Targeting IRF5 enhances S100A9-mediated granulocytic MDSC accumulation and suppressive function: a novel therapeutic...

Ulcerative colitis (UC) progression involves dysregulated immune interactions. Myeloid-derived suppressor cells (MDSCs) exhibit therapeutic potential in inflammatory bowel disease, yet the mechanisms underlying their differentiation remain unclear. This study investigates the regulation of granulocytic MDSCs (G-MDSCs) by interferon regulatory factor 5 (IRF5).

Dextran sulfate sodium (DSS)-induced murine colitis models were employed to evaluate IRF5 function, incorporating cellular analyses from IRF5 knockout (KO) and wild-type mice. Clinical relevance was assessed using peripheral blood and intestinal specimens from UC patients.

IRF5 expression was elevated in G-MDSCs from colitic mice. IRF5 deficiency markedly increased G-MDSC frequency and immunosuppressive activity, while monocytic MDSCs (M-MDSCs) remained unaffected. Rescue experiments confirmed that IRF5 KO-derived G-MDSCs alleviated colitis severity. Mechanistically, ChIP-qPCR, luciferase reporter assays, and western blotting demonstrate that IRF5 represses S100A9 transcriptionally, thereby limiting G-MDSC accumulation. S100A9 is a Ca²⁺-binding protein that is critical for MDSC expansion. Clinically, UC patients demonstrated elevated IRF5 expression, which inversely correlated with circulating G-MDSC levels.

IRF5 acts as a transcriptional brake on G-MDSC development through S100A9 signaling, establishing the IRF5/G-MDSC axis as a novel pharmacological target for UC therapy.