Impairment of B-lymphocyte differentiation induced by dual triggering of the B-cell antigen receptor and CD40 in advanced HIV-1-disease

Clinical and Molecular Properties of Human Immunodeficiency Virus-Related Diffuse Large B-Cell Lymphoma

Non-Hodgkin lymphoma is the most common malignancy affecting people living with HIV (PLWH). Among its several subtypes, diffuse large B-cell lymphoma (DLBCL) is an important manifestation within the HIV-infected compartment of the population. Since HIV is able to modulate B cells and promote lymphomagenesis through direct and indirect mechanisms, HIV-related DLBCL has specific characteristics. In this review, we address the clinical and molecular properties of DLBCL disease in the context of HIV infection, as well as the mechanisms by which HIV is able to modulate B lymphocytes and induce their transformation into lymphoma.

B-cell development and pneumococcal immunity in vertically acquired HIV infection

OBJECTIVES

Many children with HIV infection now survive into adulthood. This study explored the impact of vertically acquired HIV in the era of antiretroviral therapy on the development of humoral immunity.

DESIGN

Natural and vaccine-related immunity to pneumococcus and B-cell phenotype was characterized and compared in three groups of young adults: those with vertically-acquired infection, those with horizontally acquired infection and healthy controls.

METHODS

Serotype-specific pneumococcal (Pnc) immunoglobulin M and G concentrations before and up to 1 year post-Pnc polysaccharide (Pneumovax) immunization were determined, and opsonophagocytic activity was analysed. B-cell subpopulations and dynamic markers of B-cell signalling, turnover and susceptibility to apoptosis were evaluated by flow cytometry.

RESULTS

HIV-infected patients showed impaired natural Pnc immunity and reduced humoral responses to immunization with Pneumovax; this was greatest in those viraemic at time of the study. Early-life viral control before the age of 10 years diminished these changes. Expanded populations of abnormally activated and immature B-cells were seen in both HIV-infected cohorts. Vertically infected patients were particularly vulnerable to reductions in marginal zone and switched memory populations. These aberrations were reduced in patients with early-life viral control.

CONCLUSION

In children with HIV, damage to B-cell memory populations and impaired natural and vaccine immunity to pneumococcus is evident in early adult life. Sustained viral control from early childhood may help to limit this effect and optimize humoral immunity in adult life.

Serum free light chains in patients with HIV infection: their association with markers of disease severity and antiretroviral use

AIM

Serum free light chain measurements are used to follow-up and manage patients with monoclonal gammopathies, and abnormal ratios are associated with risk of progression in certain diseases. B cell dysfunction is well described in HIV and patients are at risk of developing B cell lymphomas. This study investigated whether HIV is associated with abnormal free light chain levels and the impact of antiretroviral treatment (ART) on these.

METHODS

κ And λ free light chain concentrations and ratios, serum albumin and immunoglobulin G (IgG) were measured in 366 HIV positive subjects and correlated with CD4+ counts, viral loads, IgG, albumin and ART use.

RESULTS

66% were women and most were black Africans (66%), 26% were of mixed ethnicity and 8% were Caucasian or of unknown or other race. 89% were on ART. κ Free light chain values ranged from 5.59 to 357.0 mg/L (median 19.6 mg/L) and λ free light chain values ranged from 9.28 to 286 mg/L (median 22.3 mg/L). Both correlated positively with viral load and IgG and negatively with CD4+ counts and albumin concentrations. The ratio only correlated with IgG concentrations. Patients on ART had significantly lower free light chain concentrations, but the ratio was not significantly affected.

CONCLUSIONS

This study demonstrated that free light chain concentrations were significantly correlated with markers of HIV disease severity, suggesting ongoing B cell dysfunction despite ART use. Free light chain ratio was not significantly affected.

Abnormal B cell memory subsets dominate HIV-specific responses in infected individuals

Recently, several neutralizing anti-HIV antibodies have been isolated from memory B cells of HIV-infected individuals. Despite extensive evidence of B cell dysfunction in HIV disease, little is known about the cells from which these rare HIV-specific antibodies originate. Accordingly, we used HIV envelope gp140 and CD4 or coreceptor (CoR) binding site (bs) mutant probes to evaluate HIV-specific responses in peripheral blood B cells of HIV-infected individuals at various stages of infection. In contrast to non-HIV responses, HIV-specific responses against gp140 were enriched within abnormal B cells, namely activated and exhausted memory subsets, which are largely absent in the blood of uninfected individuals. Responses against the CoRbs, which is a poorly neutralizing epitope, arose early, whereas those against the well-characterized neutralizing epitope CD4bs were delayed and infrequent. Enrichment of the HIV-specific response within resting memory B cells, the predominant subset in uninfected individuals, did occur in certain infected individuals who maintained low levels of plasma viremia and immune activation with or without antiretroviral therapy. The distribution of HIV-specific responses among memory B cell subsets was corroborated by transcriptional analyses. Taken together, our findings provide valuable insight into virus-specific B cell responses in HIV infection and demonstrate that memory B cell abnormalities may contribute to the ineffectiveness of the antibody response in infected individuals.

