T lymphocyte clones having defined immunological functions.

T cell clones are proving to be useful for analysis of various immunological phenomena. Although some clones grow well in IL 2-containing CM alone, the combination of antigen, "filler" cells, and CM improves cloning efficiency and may favor the retention of stable clones expressing a "normal" phenotype. The antigen recognition repertoire of T cells appears to be much larger than was predicted using conventional approaches. CTLs can react with at least 23 different determinants on the H-2Kb molecule of the MHC. CTLs demonstrate MHC-restricted recognition of viral and haptenic determinants, but the restriction is not strict for all cloned cells, and a variety of reactivity patterns are found. Antigen-responsive cloned T cells appear to recognize antigens in association with alloantigens encoded by the I-A region of the MHC. However, the relevant structures formed in hybrid animals include all possible combinations of peptides including those formed by trans-complementation of I-A and I-E region gene products. Culture supernatants from antigen-responsive cloned T cells contain a variety of biological activities including IL 2, B cell-stimulating factor, colony-stimulating factor, migration inhibition factor, interferon, and factors that modulate expression of Ia antigens on macrophages and influence production of complement components. These factors may be important in mediating interactions between T lymphocytes and other cells. Cloned T cells have proved to be useful for studying the importance of particular phenotypic characteristics associated with given immunological functions. Although expression of Lyt-2 generally correlates with cytolytic activity and Lyt-1 with helper activity, important exceptions have been found with T cell clones. Cloned T cells promise to be useful for further characterization of the molecular basis of immune responses.