Decreased survival of B cells of HIV-viremic patients mediated by altered expression of receptors of the TNF superfamily.

Human immunodeficiency virus (HIV) infection leads to numerous perturbations of B cells through mechanisms that remain elusive. We performed DNA microarray, phenotypic, and functional analyses in an effort to elucidate mechanisms of B cell perturbation associated with ongoing HIV replication. 42 genes were up-regulated in B cells of HIV-viremic patients when compared with HIV-aviremic and HIV-negative patients, the majority of which were interferon (IFN)-stimulated or associated with terminal differentiation. Flow cytometry confirmed these increases and indicated that CD21(low) B cells, enhanced in HIV-viremic patients, were largely responsible for the changes. Increased expression of the tumor necrosis factor (TNF) superfamily (TNFSF) receptor CD95 correlated with increased susceptibility to CD95-mediated apoptosis of CD21(low) B cells, which, in turn, correlated with HIV plasma viremia. Increased expression of BCMA, a weak TNFSF receptor for B lymphocyte stimulator (BLyS), on CD21(low) B cells was associated with a concomitant reduction in the expression of the more potent BLyS receptor, BAFF-R, that resulted in reduced BLyS binding and BLyS-mediated survival. These findings demonstrate that altered expression of genes associated with IFN stimulation and terminal differentiation in B cells of HIV-viremic patients lead to an increased propensity to cell death, which may have substantial deleterious effects on B cell responsiveness to antigenic stimulation.

Decreased survival of B cells of HIV-viremic patients mediated by altered expression of receptors of the TNF superfamily.

Human immunodeficiency virus (HIV) infection leads to numerous perturbations of B cells through mechanisms that remain elusive. We performed DNA microarray, phenotypic, and functional analyses in an effort to elucidate mechanisms of B cell perturbation associated with ongoing HIV replication. 42 genes were up-regulated in B cells of HIV-viremic patients when compared with HIV-aviremic and HIV-negative patients, the majority of which were interferon (IFN)-stimulated or associated with terminal differentiation. Flow cytometry confirmed these increases and indicated that CD21(low) B cells, enhanced in HIV-viremic patients, were largely responsible for the changes. Increased expression of the tumor necrosis factor (TNF) superfamily (TNFSF) receptor CD95 correlated with increased susceptibility to CD95-mediated apoptosis of CD21(low) B cells, which, in turn, correlated with HIV plasma viremia. Increased expression of BCMA, a weak TNFSF receptor for B lymphocyte stimulator (BLyS), on CD21(low) B cells was associated with a concomitant reduction in the expression of the more potent BLyS receptor, BAFF-R, that resulted in reduced BLyS binding and BLyS-mediated survival. These findings demonstrate that altered expression of genes associated with IFN stimulation and terminal differentiation in B cells of HIV-viremic patients lead to an increased propensity to cell death, which may have substantial deleterious effects on B cell responsiveness to antigenic stimulation.

Role for CD21 in the establishment of an extracellular HIV reservoir in lymphoid tissues.

Follicular dendritic cells (FDC) represent a major extracellular reservoir for HIV. A better understanding of the mechanisms of virion attachment to FDC may offer new avenues for reducing viral burdens in infected individuals. We used a murine model to investigate the establishment of extracellular HIV reservoirs in lymph nodes (LN). Consistent with findings in human tissues, CD21 was required for trapping of HIV to LN cells, as evidenced by significantly reduced virion binding when mice were pretreated with a C3 ligand-blocking anti-CD21 mAb and absence of virion trapping in CD21 knockout mice. Also consistent with findings in human tissues, the majority of HIV virions were associated with the FDC-enriched fraction of LN cell preparations. Somewhat surprisingly, HIV-specific Abs were not essential for HIV binding to LN cells, indicating that seeding of the FDC reservoir may begin shortly after infection and before the development of HIV-specific Abs. Finally, the virion-displacing potential for anti-CD21 mAbs was investigated. Treatment of mice with anti-CD21 mAbs several days after injection of HIV significantly reduced HIV bound to LN cells. Our findings demonstrate a critical role for CD21 in HIV trapping by LN cells and suggest a new therapeutic avenue for reducing HIV reservoirs.