Evolution of broadly cross-reactive HIV-1-neutralizing activity: therapy-associated decline, positive association with detectable viremia, and partial restoration of B-cell subpopulations

Little is known about the stability of HIV-1 cross-neutralizing responses. Taking into account the fact that neutralization breadth has been positively associated with plasma viral load, there is no explanation for the presence of broadly neutralizing responses in a group of patients on treatment with undetectable viremia. In addition, the B-cell profile responsible for broadly cross-neutralizing responses is unknown. Here we studied the evolution of neutralizing responses and the B-cell subpopulation distribution in a group of patients with broadly cross-reactive HIV-1-neutralizing activity. We studied neutralization breadth evolution in a group of six previously identified broadly cross-neutralizing patients and six control patients during a 6-year period with a previously described minipanel of recombinant viruses from five different subtypes. B-cell subpopulation distribution during the study was also determined by multiparametric flow cytometry. Broadly cross-neutralizing activity was transient in four broad cross-neutralizers and stable, up to 4.6 years, in the other two. In four out of five broad cross-neutralizers who initiated treatment, a neutralization breadth loss occurred after viremia had been suppressed for as much as 20 months. B-cell subpopulation analyses revealed a significant increase in the frequency of naive B cells in broadly cross-reactive samples, compared with samples with less neutralization breadth (increased from 44% to 62%). We also observed a significant decrease in tissue-like and activated memory B cells (decreased from 19% to 12% and from 17% to 9%, respectively). Our data suggest that HIV-1 broadly cross-neutralizing activity is variable over time and associated with detectable viremia and partial B-cell restoration.

Microbial TLR Agonists and Humoral Immunopathogenesis in HIV Disease

Although T cells are the primary and most-studied targets of the Human Immunodeficiency Virus (HIV), B cells, especially memory B lymphocytes, are also chronically depleted in the course of HIV disease. Although the lack of CD4+ T cell help may explain these deficiencies, intrinsic defects in B lymphocytes appear to contribute to B cell depletion and reduced antibody (Ab) production in the setting of HIV, especially of some antigens eliciting T cell-independent responses. The gut mucosal barrier is disrupted in HIV disease, resulting in increased systemic exposure to microbial products such as Toll-Like Receptor (TLR) agonists. The association of enhanced systemic levels of TLR agonists and B cell dysfunction in HIV disease is not understood. This review discusses the potential role of microbial TLR agonists in the B cell depletion, enhanced autoantibody production and impaired responses to vaccination observed in HIV-infected hosts. Increased microbial translocation in HIV infection may drive B cells to produce autoantibodies and increase susceptibilities of B cells to apoptosis through activation-induced cell death. Determining the mechanisms of B cell perturbations in HIV disease will inform the design of novel strategies of improve immune responses to vaccines, reduce opportunistic infections and slow disease progression.

Clostridium difficile infection in HIV-seropositive individuals and transplant recipients

Immunocompromise is a commonly cited risk factor for Clostridium difficile infection (CDI). We reviewed the experimental and epidemiological literature on CDI in three immunocompromised groups, HIV-seropositive individuals, haematopoietic stem cell or bone marrow transplant recipients and solid organ transplant recipients. All three groups have varying degrees of impairment of humoral immunity, a major factor influencing the outcome of CDI. Soluble HIV proteins such as nef and immunosuppressive agents such as cyclosporin, azathioprine and mycophenalate mofetil modify signalling from the key cellular pathways triggered by C. difficile toxin A, although there is a paucity of data on how these factors may interact with pathways activated by toxin B. Despite this, there has been little direct investigation into the effect of immunosuppression on the pathogenesis of CDI. Epidemiological studies consistently show increased rates of CDI in these populations, which are higher in those with greater degrees of immunocompromise such as individuals with advanced AIDS not receiving combination antiretroviral therapy or allogeneic haematopoietic stem cell transplant recipients. Less consistently data suggests immunocompromise in each group also impacts rates of severe, recurrent or complicated CDI. However all these conditions are characterised by high levels of antibiotic use and prolonged hospital stay, both powerful drivers of CDI risk.

Microbial Translocation and B Cell Dysfunction in Human Immunodeficiency Virus Disease

The gut mucosal barrier disrupted in HIV disease, resulting in increased systemic exposure to microbial products such as Lipo Polys Accharide (LPS). The association of enhanced microbial translocation and B cell dysfunction in HIV disease is not fully understood. High dose and short term exposure of microbial Toll-Like Receptor (TLR) agonists were used as vaccine adjuvants, however, low dose and long term exposure of TLR agonists could be harmful. The characteristics of B cell dysfunction in HIV disease included B cell, especially memory B cell depletion, enhanced levels of autoimmune antibodies and impaired vaccine or antigen responsiveness. This review discusses and explores the possibility of the effect of microbial translocation on memory B cell depletion and impaired vaccine responses in HIV infection. By determining the mechanisms of B cell depletion and perturbations in HIV disease, it may be possible to design interventions that can improve immune responses to vaccines, reduce selected opportunistic infections and perhaps slow disease progression.

B cell depletion in HIV-1 subtype A infected Ugandan adults: relationship to CD4 T cell count, viral load and humoral immune responses

To better understand the nature of B cell dysfunctions in subjects infected with HIV-1 subtype A, a rural cohort of 50 treatment-naïve Ugandan patients chronically infected with HIV-1 subtype A was studied, and the relationship between B cell depletion and HIV disease was assessed. B cell absolute counts were found to be significantly lower in HIV-1+ patients, when compared to community matched negative controls (p<0.0001). HIV-1-infected patients displayed variable functional and binding antibody titers that showed no correlation with viral load or CD4+ T cell count. However, B cell absolute counts were found to correlate inversely with neutralizing antibody (NAb) titers against subtype A (p = 0.05) and subtype CRF02_AG (p = 0.02) viruses. A positive correlation was observed between subtype A gp120 binding antibody titers and NAb breadth (p = 0.02) and mean titer against the 10 viruses (p = 0.0002). In addition, HIV-1 subtype A sera showed preferential neutralization of the 5 subtype A or CRF02_AG pseudoviruses, as compared with 5 pseudoviruses from subtypes B, C or D (p<0.001). These data demonstrate that in patients with chronic HIV-1 subtype A infection, significant B cell depletion can be observed, the degree of which does not appear to be associated with a decrease in functional antibodies. These findings also highlight the potential importance of subtype in the specificity of cross-clade neutralization in HIV-1 infection.

