背景:开颅手术是用于治疗颅内病变的常见神经外科手术。全世界每年进行的1400万例开颅手术中,近5%被感染,最常见于金黄色葡萄球菌(S.金黄色葡萄球菌),其在切除的骨段的表面上形成生物膜以建立对抗生素和免疫介导的清除具有顽固性的慢性感染。肿瘤坏死因子(TNF),一种典型的促炎细胞因子,与产生对各种感染的保护性免疫力有关。尽管在金黄色葡萄球菌开颅手术感染期间TNF升高,其在调节疾病发病机制中的功能重要性尚未被探索。
方法:使用金黄色葡萄球菌开颅感染的小鼠模型来研究使用TNF,TNFR1和TNFR2敲除(KO)小鼠通过定量细菌负荷,免疫浸润物,炎症介质,和RNA-seq的转录变化。补充实验检查了中性粒细胞胞外陷阱的形成,白细胞凋亡,吞噬作用,和杀菌活性。
结果:TNF短暂调节中性粒细胞和粒细胞髓源性抑制细胞募集到大脑,皮下防护罩,感染后第7天至第14天,两种细胞类型的显着减少与几种趋化因子的显着减少相吻合,在第28天恢复到野生型水平。尽管有这些缺陷,TNFKO和WT小鼠的细菌负荷相似。RNA-seq显示TNFKO粒细胞中的淋巴毒素-α(Lta)表达增强。由于TNF和LTα都通过TNFR1和TNFR2发出信号,因此检查了每种受体的KO小鼠以评估潜在的冗余;然而,两种菌株均未对金黄色葡萄球菌负荷产生任何影响.体外研究表明,TNF损失选择性地改变了巨噬细胞对金黄色葡萄球菌的反应,因为TNFKO巨噬细胞显示出明显的吞噬作用降低,凋亡,IL-6生产,和杀菌活性,以响应活的金黄色葡萄球菌,而粒细胞不受影响。
结论:这些发现暗示TNF在急性开颅手术感染期间通过对趋化因子产生的继发性作用来调节粒细胞募集,并将巨噬细胞确定为TNF作用的关键细胞靶标。然而,TNFKO动物的细菌负荷缺乏变化,提示在开颅手术感染期间,涉及指示金黄色葡萄球菌发病机制的其他信号.
BACKGROUND: Craniotomy is a common neurosurgery used to treat intracranial pathologies. Nearly 5% of the 14 million craniotomies performed worldwide each year become infected, most often with Staphylococcus aureus (S. aureus), which forms a biofilm on the surface of the resected bone segment to establish a chronic infection that is recalcitrant to antibiotics and immune-mediated clearance. Tumor necrosis factor (
TNF), a prototypical proinflammatory cytokine, has been implicated in generating protective immunity to various infections. Although
TNF is elevated during S. aureus craniotomy infection, its functional importance in regulating disease pathogenesis has not been explored.
METHODS: A mouse model of S. aureus craniotomy infection was used to investigate the functional importance of TNF signaling using TNF, TNFR1, and TNFR2 knockout (KO) mice by quantifying bacterial burden, immune infiltrates, inflammatory mediators, and transcriptional changes by RNA-seq. Complementary experiments examined neutrophil extracellular trap formation, leukocyte apoptosis, phagocytosis, and bactericidal activity.
RESULTS: TNF transiently regulated neutrophil and granulocytic myeloid-derived suppressor cell recruitment to the brain, subcutaneous galea, and bone flap as evident by significant reductions in both cell types between days 7 to 14 post-infection coinciding with significant decreases in several chemokines, which recovered to wild type levels by day 28. Despite these defects, bacterial burdens were similar in
TNF KO and WT mice. RNA-seq revealed enhanced lymphotoxin-α (Lta) expression in
TNF KO granulocytes. Since both TNF and LTα signal through TNFR1 and TNFR2, KO mice for each receptor were examined to assess potential redundancy; however, neither strain had any impact on S. aureus burden. In vitro studies revealed that
TNF loss selectively altered macrophage responses to S. aureus since
TNF KO macrophages displayed significant reductions in phagocytosis, apoptosis, IL-6 production, and bactericidal activity in response to live S. aureus, whereas granulocytes were not affected.
CONCLUSIONS: These findings implicate TNF in modulating granulocyte recruitment during acute craniotomy infection via secondary effects on chemokine production and identify macrophages as a key cellular target of TNF action. However, the lack of changes in bacterial burden in TNF KO animals suggests the involvement of additional signals that dictate S. aureus pathogenesis during craniotomy infection.