Role of B Lymphocytes In HIV Infection And Pathogenesis

在过去的一年里，我们一直在HIV疾病背景下对B细胞进行研究，重点是1）HIV疾病中未成熟/过渡期B细胞扩增的机制; 2）B细胞亚群对含CpG寡核苷酸刺激的反应; 3）抗逆转录病毒治疗（ART）开始后B细胞计数和亚群的变化;和4）HIV病毒血症个体中HIV相关B细胞耗竭的证据。在第一项针对HIV疾病背景下未成熟/过渡性B细胞扩增机制的研究中，我们研究了接受IL-7作为大型临床安全性试验一部分的HIV感染者外周血中B细胞亚群的变化。我们的研究结果表明，IL-7本身可以导致外周血中未成熟/过渡B细胞的扩增。 这是一个新的观察结果，因为IL-7对人B细胞的直接作用从未在体内建立。 在第二项研究中，发表在免疫学杂志上，我们研究了DNA寡核苷酸CpG-B（一种结合B细胞上表达的toll样受体9的配体）对从HIV感染者中分离的幼稚和记忆B细胞的增殖和效应功能的影响。 总体而言，我们的研究结果表明，CpG-B，目前被认为是一种佐剂，在疫苗制备的目的是增强免疫功能低下的个人的免疫应答，是有效的，在提高增殖和分泌免疫球蛋白和细胞因子的B细胞分离自HIV病毒血症和HIV病毒血症的个人。 虽然在HIV病毒血症个体的记忆B细胞区室中观察到某些缺陷，但来自HIV病毒血症和HIV病毒血症个体的幼稚B细胞对CpG-B都有强烈的反应，这表明疫苗中CpG-B的存在可以帮助幼稚B细胞达到对免疫原产生有效反应所需的阈值。 在发表在《传染病杂志》上的第三项研究中，我们证明了在患有活动性疾病的HIV感染者中，异常B细胞亚群（包括未成熟/过渡和过度活化的B细胞）的过度表达可以通过有效的ART逆转。有效的ART还导致B细胞计数正常化，这表明正在进行的HIV复制与B细胞的净损失有关，可能通过机制，如增加内在和外在的凋亡，这两个我们以前报道。 在发表在《实验医学杂志》上的第四项研究中，我们描述了在HIV感染病毒血症个体的外周血中扩增的异常B细胞区室中HIV相关B细胞耗竭的证据。 这种B细胞亚群，由于其与最近描述的具有免疫调节特征的扁桃体记忆B细胞亚群的相似性而被称为组织样记忆B细胞，可以通过其高表达的泛B细胞标志物CD 20和低表达水平的补体受体CD 21和CD 27（B细胞记忆的经典标志物）与其他B细胞区分开。 HIV病毒血症个体血液中存在的组织样记忆B细胞表现出许多B细胞耗竭的迹象，包括多种抑制性受体表达增加;归巢和粘附受体表达改变，类似于病毒诱导的T细胞耗竭;体内复制和体细胞超变受阻;响应于B细胞刺激的体外增殖减少;和HIV特异性而非特异性的富集，以及回忆抗原特异性应答。这些发现增加了我们对为什么HIV感染者对HIV的抗体反应很差的理解。

Over the past year we have pursued studies on B cells in the setting of HIV disease by focusing on 1) mechanisms of immature/transitional B-cell expansion in HIV disease; 2) responses of B-cell subpopulations to stimulation with CpG-containing oligonucleotides; 3) changes in B-cell counts and subpopulations that occur following initiation of antiretroviral therapy (ART); and 4) evidence of HIV-associated B-cell exhaustion in HIV-viremic individuals. In the first study addressing mechanisms of immature/transitional B-cell expansion in the setting of HIV disease, we investigated changes in B-cell subpopulations that occurred in the peripheral blood of HIV-infected individuals who received IL-7 as part of a large clinical safety trial. Our findings indicate that IL-7 itself can lead to the expansion of immature/transitional B cells in the peripheral blood. This is a novel observation given that a direct role for IL-7 on human B cells has never been established in vivo. In the second study, published in The Journal of Immunology, we investigated the effect of the DNA oligonucleotide CpG-B, a ligand that binds toll-like receptor 9 expressed on B cells, on the proliferation and effector function of naive and memory B cells isolated from HIV-infected individuals. Overall, our findings indicate that CpG-B, which is currently being considered as an adjuvant in vaccine preparations aimed at augmenting immune responses in immunocompromised individuals, was effective at enhancing the proliferation and secretion of immunoglobulins and cytokines of B cells isolated from HIV-viremic and HIV-aviremic individuals. While certain defects were observed in the memory B-cell compartment of HIV-viremic individuals, nave B cells from both HIV-viremic and HIV-aviremic individuals responded robustly to CpG-B, suggesting that the presence of CpG-B in vaccines could help nave B cells reach the threshold required to productively respond to immunogens. In the third study, published in The Journal of Infectious Diseases, we demonstrate that the over-expression of aberrant B-cell subpopulations, including immature/transitional and hyper-activated B cells, in HIV-infected individuals with active disease is reversed with effective ART. Effective ART also leads to a normalization of B-cell counts, suggesting that ongoing HIV replication is associated with a net loss of B cells, possibly through mechanisms such as increased intrinsic and extrinsic apoptosis, both of which we have previously reported. In the fourth study, published in The Journal of Experimental Medicine, we describe evidence of HIV-associated B-cell exhaustion in an abnormal B-cell compartment that is expanded in the peripheral blood of HIV-infected viremic individuals. This B-cell subpopulation, termed tissue-like memory B cells as a result of their similarities with a recently described tonsillar memory B-cell subpopulation bearing immunoregulatory features, can be distinguished from other B cells by its high expression of the pan B-cell marker CD20 and low expression levels of the complement receptor CD21 and CD27, a classic marker of B-cell memory. Tissue-like memory B cells present in the blood of HIV-viremic individuals exhibit numerous signs of B-cell exhaustion, including increased expression of multiple inhibitory receptors; an altered expression of homing and adhesion receptors similar to that observed with virus-induced T-cell exhaustion; stunted in vivo replication and somatic hypermutation; reduced in vitro proliferation in response to B-cell stimuli; and enrichment of HIV-specific but not nonspecific and recall antigen-specific responses. These findings add to our understanding of why HIV-infected individuals mount a poor antibody response against HIV.