Activation of TLR9 signaling suppresses the immunomodulating functions of CD55 lo fibroblastic reticular cells during bacterial peritonitis.

Evidence from laboratory and animal studies provides groundwork for understanding mechanisms and potential before human studies continue.

• Level A · Stronger Clinical Evidence
• Level B · Emerging clinical evidence with positive signals
• Level C · Early human research exploring benefits
• Level D · Scientific groundwork from lab and animal studies
• Emerging · Emerging topic under active research

Abstract (original English)

Fibroblastic reticular cells (FRCs) are a subpopulation of stromal cells modulating the immune environments in health and disease. We have previously shown that activation of TLR9 signaling in FRC in fat-associated lymphoid clusters (FALC) regulate peritoneal immunity via suppressing immune cell recruitment and peritoneal resident macrophage (PRM) retention. However, FRCs are heterogeneous across tissues and organs. The functions of each FRC subset and the regulation of TLR9 in distinct FRC subsets are unknown. Here, we confirmed that specific deletion of TLR9 in FRC improved bacterial clearance and survival during peritoneal infection. Furthermore, using single-cell RNA sequencing, we found two subsets of FRCs (CD55 hi and CD55 lo ) in the mesenteric FALC. The CD55 hi FRCs were enriched in gene expression related to extracellular matrix formation. The CD55 lo FRCs were enriched in gene expression related to immune response. Interestingly, we found that TLR9 is dominantly expressed in the CD55 lo subset. Activation of TLR9 signaling suppressed proliferation, cytokine production, and retinoid metabolism in the CD55 lo FRC, but not CD55 hi FRC. Notably, we found that adoptive transfer of Tlr9 -/- CD55 lo FRC from mesenteric FALC more effectively improved the survival during peritonitis compared with WT-FRC or Tlr9 -/- CD55 hi FRC. Furthermore, we identified CD55 hi and CD55 lo su

Evidence level

Evidence from laboratory and animal studies provides groundwork for understanding mechanisms and potential before human studies continue.

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