12 Ly AND Ia ANTIGENS ON T CELLS

T lymphocytes participate in many immunologic functions. For example, they may become cytotoxic cells (Tc), ~ exert helper (TH) or suppressor (Ts) effects on antibody production, or trigger the inflammatory response of delayed-type hypersensitivity (DTH) (TD). Recently, it has been demonstrated (1, 2) that some of the T cells involved in these functions may be characterized by their cell surface antigens. The Ly (2) and Ia (3) alloantigens have been especially useful in this regard. Thus cytotoxic and suppressor functions are diminished by treatment with anti-Ly-2 serum, but not by anti-Ly-1 serum (4, 5), whereas helper functions are sensitive to anti-Ly-1 serum, but not to anti-Ly-2 serum (2). Treatment with anti-Ia serum has been reported to diminish helper and suppressor functions, but not cytotoxic functions (3). In this paper we report that the cells responsible for DTH are similar to TH in their Ly phenotypes but, unlike some primed helper cells, are Ia negative.