Interactions of human T cell subsets during the induction of cytotoxic T lymphocytes: the role of interleukins.

In this work we study the role of subsets of human T cells, detectable by the OKT series of monoclonal antibodies, in the production of and the response to the lymphokine interleukin-2 (Il-2) during the course of an allogeneic cytotoxic T lymphocyte response in vitro. The results obtained establish that the Il-2 producer cells reside within the OKT4 positive T cell subset. Once produced, Il-2 mediates the clonal expansion of alloantigen-activated cytotoxic T killer cells which reside in the OKT8 positive T cell subset. Il-2 appears to have no mitogenic activity on the activated OKT4 positive T cells which produce the lymphokine. In order to release Il-2, the OKT4 positive T cell requires a stimulus, such as allogeneic cells or the lectin phytohaemagglutinin A (PHA). Macrophages are also required for Il-2 production, but the macrophage requirement can be bypassed by a soluble macrophage product as found in supernatants of lymphocyte cultures stimulated with lipopolysaccharide (LPS), the biological activity presumably representing Interleukin-1 (Il-1).