Antibody production and in vitro behavior of CD27-defined B-cell subsets: persistent hepatitis C virus infection changes the rules

Low-dose M.tb infection but not BCG or MTBVAC vaccination enhances heterologous antibody titres in non-human primates

Introduction

Mycobacteria are known to exert a range of heterologous effects on the immune system. The mycobacteria-based Freund's Complete Adjuvant is a potent non-specific stimulator of the immune response used in immunization protocols promoting antibody production, and Mycobacterium bovis Bacille Calmette Guérin (BCG) vaccination has been linked with decreased morbidity and mortality beyond the specific protection it provides against tuberculosis (TB) in some populations and age groups. The role of heterologous antibodies in this phenomenon, if any, remains unclear and under-studied.

Methods

We set out to evaluate antibody responses to a range of unrelated pathogens following infection with Mycobacterium tuberculosis (M.tb) and vaccination with BCG or a candidate TB vaccine, MTBVAC, in non-human primates.

Results

We demonstrate a significant increase in the titer of antibodies against SARS-CoV-2, cytomegalovirus, Epstein-Barr virus, tetanus toxoid, and respiratory syncytial virus antigens following low-dose aerosol infection with M.tb. The magnitude of some of these responses correlated with TB disease severity. However, vaccination with BCG administered by the intradermal, intravenous or aerosol routes, or intradermal delivery of MTBVAC, did not increase antibody responses against unrelated pathogens.

Discussion

Our findings suggest that it is unlikely that heterologous antibodies contribute to the non-specific effects of these vaccines. The apparent dysregulation of B cell responses associated with TB disease warrants further investigation, with potential implications for risk of B cell cancers and novel therapeutic strategies.

CD45RB Glycosylation and Ig Isotype Define Maturation of Functionally Distinct B Cell Subsets in Human Peripheral Blood

Glycosylation of CD45RB (RB+) has recently been identified to mark antigen-experienced B cells, independent of their CD27 expression. By using a novel combination of markers including CD45RB glycosylation, CD27 and IgM/IgD isotype expression we segregated human peripheral blood B cell subsets and investigated their IGHV repertoire and in vitro functionality. We observed distinct maturation stages for CD27-RB+ cells, defined by differential expression of non-switched Ig isotypes. CD27-RB+ cells, which only express IgM, were more matured in terms of Ig gene mutation levels and function as compared to CD27-RB+ cells that express both IgM and IgD or cells that were CD27-RB-. Moreover, CD27-RB+IgM+ cells already showed remarkable rigidity in IgM isotype commitment, different from CD27-RB+IgMD+ and CD27-RB- cells that still demonstrated great plasticity in B cell fate decision. Thus, glycosylation of CD45RB is indicative for antigen-primed B cells, which are, dependent on the Ig isotype, functionally distinct.

Early T follicular helper cell activity accelerates hepatitis C virus-specific B cell expansion

Early appearance of neutralizing antibodies during acute hepatitis C virus (HCV) infection is associated with spontaneous viral clearance. However, the longitudinal changes in antigen-specific memory B cell (MBCs) associated with divergent HCV infection outcomes remain undefined. We characterized longitudinal changes in E2 glycoprotein-specific MBCs from subjects who either spontaneously resolved acute HCV infection or progressed to chronic infection, using single-cell RNA-seq and functional assays. HCV-specific antibodies in plasma from chronically infected subjects recognized multiple E2 genotypes, while those from spontaneous resolvers exhibited variable cross-reactivity to heterotypic E2. E2-specific MBCs from spontaneous resolvers peaked early after infection (4-6 months), following expansion of activated circulating T follicular helper cells (cTfh) expressing interleukin 21. In contrast, E2-specific MBCs from chronically infected subjects, enriched in VH1-69, expanded during persistent infection (> 1 year), in the absence of significantly activated cTfh expansion. Early E2-specific MBCs from spontaneous resolvers produced monoclonal antibodies (mAbs) with fewer somatic hypermutations and lower E2 binding but similar neutralization as mAbs from late E2-specific MBCs of chronically infected subjects. These findings indicate that early cTfh activity accelerates expansion of E2-specific MBCs during acute infection, which might contribute to spontaneous clearance of HCV.

