Reduced lysis by CD8+ cytotoxic T cells in mixed lymphocyte reactions induced via CD4+ T cells exposed to chemically modified antigen presenting cells.

The resistance by T lymphocytes to activation by antigen (anergy) is well documented for CD4+ T-helper (Th) cells, although less is known about CD8+ cytotoxic T lymphocytes (CTL). One widely used method of inducing anergy of CD4+Th is presentation of antigen by ECDI (1-ethyl-3-(3-dimethylamino-propyl)carbodiimide)-fixed antigen-presenting cells (APCs). We report here that in murine mixed lymphocyte reactions (MLRs), a marked reduction in detected cytotoxicity (which is mediated predominantly by CD8+ CTL) occurs on day 7 if the bulk cultures are restimulated 2 days previously with ECDI-fixed allogeneic splenocytes. No differences were seen between untreated cultures on days 5 and 7, or on day 7 of cultures to which were added unfixed allogeneic splenocytes, fixed or unfixed syngeneic splenocytes, or 'third-party' allogeneic splenocytes, 2 days previously. The effect is not mediated directly on CD8+ cells, since MLRs depleted of CD4+ cells immediately prior to exposure to fixed allogeneic splenocytes fail to show reduced lysis. On the other hand, reduced lysis did occur if CD4+ cells, purified from the MLRs on day 4, were exposed to ECDI-fixed allogeneic splenocytes and then returned to MLRs previously depleted of CD4+ cells. Moreover the effect is overcome using exogenous interleukin-2 (IL-2). We propose that CD4+ cells, restimulated by a regimen shown previously to induce their anergy, can cause a reduction in CD(8+)-mediated cytotoxicity in MLRs.