IgA containing immune complexes in dogs bearing a spontaneous mammary adenocarcinoma.

Sera from dogs with mammary adenocarcinoma were assessed for the presence of immune complexes (IC) and the physicochemical composition of these complexes was investigated. Employing 125I-anti-canine IgG as indicator, elevated levels of C1q binding IgG were detected in sera of dogs with mammary adenocarcinoma. Polyacrylamide gel electrophoresis (PAGE) analysis of IC isolated by G-200 fractionation and protein A affinity chromatography revealed the presence of a dense polypeptide band corresponding to the alpha chain of IgA which was present in the mammary adenocarcinoma sera but not in normal dog sera or sera from dogs with other tumours. Employing monospecific radiolabelled anti-canine IgA as indicator in solid phase C1q binding radioimmunoassays, significantly elevated levels of C1q binding IgA were detected in five of eight mammary adenocarcinoma sera but not in sera of normal dogs or other tumour bearing dogs (P less than 0.05). Sera from mammary adenocarcinoma bearing dogs treated with 5% polyethylene glycol (PEG) and subjected to sucrose density gradient ultracentrifugation revealed IgA containing IC in fractions greater than 7S to greater than 19S. Findings suggest that IC are present in sera of dogs with mammary adenocarcinoma and that that IgA is a major and unique component of these complexes and, hence, may play a significant role in the development and evolution of the canine immune response to mammary adenocarcinoma.