Reduced Energy Metabolism Impairs T Cell-Dependent B Cell Responses in Patients With Advanced HBV-Related Cirrhosis

Background and Aims

Patients with decompensated HBV-related liver cirrhosis (HBV D-LC) showed compromised immune responses, which manifested as a proneness to develop infections and hyporesponsiveness to vaccines, resulting in accelerated disease progression. The alterations in T cell-dependent B cell responses in this pathophysiological process were not well understood. This study aimed to investigate T cell-dependent B cell responses in this process and discuss the mechanism from the perspective of metabolism.

Methods

Changes in phenotypes and subsets of peripheral B cells between HBV D-LC patients and healthy controls (HCs) were compared by flow cytometry. Isolated B cells were activated by coculture with circulating T follicular (cTfh) cells. After coculture, the frequencies of plasmablasts and plasma cells and immunoglobin levels were analyzed. Oxidative phosphorylation (OXPHOS) and glycolysis were analyzed by a Seahorse analyzer. Mitochondrial function and the AKT/mTOR pathway were analyzed by flow cytometry.

Results

The proliferation and differentiation capacities of B cells after T cell stimulation were impaired in D-LC. Furthermore, we found that B cells from D-LC patients showed reductions in OXPHOS and glycolysis after activation, which may result from reduced glucose uptake, mitochondrial dysfunction and attenuated activation of the AKT/mTOR pathway.

Conclusions

B cells from HBV D-LC patients showed dysfunctional energy metabolism after T cell-dependent activation. Understanding the regulations of B cell metabolic pathway and their changes may provide a new direction to rescue B cell hyporesponsiveness in patients with HBV D-LC, preventing these patients be infected and improving sensitivity to vaccines.

Impact of deranged B cell subsets distribution in the development of HCV-related cirrhosis and HCC in type two diabetes mellitus

Type II diabetes (T2D) may worsen the course of hepatitis C virus infection with a greater risk of liver cirrhosis (LC) and hepatocellular carcinoma (HCC). In chronic viral infections, the deranged B cell subset signifies uncontrolled disease. The study aimed to verify the relation between B cell subsets' distribution and liver disease progression in chronic hepatitis C (CHC) patients with T2D. A total of 67 CHC patients were divided into two groups; 33 non-diabetic and 34 with T2D. Each group was subdivided into CHC-without LC or HCC (N-CHC), CHC-with LC (CHC-LC), and CHC-with HCC (CHC-HCC). Twenty-seven healthy individuals also participated as controls. Flow cytometry was used to analyze CD19+ B cell subsets based on the expression of CD24 and CD38. CD19+CD24hiCD38hi Immature/transitional B cells elevated in diabetic than non-diabetic patients. In diabetic patients, while CD19+CD24+CD38- primarily memory B cells were higher in CHC-N and CHC-HCC groups than LC with a good predictive accuracy of LC, the opposite was observed for CD19+CD24-CD38- new memory B cells. Only in diabetic patients, the CD19+CD24intCD38int naïve mature B cells were high in CHC-HCC patients with good prognostic accuracy of HCC. Merely in diabetic patients, several correlations were observed between B cell subsets and liver function. Immature/transitional B cells increase remarkably in diabetic CHCpatients and might have a role in liver disease progression. Memory and Naïve B cells are good potential predictors of LC and HCCin diabetic CHCpatients, respectively. Further studies are needed to investigate the role of the CD19+CD24-CD38- new memory B cells in disease progression in CHC patients.

