Local Administration Of RA (Retinoic Acid) For Prolonging Skin Allograft Survival On Rat And The Possible Mechanism

It is the main task to cover and close wound for burn treatment. Besides autoskin ,the heterogeneic skin ( allo- or xeno-skin ) is the best choice for burn wound covering. Due to immune rejection , the survival of heterogeneic skin graft on burn wound is very limited which can not meet the clinical needs. But the conventional immunosuppressive agents are not adaptive for burn patients for immune dysfunction induced by this injury. So it is an important research direction for burn treatment to explore an adaptive, effective and easy protocol to prolong the survival of heterogeneic skin graft on burn wound.It has been found that cytotoxic T lymphocyte(CTL) play major role in immune rejection process. They seem to exert their cytolytic activity through two lytic pathways: FAS/FAS Ligand(FASL) and perforin/granzyme. FasL on the CTL cell surface can trimerize Fas on the target cell membrane and initiate the Fas+ cell death pathway. FAS/FASL system seem to be the single way in CD4+ T cell mediated MHCII dismatched rejection of allograft.Recently, there has been considerable interest in the role of FAS/FASL interactions in immune privilege and immune tolerance. Many researches has been proved that the mechanisms of immune privilege such eye, testis, which can survival permanately after transplantation is the apotisis of T-cell mediated by FAS/FASL passways.It has been found that the immune rejection for heterogenic skin transplantation is acute celluar rejection and CD4+ T cell play important role in rejection process of skin allograft.In the first part of this experiment, we cultured dermal fibroblasts and mixed lymphocyte of BALB/C and C57BL/6 mice with various concentrations of RA for 72h,then the proliferation was determined by MTT and FasL production in dermal fibroblasts was determined by ELISA method. We also assayed the apoptosis rate of mixed lymphocyte by means of acridine orange and EB stain. As result, we found that RA can inhibit the proliferation of dermal fibroblast in vitro and upregulated the expression of FasL. When the concentration reaches 10-3 M/L , the highest inhibitive ratio is 72.1%. We also found RA could inhibit the proliferation of mixed lymphocyte of BALB/C and C57BL/6 mice and increase apoptosis rate in mixed lymphocyte reaction ( MLR).In the second part of this experiment ,we cut off the full-thickness skin of BALB/C mice and transplanted them on the C57BL/6 mice, 10-6M RA/2ml DMSO or 2ml DMSO were administrated locally in experimental and control groups respectively, then the clinical examination and immunohistochemical staining by FasL antibodies were invested. Then we found local administration of RA could prolong significantly the survival of allo-skin graft from 10.8 days to 24.3 days. At the same time, positive expression of FasL was found in experimental ones while not in control groups.From this experiment, we draw the conclusion : it seem that local administration of RA was an effective and easy protocol to prolong the survival of allo-skin graft on burn wound, in which the possible mechanism was that the upregulation of FasL+ cell kill the Fas+ T cell and induce immune privilege.