An Animal Model of Hemophagocytic Lymphohistiocytosis

描述(申请人提供)：噬血细胞淋巴组织细胞增多症(HLH)是一种儿童免疫过度和异常激活的疾病，以严重的骨髓损害为特征，死亡率接近50%。几乎所有的HLH患者都严重缺乏T和NK细胞的细胞毒性杀伤，其中许多患者被发现含有穿孔素编码基因的突变。我们建立了一种新的这种疾病的小鼠模型，在该模型中，穿孔素缺陷(PRF)小鼠被淋巴细胞性脉络膜脑膜炎病毒(LCMV)攻击。感染后，PRF小鼠的表型与HLH型几乎相同。利用这个模型，我们发现HLH的表型是由CD8+T细胞异常过量产生干扰素-γ(IFN-g)直接驱动的。此外，我们还发现，来自PRF小鼠的DC具有更多的病毒抗原，并在感染后获得更强的刺激病毒特异性T细胞的能力。这些发现暗示，DC群体的抗原提呈增加是PRF小鼠干扰素-g过度产生的根本原因，并表明穿孔素正常功能下调抗原提呈。已知多种表达穿孔素的细胞类型与DC相互作用。为了确定这些群体中的哪些通常会下调DC的刺激，我们进行了一系列细胞耗竭、转移和骨髓移植实验。这些研究表明，表达穿孔素的细胞类型可以影响DC的功能和体内干扰素-g的产生，并提示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细胞对选定的树突状细胞的穿孔素依赖的细胞毒杀伤限制了抗原在DC群体中的进入和/或持久性，从而限制了免疫激活。为了验证我们的假设，我们将追求以下具体目标：目标1。明确LCMV感染后WT和PRF DC亚群之间的抗原处理和提呈有何不同。目标2。)确定CD8+T细胞是否是通过穿孔素依赖机制抑制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功能如何调节免疫反应，并导致改善HLH患者的治疗方法，或许还有许多其他免疫病理疾病。

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.