TGF?? REGULATES CELL-MEDIATED IMMUNITY IN LONG-TERM ALLOGRAFT RECIPIENTS

Abstract

497 Introduction: Long-term allograft acceptance, i.e. operational tolerance, develops in murine cardiac allograft recipients after short-term treatment with anti-CD4 mAb or gallium nitrate (GN). However, little is known regarding the immunologic mechanisms of allograft acceptance. One feature of cardiac allograft acceptance is the inability to mount delayed type hypersensitivity (DTH) responses when challenged with donor alloantigens. We have investigated the possible role of transforming growth factor beta(TGFβ) in DTH unresponsiveness. Methods and Results: We first determined if exogenous TGFβ could interfere with DTH responses to alloantigens or tetanus toxoid (TT). The pinnae of naïve mice were injected with TT-sensitized or allosensitized splenocytes, TT or subcellular alloantigens, and various concentrations of TGFβ DTH responses were measured as ear swelling after 24 hours. We observed that the strong, antigen-specific DTH responses made by the transferred splenocytes were reduced to baseline levels by as little as 2.5 ng of TGFβ. These DTH responses were unaffected by up to 10 ng of control cytokine, IL-2. We next determined it TGFβ participates in the donor-reactive DTH unresponsiveness that develops in long-term allograft recipients. Allograft acceptance was induced by 28 day treatment with GN, and DTH responses were evaluated no less than 30 days after GN treatment was stopped. Splenocytes from these mice were transferred into the pinnae of naïve, syngeneic mice along with donor alloantigen plus 25 µg of polyclonal rabbit anti-mouse TGFβ antibody. The presence of anti-TGFβ antibodies at the DTH challenge site allowed strong anti-donor DTH responses to be expressed. This restoration of donor-reactive DTH was not observed with control antibodies, including non-immune rabbit IgG and anti-murine IL-2 antibody. Conclusions: These studies demonstrated that long-term allograft recipients are sensitized to donor alloantigens, and have the ability to mount a donor-reactive DTH response. However, this ability is blocked by the local (antigen-induced?) production of TGFβ at the DTH challenge site. A similar regulatory mechanism may be responsible for allograft acceptance in these animals.