C1.7 monoclonal antibody designates high-avidity CD4+ cytotoxic T lymphocytes involved in clinical heart rejection

It is assumed that not all donor-specific cytotoxic T lymphocytes (CTLs), but only those with a high avidity for donor antigens, can function as terminal effector cells in transplant rejection. In the present study, we searched for markers that would exclusively designate these high-avidity CTL. FACS analysis of donor-specific CTL clones obtained from heart transplant patients revealed that high- and low-avidity CTL varied in their expression of p38, a surface molecule involved in signal transduction, which is stained by the antibody C1.7. High- and low-avidity CD8+ CTL and high-avidity CD4+ CTL expressed p38, whereas low-avidity CD4+ CTL did not. Noncytotoxic and naive CD4+ lymphocytes also lacked p38 surface expression. Therefore, we conclude that p38 is a marker for CD4+ lymphocytes with the potency to damage the transplanted heart. Accordingly, p38 might be used to analyze the contribution of CD4+ CTL in immune responses, such as transplant rejection.