Identification of immunoglobulin-secreting cells among canine peripheral blood mononuclear cells by the protein A hemolytic plaque assay.

Canine peripheral blood mononuclear cells (PBMC) were assayed for plaque-forming cells either immediately after isolation or after 6 days of culture in fetal calf serum in the presence of a B cell mitogen. Immediately-assayed PBMC produced a mean of 4870 IgG-related, 1610 IgM-related, and 760 IgA-related plaques per 10(6) PBMC. Many of the plaques formed by freshly isolated PBMC, however, appeared to represent release of previously adsorbed antibody. In contrast, plaques formed by cultured cells clearly identified immunoglobulin-secreting cells. We therefore used a system with culture conditions optimized for maximum plaque production to quantify pokeweed mitogen-stimulated plaque formation by normal canine PBMC. A mean of 560 IgG, 180 IgM, and 18 IgA plaque-forming cells could be identified among PMBC of 22 normal dogs. This assay will be useful for further characterization of canine lymphocyte subpopulations and facilitate the study of immunologic disorders in canine models.