Demonstration of immunoglobulins and complement in canine and feline autoimmune and non-autoimmune skin diseases with the direct immunofluorescence and indirect immunoperoxidase method.

Skin sections from 71 dogs and 10 cats with bullous autoimmune skin diseases and various non-autoimmune dermatopathies were studied for the presence of immunoglobulins (canine IgG, IgM, IgA; feline IgG) and complement (canine C3) using the direct immunofluorescence method (DIF) and the indirect immunoperoxidase method (IIP). In cases of autoimmune skin diseases (9 dogs, 3 cats) both methods were of comparable sensitivity for the detection of epidermal deposits. In canine cases with non-autoimmune dermatopathies, epidermal immunoreactivity was found in 16.1% of cases with the DIF method, and in 29.0% of cases with the IIP method. With both methods, epidermal deposits were most frequently seen in skin sections of dogs with bacterial diseases. Furthermore, positive reactions were found in canine cases with hypersensitivity disorders, endocrine dermatosis, dermatomycosis, parasitic disease, cutaneous Leishmaniasis and in cases with non-specific dermatopathies of uncertain aetiology. In the majority of canine cases intercellular deposits of IgG were found. Immunohistological results should always be interpreted in conjunction with clinical and histomorphological findings in order to establish a diagnosis of autoimmune skin disease and to prevent misdiagnoses.