Cellular interactions in the generation of cytolytic T lymphocyte responses Analysis of the helper T cell pathway

Murine splenic lymphocytes exhibit a requirement for helper T cells for the induction of a cytolytic T lymphocyte response to suboptimal doses of allogeneic cells, membranes from allogeneic cells, or purified H‐2 antigen in liposomes. The conditions where a requirement for help is apparent are the same conditions where a dependence on splenic adherent cells (SAC) has been demonstrated (Weinberger, O. et al., Proc. Natl. Acad. Sci. USA 1980. 77: 6091). Help can be provided in the form of primed, radioresistant, Ly‐1⁺ spleen or lymph node cells or helper factor (interleukin 2, IL‐2). A factor generated from phytohemagglutinin‐stimulated human lymphocytes, when added to culture in the presence of antigen, bypassed the requirement for Ia⁺ SAC and helper cells. IL‐2 reconstituted the response to H‐2K^k in liposomes in cultures depleted of SAC, strongly suggesting that the helper cell must see antigen re‐expressed by an antigen‐presenting cell, whereas the prekiller does not. IL‐2 could be generated by culturing Ly‐1⁺ murine spleen cells with H‐2K^k pulsed on SAC.