Suppression of macrophage-mediated xenogeneic rejection by the ectopic expression of human CD177.

Cellular xenogeneic rejection by the innate immune system is a major immunological obstruction that needs to be overcome for the successful clinical use of xenografts. Our focus has been on macrophage-mediated xenogeneic rejection, since suppressing macrophage function has considerable potential for practical applications in the area of xenotransplantation. We report herein on an investigation of the suppressive effect of human CD177 (hCD177) against macrophage-mediated xenogeneic rejection. Wild type swine aortic endothelial cell (SEC) and an SEC transfectant with hCD177 (SEC/hCD177) were co-cultured with macrophages, and the degree of cytotoxicity was evaluated by WST-8 assays, and phagocytosis was examined using Calcein-AM labeling methods. The expression of anti/pro-inflammatory cytokines was evaluated by RT-qPCR and the phosphorylation of SHP-1 on macrophages in co-culture was evaluated by Western blotting. The result of cytotoxicity assays indicated that hCD177 suppressed M1 macrophage-mediated xenogeneic rejection (vs. SEC, p < 0.0001). Similarly, the result of phagocytosis assays indicated that hCD177 suppressed it (vs. SEC, p < 0.05). In addition, hCD177 significantly suppressed the expression of IL-1ß, a pro-inflammatory cytokine, in M1 macrophages (vs. SEC, p < 0.01). Luciferase assays using THP1-Lucia NF-kB also showed a significant difference in NF-kB activation (vs. SEC, p < 0.001). In addition, hCD177 was found to induce the phosphorylation of SHP-1 in M1 macrophages (vs. SEC, p < 0.05). These findings indicate that hCD177 suppresses M1 macrophage-mediated xenogeneic rejection, at least in part via in the phosphorylation of SHP-1.

The Regulation of Neutrophil Extracellular Trap-induced Tissue Damage by Human CD177.

BACKGROUND: Neutrophil-induced tissue damage contributes to the rejection in xenotransplantation. Therefore, suppressing neutrophil function could be effective in suppressing xenogeneic rejection. In a previous study, we demonstrated that the ectopic expression of human cluster of differentiation 31 (CD31) on porcine endothelial cells (PEC) significantly suppressed neutrophil-mediated cytotoxicity through the homophilic binding of CD31. Cluster of differentiation 177 (CD177) was recently reported to be a high-affinity heterophilic binding partner for CD31 on endothelial cells. Thus, we hypothesized that human CD177 on PEC might induce a stronger suppression in neutrophil-mediated cytotoxicity compared with CD31. In this study, the inhibitory function of human CD177 on PEC in neutrophil-mediated cytotoxicity was investigated. METHODS: PEC were transfected with a cloning plasmid containing cDNA inserts that encoded for hCD177 and hCD31 genes. Neutrophil-induced cytotoxicity was evaluated by flow cytometry after coculturing with PEC or PEC/CD177 in the presence of phorbol 12-myristate 13-acetate. To elucidate the mechanisms responsible for hCD177-induced suppression, the phosphorylation of src homology region 2 domain containing phosphatase 1 was measured by immunoblot analysis. RESULTS: Human CD177 on PEC induced a significant reduction in neutrophil-induced cytotoxicity. In addition, CD177 on PEC induced a significant increase in the phosphorylation of src homology region 2 domain-containing phosphatase 1 in neutrophils and suppressed NETosis. CONCLUSIONS: These findings suggest that human CD177 suppresses neutrophil-mediated cytotoxicity through the inhibition of NETosis.

Human TIGIT on porcine aortic endothelial cells suppresses xenogeneic macrophage-mediated cytotoxicity.

PURPOSE: The delayed rejection caused by strong cell-mediated innate and adaptive xenogeneic immune responses continues to be a major obstacle. Therefore, suppressing macrophage function could be effective in avoiding this type of rejection. In this study, the suppression of T-cell immunoglobulin and ITIM domain (TIGIT) function against macrophage-mediated xenogeneic rejection was investigated. MATERIAL AND METHODS: Naïve porcine aortic endothelial cell (PAEC) and PAEC transfectant with TIGIT (PAEC/TIGIT) were co-cultured with M1 macrophages, and the degree of cytotoxicity was determined by a counting beads assay. The anti/pro-inflammatory gene expression was determined by RT-PCR and the phosphorylated SHP-1 in the macrophages after co-culturing with PAEC or PAEC/TIGIT was evaluated by western blotting. RESULTS: CD155 was expressed at essentially equal levels on both M1 and M2 macrophages, whereas TIGIT was highly expressed on M2 macrophages but not in M1 macrophages. TIGIT on PAEC significantly reduced the cytotoxicity of M1 macrophages but no significant suppression of phagocytosis was detected. TIGIT also caused a decrease in the expression of pro-inflammatory cytokines, namely TNFα, IL-1ß and IL-12 in M1 macrophages. Furthermore, PAEC/TIGIT caused a significant increase in phosphorylated SHP-1 in M1 macrophages compared to PAEC. CONCLUSION: The findings of this study indicate that TIGIT suppresses xenogeneic M1 macrophage-induced cytotoxicity, probably at least in part, via the phosphorylation of SHP-1. In addition, the reduced expression of some pro-inflammatory cytokines, namely TNFα, IL-1ß and IL-12, was observed in M1 macrophages that had been cultured with PAEC/TIGIT.