Role of Innate and Adaptive Immune Systems in Drug-Induced Liver Disease

尽管临床证据表明，许多DILD病例是由药物的肝蛋白加合物以及适应性和先天免疫系统介导的，但由于缺乏动物模型，这种毒性机制的详细实验证据仍然难以捉摸。我们假设DILD在动物中与人类一样罕见，至少部分原因是肝脏的耐受性，它由适应性免疫系统的多个负调节因子组成。这个想法现在已经在一个已建立的卤烷诱导肝损伤的小鼠模型中进行了测试，其中毒性是由卤烷代谢形成三氟乙酰化的肝脏蛋白质引起的，并由先天免疫系统增强。据其他研究人员报道，雌性Balb/cJ小鼠用氟烷处理24小时后，肝脏分析显示静脉周围坏死和CD11b+ gr -1高中性粒细胞浸润。进一步的研究表明，中性粒细胞含有一个髓源性抑制细胞（MDSC）亚群，可以抑制从幼稚小鼠分离的CD4+和CD8+ T细胞的增殖。当在两次氟烷处理之前用Gr-1抗体从肝脏中去除MDSC时，与在氟烷处理之前用同型对照抗体预处理的小鼠相比，在第二次氟烷暴露后9天观察到肝损伤的增强。此外，肝损伤与肝嗜酸性粒细胞、肝T细胞和血清抗体水平升高有关，两者都与从氟烷处理小鼠中分离的三氟乙酰化肝蛋白发生反应。由此产生的肝损伤似乎至少部分是由CD4+ T细胞介导的，正如在肝毒性发作前CD4+ T细胞被耗尽时对肝损伤的显著保护所表明的那样。进一步研究tfa加合物特异性血清抗体显示IgG1和IgE亚类显著增加，表明II型适应性免疫应答。

Although clinical evidence suggests that many cases of DILD are mediated by hepatic protein adducts of drugs and the adaptive and innate immune systems, detailed experimental proof for this mechanism of toxicity has remained elusive due to the lack of animal models. We have hypothesized that DILD is as rare in animals as it is in humans due at least in part to the tolerogenic nature of the liver, which consists of multiple negative regulators of the adaptive immune system. This idea has now been tested in an established murine model of halothane-induced liver injury where the toxicity is initiated by the metabolism of halothane to form trifluoroacetylated liver proteins and enhanced by the innate immune system. Twenty-four hours after female Balb/cJ mice were treated with halothane, analysis of the liver revealed perivenous necrosis and an infiltration of CD11b+ Gr-1High neutrophils, as reported by other researchers. Further study revealed that the neutrophils contained a subpopulation of myeloid-derived suppressor cells (MDSC) that inhibited the proliferation of both CD4+ and CD8+ T cells isolated from naive mice. When MDSC were depleted from the liver with Gr-1 antibodies prior to two treatments with halothane, enhanced liver injury was observed nine days after the second exposure of halothane as compared to mice that were pretreated with isotype control antibodies before halothane treatments. Moreover, the liver injury was associated with elevated levels of hepatic eosinophils and hepatic T cells and serum antibodies that both reacted with trifluoroacetylated liver proteins isolated from halothane treated mice. The resulting liver injury appears to be mediated at least in part by CD4+ T cells, as indicated by significant protection against liver injury when CD4+ T cells are depleted prior to the onset of hepatotoxicity. Further investigation of TFA-adduct specific serum antibodies reveals a significant increase in IgG1 and IgE subclasses indicative of a Type II adaptive immune response. Liver eosinophilia has been associated with incidences of drug-induced liver disease (DILD) for more than 50 years, though its role in the etiology of this disease has remained unclear. We reported for the first time a pathogenic role of eosinophils in DILD using a murine model of halothane-induced liver injury (HILI). When female Balb/cJ mice were administered halothane, eosinophils were detected in the liver within 12 hours and increased thereafter proportionally to liver damage. Eosinophil associated chemokines, eotaxins, and the activator/growth factor interleukin-5 (IL-5) increased in response to halothane-treatment. Immunohistochemical staining for major basic protein (MBP), a cytotoxic eosinophil granule protein, revealed that eosinophils accumulated exclusively around areas of hepatocellular necrosis and appeared to show signs of degranulation as MBP staining was more diffuse than in the livers from vehicle controls. The severity of HILI was decreased significantly when the study was repeated in wild-type mice partially depleted of eosinophils and in the eosinophil knockout mice. Conversely, animals with selective depletion of neutrophils, which have been previously reported to play a pathogenic role in this model, failed to reduce the extent of HILI when levels of eosinophils remained unchanged. These findings indicate that eosinophils, not neutrophils, have a pathologic role in HILI in mice. More recently, we have shown that the epithelial derived cytokine, thymic stromal lymphopoetin (TSLP), and its corresponding receptor TSLPR also play a pathogenic role in HILI in mice that is mediated by type 2 immunity. In this regard,the severity of HILI was reduced in both TSLPR and IL-4 knockout mice and was accompanied by decreases in serum levels of IL-5 and eotaxins and hepatic eosinophilia. In addition, we found that murine and human hepatocytes treated with IL-4 secreted TSLP and eotaxins. Conclusion: Collectively, these data provide a rational approach for developing animal models of DILD that are mediated by the adaptive and innate immune system and suggest that deficiencies in liver tolerance may predispose patients to DILD. These findings also establish a pathologic role for type 2 immunity in HILI in mice and suggest that similar signaling pathways may be involved in DILD caused by a variety of drugs in humans.