Processing and Presentation of Minor Histocompatibility Antigens that Cause GvHD

描述（由申请人提供）：次要组织相容性(H)抗原（Ags）在移植物抗宿主病（GvHD）的免疫发病机制中起不利作用，即使在HLA相同的骨髓移植接受者中也是如此。在本研究中，受体小H Ags由供体ag呈递细胞（apc）获得，并由MHC I类分子在交叉呈递过程中加工和呈递，或由II类分子在间接呈递过程中加工和呈递。在实体器官移植环境中，间接呈递需要由受体APCs获取、处理和呈递供体同种抗原。在肿瘤和微生物Ags的情况下，类似于受体细胞的II类+ apc获得存在于类似于供体细胞的II类阴性细胞中的Ag，并将其加工并提呈给同源的CD4+ (T)细胞。我们对间接递呈H的机制研究表明，雄性pHY和单核细胞增生李斯特菌衍生的pLLO Ags在受体APCs获得后进入细胞质。在这里，pHY的间接呈现是免疫蛋白酶体依赖的，而TAP（细胞质到内质网肽转运体）和ERAAP（内质网相关氨基肽酶）是独立的。令人惊讶的是，TAP和ERAAP都转移或破坏了pHY和pLLO，从而减少了它们向TH细胞的呈递。这些发现导致了两个关键问题：(a) I类Ag加工（CAP）机械是否在全球范围内影响ii类限制Ag的呈现；(b)胞质ag如何进入内端/溶酶体进行间接呈递？在试图理解胞质pHY如何返回到内切酶/溶酶体呈递的过程中，我们排除了宏观自噬的作用，因为在树突状细胞条件缺乏Atg5的小鼠中，HY的间接呈递继续进行。相反，我们发现同二聚体的tap -样(TAP-L)-一种孤儿内切/溶酶体肽转运体，不同于er驻留的TAP1/ tap2 -需要间接呈现pHY。基于我们的功能研究，在此，我们寻求获得间接呈现机制的生化见解。因此，我们将检验中心假设，即I类Ag加工机制调节可用于ii类受限间接呈现的某些细胞质Ag池。这些ag在细胞质中加工，并以tap - l依赖的机制运输到内切酶/溶酶体。为了验证这一假设，我们将(a)确定CAP机制是否在全球范围内影响h2ab限制的自身或微生物来源的胞质Ags的加工和呈现；(b)测定胞质内Ags如何进入内酶/溶酶体进行间接呈递；(c)确定CAP机制是否影响胞浆Ag特异性CD4+ T细胞库。这项工作的成功完成将为II类分子间接呈现银提供新的生化见解。了解ii类限制性间接银呈递的机制不仅对开发规避/治疗GvHD的方法至关重要，而且对疫苗设计也至关重要，因为这一过程在向TH细胞呈递细胞质银（病毒、细菌、寄生虫）中起作用，因此对针对肿瘤和病原体的疫苗设计也至关重要。

DESCRIPTION (provided by applicant): Minor histocompatibility (H) antigens (Ags) play a detrimental role in the immunopathogenesis of graft-vs-host disease (GvHD) even in recipients of HLA identical bone marrow transplants. Herein, recipient minor H Ags are acquired by donor Ag-presenting cells (APCs) and processed and presented either by MHC class I molecules in a well-studied process termed cross-presentation or by class II molecules in a less well understood process called indirect presentation. In a solid organ transplant setting, indirect presentation entails the acquisition, processing and presentation of donor alloantigens by the recipient's APCs. In the case of tumour and microbial Ags, a class II+ APC-likened to a recipient cell-acquires the Ag residing in a class II-negative cell-likened to a donor cell-and processes and presents it to cognate CD4+ (T) cells. Our mechanistic studies into indirect H presentation revealed that the male pHY and Listeria monocytogenes-derived pLLO Ags upon acquisition by the recipient APCs gained access to the cytosol. Herein, the indirect presentation of pHY was immunoproteasome-dependent yet TAP (cytosol to ER peptide transporter)- and ERAAP (ER-associated amino-peptidase)-independent. Surprisingly, both TAP and ERAAP either diverted or destroyed pHY and pLLO thereby reducing their presentation to TH cells. These finding led to two critical questions: (a) does the class I Ag processing (CAP) machinery globally impact class II-restricted Ag presentation; and (b) how do cytosolic Ags gain access to the endo/lysosomes for indirect presentation? In trying to understand how the cytosolic pHY returned to the endo/lysosomes for presentation, we ruled out the role for macro-autophagy as indirect presentation of HY proceeded in mice in which dendritic cells were conditionally deficient for Atg5. Instead, we found that the homodimeric TAP-like (TAP-L)-an orphan endo/lysosomal peptide transporter distinct from ER-resident TAP1/TAP2-was needed for indirect pHY presentation. Predicated on our functional studies, herein, we seek to gain biochemical insights into indirect presentation mechanism(s). Hence, we will test the central hypothesis that the class I Ag processing machinery regulates the pool of certain cytosolic Ags available for class II-restricted indirect presentation. Such Ags are processed in the cytosol and transported to the endo/ lysosomes in a TAP-L-dependent mechanism. To test this hypothesis, we will (a) determine whether the CAP machinery globally impacts H2Ab-restricted processing and presentation of self- or microbe-derived cytosolic Ags; (b) determine how cytosolic Ags enter the endo/lysosomes for indirect presentation; and (c) determine whether the CAP machinery impacts cytosolic Ag specific CD4+ T cell repertoire. Successful completion of this work will yield new biochemical insight(s) into indirect Ag presentation by class II molecules. A mechanistic understanding of class II-restricted indirect Ag presentation is critical not only for developing ways to circumvent/treat GvHD but also for vaccine design as this process is operative in the presentation of cytosolic Ags (viral, bacterial, parasitic) to TH cells and, hence for vaccine design against tumours and pathogens.