Evidence of early B-cell dysregulation in simian immunodeficiency virus infection: rapid depletion of naïve and memory B-cell subsets with delayed reconstitution of the naïve B-cell population

Despite eliciting a robust antibody response in humans, several studies in human immunodeficiency virus (HIV)-infected patients have demonstrated the presence of B-cell deficiencies during the chronic stage of infection. While several explanations for the HIV-induced B-cell deficit have been proposed, a clear mechanistic understanding of this loss of B-cell functionality is not known. This study utilizes simian immunodeficiency virus (SIV) infection of rhesus macaques to assess B-cell population dynamics beginning at the acute phase and continuing through the chronic phase of infection. Flow cytometric assessment demonstrated a significant early depletion of both naïve and memory B-cell subsets in the peripheral blood, with differential kinetics for recovery of these populations. Furthermore, the altered numbers of naïve and memory B-cell subsets in these animals corresponded with increased B-cell activation and altered proliferation profiles during the acute phase of infection. Finally, all animals produced high titers of antibody, demonstrating that the measurement of virus-specific antibody responses was not an accurate reflection of alterations in the B-cell compartment. These data indicate that dynamic B-cell population changes in SIV-infected macaques arise very early after infection at the precise time when an effective adaptive immune response is needed.

Memory B cell function in HIV-infected children-decreased memory B cells despite ART

B cell dysfunction is a well-studied complication of HIV infection in adults. Data on B cell differentiation in normal and HIV-infected children are lacking. We show the distribution of B cell subsets and immunoglobulin levels in HIV-infected children compared with controls. Furthermore, we observe the long-term B cell reconstitution of vaccine-specific immunity after antiretroviral therapy (ART). Phenotype of B cells (naive, non-switched memory, switched memory) was analyzed in 48 infected children and 62 controls. In nine HIV-infected children, functional reconstitution was quantified by tetanus-specific antibodies and by performing a lymphocyte transformation test (LTT) in a longitudinal approach. Switched memory B cells are significantly reduced in HIV-infected children. Vaccine-specific antibodies and response to LTT increase after initiation of ART. Our data indicate a significant dysfunction in the B cell system, despite effective ART. Partial reconstitution of humoral immunity may have therapeutic implications in a subset of HIV-infected children.

B cells in HIV infection and disease

In recent years, intense research efforts have been dedicated to elucidating the pathogenic mechanisms of HIV-associated disease progression. In addition to the progressive depletion and dysfunction of CD4(+) T cells, HIV infection also leads to extensive defects in the humoral arm of the immune system. The lack of immune control of the virus in almost all infected individuals is a great impediment to the treatment of HIV-associated disease and to the development of a successful HIV vaccine. This Review focuses on advances in our understanding of the mechanisms of B-cell dysfunction in HIV-associated disease and discusses similarities with other diseases that are associated with B-cell dysfunction.

Functional Epstein-Barr virus reservoir in plasma cells derived from infected peripheral blood memory B cells

The Epstein-Barr virus (EBV) causes infectious mononucleosis, establishes latency in resting memory B lymphocytes, and is involved in oncogenesis through poorly understood mechanisms. The EBV lytic cycle is initiated during plasma cell differentiation by mRNAs transcripts encoded by BZLF1, which induce the synthesis of EBV proteins such as the immediate-early antigen ZEBRA and the late membrane antigen gp350. Therefore, we assessed the capacity of circulating EBV-infected B lymphocytes from healthy EBV-seropositive subjects to enter and complete the EBV lytic cycle. Purified B lymphocytes were polyclonally stimulated and BZLF1- or gp350-secreting cells (BZLF1-SCs or gp350-SCs) were enumerated by ELISpot assays. The number of BZLF1-SCs ranged from 50 to 480/107 lymphocytes (median, 80; 25th-75th percentiles, 70-150) and gp350-SCs from 10 to 40/107 lymphocytes (median, 17; 25th-75th percentiles, 10-20). gp350-SCs represented only 7.7% to 28.6% of BZLF1-SCs (median, 15%; 25th-75th percentiles, 10.5%-20%). This EBV functional reservoir was preferentially restricted to plasma cells derived from CD27(+) IgD(-) memory B lymphocytes. In 9 of 13 subjects, EBV DNA quantification in B-cell culture supernatants gave evidence of completion of EBV lytic cycle. These results demonstrate that EBV proteins can be secreted by EBV-infected B lymphocytes from healthy carriers, a majority generating an abortive EBV lytic cycle and a minority completing the cycle.

Evidence for a pathogenic determinant in HIV-1 Nef involved in B cell dysfunction in HIV/AIDS

B lymphocyte hyperactivation and elevated immunoglobulin levels (hypergammaglobulinemia) are pathogenic manifestations of HIV-1 infection. Here we provide evidence that these hallmarks are caused by a soluble factor whose production by infected macrophages is induced by the HIV-1 Nef protein. In vitro, HIV-1-infected macrophages or macrophages expressing Nef promoted B cell activation and differentiation to immunoglobulin-secreting cells. Nef-mediated activation of NF-kappaB in macrophages induced secretion of the acute-phase protein ferritin, and ferritin was necessary and sufficient for the observed Nef-dependent B cell changes. The extent of hypergammaglobulinemia in HIV-1-infected individuals correlated directly with plasma ferritin levels and with viral load. Furthermore, the induction of ferritin production and hypergammaglobulinemia was recapitulated when Nef was specifically expressed in macrophages and T cells of transgenic mice. Collectively, these results indicate that the HIV-1 Nef protein carries a pathogenic determinant that governs B cell defects in HIV-1 infection.

