Keratinocytes induce local tolerance to skin graft by activating interleukin-10-secreting T cells in the context of costimulation molecule B7-H1

Background. Intermingled skin grafting using autologous skin islets inlaid in allogeneic skin sheets was found to delay graft rejection, contributing to a significant reduction in mortality for patients with severe burns. In this study we examine the down-regulatory mechanisms underlying the effect of the autologous skin islets. Methods. Mixed culture of lymphocytes with epidermal cells of autologous and allogeneic origin were performed with a comparing of cell activity from cytokine-knockout mice. And the Th1/Th2-related cytokine profiles were examined. Results. Autologous keratinocytes act as potent inducers of suppression in the mixed culture by making a shift of the cytokine profile from Th1 to Th2. The observed suppression is predominantly mediated by interleukin (IL)-10, because, the effect could be reversed by application of a neutralizing antibody to IL-10. The results of reconstitution experiments in BALB/c mice, with or without IL-10 gene-knockout, are consistent with this finding. These demonstrated that T cells were main effective components for the IL-10-related suppression. Furthermore, a newly identified member of the human B7 family (B7-H1) is found to play an important role in activating human IL-10-secreting lymphocytes. When transfected with the CD80 gene, autologous keratinocytes lost the ability to down-regulate the mixed cell culture, which effect could be reversed by introduction of the anti-CD80 antibody. Conclusions. Our study provides new evidence that autologous keratinocytes present in intermingled skin grafts are inducers for local immune tolerance by expression of B1-H1 in their activation of the IL-10-secreting T cells.