Pitfalls in immunofluorescence testing in dermatology. II. Pemphigus-like antibodies in the cat, and direct immunofluorescence testing of normal dog nose and lip.

Indirect immunofluorescence testing for pemphigus-like antibodies was performed on 75 cats: 25 cats with various nonpemphigus dermatologic diseases, 25 cats with various nondermatologic diseases, and 25 normal cats. Pemphigus-like antibodies were not detected. It was concluded that neither true pemphigus antibodies, nor pemphigus-like antibodies are commonly detected by indirect immunofluorescence testing in the cat. Direct immunofluorescence testing for IgG, IgA, IgM, and C3 was performed on the nose and lip of 15 normal dogs. Granular deposition of IgM at the basement membrane zone of the nose was demonstrated in 11 of the 15 dogs. Lip was consistently negative. It was concluded that direct immunofluorescence testing of canine nose by only polyvalent immunoglobulin antisera or anti-IgM antisera may lead to misinterpretation and misdiagnosis in up to 73% of all dogs tested.