CpG oligonucleotides enhance proliferative and effector responses of B Cells in HIV-infected individuals

Stimulation through TLR represents a new therapeutic approach for enhancing Ab responses to vaccination. Considering that Ab responses are decreased in HIV disease and that B cells express TLR9 and respond to TLR9 agonists, we investigated the responsiveness of B cell subpopulations from HIV-infected and uninfected individuals to the TLR9 agonist CpG oligonucleotide type B (CpG-B) in the presence and absence of BCR ligation and T cell help (CD40L). CpG-B was equally effective in stimulating the proliferation of naive B cells of HIV-infected individuals and HIV-negative individuals, and, when combined with BCR and CD40 ligation, cytokine secretion by naive B cells was also comparable in HIV-infected and uninfected individuals. In contrast, CD27(+) memory/activated B cells of HIV-infected individuals with active disease were less responsive to CpG-B in terms of proliferation and cytokine secretion when compared with CD27(+) B cells of HIV-negative and HIV-infected individuals whose viremia was controlled by antiretroviral therapy. These findings suggest that despite abnormalities in memory B cells of HIV-infected individuals with active disease, naive B cells of HIV-infected individuals, irrespective of disease status, can respond to TLR9 agonists and that the incorporation of such agents in vaccine formulations may enhance their Ab responses to vaccination.

Human immunodeficiency virus type 1-associated CD40 ligand transactivates B lymphocytes and promotes infection of CD4+ T cells

Abnormal activation of B lymphocytes is a feature commonly seen in human immunodeficiency virus type 1 (HIV-1)-infected persons. However, the mechanism(s) responsible for this dysfunction is still poorly understood. Having recently shown that CD40L, the ligand for CD40, is inserted within emerging HIV-1 particles, we hypothesized that the contact between virus-anchored host CD40L and CD40 on the surface of B lymphocytes might result in the activation of this cell type. We report here that CD40L-bearing viruses, but not isogenic virions lacking host-derived CD40L, can induce immunoglobulin G and interleukin-6 production. Furthermore, such viral entities were found to induce B-cell homotypic adhesion. These effects were paralleled at the intracellular level by the nuclear translocation of the ubiquitous transcription factor NF-kappaB. The presence of host-derived CD40L within virions resulted in an increased virus attachment to B cells and a more-efficient B-cell-mediated transfer of HIV-1 to autologous CD4(+) T lymphocytes. All the above processes were independent of the virus-encoded envelope glycoproteins. Altogether, the data gathered from this series of investigations suggest that the incorporation of host-encoded CD40L in HIV-1 is likely to play a role in the B-cell abnormalities that are seen in infected individuals.

The intraspleen huPBL NOD/SCID model to study the human HIV-specific antibody response selected in the course of natural infection

The intrasplenic injection of human peripheral blood mononuclear cells (PBMCs) into severely immune deficient NOD/SCID mice, causes a massive and transient dominant expansion of human B cells in the spleen. This permits the easy isolation of human monoclonal antibodies specific for different antigens by a Kohler and Milstein-based method. Here we studied the human HIV-specific antibody response in the circulation of mice after intrasplenic transfer of PBMC from untreated HIV-infected patients with detectable to high viral load as well as from HAART-treated and from untreated patients, who kept an undetectable viral load (the latter referred to as “natural suppressors”). Excellent B cell expansion was obtained for all PBMC. High level replication of virus was observed after transfer of PBMC of untreated viremic patients only. A strong and multispecific HIV-specific antibody response was observed after transfer of PBMC of untreated viremic patients and natural suppressors. In contrast, only a weak and pauci-specific antibody response was detected in mice reconstituted with PBMC from successfully treated patients. Based on these observations we conclude that the use of the intraspleen mouse model confirmed a) the presence of HIV-specific circulating memory B cells in untreated patients and natural suppressors; b) the nearly complete absence of circulating memory B cells in patients receiving highly active antiretroviral therapy. Using the intraspleen model we generated large numbers of immortalized B cells and isolated two anti-p24 human monoclonal antibodies. We further conclude that the intraspleen huPBL NOD/SCID model is a small animal model useful for the analysis of the antibody response against HIV found in patients.

Viral load determines the B-cell response in the cerebrospinal fluid during human immunodeficiency virus infection

OBJECTIVE

Human immunodeficiency virus (HIV) infection of the central nervous system (CNS) is frequently associated with intrathecal immunoglobulin synthesis and cerebrospinal fluid (CSF) pleocytosis, but little is known about the B-cell response in the CSF of these patients. In this study, we investigated the relation between virus load and the frequency and phenotype of B cells in the CSF of HIV-infected patients.

METHODS

The distribution of T cells, B cells, short-lived plasmablasts, and long-lived plasma cells was analyzed by flow cytometry in CSF and peripheral blood of 33 patients with HIV infection compared with 12 patients with noninfectious CNS diseases. HIV RNA copy number in CSF and serum was quantified by kinetic polymerase chain reaction.

