结核病仍然是严重危害人类健康的慢性传染性疾病，目前结核病防控形势严峻，宿主导向疗法可能是一种值得关注和探究的新的抗结核治疗方式。本研究旨在探究G蛋白偶联受体(G protein-coupled receptor, GPCR)家族成员GPR84在小鼠感染牛分枝杆菌卡介苗(Mycobacterium bovis Bacillus Calmette-Guérin, BCG)中的调控作用。本研究将野生型C57BL/6小鼠(WT组)和Gpr84基因缺陷小鼠(Gpr84－/－组)作为对照建立高剂量BCG感染小鼠模型，通过平板菌落形成(colony-forming unit，CFU)实验、肺组织苏木精-伊红染色(hematoxylin-eosin staining, HE staining)和抗酸染色评估Gpr84基因缺陷小鼠和野生型小鼠肺、脾、肝、肾等脏器荷菌量以及肺部病理损害严重程度的差异，并观察两组小鼠感染后的体重和一般状态变化。提取小鼠肺细胞，通过流式细胞术分析小鼠肺组织髓系细胞群变化。发现Gpr84基因缺陷小鼠感染BCG后较未感染时体重有明显下降，CFU结果和抗酸染色结果均显示Gpr84－/－组小鼠肺组织中荷菌量高于WT组，脾脏、肝脏中荷菌量的差异与肺中一致；HE染色结果显示，BCG感染后Gpr84－/－组小鼠肺组织正常肺泡结构损坏明显比WT组严重，病灶数多于WT组；流式细胞术分析小鼠肺细胞结果显示，未感染时，Gpr84敲除对肺中常驻肺泡巨噬细胞(alveolar macrophages, AMs)和肺间质巨噬细胞(interstitial macrophages, IMs)的数量无明显影响，急性感染时，Gpr84－/－组小鼠肺中AMs比例明显较WT组升高，而IMs比例较WT组明显降低，单核吞噬细胞(mononuclear phagocytes, MNPs)Ly6Chi亚群比例升高，Ly6Clo亚群数量减少，中性粒细胞(neutrophils, Neuts)浸润增加。结果表明，Gpr84敲除后加重的细菌负荷和病理损害可能与IMs/AMs相对比例的降低，Ly6Chi MNPs亚群增加及其向Ly6Clo亚群转化受阻，增加Neuts浸润有关。因此，Gpr84基因可能通过调节机体免疫功能成为宿主导向治疗结核病的候选靶点之一。
Tuberculosis remains a chronic infectious disease that poses a serious threat to human health and the work to control tuberculosis remains very challenging. Host-directed therapy (HDT) may represent a novel anti-tuberculosis treatment strategy worthy of attention and further exploration. The purpose of this study was to investigate the regulatory role of GPR84, a member of the G protein-coupled receptor (GPCR) family in Mycobacterium bovis Bacillus Calmette-Guérin(BCG) infection. In this study, wild-type C57BL/6 mice (WT Group) and Gpr84 gene-deficient mice (Gpr84－/－ group) were used as controls to establish a high-dose BCG infection mouse model. The differences in the amount of bacteria in lungs, spleen, liver, kidney and other organs and the severity of lung pathological damage between Gpr84 gene-deficient mice and wild-type mice were evaluated by CFU assay, lung tissue HE staining and acid-fast staining. The changes of body weight and general condition of mice in the two groups were observed. The results showed that Gpr84 gene-deficient mice infected with BCG exhibited a significant decrease in body weight compared to uninfected mice. The colony-forming unit (CFU) results and acid-fast staining showed that bacterial load in lung tissues of Gpr84－/－ group was higher than that of WT group, and the differences of bacterial load in spleen and liver were consistent with those in lung. HE staining revealed that the normal alveolar structure of lung tissues of Gpr84－/－ group was significantly more damaged than that of WT group after BCG infection, with a higher number of lesions observed. Flow cytometric analysis of lung cells of mice indicated that in the absence of infection, the knockout of Gpr84 had no significant effect on the number of resident alveolar macrophages (AMs) and interstitial macrophages (IMs) in the lungs. And in acute infection, the proportion of AMs in the lungs of mice in Gpr84 －/－group was significantly higher than in WT group, while the proportion of IMs was significantly lower than in WT group, the proportion of mononuclear phagocytes (MNPs) Ly6Chi subpopulation was increased. The number of Ly6Clo subpopulation was decreased, and neutrophils (Neuts) infiltration was increased. The results revealed that the aggravated bacterial load and pathological damage after Gpr84 knockout may be related to the reduction of the relative ratio of IMs/AMs and the increase of the Ly6Chi MNPs subgroup, affecting its transformation to the Ly6Clo subgroup and increasing the infiltration of Neuts. Therefore, Gpr84 may serve as a potential target for host-directed therapy of tuberculosis through its role in immune regulation.
