Effect of antigen priming on T-cell suppression. I. Activity of Ly 1+2+ feedback suppressor T-cell precursors after isolation from competing Ly 2-T cells.

Previous experiments have demonstrated that feedback suppression of murine antibody responses occurs in vitro after exposure of unprimed T-cell subsets to suppression-inducing signals from primed cells, resulting in suppression of primary and secondary IgM as well as IgG anti-SRBC responses. However, following priming with antigen when cells appear which are capable of inducing feedback suppression, the ability of unfractionated splenic T-cell populations to mediate detectable feedback suppression in vitro rapidly disappears, suggesting that priming alters the expression of feedback suppression at the same time as providing for its induction. In the present study, we have succeeded in isolating active feedback suppressor T-cell precursors (preTs) in the Ly 1+2+ and L3T4- T-cell populations from SRBC-primed as well as from unprimed mice, demonstrating that preTs are not lost after priming. The preTs isolated from primed mice resemble those isolated from unprimed mice in Ly and L3T4 phenotype, cell dose requirements, kinetics, level of suppression, and requirement for in vitro activation by primed cells. These results imply that antigen priming neither significantly depresses nor enhances the ability of Ly 1+2+ preTs to participate in feedback suppression and that activated suppressor effector cells are not detectable in the Ly 1+2+ splenic T-cell subset. Priming does, however, induce an enhancing activity in Ly 2-, L3T4+ T cells which appears to compete with feedback suppression and thus may account for the absence of detectable feedback suppression when unfractionated T cells from primed mice are the only source of preTs.