RESULTS

B-cell and plasmablast levels were increased in the CSF of HIV-infected patients compared with patients with noninfectious CNS diseases. Whereas CSF B cells were found at similar frequency during early and late stages of HIV infection, plasmablasts were more prevalent in the CSF during early infection. Plasmablasts in the CSF correlated with intrathecal IgG synthesis and even stronger with HIV RNA copy numbers in CSF, in particular, in untreated, early HIV-infected individuals. Initiation of antiviral treatment in therapy-naive patients strongly decreased HIV copy numbers and plasmablasts in CSF.

INTERPRETATION

Our findings demonstrate that HIV infection of the CNS triggers an early profound B-cell response, with plasmablasts serving as the main virus-related B-cell subset in the CSF.

Direct impact of inactivated HIV-1 virions on B lymphocyte subsets

Although there is no convincing evidence that HIV infects primary B cells, marked changes in B cell responses have been described in HIV-1-infected subjects, including B cell repertoire perturbations, depression of B cell memory and paucity of CD5(+) B cells. As it is hard to assess the consequences of these in vitro and ex vivo observations in patients, the pathogenic mechanisms responsible for the B cell deficit are unclear, and direct and indirect effects of HIV-1 remain possible. To gain further insight into the impact of HIV-1 on the B cell compartment in vivo, we used XenoMouse mice, mice genetically engineered to express human antibodies with an absence of mouse antibody expression. In these transgenic animals, B cells expressing a virtually full human Ig repertoire develop, which allows investigation of the in vivo consequences of confronting B cells expressing human immunoglobulins with HIV-1. We found that soluble gp120 induced an inversion in the B-1a/B-1b cell ratios, without impacting B-2 cells or affecting substantially the T cell compartment. Virion treatment specifically and dramatically depressed B-1a cells, which represent the majority of B-1 cells in normal mice. The observed B cell changes were associated with a functional alteration of the humoral response to tetanus toxoid. Thus, the results reveal a capacity of HIV-1 to specifically impact a highly specialized B cell subpopulation. Because there is evidence that human IgM memory B cells are functionally equivalent to murine B-1a cells, our findings suggest that gp120 may have a direct deleting activity on B cell memory.

Persistent anti-gag, -Nef, and -Rev IgM levels as markers of the impaired functions of CD4+ T-helper lymphocytes during SIVmac251 infection of cynomolgus macaques

This study analyzed the antigen-specific (Gag, Nef, Rev, and Tat) IgM, IgG, and IgA humoral responses during the first 200 days of SIVmac251 infection in cynomolgus macaques. These responses were tested for correlation with the CD4(+) T-cell-related hematologic parameters and viral load throughout the course of the study (acute and chronic infection, during and after antiretroviral therapy). Strong inverse correlations were observed between the percentage of CD4(+) T cells at almost every timepoint of the study and the levels of IgM (but not IgG and IgA) against Gag, Nef, and Rev (but not Tat) measured after, but not during, the primary peak of IgM response. Significant levels of persistent antigen-specific IgMs may reflect the prevalence of mature plasma cells that have not undergone immunoglobulin class switching, possibly due to defects in helper T-cell function. Strong correlations were observed between the preinfection CD4(+) T-cell count or CD4/CD8 ratio and the same parameters measured throughout the study, suggesting the importance of preinfection immune status as a determinant of disease progression. The negative correlations between the post-acute-phase IgM levels and the percentage of CD4(+) T cells at later times during the study suggest the potential prognostic value of this measurement.

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.

Noninfectious X4 but not R5 human immunodeficiency virus type 1 virions inhibit humoral immune responses in human lymphoid tissue ex vivo

Ex vivo human immunodeficiency virus type 1 (HIV-1) infection of human lymphoid tissue recapitulates some aspects of in vivo HIV-1 infection, including a severe depletion of CD4(+) T cells and suppression of humoral immune responses to recall antigens or to polyclonal stimuli. These effects are induced by infection with X4 HIV-1 variants, whereas infection with R5 variants results in only mild depletion of CD4(+) T cells and no suppression of immune responses. To study the mechanisms of suppression of immune responses in this ex vivo system, we used aldrithiol-2 (AT-2)-inactivated virions that have functional envelope glycoproteins but are not infectious and do not deplete CD4(+) T cells in human lymphoid tissues ex vivo. Nevertheless, AT-2-inactivated X4 (but not R5) HIV-1 virions, even with only a brief exposure, inhibit antibody responses in human lymphoid tissue ex vivo, similarly to infectious virus. This phenomenon is mediated by soluble immunosuppressive factor(s) secreted by tissue exposed to virus.

Increased frequency of CD27- (naive) B cells and their phenotypic alteration in HIV type 1-infected patients

To investigate HIV-1-related B cell disorders, the quantity of peripheral CD27 negative (CD27-) B cells, their CD38, CD95, and bcl-2 intensities, and their apoptosis susceptibility were examined by flow cytometry analysis in 16 drug-naive patients, 27 HAART-treated patients, and 20 uninfected controls. CD27- B cells have been recognized as naive B cells. The mean percentage of CD27- B cells was significantly higher in drugnaive patients (88.1%) and in HAART-treated patients (83.9%) than in controls (68.6%) (p < 0.01). The intensities of CD38 and CD95 on CD27- B cells were significantly higher in drug-naive patients than in controls (p < 0.01). The intensity of CD95 on CD27- B cells in HAART-treated patients was lower than that of drug-naive patients, but significantly higher than that of controls (p < 0.01). The intensity of bcl-2 on CD27- B cells in drug-naive patients was lower than that of controls. In drug-naive patients, CD27-B cells with high CD38 expression represented low bcl-2 expression. The CD27- B cells of drug-naive patients showed an increased susceptibility to apoptosis, characterized by diminished cell size and a high frequency of annexin-V binding, compared with controls and HAART-treated patients. These findings suggested that HIV-1 infection affects peripheral CD27- (naive) B cells as well as CD27+ (memory) B cells and that CD27- B cells might be activated and rendered highly susceptible to apoptosis by HIV-1 infection. Some phenotypic alterations in CD27- B cells may continue after the reduction of HIV-1 loads by effective antiviral therapy.