Modulation of Memory B Cell Phenotypes and Toll-Like Receptor-7 in Chronic Hepatitis C Virus Infection During Direct-Acting Antiviral Interferon-Free Therapy: Correlation with Interleukin-7

Hepatitis C virus (HCV) infection is a major worldwide problem with the highest incidence rates in Egypt. It affects B cells that serve as reservoirs for persistent HCV, resulting in phenotypic B cell alterations. Interleukin-7 (IL-7) is a cytokine with antiviral activity, important for B cell physiology. In addition, B cell-intrinsic toll-like receptor-7 (TLR7) signaling is required for optimal B cell responses during chronic viral infection, and the deficiency of TLR7 in B cells is sufficient to significantly impact antibody responses. Based on their known immunomodulatory effects, we hypothesized that direct-acting antiviral interferon-free therapy may affect TLR7 expression and the exhausted peripheral B cell compartment with the possibility of their restoration in patients who achieved a sustained virological response and their correlation to IL-7 level. This prospective study was accomplished on 80 Egyptian HCV patients and 75 controls. Frequencies of peripheral B cell subsets, TLR7 gene expression, TLR7 protein, and serum IL-7 levels were investigated by flow cytometry, quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay, respectively. B cell subpopulations were exhausted and partially restored among HCV patients after receiving treatment, but not recovered with regard to activated mature or resting memory B cells. Almost all responders to direct antiviral drugs showed upregulation of TLR7 gene expression and correlated with the frequency of memory B cell, but not with IL-7. Moreover, IL-7 was not significantly different between groups although correlated with immature transitional B cells. Results may indicate the interplay between TLR7 and B cells during remission or progression of HCV. Thus, TLR7 could be used as a promising biomarker for assessment of antiviral treatment efficacy among chronically infected HCV patients, and that targeting TLR7 may be used as a potential prophylactic and/or therapeutic agent during chronic HCV as well as immune-potentiation of memory B cells.

Mycobacterium tuberculosis infection is associated with increased B cell responses to unrelated pathogens

Antigens from Mycobacterium tuberculosis (M.tb), have been shown to stimulate human B cell responses to unrelated recall antigens in vitro. However, it is not known whether natural M.tb infection or whether vaccination with, Mycobacterium bovis BCG, has a similar effect. This study investigated the effects of M.tb infection and BCG vaccination on B cell responses to heterologous pathogen recall antigens. Antibodies against several bacterial and viral pathogens were quantified by ELISA in 68 uninfected controls, 62 individuals with latent TB infection (LTBI) and 107 active pulmonary TB (APTB) cases, and 24 recently BCG-vaccinated adolescents and naive controls. Antibody avidity was investigated using surface plasmon resonance and B cell ELISPOTs were used to measure plasmablast and memory B cell responses (MBC) in APTB cases and healthy donor controls. APTB was associated with higher levels of antibodies to respiratory syncytial virus and measles virus, compared to uninfected controls. BCG vaccination did not alter levels of antibodies against heterologous pathogens. Tetanus toxoid (TT)-specific antibody avidity was increased in APTB cases in comparison to uninfected individuals and the ratio of TT-specific plasmablasts to MBCs in the APTB cases was 7:1. M.tb infection is associated with increased antibody responses to heterologous pathogens in human subjects.

Infectious Complications of Biological and Small Molecule Targeted Immunomodulatory Therapies

The past 2 decades have seen a revolution in our approach to therapeutic immunosuppression. We have moved from relying on broadly active traditional medications, such as prednisolone or methotrexate, toward more specific agents that often target a single receptor, cytokine, or cell type, using monoclonal antibodies, fusion proteins, or targeted small molecules. This change has transformed the treatment of many conditions, including rheumatoid arthritis, cancers, asthma, and inflammatory bowel disease, but along with the benefits have come risks. Contrary to the hope that these more specific agents would have minimal and predictable infectious sequelae, infectious complications have emerged as a major stumbling block for many of these agents. Furthermore, the growing number and complexity of available biologic agents makes it difficult for clinicians to maintain current knowledge, and most review articles focus on a particular target disease or class of agent. In this article, we review the current state of knowledge about infectious complications of biologic and small molecule immunomodulatory agents, aiming to create a single resource relevant to a broad range of clinicians and researchers. For each of 19 classes of agent, we discuss the mechanism of action, the risk and types of infectious complications, and recommendations for prevention of infection.

