An Animal Model of Hemophagocytic Lymphohistiocytosis

描述（由申请人提供）：噬血细胞性淋巴组织细胞增多症（HLH）是一种过度和异常免疫激活的儿童疾病，以骨髓严重损伤为特征，死亡率接近50%。几乎所有的HLH患者都严重缺乏T细胞和NK细胞的细胞毒杀伤能力，其中许多患者被发现在编码穿孔素的基因中存在突变。我们开发了一种新的小鼠模型，穿孔素缺陷（prf）小鼠受到淋巴细胞性脉络丛脑膜炎病毒（LCMV）的攻击。感染后，prf小鼠产生一种与HLH几乎相同的表型。使用该模型，我们发现HLH表型是由CD8+ T细胞异常过量产生干扰素γ (IFN-g)直接驱动的。此外，我们发现来自prf小鼠的DC's在感染后携带更多的病毒抗原，并获得更大的刺激病毒特异性T细胞的能力。这些发现暗示DC群体抗原呈递增加是prf小鼠中IFN-g过量产生的潜在原因，并表明穿孔素通常具有下调抗原呈递的功能。多种表达穿孔素的细胞类型已知与DC相互作用。为了确定这些人群中的哪一个通常会下调DC的刺激，我们进行了一系列的细胞消耗、转移和骨髓移植实验。这些研究表明，表达perforin的细胞类型可以影响DC功能和体内IFN-g的产生，并表明CD8+ T细胞是发挥这种调节作用的最关键的细胞类型。根据我们的初步研究，我们假设CD8+ T细胞对特定树突状细胞的穿孔依赖性细胞毒性杀伤限制了抗原在DC群体中的进入和/或持久性，从而限制了免疫激活。为了检验我们的假设，我们将追求以下具体目标：定义LCMV感染后WT和prf DC亚群抗原处理和表现的差异。目标2。)确定CD8+ T细胞是否是通过性能依赖机制抑制DC刺激功能的主要细胞类型。该项目将有助于更好地了解细胞毒性功能如何调节免疫反应，并改善HLH患者和许多其他免疫病理疾病的治疗方法。

DESCRIPTION (provided by applicant): Hemophagocytic lymphohistiocytosis (HLH) is a childhood disorder of excessive and abnormal immune activation, characterized by severe damage to the bone marrow, and a mortality rate approaching 50%. Nearly all patients with HLH have a severe deficiency of cytotoxic killing by T and NK cells, and many of these patients have been found to harbor mutations in the gene encoding perforin. We developed a novel murine model of this disorder, in which perforin deficient (prf) mice are challenged with lymphocytic choriomeningitis virus (LCMV). Following infection, prf mice develop a phenotype that is nearly identical to HLH. Using this model, we have discovered that the HLH phenotype is directly driven by the abnormal overproduction of interferon gamma (IFN-g) by CD8+ T cells. Additionally, we have found that DC's from prf mice harbor increased amounts of viral antigen and acquire increased capacity to stimulate virus-specific T cells after infection. These findings implicate increased antigen presentation by DC populations as the underlying cause of IFN-g overproduction in prf mice, and suggest that perforin normally functions to down modulate antigen presentation. Multiple cell types that express perforin are known to interact with DC's. In order to identify which of these populations would normally down modulate stimulation by DC's, we have performed a series of cell depletion, transfer, and bone marrow transplantation experiments. These studies have revealed that perforin-expressing cell types can influence both DC function and in vivo IFN-g production, and suggest that CD8+ T cells are the most critical cell type exerting this regulatory effect. Based on our preliminary studies, we hypothesize that perforin-dependant cytotoxic killing of selected dendritic cells by CD8+ T cells limits the entry and/or persistence of antigen in DC populations, and thereby limits immune activation. To test our hypothesis, we will pursue the following specific aims: Aim 1.) Define how antigen handling and presentation differ between WT and prf DC subsets after LCMV infection. Aim 2.) Determine whether CD8+ T cells are the principle cell type that suppresses DC stimulatory function via a perforin-dependant mechanism. This project will lead to better understanding of how cytotoxic function regulates the immune response and lead to improved therapies for patients with HLH and perhaps many other immunopathologic disorders.