Guinea pig Ia antigens are not derivatised on trinitrophenyl-modified cells.

THE proliferative response of hapten-reactive guinea pig T lymphocytes to trinitrophenyl (TNP)-modified macrophages is regulated by the I-region of the major histocompatibility complex (MHC) of the priming macrophage1. Recent studies2,3 have suggested that the immunogen recognised by the T cell contains both TNP determinants and Ia antigens, as proliferation can be specifically blocked by anti-TNP serum as well as by anti-Ia sera directed against the stimulator macrophage. However, the precise nature of the association between the TNP determinant and the Ia antigens forming this immunogen remains unclear. In an effort to clarify the nature of the TNP-specific immunogen recognised by the T cell, we have analysed, by chemical methods, the membrane proteins of TNP-modified guinea pig macrophages. We report here experiments which demonstrate that macrophage Ia antigens are not directly trinitrophenyl-derivatised on TNP-modified macrophages.