Inhibition of CCL1-CCR8 interaction prevents aggregation of macrophages and development of peritoneal adhesions.

Peritoneal adhesions are a significant complication of surgery and visceral inflammation; however, the mechanism has not been fully elucidated. The aim of this study was to clarify the mechanism of peritoneal adhesions by focusing on the cell trafficking and immune system in the peritoneal cavity. We investigated the specific recruitment of peritoneal macrophages (PMphi) and their expression of chemokine receptors in murine models of postoperative and postinflammatory peritoneal adhesions. PMphi aggregated at the site of injured peritoneum in these murine models of peritoneal adhesions. The chemokine receptor CCR8 was up-regulated in the aggregating PMphi when compared with naive PMphi. The up-regulation of CCR8 was also observed in PMphi, but not in bone marrow-derived Mphi, treated with inflammatory stimulants including bacterial components and cytokines. Importantly, CCL1, the ligand for CCR8, a product of both PMphi and peritoneal mesothelial cells (PMCs) following inflammatory stimulation, was a potent enhancer of CCR8 expression. Cell aggregation involving PMphi and PMCs was induced in vitro in the presence of CCL1. CCL1 also up-regulated mRNA levels of plasminogen activator inhibitor-1 in both PMphi and PMCs. CCR8 gene-deficient mice or mice treated with anti-CCL1-neutralizing Ab exhibited significantly reduced postoperational peritoneal adhesion. Our study now establishes a unique autocrine activation system in PMphi and the mechanism for recruitment of PMphi together with PMCs via CCL1/CCR8, as immune responses of peritoneal cavity, which triggers peritoneal adhesions.