Nadir B cell counts are significantly correlated with the risk of Kaposi's sarcoma

Infection with HIV-1 is known to impair B cell function. To further elucidate the role of B cells during infection and tumorigenesis, we studied their numbers in cases of AIDS-related Kaposi's sarcoma (KS) during the HAART era. Patients with AIDS-related KS were identified from a database of 4,480 HIV-1 positive individuals and the incidence of KS and rate ratio was stratified according to nadir number of B cells, measured as the CD19 count. In an unadjusted model, we observed that lower B cell counts were associated with a statistically significant increased risk of KS development (p < 0.001). We also observed a trend toward increased counts during KS resolution. When adjusted for nadir CD4 count in a multi-variable model, higher B cell counts were protective against KS development (p = 0.015). These data highlight a potential role for B cells and therefore the humoral immune system in KS aetiopathogenesis.

Detection of peripheral HIV-1-specific memory B cells in patients untreated or receiving highly active antiretroviral therapy

OBJECTIVES

To examine whether polyclonal activation of circulating B cells, in a process that involves CD40-CD40 ligand and cytokine interactions, could induced HIV-1-specific memory B cells to synthesize HIV-1-specific antibodies.

METHODS

B cells from 26 HIV-1-infected patients were cultured with a CD40L-transfected cell line plus interleukins 2 and 10 and tested for their secretion of HIV-1- and Toxoplasma gondii-specific antibodies.

RESULTS

In vitro activated B lymphocytes from HIV-1-infected patients secreted anti-HIV-1-specific antibodies. B cells from HIV-1-infected patients as well as those from controls chronically infected by T. gondii synthesized T. gondii-specific antibodies. HIV-1-specific IgG-, IgA- or IgM-secreting B cells represented approximately 1 x 10(-4) to 1 x 10(-5) of total circulating B cells and 1 x 10(-2) to 1 x 10(-3) of immunoglobulin-secreting cells. HIV-1-specific memory B cells were found in 9/9 untreated patients and in 8/17 patients receiving highly active antiretroviral therapy (HAART). The other nine patients showed a normal CD40-CD40L B cell response and six of them produced T. gondii-specific antibody B cells. The follow-up of seven patients indicated that HIV-1-specific memory B cells became undetectable after 8 to 46 months of HAART, whereas T. gondii-specific memory B cells persisted in parasite coinfected patients.

CONCLUSIONS

Circulating memory HIV-1-specific B cells were detected in untreated patients and in about half of the patients taking HAART, suggesting that persistent low-level ongoing viral replication is not sufficient to maintain HIV-1-specific memory B cells.

HIV, 'an evolving species'. Roles of cellular activation and co-infections

Each small variation of the genome of a species can be preserved if it is useful for the survival of the species in a given environment. Within this framework, the finality of the biological cycle of HIV consists in a search for harmony (biological coherence) with man, which is to say a stable condition. Cellular activation appears to be the strategy developed by HIV in order to achieve this coherence. The price of this strategy is the AIDS. The first contact between HIV and immune system appears to determine the subsequent clinical outcome and the future of HIV. Lymphocytic activation varies during the course of the vital cycle of HIV. For each individual, this lymphocytic activation depends on both the HLA repertoire acquired during thymic ontogenesis and the antigenic experience before and after HIV infection. Thus intercurrent infections alter the immune condition of the organism and influence the outcome of HIV. We described a synthetic analysis of the effects of HIV on the surface protein expression and the cellular activation pathways which should provide insights in the evolutionary relationship between HIV and man and should permit to do a more physiological therapeutic approach.

Deleterious effect of HIV-1 plasma viremia on B cell costimulatory function

HIV infection leads to numerous immunologic defects, including impaired B cell function. An effective humoral response requires bidirectional interactions between B cells and CD4(+) T cells, critical of which are interactions between CD80/CD86 expressed on activated B cells and CD28 expressed on responder CD4(+) T cells. In the present study, we examined the effect of active HIV replication on B cell costimulatory function. Induction of CD80/CD86 on B cells following B cell receptor and CD40 triggering and responsiveness of CD4(+) T cells to activated B cells were investigated in a system where B cells of HIV-infected patients were compared concurrently to B cells of HIV-negative donors. In contrast to HIV-aviremic patients, B cells of HIV-viremic patients were ineffective at stimulating CD4(+) T cells, as measured by the induction of activation markers and proliferation. The importance of interactions of CD80/CD86 and CD28 in activating CD4(+) T cells was clear; the ablation of a normal response following the addition of neutralizing anti-CD86/CD80 Abs mirrored the response of CD4(+) T cells to B cells of HIV-viremic patients, while the addition of exogenous CD28 ligands partially restored the poor CD4(+) T cell response to the B cells of HIV-viremic patients. Ineffective B cell costimulatory function in HIV-viremic patients was associated with low induction of CD80/CD86 expression on B cells. Our findings further delineate the scope of defects associated with cognate B cell-CD4(+) T cell interactions in HIV infection and suggest that therapeutic interventions designed to enhance CD28-dependent costimulatory pathways may help restore immune functions.

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.

