Evaluation of serum obtained from atopic dogs with dermatitis attributable to Malassezia pachydermatis for passive transfer of immediate hypersensitivity to that organism

OBJECTIVE: To determine the functionality of canine anti-Malassezia IgE via the passive transfer of immediate hypersensitivity localized to the skin (ie, cutaneous anaphylaxis) from atopic dogs with dermatitis attributable to overgrowth of Malassezia pachydermatis (Malassezia dermatitis MD]) to healthy recipient dogs by use of the Prausnitz-Küstner (P-K) technique. ANIMALS: 7 clinically normal dogs, 32 atopic dogs with MD, serum from 11 atopic dogs with MD, and 3 healthy dogs without prior sensitization to M pachydermatis. PROCEDURE: Serum from atopic dogs with MD was used for P-K tests in 3 clinically normal recipient dogs. Serial dilutions of untreated, heat-inactivated, IgE-absorbed, and bovine serum albumin (BSA)-absorbed (control) aliquots of serum were injected ID in triplicate for dermal sensitization. Twenty-four, 48, and 72 hours later, a crude extract of M pachydermatis was injected ID into the sites used for sensitization injections, and immediate hypersensitivity reactions were graded on a 4-point scale. RESULTS: Untreated serum caused P-K reactivity beginning 24 hours after passive sensitization and persisting through 72 hours (titers, 1:32 to 1:64). Heat inactivation and IgE-absorption of serum eliminated P-K reactivity, whereas treatment of serum with BSA did not. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of P-K test results supports the passive transfer of cutaneous anaphylaxis by anti-Malassezia IgE and indicates it is functional in type-1 hypersensitivity reactions of atopic dogs with MD. Reduction or blockade of anti-Malassezia IgE in atopic dogs with MD may provide better clinical control of the disease.