Fibroblasts are a major structural cell in the human lung, being responsible for the production of extracellular matrix components that provide the intricate structure necessary for correct lung function. Generally located in the submucosa, fibroblasts do not usually directly interact with the commensal microbes that we now know are resident in the airways. However, during situations in which alveolar macrophages and epithelial cells are impaired, for example, during severe viral infections leading to pneumonia, bacteria can invade the lung mesenchyme. In these circumstances, fibroblasts may represent another immunological barrier to bacterial invasion, not just as innate immune effectors, but also by interacting with migrating and tissue-resident adaptive immune cell populations, such as CD4+ T cells. The cytokines produced by CD4+ T helper cells are integral in directing appropriate innate and adaptive immune responses against bacteria, but the nature of fibroblast-CD4+ cell interaction, unlike the CD8+ T-cell interaction, is not clearly established. Here, we review the responses of lung fibroblasts to bacteria and discuss emerging data indicating a key role for these cells in directly presenting bacterial antigens to CD4+ T cells.

中文翻译：

---

设置路障：肺成纤维细胞和CD4 + T细胞是抵抗细菌入侵的最后一道防线吗？

成纤维细胞是人肺中的主要结构细胞，负责产生细胞外基质成分，这些成分提供了正确的肺功能所必需的复杂结构。成纤维细胞通常位于粘膜下层，通常不与我们现在所知的驻留在气道中的共生微生物直接相互作用。但是，在肺泡巨噬细胞和上皮细胞受损的情况下，例如在导致肺炎的严重病毒感染期间，细菌会侵入肺间质。在这些情况下，成纤维细胞可能代表细菌入侵的另一种免疫屏障，不仅是先天免疫效应物，而且还可能与迁移的和组织驻留的适应性免疫细胞群（例如CD4 + T细胞）相互作用。由CD4 + T辅助细胞产生的细胞因子在指导针对细菌的固有和适应性免疫反应中是不可或缺的，但是与CD8 + T细胞相互作用不同，成纤维细胞-CD4 +细胞相互作用的性质尚不清楚。在这里，我们审查了肺成纤维细胞对细菌的反应，并讨论了新兴数据，这些数据表明这些细胞在直接将细菌抗原呈递给CD4 + T细胞方面具有关键作用。