Soluble bacterial antigen induces specific helper and cytotoxic responses by human lymphocytes in vitro

Fresh human T lymphocytes respond proliferatively to soluble antigens, such as PPD, provided the cell donor has been immunized to those antigens in vivo. This proliferative response requires the addition of antigen-presenting cells bearing autologous HLA-D antigens. This report demonstrates that the proliferative response to PPD activates a collaborative response that aids in the activation of alloreactive cytotoxic T cells (Tc). Furthermore, the proliferative response to "soluble" PPD alone activates a population of Tc specifically able to destroy autologous target cells passively labeled with PPD. Allogeneic PPD-labeled targets are killed less effectively. This PPD-specific cytotoxicity is not inhibited by soluble PPD, but is competitively inhibited by PPD-labeled autologous cells. Thus, in vitro stimulation with "soluble" bacterial antigen activates both helper and cytotoxic recognition of antigen-altered self by a mechanism comparable to the recognition of viral or hapten-altered cells.