydermatis extracts have been reported. The purpose of this study was to evaluate the functionality of anti‐Malassezia IgE by the transfer of passive cutaneous anaphylaxis (PCA testing). Three nonatopic dogs were used as recipients. Two test sera were utilized: pooled sera from 10 atopic dogs with MD that were skin test positive to M. pachydermatis extract; and serum from an atopic dog with MD that exhibited high levels of anti‐Malassezia IgE on an ELISA assay. One aliquot of each untreated serum, one aliquot of each serum heated at 56 oC for 4 h and two aliquots of the ELISA‐positive serum adsorbed with either mouse anticanine IgE or bovine serum albumin (as a control) were utilized. Six serial dilutions of all six aliquots were injected intradermally in triplicate, along with a 20 µg mL−1 extract of M. pachydermatis to rule out prior sensitization to the yeast. At 24‐, 48‐ and 72‐h intervals, the yeast extract was injected intradermally at the sites of prior serum injections and wheal/flare responses were graded 0–4+ compared with saline and histamine controls. Through 72 h, all dogs showed > 2+ reactions at the injection sites of both the untreated sera and the BSA‐treated sera (titers = 1:64), but no reactions at the sites of heat‐inactivated and IgE‐adsorbed sera. These results support the transfer of PCA by anti‐Malassezia IgE and implicate it to be functional in type 1 hypersensitivity. Funded by the Canine Health Foundation of the American Kennel Club.