A potential role of TLR2 in xenograft rejection of porcine iliac endothelial cells: An in vitro study.

BACKGROUND:Porcine vascular endothelial cells are a major participant in xenograft rejection. The Toll-like receptor 2 (TLR2) pathway plays an important role in both innate and adaptive immunity. The specific role of TLR2 in the response to a xenograft has not been reported. Whether the TLR2 pathway in pig vascular endothelial cells is involved in acute rejection needs to be investigated, and the mechanism is explored. METHODS:We used a modified antibody-dependent complement-mediated cytotoxicity (ADCC) assay to conduct in vitro experiments. In porcine iliac artery endothelial cells (PIECs), siRNA was used to knock down the expression of TLR2, CXCL8, and CCL2. The effect of human serum or inactivated human serum on the expression of TLR2 was analyzed by real-time PCR and Western blotting, and transwell assays were used to assess the chemotactic efficiency of PIECs on human monocyte-macrophages (THP-1 cells) and human neutrophils. The downstream signaling pathways activated by human serum were detected by Western blotting, and the regulation of proinflammatory chemokines and cytokines by TLR2 signaling was assessed by real-time PCR and ELISA. RESULTS:TLR2 was significantly upregulated in PIECs after exposure to human serum, and porcine proinflammatory chemokines, CXCL8 and CCL2, were induced, at least partially, in a TLR2-dependent pattern; the upregulated chemokines participated in the chemotaxis of human neutrophils and THP-1 cells across the species barrier. CONCLUSIONS:(i) TLR2 is significantly upregulated in PIECs by human serum, (ii) the elevated TLR2 participates in the chemotaxis of inflammatory cells through the secretion of chemokine CCL2 and CXCL8, and (iii) blockade of TLR2 would be beneficial for xenograft survival.

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