Regulatory T Cell Function, Antigen Recognition, and an Immunological Decision Point

Abstract

Since their discovery, thymus dependent (T) lymphocytes have held the promise of a key to the fundamental mystery of the immune system: the discrimination of self from nonself. There are two reasons for this. The first is that helper T cells, which are required for the vast majority of immune responses, only respond to their antigens in the presence of products of the major histocompatibility complex (MHC) (1). Thus, they respond to a combination of nonself (antigen) and a form or marker of self (class II MHC molecules). The second reason is that another type of T cell, the suppressor T cell, is capable of inhibiting immune responses to specific antigens. Thus, one can imagine that these cells normally prevent unwanted responses to self antigens while allowing responses to non-self antigens. In fact, examples of such control have been described (2,3). Unlike helper T cells, however, the antigenspecific products of suppressor T cells respond to antigen in the absence of MHC molecules. One therefore has the feeling that if we could fully understand the basis for each type of response to antigen (help vs suppression) we would reveal the hidden mechanisms of self-nonself discrimination.