Human peritoneal macrophage show functional characteristics of M-CSF-driven anti-inflammatory type 2 macrophages

We have recently shown that in vitro polarized M-CSF-driven anti-inflamniatory macrophages (M Phi 2) have the unique capacity to preferentially bind and ingest early apoptotic cells. However, these data are based on in vitro polarized cells and it is unclear whether M Phi 2-like cells exist in vivo. Here we used CD163 as a cell surface marker to distinguish M Phi 2 from the pro-inflammatory M Phi 1. We show that human peritoneal M(D (pM Phi) freshly isolated from patients on peritoneal dialysis have the phenotypical characteristics of M Phi 2, including CD163 surface expression and lack of CD16. Like M Phi 2, pM Phi have the capacity for endocytosis and macropinocytosis, are able to preferentially bind and ingest early apoptotic cells, and produce large amounts of IL-10 upon stimulation with LPS. Moreover, upon LPS stimulation both pM Phi and M Phi 2 downregulate CD86, resulting in a reduced capacity to stimulate proliferation of allogeneic T cells and an inhibition of Th1 cytokine release of these T cells. Our data provide the evidence for the first time that in vitro polarized M Phi 2 exist in vivo, and human pM Phi resemble the anti-inflammatory M Phi 2. We propose that pM Phi have the potential to maintain an anti-inflammatory condition in the peritoneal cavity.