A role for helper cell subpopulations in a genetically controlled cytolytic T lymphocyte response to the H-2Db antigen.

The primary cytolytic T lymphocyte (CTL) response to the H-2Db antigen in several strain combinations appears to be under genetic control. Our studies were undertaken to determine the mechanisms involved in responders that were absent from the nonresponders and that led to CTL generation. In these studies, H-2Dk-anti-H-2Db combinations served as CTL responders, and H-2Dd-anti-H-2Db combinations served as CTL nonresponders. The nonresponsiveness of the H-2Dd-anti-H-2Db strain combinations appeared to be due to the inability of the Db antigen to activate a helper cell subpopulation. The activation of this helper cell subpopulation, as demonstrated in the H-2Dk-anti-H-2Db response, resulted in the production of factors that led to the induction of CTL differentiation. Antigen-specific pre-CTL for Db were present in the nonresponders as well as in the responders. Interleukin 2 (IL 2)-producing cells were also present in both nonresponders and responders, because all strain combinations tested in this system produced detectable levels of IL 2. Additional analysis of these data suggested that different determinants on the H-2Db antigen were recognized by distinct populations of cells. The activation of pre-CTL and IL 2-producing cells by the recognition of determinants on the H-2Db antigen was not sufficient for the generation of effector CTL, as demonstrated in the H-2Dd-anti-H-2Db response. We suggest that determinants on the H-2Db antigen that are distinct from those recognized by pre-CTL and IL 2-producing cells are recognized by a helper cell subpopulation in the H-2Dk strains, and that activation of this subpopulation is required for the production of factors that mediate CTL differentiation. This is the first description of the role that CTL differentiation factors play in a genetically controlled response.