S100A8/A9-High Macrophages Activate Intestinal Fibroblasts via mCCL6/hCCL15-CCR1 Axis to Drive Intestinal Fibrosis in Crohn's Disease.

Intestinal fibrosis presents a major clinical challenge in Crohn's disease (CD) due to the lack of effective pharmacological interventions. The underlying mechanisms of intestinal fibrosis remain largely elusive. Reanalysis of the single-cell RNA-seq data from full-thickness CD tissue identifies a distinct profibrotic macrophage subset characterized by high S100A8 and S100A9 expression. CellChat analysis indicates strong communication between this S100A8/A9-high (S100A8/A9hi) macrophage subset and fibroblasts. Adoptive transfer of S100A8/A9hi macrophages exacerbate intestinal fibrosis in mice with chronic dextran sulfate sodium (DSS)-induced colitis. Consequently, pharmacological inhibition of S100A8/A9 significantly ameliorates intestinal fibrosis in murine chronic colitis. Proteomic analysis further identifies murine CCL6 (mCCL6) as the key pro-fibrotic mediator secreted by S100A8/A9hi macrophages, which acts via CC chemokine receptor 1 (CCR1) to regulate fibroblasts. Antibody blockade of mCCL6 alleviates established intestinal fibrosis in a DSS-induced colitis model. Mechanistically, S100A8/A9hi macrophages drive mCCL6 production via STAT3 activation. Similarly, the human ortholog of CCL6, CCL15 (hCCL15), exerts pro-fibrotic effects on fibroblasts via the CCR1 receptor. Our findings reveal that targeting S100A8/A9hi macrophage may be a therapeutic strategy against intestinal fibrosis in CD.