Follicular helper T cell and memory B cell immunity in CHC patients

Chronic hepatitis C (CHC) is associated with biological activity of T follicular helper (Tfh) cells and memory B cells (MBCs). However, the nature of Tfh cell subsets that are responsible for MBCs in CHC patients has not been evaluated. This study aimed to investigate Tfh and MBC immunity before and after direct-acting antiviral (DAA) therapy in patients with CHC. A total of 31 CHC patients and 15 healthy controls (HCs) were recruited. Individual patients were treated with sofosbuvir/ribavirin (SOF/RBV) or in combination with pegylated interferon alpha-2a (PEG-IFN-α-2a) for 12 weeks. Immunofluorescence revealed the frequency of ICOS⁺CD4⁺CXCR5⁺ active Tfh cells in liver tissue of CHC patients was higher than that of healthy control. Tfh and B cell co-culture experiments showed that Tfh2 cells from CHC patients have potential ability to induce B cell differentiation and IgG production. Flow cytometry showed that the frequencies of CD21^-CD27⁺IgD^- activated MBCs, ICOS⁺CD4⁺CXCR5⁺ activated Tfh cells, Tfh1 (IFN-γ⁺CD4⁺CXCR5⁺) cells, and Tfh2 (IL-4⁺CD4⁺CXCR5⁺) cells, but not of Tfh17 (IL-17⁺CD4⁺CXCR5⁺) cells, increased in CHC patients before and after DAA therapy. Collectively, ICOS⁺ Tfh, Tfh1, Tfh2 cells, and MBCs participated in the antiviral treatment process of SOF/RBV with or without PEG-IFN-α-2a in CHC patients, and their activity was further enhanced during the treatment. KEY MESSAGES: This study aimed to investigate Tfh cells and MBC immunity in CHC patients. CD21^-CD27⁺IgD^- activated MBCs increased in CHC patients before and after treatment. Tfh1 and Tfh2 cells increased in CHC patients before and after antiviral treatment. Intrahepatic activated Tfh cells increased in CHC patients before treatment. Tfh2 cells from CHC patients have a stronger ability to induce B cell differentiation.

Abnormal phenotypic features of IgM+B cell subsets in patients with chronic hepatitis C virus infection

Hepatitis C virus (HCV) infection is associated with B cell abnormality; however the phenotypic profiles of immunoglobulin (Ig)M+B cell subsets in patients with HCV infection remain unclear. In the current study, the effect of HCV infection on IgM+B cell subsets was evaluated. The percentages, as well as the differentiation and activation features of peripheral IgM+B naive subsets [cluster of differentiation (CD)27-IgM+B cells] and IgM+B memory subsets (CD27+IgM+B cells) were assessed using flow cytometry in 27 patients with chronic hepatitis C (CHC) and 20 healthy controls (HCs). The frequency of CD27+IgM+B memory subsets detected in patients with CHC was significantly higher than that in HCs (P<0.05). Although the frequency of CD27-IgM+B naive subsets was similar in both groups, there was a significantly higher proportion of CD5+B cells detected in the CD27-IgM+B subsets of patients with CHC compared with HCs (P<0.05). Among CD27-IgM+B subsets, abnormal differentiation was associated with HCV infection, with significantly increased percentages of IgD+B cells and CD38+B cells in patients with CHC compared with HCs (P<0.05). In CD27+IgM+B memory subsets, the abnormality of cell differentiation was associated with a significantly increased percentage of CD38+B cells in patients with CHC compared with HCs (P<0.05). In addition, the percentage of activated CD27+IgM+B subsets in patients with CHC were significantly higher than those observed in HCs (P<0.05). The number of CD27-IgD+IgM+B, CD27-CD38+IgM+B and CD27+CD38+IgM+B cells were negatively correlated with HCV RNA in patients with CHC. These results suggest that HCV infection contributes to abnormalities in the percentage, differentiation and activation of IgM+B cell subsets and may disrupt the immune response mediated by IgM+B cells.

