Suppression of human macrophages by human CD200 and human CD47 during xenogeneic immune response

Abstract

Background: CD200 and CD47 are inhibitory proteins expressed on a variety of cells and they bind to their receptors to exert inhibitory functions. CD47 suppresses the phagocytic activity of macrophages through SIRPα ligation and CD200-CD200R interaction induces the intracellular signaling of CD200R and promotes immune modulation such as suppression of cell adhesion and cytokine release, thus enhancing engraftment and immune tolerance. The aim of this study is to compare the suppressive activity of human CD200 and human CD47 against human macrophages and assess the additive effects of both molecules in the interaction of porcine endothelial cells (PECs) and human macrophages. Materials and Methods: Porcine endothelial cell lines that stably overexpress human CD200 or CD47 were established by human CD200 or CD47 containing recombinant lentivirus construction followed by viral transduction. Human macrophages were incubated with recombinant PECs to evaluate suppressive effect of human CD200 and CD47 on cytotoxicity, phagocytosis, secretion of pro-inflammatory cytokines and proliferation of human macrophages during in the xenogeneic immune reaction. Results: The present study demonstrated that overexpression of both human CD200 and human CD47 in PECs suppressed the xenogeneic immune response of human macrophages. Human CD200 and CD47 inhibited cytotoxicity such as cell necrosis and early and late apoptosis and suppressed phagocytosis of human macrophages. Also, human CD200 and CD47 negatively controlled pro-inflammatory cytokine secretion and proliferation of human macrophages in response to xenogeneic stimulation. Furthermore, the co-expression of human CD200 and human CD47 had additive effects in suppressing macrophage activation in response to xenogeneic stimulation. Conclusion: both human CD200 and human CD47 suppressed the activation of human macrophages in response to xenogeneic stimulation. Moreover, the suppressive activity of the co-expression of human CD200 and human CD47 was more effective against macrophage activation than that of the expression of either CD200 or CD47 alone. Therefore, the generation of double-transgenic pigs with human CD200 and human CD47 could be a promising approach for improving xenograft survival.