Department of Surgery, University of Pittsburgh, Pittsburgh, PA, United States.
Institute of Molecular Medicine, Feinstein Institutes for Medical Research, New York, NY, United States.
Front Immunol. 2024 May 17;15:1337384. doi: 10.3389/fimmu.2024.1337384. eCollection 2024.
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 and CD55) in the mesenteric FALC. The CD55 FRCs were enriched in gene expression related to extracellular matrix formation. The CD55 FRCs were enriched in gene expression related to immune response. Interestingly, we found that TLR9 is dominantly expressed in the CD55 subset. Activation of TLR9 signaling suppressed proliferation, cytokine production, and retinoid metabolism in the CD55 FRC, but not CD55 FRC. Notably, we found that adoptive transfer of CD55 FRC from mesenteric FALC more effectively improved the survival during peritonitis compared with WT-FRC or CD55 FRC. Furthermore, we identified CD55 and CD55 subsets in human adipose tissue-derived FRC and confirmed the suppressive effect of TLR9 on the proliferation and cytokine production in the CD55 subset. Therefore, inhibition of TLR9 in the CD55 FRCs from adipose tissue could be a useful strategy to improve the therapeutic efficacy of FRC-based therapy for peritonitis.
纤维母细胞网状细胞（FRC）是调节健康和疾病中免疫环境的基质细胞亚群之一。我们之前已经表明，脂肪相关淋巴簇（FALC）中的 FRC 中 TLR9 信号的激活通过抑制免疫细胞募集和腹膜常驻巨噬细胞（PRM）的保留来调节腹膜免疫。然而，FRC 在不同的组织和器官中具有异质性。每个 FRC 亚群的功能以及 TLR9 在不同 FRC 亚群中的调节作用尚不清楚。在这里，我们证实了 FRC 中 TLR9 的特异性缺失可改善腹膜炎期间的细菌清除和生存。此外，使用单细胞 RNA 测序，我们在肠系膜 FALC 中发现了两种 FRC 亚群（CD55 和 CD55）。CD55 FRC 富集了与细胞外基质形成相关的基因表达。CD55 FRC 富集了与免疫反应相关的基因表达。有趣的是，我们发现 TLR9 在 CD55 亚群中占主导地位。TLR9 信号的激活抑制了 CD55 FRC 的增殖、细胞因子产生和视黄酸代谢，但不抑制 CD55 FRC。值得注意的是，我们发现从肠系膜 FALC 中过继转移 CD55 FRC 比 WT-FRC 或 CD55 FRC 更有效地提高了腹膜炎期间的生存率。此外，我们在人脂肪组织衍生的 FRC 中鉴定出 CD55 和 CD55 亚群，并证实了 TLR9 对 CD55 亚群增殖和细胞因子产生的抑制作用。因此，抑制脂肪组织中 CD55 FRC 中的 TLR9 可能是提高基于 FRC 治疗腹膜炎疗效的一种有用策略。
