Induction Of Cardiac Allograft Specific Tolerance By All-trans Retinoic Acid In Mice

Background. All-trans retinoic acid (At-RA) has been shown to have a variety of functions including roles in inhibiting inflammation and modulating immune function, as well as inducing cell differentiation. Since inflammatory and immunological factors appear to be major pathological elements of allograft rejection, we speculated that At-RA may offer therapeutic promise. Here, we investigated the role of At-RA in allograft rejection in a murine cardiac transplantation model.Methods. We performed fully MHC-mismatched heterotopic murine cardiac transplantation. In acute rejection, recipient mice were given At-RA (3 mg·kg-1·d-1) or vehicle orally beginning 1 day before cardiac transplantation. Seven days after transplantation, allografts were harvested for histological, immunohistochemical and western blot examination. In addition, recipient spleens were studied by mixed lymphocyte reaction, western blot and flow cytometry. In chronic rejection, recipient mice were given anti-CD 154 antibody MR1 (10mg·kg-1) intraperitoneally on days 1,3 and 5 or anti-CD 154 antibody MR1 (10mg·kg-1) on days 1,3 and 5 plus At-RA (3 mg·kg-1·d-1) beginning day-1 for 60 consective days. Allografts were harvested for histological, immunohistochemical and PCR study 100 days after transplantation. Then we transfered CD11c+ dendritic cells (DC) from At-RA-treated long-term graft accepting hosts into mice that recently underwent transplantation. Recipient spleens were harvested for flow cytometry analysis at 7 days after transplantation.Results. In acute rejection, animals given At-RA showed significantly longer cardiac allograft survival than control mice (95.17±12.40 days versus 9.67±0.62 days, P＜0.05). Splenocytes isolated from At-RA-treated mice elicited a significantly lower proliferation in response to donor (BALB/c) but not third-party (C3H/He) splenocytes than controls. In vivo At-RA treatment increased frequency of splenic CD4+CD25+ Foxp3+ regulatory T cells (Treg) and reduced frequency of splenic CD4+IL-17+Th17 cells. Moreover, At-RA treatment increased the expression of Foxp3 in allografts. Interestingly, At-RA increased the expression of TGF-βand prevented the expression of IL-6 in spleens and allografts. At-RA induced low expression of CD40, CD80, CD86, and MHCⅡmolecules of CD 11 c+ DC in vivo. In chronic rejection, neointimal hyperplasia was significantly lower in allografts from mice treated with MR1 plus At-RA (luminal occlusion,26.99±6.54%) than in those from control mice (47.27±5.27%, P<0.05). Allografts from MR1 plus At-RA-treated recipients showed significantly reduced expression of IFN-y and IL-10. Furthermore, transfer of CD11c+ DC from At-RA-treated long-term graft accepting hosts into mice that recently underwent transplantation resulted in donor (BALB/c)-specific graft acceptance and in a significantly higher frequency of splenic Treg and a significantly lower frequency of splenic Th17 cells.Conclusions. At-RA prolongs allograft survival through direct and DC-mediated effects on Treg and Thl7 cells. Our data indicate that At-RA may have therapeutic properties ideally served for the treatment of allograft rejection.