BACKGROUND Candida albicans is the most common opportunistic human fungal pathogen. The chemokine ligand CXCL1 plays a protective role in fungal infection through the recruitment of neutrophils. TRAF1 (tumor necrosis factor-associated factor 1) can be highly induced by proinflammatory stimuli such as LPS and TNF and has been implicated in septic shock. However, the role of TRAF1 in infection, especially fungal infection, remains elusive. Herein, we reveal that TRAF1 suppresses the antifungal immune response to Candida albicans intradermal infection through the regulation of CXCL1 induction and neutrophil recruitment. METHODS A mouse model of C. albicans intradermal infection was established. The Traf1-/- mice and Traf1-/- immortalized human keratinocytes were generated. The p65 inhibitor triptolide, STAT1 inhibitor fludarabine, neutrophil-depletion antibody Ly6G, and neutralizing antibody for CXCL1 were utilized. The expression of proinflammatory cytokines and chemokines was assessed by real-time PCR and ELISA, and the activation of signaling molecules was analyzed by Western blotting. Hematoxylin and eosin staining and periodic acid Schiff staining were used for histology or fungal detection, respectively. The immunofluorescence and flow cytometry analyses were employed in the assessment of immune cell infiltration. Bone marrow transplantation and adoptive transfer experiments were conducted to establish a role for TRAF1 in the macrophage compartment in fungal skin infection. RESULTS TRAF1-deficient mice demonstrated improved control of Candida albicans intradermal infection, and concomitant increase in neutrophil recruitment and reduction in fungal burden. The chemokine CXCL1 was upregulated in the TRAF1-deficient macrophages treated with heat-killed C. albicans. Mechanistically, TRAF1-deficient macrophages showed increased activation of transcription factor NFκB p65. The human CXCL8 was also highly induced in the TRAF1-deficient human keratinocytes upon TNF stimulation through decreasing the activation of transcription factor STAT1. TRAF1-deficient macrophages played a critical role in containing the C. albicans skin infection in vivo. CONCLUSION TRAF1-deficient mice can better control fungal infection in the skin, a process attributable to the CXCL-neutrophil axis. Mechanistically, TRAF1 likely regulates CXCL1 expression in both macrophages and keratinocytes through the transcriptional factor NFκB and STAT1, respectively. Our finding offers new insight into the understanding of the immune regulatory mechanisms in host defense against C. albicans infection.

中文翻译：

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TRAF1在白色念珠菌皮内感染期间通过CXCL1介导的嗜中性白细胞募集抑制抗真菌免疫力。

背景技术白色念珠菌是最常见的机会性人类真菌病原体。趋化因子配体CXCL1通过募集嗜中性粒细胞在真菌感染中起保护作用。TRAF1（肿瘤坏死因子相关因子1）可以被促炎性刺激（如LPS和TNF）高度诱导，并与败血性休克有关。但是，TRAF1在感染（尤其是真菌感染）中的作用仍然难以捉摸。在这里，我们揭示TRAF1通过调节CXCL1诱导和嗜中性白细胞募集抑制对白色念珠菌皮内感染的抗真菌免疫反应。方法建立白色念珠菌皮内感染小鼠模型。产生了Traf1-/-小鼠和Traf1-/-永生化的人类角质形成细胞。p65抑制剂雷公藤甲素，STAT1抑制剂氟达拉滨，利用了中性粒细胞耗竭抗体Ly6G和CXCL1的中和抗体。通过实时PCR和ELISA评估促炎细胞因子和趋化因子的表达，并通过蛋白质印迹分析信号分子的活化。苏木精和曙红染色和高碘酸席夫氏染色分别用于组织学或真菌检测。免疫荧光和流式细胞仪分析用于评估免疫细胞浸润。进行了骨髓移植和过继转移实验，以建立TRAF1在真菌皮肤感染的巨噬细胞区室中的作用。结果缺乏TRAF1的小鼠表现出对白色念珠菌皮内感染的控制得到改善，并伴有嗜中性白细胞募集增加和真菌负担减轻。在用热灭活的白色念珠菌治疗的TRAF1缺陷型巨噬细胞中，趋化因子CXCL1上调。从机制上讲，缺乏TRAF1的巨噬细胞显示出转录因子NFκBp65的激活增加。通过降低转录因子STAT1的激活，在TNF刺激下，在TRAF1缺陷型人角质形成细胞中也高度诱导了人CXCL8。缺乏TRAF1的巨噬细胞在体内遏制白色念珠菌皮肤感染中起着关键作用。结论缺乏TRAF1的小鼠可以更好地控制皮肤中的真菌感染，这一过程可归因于CXCL-中性粒细胞轴。从机制上讲，TRAF1可能通过转录因子NFκB和STAT1分别调节巨噬细胞和角质形成细胞中CXCL1的表达。