Dynamics of spontaneous HIV-1 specific and non-specific B-cell responses in patients receiving antiretroviral therapy

OBJECTIVES

As spontaneous anti-HIV-1 antibody and IgG secretion by peripheral blood mononuclear cells (PBMC) reflect immune system activation by HIV-1 antigens, we evaluated the impact of antiretroviral therapies on HIV-1 specific and non-specific B cell responses.

METHODS

Anti-HIV-1 antibody and non-specific IgG were measured by ELISA in supernatants of PBMC cultured during 7 day from 30 patients initiating an antiretroviral therapy at baseline, 8, 16, 24, 36 and 48 weeks.

RESULTS

An early and sustained fall in plasma viral load to below the detection limit (20 copies/ml) was observed in 17 sustained responder patients (SR), whereas HIV-1 RNA remained detectable in 13 others incomplete responders. In both groups, HIV-1 specific antibody secretion decreased significantly in parallel with plasma viral load and polyclonal immunoglobulin production became similar to that of PBMC controls. However, HIV-1 specific antibody production became negative in only six SR, exhibiting a greater increase of CD4 T-cell counts and higher levels of the spontaneous HIV-1 specific IgA secretion at baseline than the other SR.

CONCLUSIONS

Antiretroviral therapy induced a rapid and dramatic decrease of spontaneous HIV-1 specific and non-specific B cell responses. These results pointed out that HIV-1 specific antibody secretion persisted in 11 out of 17 SR patients, suggesting persistent immune system activation by residual HIV-1 antigens.

Spontaneous secretion of immunoglobulins and anti-HIV-1 antibodies by in vivo activated B lymphocytes from HIV-1-infected subjects: monocyte and natural killer cell requirement for in vitro terminal differentiation into plasma cells

Peripheral blood mononuclear cells from HIV-1-infected subjects secrete spontaneously in vitro immunoglobulins (Ig) and anti-HIV-1 antibodies (Ab). Purified B lymphocytes secrete only minute amounts of Ig and anti-HIV-1 Ab compared with unfractionated cells. Monocytes and natural killer cells enhanced both secretions by cell-to-cell contacts, involving adhesion and CD27, CD80 costimulatory molecules and IL-6. Cell interactions prolonged the survival and allowed the terminal maturation of in vivo activated B cells. The secreting cell precursors were highly differentiated B cells expressing a broad diversity of maturation markers (CD27(+), CD38(+), CD20(+/-), CD37(+/-), CD71(+/-), HLA-DQ(+/-), sIg(+/-)) but not sIgD, CD28, or CD40. This phenotype and the cytologic aspect of purified B cells suggest that these cells are early plasma cells originated from germinal center. Ex vivo secreting peripheral B cells had probably gone beyond the CD40/CD40 ligand interaction; then following CD28/CD80 and CD27/CD27 ligand (CD70) interactions in the presence of IL-6, they achieved in vitro their differentiation into plasma cells.

HIV-1 induces phenotypic and functional perturbations of B cells in chronically infected individuals

A number of perturbations of B cells has been described in the setting of HIV infection; however, most remain poorly understood. To directly address the effect of HIV replication on B cell function, we investigated the capacity of B cells isolated from HIV-infected patients to respond to a variety of stimuli before and after reduction of viremia by effective antiretroviral therapy. B cells taken from patients with high levels of plasma viremia were defective in their proliferative responses to various stimuli. Viremia was also associated with the appearance of a subpopulation of B cells that expressed reduced levels of CD21. After fractionation into CD21(high)- and CD21(low)-expressing B cells, the CD21(low) fraction showed dramatically reduced proliferation in response to B cell stimuli and enhanced secretion of immunoglobulins when compared with the CD21(high) fraction. Electron microscopic analysis of each fraction revealed cells with plasmacytoid features in the CD21(low) B cell population but not in the CD21(high) fraction. These results indicate that HIV viremia induces the appearance of a subset of B cells whose function is impaired and which may be responsible for the hypergammaglobulinemia associated with HIV disease.

Loss of memory (CD27) B lymphocytes in HIV-1 infection

OBJECTIVES

The mechanisms of B-cell dysfunction during HIV-1 infection, including polyclonal B-cell activation, are poorly understood. We studied the phenotype and the functionality of peripheral memory B cells in HIV-1-infected subjects.

DESIGN

The phenotype of B cells and the responsiveness to T-cell dependent activation in vitro were analysed in 36 HIV-1-infected and 34 healthy subjects.

METHODS

Phenotyping of B and T cells was performed by FACS. IgG content was measured in plasma (by nephelometry) and cultures (by enzyme-linked immunosorbent assay) of B lymphocytes activated through CD40 or CD27 ligation. Expression of Fas and Fas ligand was performed by FACS on B-cell subpopulations from five HIV-1-infected and four uninfected subjects.

RESULTS

The peripheral memory (CD27) B cells were significantly reduced in HIV-1-infected subjects. The amount of memory B cells was low in both drug-naive subjects and patients undergoing antiretroviral therapy. Ex vivo expression of CD70 (CD27 ligand) on T cells was significantly higher in HIV-1-infected subjects and inversely correlated with the frequency of memory B cells. In spite of the reduced number of memory B cells, in vitro spontaneous and activation-induced IgG secretion was higher in HIV-1-infected patients than in uninfected controls. The hyperactivation status of B lymphocytes in HIV-1-infected patients was further confirmed by the finding of upregulation of Fas and FasL expression on memory B cells.

CONCLUSIONS

Memory B lymphocytes are depleted from peripheral blood in HIV-1-infected subjects. Our ex vivo findings suggest that persistent T-cell activation may contribute to loss of memory B cells through upregulation of Fas/FasL on these cells and terminal differentiation into plasma cells.

