Separation of helper T cells from suppressor T cells expressing different Ly components. II. Activation by antigen: after immunization, antigen-specific suppressor and helper activities are mediated by distinct T-cell subclasses.

Cells of the Lyl subclass generate helper activity in both primary and secondary responses to sheep erythrocytes (SRBC). In contrast, after priming with SRBC, cells of the Ly-2+ subclasses, in particular Ly23 cells, have suppressive activity. The degree of Ly23-mediated suppression is directly proportional to the amount of antigen (SRBC) used for priming. Suppression by Ly23 cells is specific, because Ly23 cells from SRBC-primed animals do not suppress the response to horse erythrocytes, and vice versa. Thus, both cytotoxic and specific suppressor functions are mediated by T cells of a subclass, provisionally designated TCS, which can be distinguished from helper T cells (TH), by their Ly phenotypes. It remains to be determined whether killing and suppression are functionally interrelated properties of a single Ly23 subclass, or whether the Ly23 population comprises two subclasses whose surface phenotypes are not yet distinguishable by immunogenetic criteria.