Lymphocyte Response as a Model of Cell-Mediated Immunity**Supported by ONR grant N00014-67-A-0128-0003, NIH grants GM 15422 and AI 08439. This is paper No. 1474 from the Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706

Publisher Summary This chapter focuses on lymphocyte response as a model of cell-mediated immunity. The initial response (recognition) by lymphocytes to either antigens to which the donor of the cells is sensitized or to allogeneic cells involves, at least in part, different cell populations responding to the different stimuli. Likewise, at least partial specificity was demonstrated by cells sensitized in vitro in the mixed leukocyte culture reaction in terms of an in vitro cytotoxic reaction mediated by such cells. On the other hand, the adherent cell requirement for the MLC reaction appeared to be nonspecific, as were a variety of soluble “factors” which could influence lymphocyte response. Lymphocytes from animals primed with certain antigens undergo blast transformation and mitosis in vitro when cultured with the priming antigen. It was demonstrated that different populations of antigen-specific precursor cells exist in the spleens of immunized mice. It was also observed that addition of cell-lethal amounts of tritiated thymidine to cultured cells dividing in response to sheep erythrocytes left a cell population which could no longer produce plaque-forming cells to the homologous antigen but would produce plaque-forming cells in response to a heterologous non-cross-reacting antigen.