T-bet-expressing B cells during HIV and HCV infections

T-bet-expressing B cells, first identified as perpetuators of autoimmunity, were recently shown to be critical for murine antiviral responses. While their role in human viral infections remains unclear, B cells expressing T-bet or demonstrating a related phenotype have been described in individuals chronically infected with HIV or HCV, suggesting these cells represent a component of human antiviral responses. In this review, we discuss the induction of T-bet in B cells following both HIV and HCV infections, the factors driving T-bet⁺ B cell expansions, T-bet's relationship to atypical memory B cells, and the consequences of T-bet induction. We propose potential antiviral roles for T-bet⁺ B cells and discuss whether this population poses any utility to the HIV and HCV immune responses.

The dynamics of HCV-specific antibody responses in HIV/HCV patients on long-term antiretroviral therapy

Antibody responses have not been fully characterised in chronically HIV/HCV patients receiving antiretroviral therapy (ART). Seventeen HIV/HCV patients receiving ART were followed for a median (range) interval of 597 (186-766) weeks. Prior to ART, HIV/HCV patients had lower levels of antibodies reactive with HCV core and JFH-1, and lower genotype cross-reactive neutralising antibodies (nAb) titres, than HCV patients. Levels of JFH-1 reactive antibody increased on ART, irrespective of CD4⁺ T-cell counts or changes in serum ALT levels. The appearance of nAb coincided with control of HCV viral replication in five HIV/HCV patients. In other patients, HCV viral loads remained elevated despite nAb responses. Sustained virological responses following HCV therapy were associated with reduced antibody responses to JFH-1 and core but elevated responses to non-structural proteins. We conclude that nAb responses alone may fail to clear HCV, but contribute to control of viral replication in some HIV/HCV patients responding to ART.

Type-I Interferon Responses: From Friend to Foe in the Battle against Chronic Viral Infection

Type I interferons (IFN-I) have long been heralded as key contributors to effective antiviral responses. More widely understood in the context of acute viral infection, the role of this pleiotropic cytokine has been characterized as triggering antiviral states in cells and potentiating adaptive immune responses. Upon induction in the innate immune response, IFN-I triggers the expression of interferon-stimulated genes (ISGs), which upregulate the effector function of immune cells (e.g., dendritic cells, B cells, and T cells) toward successful resolution of infections. However, emerging lines of evidence reveal that viral persistence in the course of chronic infections could be driven by deleterious immunomodulatory effects upon sustained IFN-I expression. In this setting, elevation of IFN-I and ISGs is directly correlated to viral persistence and elevated viral loads. It is important to note that the correlation among IFN-I expression, ISGs, and viral persistence may be a cause or effect of chronic infection and this is an important distinction to make toward establishing the dichotomous nature of IFN-I responses. The aim of this mini review is to (i) summarize the interaction between IFN-I and downstream effector responses and therefore (ii) delineate the function of this cytokine on positive and negative immunoregulation in chronic infection. This is a significant consideration given the current therapeutic administration of IFN-I in chronic viral infections whose therapeutic significance is projected to continue despite emergence of increasingly efficacious antiviral regimens. Furthermore, elucidation of the interplay between virus and the antiviral response in the context of IFN-I will elucidate avenues toward more effective therapeutic and prophylactic measures against chronic viral infections.

Type I Interferon Impairs Specific Antibody Responses Early during Establishment of LCMV Infection

Elicitation of type I interferon (IFN-I) has been shown to both enhance and impair cell-mediated immune responses in acute and persistent viral infections, respectively. Here, we show that, in addition to its effect on T cells, IFN-I drives impairment of specific antibody responses through interaction with B cells in the acute phase of lymphocytic choriomeningitis virus (LCMV) infection. This impairment was limited to the T cell-dependent B cell response and was associated with disruption of B cell follicles, development of hypergammaglobulinemia (HGG), and expansion of the T follicular helper cell population. Antigen-specific antibody responses were restored by ablation of IFN-I signaling through antibody-mediated IFN-I receptor blockade and B cell-specific IFN-I receptor knockout. Importantly, IFN-I receptor deficiency in B cells also accelerated the development of LCMV neutralizing antibodies and alleviated HGG. These results provide a potential therapeutic target toward efficient treatment measures that limit immunopathology in persistent viral infections.

