Role Of B Lymphocytes In HIV Infection And Pathogenesis

我们已经证明了一些关于B细胞在HIV-1免疫发病机制中的作用的新观察。根据我们的开创性观察，具有复制能力的HIV-1通过涉及病毒粒子上的补体片段和B细胞上的CD21的相互作用在体内的B细胞上循环，我们开始详细研究这些相互作用的原因和后果。HIV-B细胞结合事件的一个后果是B细胞促进了病毒在外周血液和淋巴组织之间的传播。通过对B细胞上发现的病毒和外周血和淋巴结中的CD4+T细胞以及HIV感染的病毒症患者血浆中发现的病毒进行系统发育分析，我们确定了B细胞通过这些不同的区段参与了HIV的传播。我们还观察到病毒症患者B细胞上CD21的表达降低。我们用定量的流式细胞术和mRNA测量进一步研究了这一现象，发现CD21在病毒血症期间的表达显著降低，在病毒血症抑制后显著上调至正常水平。我们还对几名慢性感染患者在抗逆转录病毒治疗前后的B细胞功能进行了纵向分析。高病毒载量显然与B细胞功能的降低有关，这是通过对各种B细胞刺激的体外增殖来衡量的。在对B细胞受体刺激的反应中，观察到的功能障碍程度最高，类似于体内B细胞遇到抗原或其他参与抗原反应的免疫细胞时可能发生的情况，如CD4+T细胞。此外，当病毒症患者的B细胞被分成两个亚群时，我们观察到了显著的二分性效应；一个亚群表达低水平的CD21，一个亚群表达高水平的CD21。CD21low B细胞虽然表现出对B细胞刺激的反应大大降低了增殖水平，但与CD21高水平的B细胞相比，发现它们自发地分泌高水平的免疫球蛋白(Ig)。这一观察结果使我们推测，病毒感染患者的CD21low B细胞与终末分化的分泌Ig的B细胞有关，这种细胞被称为浆细胞，通常在健康人的外周血中不存在，但在某些炎症性和肿瘤性疾病中已观察到。通过电子显微镜观察B细胞的形态，我们观察到HIV感染的病毒症患者的CD21low B细胞组分中富含具有典型浆细胞特征的细胞，而相应的CD21High B细胞组分中则没有。这些发现表明，HIV病毒血症与高度功能失调的B细胞的出现是一致的。此外，这些观察为HIV感染者体液免疫反应缺陷的机制提供了新的见解。

We have demonstrated several new observations regarding the role of B cells in HIV-1 immunopathogenesis. Following our seminal observation that replication-competent HIV-1 circulates on B cells in vivo through interactions involving complement fragments on virions and CD21 on B cells, we began a detailed study of the causes and consequences of these interactions. One consequence of HIV-B cell binding events is that B cells contribute to the trafficking of virus between peripheral blood and lymphoid tissues. Using phylogenetic analyses of virus found on B cells and virus found in CD4+ T cells of peripheral blood and lymph nodes, as well as in the plasma of HIV-infected viremic patients, we established that B cells participate in HIV dissemination through these various compartments. We have also observed that CD21 expression was reduced on B cells of viremic patients. We have further investigated this phenomenon by using quantitative flow cytometry and mRNA measurements to demonstrate that CD21 expression was significantly reduced during viremia and significantly upregulated to normal levels following suppression of viremia. We also conducted longitudinal analyses of B cell function on several chronically infected patients, before and after reduction of viral load by anti-retroviral therapy. High viral load was clearly associated with a reduction in B cell function, as measured by proliferation in vitro in response to a variety of B cell stimuli. The highest degree of dysfunction was observed in response to B cell receptor stimulation, similar to what may occur in vivo when B cells encounter antigen or other immune cells involved in antigenic responses, such as CD4+ T cells. Furthermore, we observed strikingly dichotomous effects when B cells of viremic patients were separated into two sub-populations; one expressing low levels of CD21 and one expressing high levels of CD21. CD21low B cells, while demonstrating profoundly reduced levels of proliferation in response to B cell stimuli, were found to spontaneously secrete high levels of immunoglobulins (Ig) when compared to their CD21high counterpart. This observation led us to speculate that the CD21low B cells of viremic patients were related to terminally differentiated Ig-secreting B cells, called plasma cells, that are generally absent from the peripheral blood of healthy individuals yet have been observed in certain inflammatory and neoplastic diseases. By using electron microscopy to look at B cell morphology, we observed that cells with typical plasma cell features were enriched in the CD21low B cell fraction of HIV-infected viremic patients and were absent from their corresponding CD21high B cell fraction. These findings indicate that HIV viremia coincides with the appearance of highly dysfunctional B cells. In addition, these observations offer new insights into the mechanisms of the defects of the humoral immune responses known to be present in HIV-infected individuals.