Fibroblast-derived CSF1 maintains colonization of gut mucosal macrophage to resist bacterial infection.

Macrophages play essential roles in immune defense and tissue homeostasis, but the mechanisms underlying their colonization in the gut mucosa remain incompletely understood. Here, we identify CSF1, primarily derived from fibroblasts, as the dominant factor maintaining mucosal macrophage colonization, whereas IL-34 deficiency alone has a minimal impact. We reveal that CSF1R ligands originate from distinct cellular sources: macrophages at the upper villus region depend on fibroblast-derived CSF1 and IL-34, while macrophages in the lower villus and the submucosal (lower villus + SM) region are regulated by CSF1 from both fibroblasts and endothelial cells. Additionally, within the lower villus + SM region, CSF1-producing CD81+ LepR+ fibroblasts directly interact with CD163+ macrophages, forming a localized niche. The loss of CSF1 in fibroblasts results in accelerated systemic dissemination of Salmonella Typhimurium, highlighting fibroblast-derived CSF1 as a key regulator of gut macrophage function in host defense. Collectively, our findings uncover a previously unrecognized fibroblast-macrophage crosstalk that governs gut macrophage homeostasis and immunity.