Endotoxemia contributes to CD27+ memory B-cell apoptosis via enhanced sensitivity to Fas ligation in patients with Cirrhosis

Peripheral CD27⁺ memory B-cells become quantitatively reduced and dysfunctional in patients with cirrhosis through poorly characterized mechanisms. We hypothesized that the disappearance of CD27⁺ memory B-cells results from enhanced sensitivity to apoptosis caused by exposure to gut microbial translocation products. Using isolated naïve and memory B-cells from patients with cirrhosis and age-matched controls, ex vivo and activation-induced sensitivity to Fas-mediated apoptosis was assessed under relevant experimental conditions. We observed differential expression of CD95(Fas) in CD27⁺ B-cells from cirrhotic patients that was inversely correlated with peripheral CD27⁺ B-cell frequency. While memory B-cells from cirrhotic patients were resistant to Fas-mediated apoptosis ex vivo, Toll-like receptor 4(TLR4)-ligation restored Fas-sensitivity. Sensitivity to Fas-mediated apoptosis could be transferred to healthy donor memory B-cells by co-culturing these cells with plasma from cirrhotic patients, a sensitivity partially mediated by Fas and TLR4 signaling, and partially rescued via B-cell receptor crosslinking. We conclude that peripheral CD27⁺ memory B-cells in cirrhosis exhibit increased sensitivity to Fas-induced apoptosis in an activation-dependent manner to which endotoxin contributes, associated with reduced frequency of circulating memory B-cells. Destruction of this critical cell subset may contribute to the cirrhotic immunodeficiency state and heightened risk of systemic infections in advanced liver disease.

Remodeling of B-Cell Subsets in Blood during Pegylated IFNα-2a Therapy in Patients with Chronic Hepatitis B Infection

The ultimate goal of pegylated interferon-alfa-2a (Peg-IFN-α) therapy in chronic hepatitis B (CHB) infection is HBsAg seroconversion. Even though B cells are major mediators of a positive clinical outcome, their modulation during Peg-IFN-α therapy has not yet been described. We investigated here the effects of Peg-IFN-α on eight circulating B-cell subsets thanks to an original multi-gating approach based on CD19, CD27, IgD, CD10, and CD38 markers in patients with CHB treated with nucleos(t)ide analog alone or in combination with Peg-IFN-α. These dynamic changes were analyzed during the 48-weeks of Peg-IFN-α therapy and up to 2 years after the cessation of treatment. The CD19+CD27-IgD+CD10+CD38high transitional B cells and the CD19+CD27+IgD-CD10-CD38high plasmablasts continuously increased, whereas the CD19+CD27-IgD+CD10-CD38low naive, CD19+CD27+IgD+ natural memory, and CD19+CD27+IgD-CD10-CD38low post-germinal center B cells decreased during the course of Peg-IFNα treatment. Such modulations correlated with a sustained increase in sCD30 levels and the decrease in plasma HBsAg. However, no seroconversion occurred and all parameters returned to baseline after the stop of the treatment. Peg-IFN-α therapy mediates a remodeling of B-cell compartmentalization, without clinical relevance. Our study provides new insights into the immunomodulatory effects of Peg-IFN-α on circulating B-cells, and questioned the benefit of the add-on Peg-IFN-α treatment in CHB.

CD4+CXCR5+ T cells activate CD27+IgG+ B cells via IL-21 in patients with hepatitis C virus infection

BACKGROUND

Chronic hepatitis C virus (HCV) infection causes the skewing and activation of B cell subsets, but the characteristics of IgG+ B cells in patients with chronic hepatitis C (CHC) infection have not been thoroughly elucidated. CD4+CXCR5+ follicular helper T (Tfh) cells, via interleukin (IL)-21 secretion, activate B cells. However, the role of CD4+CXCR5+ T cells in the activation of IgG+ B cells in CHC patients is not clear.