Compromised B cell responses to influenza vaccination in HIV-infected individuals.

BACKGROUND: Yearly influenza vaccination, although recommended for human immunodeficiency virus (HIV)-infected individuals, has not received thorough evaluation in the era of antiretroviral therapy. We assessed the impact of HIV disease on B cell responses to influenza vaccination. METHODS: Sixty-four HIV-infected and 17 HIV-negative individuals received the 2003-2004 trivalent inactivated influenza vaccine. Frequencies of influenza-specific antibody-secreting cells (ASCs) were measured by enzyme-linked immunospot (ELISPOT) assay, and antibody responses were measured by hemagglutination-inhibition (HI) assay. Memory responses to influenza were measured by ELISPOT assay after polyclonal activation of B cells in vitro. RESULTS: Prevaccination HI titers were significantly higher in HIV-negative than in HIV-infected individuals. Peak HI titers and influenza-specific ASC frequencies were directly correlated with CD4+ T cell counts in HIV-infected individuals. Influenza-specific memory B cell responses were significantly lower in HIV-infected than in HIV-negative individuals and were directly correlated with CD4+ T cell counts. CONCLUSIONS: HIV infection is associated with a weak antibody response to influenza vaccination that is compounded by a poor memory B cell response. CD4+ T cell count is a critical determinant of responsiveness to influenza vaccination, and the contribution of plasma HIV RNA level is suggestive and warrants further investigation.

Perturbations in B cell responsiveness to CD4+ T cell help in HIV-infected individuals.

HIV infection induces a wide array of B cell dysfunctions. We have characterized the effect of plasma viremia on the responsiveness of B cells to CD4(+) T cell help in HIV-infected patients. In HIV-negative donors, B cell proliferation correlated with CD154 expression on activated CD4(+) T cells and with the availability of IL-2, whereas in HIV-infected viremic patients, reduced B cell proliferation was observed despite normal CD154 expression on activated CD4(+) T cells. Reduced triggering of B cells by activated CD4(+) T cells was clearly observed in HIV-infected viremic patients compared with aviremic patients with comparable CD4(+) T cell counts, and a dramatic improvement in B cell function was observed in patients whose plasma viremia was controlled by effective antiretroviral therapy. The degree of B cell dysfunction in viremic patients correlated strongly with the inability of B cells to express CD25 in response to activated CD4(+) T cells, resulting in an inability to mount a normal proliferative response to IL-2. Similar defects in responsiveness to IL-2 were observed in the B cells of HIV-infected viremic patients in the context of B cell receptor stimulation. These data provide new insight into the mechanisms associated with ineffective humoral responses in HIV disease.

Human immunodeficiency virus type 1 bound to B cells: relationship to virus replicating in CD4+ T cells and circulating in plasma.

Human immunodeficiency virus type 1 (HIV-1) virions bind to B cells in the peripheral blood and lymph nodes through interactions between CD21 on B cells and complement-complexed virions. B-cell-bound virions have been shown to be highly infectious, suggesting a unique mode of HIV-1 dissemination by B cells circulating between peripheral blood and lymphoid tissues. In order to investigate the relationship between B-cell-bound HIV-1 and viruses found in CD4+ T cells and in plasma, we examined the genetic relationships of HIV-1 found in the blood and lymph nodes of chronically infected patients with heteroduplex mobility and tracking assays and DNA sequence analysis. In samples from 13 of 15 patients examined, HIV-1 variants in peripheral blood-derived B cells were closely related to virus in CD4+ T cells and more divergent from virus in plasma. In samples from five chronically viremic patients for whom analyses were extended to include lymph node-derived HIV-1 isolates, B-cell-associated HIV-1 and CD4+-T-cell-associated HIV-1 in the lymph nodes were equivalent in their divergence from virus in peripheral blood-derived B cells and generally more distantly related to virus in peripheral blood-derived CD4+ T cells. These results indicates virologic cross talk between B cells and CD4+ T cells within the microenvironment of lymphoid tissues and, to a lesser extent, between cells in lymph nodes and the peripheral blood. These findings also indicate that most of the virus in plasma originates from cells other than CD4(+) T cells in the peripheral blood and lymph nodes.