Role of CD4(+) regulatory T cells in hyperbaric oxygen-mediated immune nonresponsiveness

We have previously shown that hyperbaric oxygen culture (HOC [95% O-2, 5% C O2, 25 psi]) is an effective pretransplant tissue-modification technique th at results in long-term allograft survival and the induction of systemic im mune tolerance in a murine model. Here we address the immune modulatory eff ects of HOC-treatment of human immune responses using the in vitro mixed ly mphocyte: reaction (MLR). Pretreatment of allogeneic stimulator cells with HOC results in abrogation of cytotoxic T lymphocyte (CTL) activity, prolife rative responses, and IFN gamma production in a 7-day MLR. These responses can be restored either by the addition of IFN gamma or IL-2 on day 0, or by blocking the activity of IL-4 and IL-10. The addition of IL-2 on day 4 doe s nor restore allospecific CTL activity. The failure of HOC-treated cells t o induce allospecific CTL is not due to the induction of anergy, demonstrat ed by the failure to restore responses after restimulation with allogeneic cells in the presence of IL-2. Removal of CD4(+) cells prior to restimulati on, results in restoration of CTL activity in MLR cultures restimulated wit h HOC-treated allogeneic cells. These results suggest chat HOC-induced immu ne nonresponsiveness is mediated by the development of CD4(+) regulatory ce lls in a Th2-type environment. (C) American Society for Histocompatibility and Immunogenetics, 2000. Published by Elsevier Science Inc.