METHODS

The frequency of IgG+ B cells, including CD27-IgG+ B and CD27+IgG+ B cells, the expression of the activation markers (CD86 and CD95) in IgG+ B cells, and the percentage of circulating CD4+CXCR5+ T cells were detected by flow cytometry in CHC patients (n=70) and healthy controls (n=25). The concentrations of serum IL-21 were analyzed using ELISA. The role of CD4+CXCR5+ T cells in the activation of IgG+ B cells was investigated using a co-culture system.

RESULTS

A significantly lower proportion of CD27+IgG+ B cells with increased expression of CD86 and CD95 was observed in CHC patients. The expression of CD95 was negatively correlated with the percentage of CD27+IgG+ B cells, and it contributed to CD27+IgG+ B cell apoptosis. Circulating CD4+CXCR5+ T cells and serum IL-21 were significantly increased in CHC patients. Moreover, circulating CD4+CXCR5+ T cells from CHC patients induced higher expressions of CD86 and CD95 in CD27+IgG+ B cells in a co-culture system; the blockade of the IL-21 decreased the expression levels of CD86 and CD95 in CD27+IgG+ B cells.

CONCLUSIONS

HCV infection increased the frequency of CD4+CXCR5+ T cells and decreased the frequency of CD27+IgG+ B cells. CD4+CXCR5+ T cells activated CD27+IgG+ B cells via the secretion of IL-21.

Presence of Rheumatoid Factor during Chronic HCV Infection Is Associated with Expansion of Mature Activated Memory B-Cells that Are Hypo-Responsive to B-Cell Receptor Stimulation and Persist during the Early Stage of IFN Free Therapy

Approximately half of those with chronic hepatitis C virus (HCV) infection have circulating rheumatoid factor (RF), and a portion of these individuals develop cryoglobulinemic vasculitis. B cell phenotype/function in relation to RF in serum has been unclear. We examined B cell subset distribution, activation state (CD86), cell cycle state (Ki67), and ex-vivo response to BCR, TLR9 and TLR7/8 stimulation, in chronic HCV-infected donors with or without RF, and uninfected donors. Mature-activated B-cells of HCV-infected donors had lower CD86 expression compared to uninfected donors, and in the presence of RF they also showed reduced CD86 expression in response to BCR and TLR9 stimulation. Additionally, mature activated memory B cells of HCV RF+ donors less commonly expressed Ki67+ than HCV RF- donors, and did not proliferate as well in response to BCR stimulation. Proportions of mature-activated B cells were enhanced, while naïve B-cells were lower in the peripheral blood of HCV-RF+ compared to RF- and uninfected donors. None of these parameters normalize by week 8 of IFN free direct acting antiviral (DAA) therapy in HCV RF+ donors, while in RF- donors, mature activated B cell proportions did normalize. These data indicate that while chronic HCV infection alone results in a lower state of activation in mature activated memory B cells, the presence of RF in serum is associated with a more pronounced state of unresponsiveness and an overrepresentation of these B cells in the blood. This phenotype persists at least during the early time window after removal of HCV from the host.

Immunopathogenesis of Hepatitis C Virus Infection

Despite advances in therapy, hepatitis C virus infection remains a major global health issue with 3 to 4 million incident cases and 170 million prevalent chronic infections. Complex, partially understood, host-virus interactions determine whether an acute infection with hepatitis C resolves, as occurs in approximately 30% of cases, or generates a persistent hepatic infection, as occurs in the remainder. Once chronic infection is established, the velocity of hepatocyte injury and resultant fibrosis is significantly modulated by immunologic as well as environmental factors. Immunomodulation has been the backbone of antiviral therapy despite poor understanding of its mechanism of action.

