Role of B Lymphocytes In HIV Infection And Pathogenesis

在过去的一年里，我们对HIV疾病背景下的B细胞进行了研究，重点是1)HIV疾病中未成熟/过渡性B细胞的增殖机制；2)B细胞亚群对含CpG的寡核苷酸刺激的反应；3)B细胞计数和亚群在开始抗逆转录病毒治疗(ART)后发生的变化；以及4)HIV病毒携带者中HIV相关B细胞耗尽的证据。在第一项研究中，我们调查了接受IL-7治疗的HIV感染者外周血中B细胞亚群的变化，这是一项大型临床安全性试验的一部分，该研究解决了HIV疾病背景下未成熟/过渡性B细胞增殖的机制。我们的研究结果表明，IL-7本身可以导致外周血中未成熟/过渡性B细胞的扩张。这是一个新的观察结果，因为IL-7对人类B细胞的直接作用在体内从未得到证实。 在发表在《免疫学杂志》上的第二项研究中，我们研究了DNA寡核苷酸CpG-B对从HIV感染者分离的幼稚和记忆B细胞的增殖和效应功能的影响。CpG-B是一种与表达在B细胞上的Toll样受体9结合的配体。总体而言，我们的发现表明，CpG-B目前被认为是旨在增强免疫低下个体免疫反应的疫苗制剂中的佐剂，它有效地促进了从HIV病毒携带者和HIV无核携带者分离的B细胞的增殖和免疫球蛋白和细胞因子的分泌。虽然在HIV病毒携带者的记忆B细胞室中观察到了某些缺陷，但来自HIV病毒携带者和HIV携带者的初始B细胞对CpG-B的反应很强，这表明疫苗中CpG-B的存在可以帮助初始B细胞达到对免疫原产生反应所需的阈值。 在发表在《传染病杂志》上的第三项研究中，我们证明了通过有效的抗逆转录病毒治疗，艾滋病毒感染者体内异常B细胞亚群的过度表达，包括未成熟/过渡性和高度激活的B细胞，可以被逆转。有效的抗逆转录病毒治疗还导致B细胞计数正常化，这表明正在进行的艾滋病毒复制与B细胞的净损失有关，可能是通过内在和外在凋亡增加等机制，我们之前已经报道过这两种机制。 在发表在《实验医学杂志》上的第四项研究中，我们描述了HIV感染病毒症患者外周血中异常B细胞隔室中与HIV相关的B细胞耗尽的证据。这种B细胞亚群被称为组织样记忆B细胞，因为它们与最近描述的具有免疫调节功能的扁桃体记忆B细胞亚群相似，可以通过高表达PAN B细胞标记CD20和低表达补体受体CD21和CD27来区别于其他B细胞，补体受体CD21和CD27是B细胞记忆的经典标记。HIV病毒携带者血液中存在的组织样记忆B细胞表现出许多B细胞衰竭的迹象，包括多种抑制受体的表达增加；归巢和黏附受体的表达改变，类似于病毒诱导的T细胞衰竭；体内复制受阻和体细胞过度突变；对B细胞刺激的体外增殖减少；以及HIV特异性但不是非特异性和召回抗原特异性反应的丰富。这些发现增加了我们对艾滋病毒感染者对艾滋病毒抗体反应较差的理解。

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.