Regulation of antibody diversification and production in HIV-1 infection

描述（由申请人提供）：本提案的目的是阐明HIV-1逃避体液免疫的机制。抗体反应，包括类开关DNA重组（CSR）和体细胞超突变（SHM），是阻止HIV-1进入和传播所必需的。CSR用IgG或IgA替代IgM，从而赋予抗体新的效应功能，增强病毒在系统和粘膜进入部位的清除。SHM在编码抗体抗原结合可变区域的基因中引入点突变，从而为病毒抗原选择高亲和力的IgG和IgA突变体提供了结构相关性。CSR和SHM需要激活诱导胞苷脱氨酶（AID），这是一种由次级淋巴器官生发中心（GC）的B细胞表达的酶。这种特殊的微环境由CD4+ T细胞组成，通过CD154和IL-4激活B细胞。最终，GC B细胞分化为浆细胞，浆细胞分泌大量IgG和IgA抗体。HIV-1通过尚不清楚的机制损害对病毒抗原、机会性病原体和疫苗的全身和粘膜IgG和IgA反应。虽然CD4+ T细胞的进行性损失当然是重要的，但B细胞的内在异常，包括B细胞对CD154的反应性差，也涉及其中。在本研究中，我们认为HIV-1蛋白Nef参与了HIV-1感染过程中B细胞内在缺陷的发生。我们认为，Nef减弱了cd154依赖性的CSR、SHM以及系统和粘膜GCs中病毒特异性IgG和IgA的产生。我们还假设Nef通过从hiv -1感染细胞发出的远程隧道纳米管来靶向B细胞。最后，我们提出多个Nef结构域有助于抑制B细胞中CD154和IL-4信号转导的激酶。提出了三个具体目标。目的1是确定nef充足和nef缺乏的HIV-1在全身和粘膜B细胞中减弱CSR、SHM和抗原特异性IgG和IgA产生的能力。目的2是评估长距离隧道纳米管将膜结合和囊泡相关的Nef从感染细胞转运到B细胞的能力。目的3是阐明nef介导的B细胞中CD154和IL-4信号抑制的分子相互作用。这些研究的结果将有助于更好地理解HIV-1逃避抗体反应的机制。此外，拟议的研究可能有助于开发针对HIV-1的新型治疗和疫苗策略。

DESCRIPTION (provided by applicant): The goal of this proposal is to elucidate the mechanisms by which HIV-1 evades humoral immunity. Antibody responses, including class switch DNA recombination (CSR) and somatic hypermutation (SHM), are essential to block HIV-1 entry and spread. CSR substitutes IgM with IgG or IgA, thereby endowing antibodies with novel effector functions that enhance viral clearance systemically and at mucosal sites of entry. SHM introduces point mutations in genes encoding the antigen-binding variable region of antibodies, thereby providing the structural correlate for selection by viral antigens of higher affinity IgG and IgA mutants. CSR and SHM require activation-induced cytidine deaminase (AID), an enzyme expressed by B cells in the germinal center (GC) of secondary lymphoid organs. This specialized microenvironment comprises CD4+ T cells that activate B cells through CD154 and IL-4. Ultimately, GC B cells differentiate into plasma cells, which secrete large amounts of IgG and IgA antibodies. HIV-1 impairs systemic and mucosal IgG and IgA responses to viral antigens, opportunistic pathogens and vaccines through mechanisms that remain poorly understood. Although progressive loss of CD4+ T cells is certainly important, B cell-intrinsic abnormalities, including poor responsiveness of B cells to CD154, are also involved. In this proposal, we argue that the HIV-1 protein Nef contributes to the genesis of B cell-intrinsic defects arising during HIV-1 infection. We contend that Nef attenuates CD154-dependent CSR, SHM as well as virus-specific IgG and IgA production in systemic and mucosal GCs. We also hypothesize that Nef targets B cells by traveling through long-range tunneling nanotubules emanating from HIV-1-infected cells. Finally, we propose that multiple Nef domains contribute to the inhibition of kinases transducing CD154 and IL-4 signaling in B cells. Three specific aims are proposed. Aim 1 is to determine the ability of Nef-sufficient and Nef-deficient HIV-1 to attenuate CSR, SHM and antigen-specific IgG and IgA production in systemic and mucosal B cells. Aim 2 is to assess the ability of long- distance tunneling nanotubules to shuttle membrane-bound and vesicle-associated Nef from infected cells to B cells. Aim 3 is to elucidate the molecular interactions involved in Nef-mediated inhibition of CD154 and IL-4 signaling in B cells. Findings resulting from these studies should lead to a better understanding of the mechanisms whereby HIV-1 evades the antibody response. In addition, the proposed studies might facilitate the development of novel therapeutic and vaccine strategies against HIV-1. PUBLIC HEALTH RELEVANCE: HIV-1 profoundly impairs antibody responses against viral proteins, opportunistic agents and vaccines. Growing evidence indicates that this antibody deficiency is caused not only by loss of CD4+ T cells, but also by B cell-intrinsic defects. The goal of this application is to elucidate the mechanisms by which HIV-1 causes B cell dysfunctions. Ultimately, findings deriving from the proposed studies should help develop more effective vaccines against HIV-1.