Centre for Inflammation and Tissue Repair, UCL Respiratory, Division of Medicine, University College Medical School, Rayne Institute, London, United Kingdom.
Division of Infection and Immunity, University College London, London, United Kingdom.
mBio. 2019 Sep 24;10(5):e02144-19. doi: 10.1128/mBio.02144-19.
Both intracellular immune sensing and extracellular innate immune sensing have been implicated in initiating macrophage proinflammatory cytokine responses to The capsule, a major virulence determinant, prevents phagocytosis, and we hypothesized that this would reduce activation of host innate inflammatory responses by preventing activation of intracellular proinflammatory signaling pathways. We investigated this hypothesis in human monocyte-derived macrophages stimulated with encapsulated or isogenic unencapsulated mutant Unexpectedly, despite strongly inhibiting bacterial internalization, the capsule resulted in enhanced inflammatory cytokine production by macrophages infected with Experiments using purified capsule material and a mutant expressing an serotype 4 capsule indicated these differences required whole bacteria and were not due to proinflammatory effects of the capsule itself. Transcriptional profiling demonstrated relatively few differences in macrophage gene expression profiles between infections with encapsulated and those with unencapsulated , largely limited to reduced expression of proinflammatory genes in response to unencapsulated bacteria, predicted to be due to reduced activation of the NF-κB family of transcription factors. Blocking internalization using cytochalasin D had minimal effects on the inflammatory response to Experiments using murine macrophages indicated that the affected genes were dependent on Toll-like receptor 2 (TLR2) activation, although not through direct stimulation of TLR2 by capsule polysaccharide. Our data demonstrate that the early macrophage proinflammatory response to is mainly dependent on extracellular bacteria and reveal an unexpected proinflammatory effect of encapsulated that could contribute to disease pathogenesis. Multiple extra- and intracellular innate immune receptors have been identified that recognize , but the relative contributions of intra- versus extracellular bacteria to the inflammatory response were unknown. We have shown that intracellular contributes surprisingly little to the inflammatory responses, with production of important proinflammatory cytokines largely dependent on extracellular bacteria. Furthermore, although we expected the polysaccharide capsule to block activation of the host immune system by reducing bacterial internalization and therefore activation of intracellular innate immune receptors, there was an increased inflammatory response to encapsulated compared to unencapsulated bacteria, which is likely to contribute to disease pathogenesis.
胞内免疫感应和细胞外固有免疫感应都与引发巨噬细胞原炎症细胞因子反应有关。荚膜是一种主要的毒力决定因素，可阻止吞噬作用，我们假设这将通过阻止细胞内炎症信号通路的激活来减少宿主固有炎症反应的激活。我们在人类单核细胞衍生的巨噬细胞中研究了这一假设，这些巨噬细胞受到了包裹或同基因未包裹的突变体的刺激。出乎意料的是，尽管强烈抑制了细菌的内化，荚膜仍导致感染的巨噬细胞产生更强的炎症细胞因子。使用纯化的荚膜材料和表达 4 型荚膜的 突变体进行的实验表明，这些差异需要完整的细菌，并且不是由于荚膜本身的促炎作用。转录谱分析表明，感染包裹和未包裹的 之间的巨噬细胞基因表达谱差异相对较少，主要局限于未包裹细菌的炎症基因表达减少，这被预测是由于 NF-κB 家族转录因子的激活减少。使用细胞松弛素 D 阻断 内化对 炎症反应的影响很小。使用鼠巨噬细胞进行的实验表明，受影响的基因依赖于 Toll 样受体 2 (TLR2) 的激活，尽管不是通过荚膜多糖直接刺激 TLR2。我们的数据表明，巨噬细胞对 的早期原炎症反应主要依赖于细胞外细菌，并揭示了包裹的意想不到的促炎作用，这可能有助于疾病发病机制。已经鉴定出多种细胞外和细胞内固有免疫受体来识别 ，但炎症反应中外源和细胞内细菌的相对贡献尚不清楚。我们已经表明，细胞内 对炎症反应的贡献出人意料地较小，重要的前炎症细胞因子的产生主要依赖于细胞外细菌。此外，尽管我们预计 多糖荚膜通过减少细菌内化从而减少细胞内固有免疫受体的激活来阻止宿主免疫系统的激活，但与未包裹的细菌相比，对包裹的细菌的炎症反应增加，这可能有助于疾病发病机制。
