Suppressive and Enhancing T-cell Factors as I-region Gene Products: Properties and the Subregion Assignment

A considerable body of evidence has been accumulated suggesting that cell interactions in the initiation and regulation of immune responses are achieved via complementary interactions of cell-surface molecules expressed on different subsets of immunocompetent cells. Among these molecules, much attention has been focused on the role of products of the major histocompatibility gene complex (MHC) as devices for such cell-to-cell communication (reviewed by Katz and Benacerraf 1975). Thus the diversity of the phenotypic expression of different MHC genes on functionally different subsets of lymphoid cells is indeed a crucial problem in understanding the network of immunocompetent cell interactions. This has been strengthened by recent discoveries of various T-cell factors carrying I-region-associated determinants (Taussig and Munro 1974; Armerding and Katz 1974; Takemori and Tada 1975; Erb and Feldmann 1975; Kapp et al. 1976) which enhance or suppress humoral antibody responses in mice. These factors now provide important clues for studying interactions...