IMMUNOREGULATION BY CD4 T-CELLS IN THE INDUCTION OF SPECIFIC IMMUNOLOGICAL-UNRESPONSIVENESS TO ALLOANTIGENS IN-VIVO - EVIDENCE FOR A REDUCTION IN THE FREQUENCY OF ALLOANTIGEN-SPECIFIC CYTOTOXIC T-CELLS IN-VITRO

Donor-specific unresponsiveness to allogeneic cardiac allografts in mi ce can be induced by the combined pretreatment with donor alloantigen and anti-CD4 antibody (anti-CD4+DST). We have investigated whether the induction of unresponsiveness in this model is due to the. presence o f T cells that regulate immune responsiveness towards the allograft. F irst, we analysed the functional characteristics of splenocytes from p retreated mice at the time of transplantation. A significant reduction in the frequency of donor specific cytotoxic precursor was found only after the anti-CD4+DST treatment. Next, we designed an in vitro assay to identify the phenotype of the splenocyte population responsible. C D4(+) and CD4(-) fractions were purified from mice treated with anti-C D4+DST or anti-CD4 alone (controls) by cell sorting. Interestingly, on ly the addition of CD4(+) cells from anti-CD4+DST created mice resulte d in a selective reduction and a bimodal distribution in the donor spe cific CTLp response, indicating the presence of a regulatory populatio n. CD4(+) cells from controls did not have this effect. These in vitro findings were substantiated by adoptive transfer experiments in vivo. These data demonstrate that CD4(+) cells with the ability to regulate immune responsiveness to a cardiac allograft are present at the time of transplantation following pretreatment with donor alloantigen in co mbination with anti-CD4. (C) American Society for Histocompatibility a nd Immunogenetics, 1998. Published by Elsevier Science Inc.