Cellular responses and Mycobacterium bovis BCG growth inhibition by bovine lymphocytes

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Abstract
Cellular responses of a group of cattle immunized subcutaneously with a low dose of Mycobacterium bovis bacille Calmette-Guérin vaccine (BCG) were measured in vitro and compared with non-immunized control animals. PBMC taken from immunized animals proliferated and produced IFN-y in the presence of M. bovis BCG culture filtrate proteins. The addition of PBMC from immunized animals to M. bovis BCG-infected autologous macrophages also resulted in secretion of IFN-. In contrast, the responses of PBMC from control animals were comparatively low over the period of study. In experiments to study the interaction of non-adherent lymphocytes with infected macrophages, M. bovis BCG growth was inhibited in cultures containing autologous PBMC from immunized and non-immunized control animals. The degree of inhibition was related to lymphocyte concentration but did not correlate with IFN- production. Treatment of macrophages with recombinant IFN-y prior to, or postintection did not alter the intracellular growth kinetics of mycobacferia. It appears, therefore, that although M. bovis BCG immunization of cattle stimulates the generation of a T cell-mediated immune response to M. bovis BCG, the cattle may already possess a high level of innate resistance to M. bovis BCG that requires the presence of lymphocytes.

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