In vitro anti-Toxoplasma gondii antibody production by peripheral blood mononuclear cells in the diagnosis and the monitoring of toxoplasmic encephalitis in AIDS-related brain lesions

The spontaneous secretion in vitro of anti-Toxoplasma gondii antibodies by peripheral blood mononuclear cells was assessed in 69 patients with AIDS-related brain lesions. The sensitivity and specificity of this assay in the diagnosis of toxoplasmic encephalitis (TE) were found to be 85.4% and 92.8%, respectively. Twenty-four patients with TE were observed during 1-year follow-up after initiation of anti-Toxoplasma treatment and classified on the basis of their clinical and radiologic responses as sustained responders (SR; n = 11), incomplete responders (IR; n = 7) or transient responders (TR; n = 6). In vitro anti-T. gondii antibody secretion decreased as early as the first month after initiation of treatment and disappeared within the year in SRs, persisted in IRs, and decreased but rebounded at relapse in the TR patients. In vitro anti-T. gondii antibody, which reflects immune system activation by parasitic antigens, could be a surrogate marker of TE in AIDS patients.

gp120- and TNF-alpha-induced modulation of human B cell function: proliferation, cyclic AMP generation, Ig production, and B-cell receptor expression

BACKGROUND

It is well known that HIV-1 infection induces profound alterations in the immune system, including hyperactivation of B cells. TNF-alpha induces HIV-1 replication and immunodysregulation, including polyclonal B-cell activation.

OBJECTIVE

We sought to determine the effects of surface-binding HIV-1 envelope glycoprotein (gp120) and TNF-alpha on human B-cell function.

METHODS

HIV-1 seronegative peripheral blood human B cells were purified and activated by CD40 mAb and IL-4. In vitro studies of B-cell proliferation, cyclic AMP (cAMP) generation, receptor expression, and Ig production were performed.

RESULTS

gp120, an Ig superantigen, stimulated HIV-1 seronegative and HIV-1 seropositive human B-cell cAMP generation, proliferation, and Ig production. These gp120-induced B-cell responses were demonstrated to be specific as evidenced by the abrogation of the stimulatory response in the presence of anti-gp120 mAb, blocking of CD4 resulting in no change on gp120-induced B-cell responses, and the binding of gp120 in these B cells. TNF-alpha also stimulated cAMP generation, proliferation, and Ig production in B cells, and the binding of gp120 to these B cells stimulated by TNF-alpha further enhanced cell proliferation, cAMP generation, and Ig production. Antigenic expression of the B-cell receptor CD79b was down-regulated by gp120 but was not altered by the addition of TNF-alpha.

CONCLUSION

gp120 modulation of TNF-alpha-induced B-cell receptor- and cAMP-mediated signal transduction events may be involved in the B-cell abnormalities observed in HIV-1 infection.

CD40-Mediated induction of CD4 and CXCR4 on B lymphocytes correlates with restricted susceptibility to human immunodeficiency virus type 1 infection: potential role of B lymphocytes as a viral reservoir

Human immunodeficiency virus type 1 (HIV-1) replicates primarily in lymphoid tissues where it has ready access to activated immune competent cells. We used one of the major pathways of immune activation, namely, CD40-CD40L interactions, to study the infectability of B lymphocytes isolated from peripheral blood mononuclear cells. Highly enriched populations of B lymphocytes generated in the presence of interleukin-4 and oligomeric soluble CD40L upregulated costimulatory and activation markers, as well as HIV-1 receptors CD4 and CXCR4, but not CCR5. By using single-round competent luciferase viruses complemented with either amphotropic or HIV-derived envelopes, we found a direct correlation between upregulation of HIV-1 receptors and the susceptibility of the B lymphocytes to infection with dual-tropic and T-tropic strains of HIV-1; in contrast, cells were resistant to M-tropic strains of HIV-1. HIV-1 envelope-mediated infection was completely abolished with either an anti-CD4 monoclonal antibody or a peptide known to directly block CXCR4 usage and partially blocked with stromal cell-derived factor 1, all of which had no effect on the entry of virus pseudotyped with amphotropic envelope. Full virus replication kinetics confirmed that infection depends on CXCR4 usage. Furthermore, productive cycles of virus replication occurred rapidly yet under most conditions, without the appearance of syncytia. Thus, an activated immunological environment may induce the expression of HIV-1 receptors on B lymphocytes, priming them for infection with selective strains of HIV-1 and allowing them to serve as a potential viral reservoir.

Activation sensitizes human memory B cells to B-cell receptor-induced apoptosis

The outcome of antigen receptor (B-cell receptor; BCR) ligation on B-cell survival can be influenced by multiple parameters. They are linked to the physical properties of the antigen itself, the maturational stage of the cells and the costimuli provided by different components of the innate and acquired immunity. Here we report that apoptosis prevails over stimulation when a BCR agonist is applied to human memory B cells which have been preactivated by CD40 ligand or anti-immunoglobulin antibodies. The susceptibility of activated memory B cells to BCR-induced killing is correlated with their enhanced expression of the transcripts encoding the pro-apoptotic molecules Bax, c-Myc and p53. The BCR-mediated apoptosis of activated memory B cells does not require extensive cross-linking of the antigen receptors and relies neither on engagement of the FcgammaRII nor on the Fas/Fas ligand (Fas-L) system. Our findings suggest that activation stimuli open the BCR-induced apoptotic pathway in memory B cells. Therefore we propose that the concept of activation-induced cell death (AICD), originally described for T cells, also applies to mature B lymphocytes. The functions fulfilled by the AICD of mature B cells in the regulation of B-cell responses are discussed.