Mesothelial cell CSF1 sustains peritoneal macrophage proliferation.

Macrophages play a central role during infection, inflammation and tissue homeostasis maintenance. Macrophages have been identified in all organs and their core transcriptomic signature and functions differ from one tissue to another. Interestingly, macrophages have also been identified in the peritoneal cavity and these cells have been extensively used as a model for phagocytosis, efferocytosis and polarization. Peritoneal macrophages are involved in B-cell IgA production, control of inflammation and wound healing following thermal-induced liver surface injury. These cells presumably require and interact with the omentum, where milky spot stromal cells have been proposed to secrete CSF1 (colony stimulating factor 1). Peritoneal macrophages depend on CSF1 for their generation and survival, but the identity of CSF1 producing cells inside the large peritoneal cavity remains unknown. Here we investigated peritoneal macrophage localization and their interaction with mesothelial cells, the major cell type predicted to secrete CSF1. Our data revealed that mesothelial cells produce membrane bound and secreted CSF1 that both sustain peritoneal macrophage growth.