FAILURE OF TGF-BETA-1 AND IL-12 TO REGULATE HUMAN FASL AND MTNF ALLOREACTIVE CYTOTOXIC T-CELL PATHWAYS

The effect of TGF beta 1 and IL-12 on calcium-independent cytotoxic pa thways was investigated we have previously demonstrated that the regul atory effect of TGF beta 1 and IL-12 on human alloreative CTL activity was associated with regulation of perforin and granzyme B gene expres sion. To determine the effect of both cytokines on the alternative cyt otoxic pathway involving Fast and mTNF, we first investigated the expr ession of both molecules on human primary alloactivated T cells. Our r esults show that human allostimulated T lymphocytes express Fast. Cell lysis experiments demonstrate that the Fast cytotoxic pathway is invo lved in the killing of specific target cells mediated by human allorea ctive CTL. In addition, allogeneic stimulation induced significant mTN F expression on both CD4+ and CD8+ responder T cells. Using TNF-sensit ive target cells, we also demonstrate that the mTNF-mediated cytotoxic pathway is involved in the cytotoxic activity oi human primary allost imulated T lymphocytes. Neither TGF beta 1 nor IL-12 had an effect on Fast or mTNF expression. Furthermore, addition of TGF beta 1 or IL-12 al the initiation of the MLR had no significant effect on Fas-and mTNF -mediated cytotoxicity. Taken together, our results provide a novel in sight into the differences between regulation by cytokines of perforin -dependent and -independent cytotoxic mechanisms. Unlike their role in the perforin/granzyme B pathway, TGF beta 1 and IL-12 do not appear t o mediate any regulatory effect on Fast and mTNF cytotoxic pathways us ed by human alloreactive primary CTL.