Cloned T Suppressor Cells BY YOSHIHIRO ASANO

The activation of antigen-specific B cell responses can be modulated by a number of T cell regulatory influences. It was first observed (1-3) that B cell responses to many antigens require the participation of T helper (Th) ~ cells. Studies (4, 5) using both heterogeneous and, more recently, cloned Th populations have shown that distinct B cell activation pathways exist in which Th cellB cell interactions may be either major histocompatibility complex (MHC)restricted or -unrestricted. It has also been shown (6-14) that these B cell responses are subject to the regulatory effects of T suppressor (Ts) cells, and that these suppressive effects may also involve antigen-specific and genetically restricted cell interactions. The overall complexity of T cell regulation is further increased by the activation of both augmenting (Ta) (15, 16) and contrasuppressor (Tcs) (17) T cells, which appear to further modify T cell-dependent (TD) B cell activation. Previous studies (4, 5) have shown that both cloned and heterogeneous populations of Th cells are capable of activating B cells in a manner that requires both MHC-restricted Th cell-B cell interaction and carrier-hapten linkage. The MHC-restricted activation of B cells by cloned Th cells was found (16) to be enhanced substantially by a population of MHC-restricted Lyt-l+,2 Ta cells present in unprimed spleen. In addition, suppression of TD B cell responses in vitro has been shown using both heterogeneous (14, 18, 19) and cloned (20) populations of Ts cells. Given the potential complexity of interactions that may occur among T cell subpopulations present in heterogeneous T cells, the exclusive use of highly selected or monoclonal T cell populations offers a significant advantage to studies of T cell regulation. Further studies were therefore initiated to investigate the interaction of cloned Th and cloned Ts cells in an effort to define the mechanisms of their actions on B cell activation. Recently (21), we showed that cloned Ts