<em>In vitro</em> Response of the Bovine Peripheral Lymphocyte to Stimulation with Cellular Antigens of Group B Streptococcus and Phytohaemagglutinin.

This investigation was conducted in two parts: first establishing separatory and cultural procedures for bovine lymphocytes, and then studying the in vitro response of these cells following stimulation with phytohaemagglutinin (PHA) and cellular constituents of Streptococcus agalactiae (St. ag.). Peripheral lymphocytes from normal animals, those with chronic St. ag. udder infections, and animals hyperimmunized with cellular constituents of St. ag. were studied. The bovine lymphocyte responded to PHA with blastogenic changes similar to those of the human lymphocyte. No changes in cellular morphology or cytochemistry were detected following in vitro stimulation with cell antigens of St. ag. Lymphocytes from hyperimmunized animals were shown to be capable of in vitro transformation in response to a different antigenic stimulation. Several explanations for this immunological inertia are presented.