Studies on in vitro lymphocyte stimulation assay in cattle naturally infected with Brucella abortus and in cattle vaccinated with strain 19.

Cell-mediated immune responses of cattle in infected herds vaccinated with Brucella abortus, strain 19, and of nonexposed controls were studied by an in vitro lymphocyte stimulation test (LST). Brucella abortus soluble antigen was used as a specific stimulator of lymphocytes. Lymphocyte suspensions were prepared from peripheral blood of cattle by the Ficoll-diatrizoate technique. Cultures were labeled with [3H]thymidine and were assayed for [3H]thymidine incorporation into DNA by liquid scintillation spectrometry. Seroagglutination tests and cultures from Brucella were conducted simultaneously with LST. Brucella abortus soluble antigen induced significantly higher (P less than or equal to 0.005) lymphocyte stimulation responses in lymphocytes from cattle infected with B abortus than in lymphocytes from cattle vaccinated with strain 19 or from nonexposed controls. There was a significant P = agreement in results of LST and seroagglutination tests in infected cattle. Among seropositive-vaccinated cattle and controls, the LST was negative.