CCR2 and peritonitis: This finding is consistent with the results of the present study demonstrating that the SPM cluster is characterized by low expression of Adgre1, but high expression of Cd74. In addition, scRNA-seq and flow cytometry analyses demonstrated reduced phagocytic activity of PMs, and increases in CCR2-, THBS1-, and IL-1α-positive macrophages in histamine signal-deficient PMs, which may increase the susceptibility to infectious diseases such as peritonitis.