Epstein-Barr virus and Interleukin-28B polymorphism in the prediction of response to interferon therapy in hepatitis C patients

BACKGROUND AND STUDY AIMS

In chronic hepatitis C virus (HCV), viral and host factors are known to be predictors for anti-viral therapy. IL-28B genotype strongly influences treatment outcome, while Epstein-Barr virus (EBV) co-infection could accelerate the course of chronic HCV infection. This study was conducted to assess whether EBV co-infection adds to the predictive value of IL-28B.

PATIENTS AND METHODS

A total of 105 patients with chronic HCV were classified according to their response to treatment into two groups: 38 sustained virological responders (SVRs) and 67 nonresponders (NRs). Collected sera at baseline and follow-up (FUP) were used for assessing EBV antibodies by enzyme-linked immunosorbent assay (ELISA) and the expression of EBV genes (BNLF-1, BZLF-1, and EBER-2) by polymerase chain reaction (PCR). Collected peripheral blood was used for detecting IL-28B rs.12979860 single-nucleotide polymorphism.

RESULTS

Regarding IL-28B genotype frequencies, a significant difference (p=0.003) was observed between SVRs (C/C=51.4%, C/T=48.6%, T/T=0%) and NRs (C/C=25%, C/T=55%, T/T=20%). On assessing EBV infection at baseline and FUP, it was found that 61% and 55% were positive, respectively, with no significant difference between SVRs and NRs. As for anti-viral capsid antigen (VCA) antibodies, the NRs had significantly higher baseline anti-VCA immunoglobulin M (IgM) levels than SVRs (p=0.01). While FUP anti-Epstein-Barr nuclear antigen-1 (EBNA-1) IgG reported a significant decline within SVR patients (p=0.02), neither baseline nor FUP anti-VCA IgG levels showed a statistically significant viral response. Finally, on comparing EBV markers with CC versus CT and TT genotypes, it was found that FUP anti-VCA IgG levels were significantly increased in CC genotype (p=0.003).

CONCLUSION

Interleukin-28B polymorphism could be a possible predictor of response to pegylated interferon/ribavirin therapy (PEG-IFN/RBV). Furthermore, co-infection with EBV did not affect the response to IFN-based therapy in HCV-infected patients.

Abnormal CD4 + T helper (Th) 1 cells and activated memory B cells are associated with type III asymptomatic mixed cryoglobulinemia in HCV infection

Background

Mixed cryoglobulinemia (MC) in hepatitis C virus (HCV) infection is associated with abnormal immune responses mediated by T cells and B cells, while the relationships of different subsets of CD4 + T helper (Th) cells, B cells and associated cytokines with type III asymptomatic MC in HCV infection are poorly understood.

Methods

Fifty-four chronic hepatitis C (CHC) patients and 23 healthy controls (HCs) were enrolled in the study. Serum cryoglobulins were detected by cryoprecipitation. The types of cryoglobulin were determined by western blot. The phenotypes and frequencies of Th cell and B cell subsets were detected by flow cytometric analysis. The cytokines IFN-γ, IL-4, IL-17, IL-21, IL-22, and TGF-β were measured by enzyme-linked immunosorbent assay.

Results

Twenty-six CHC patients were detected with type III asymptomatic MC. The frequencies of Th2, Th17, follicular helper T (Tfh cells), Th22, and tissue-like B cells were significantly higher in CHC patients compared to HCs, while these cell subsets were not significantly different between CHC patients and HCV-related MC patients. The frequencies of Th1 and activated memory B cells increased in HCV-related MC patients compared to HCs, although the difference between the two cell subsets in CHC patients and HCs was not significant. The frequency of regulatory T cells (Treg cells) was higher in CHC patients than in HCV-related MC patients and HCs. Higher expressions of serum IFN-γ, IL-17, IL-21, and IL-22 were observed in CHC patients than in HCs, but the differences were not significantly different in CHC patients and HCV-related MC patients. The frequency of Th1 cells was associated with activated memory B cells in HCV-related MC patients, and the frequency of Th1 cells and activated memory B cells was closely related to HCV RNA in HCV-related MC patients.

Conclusions

The increased frequencies of Th17 cells, Tfh cells, Th22 cells, Treg cells, cytokines IL-17, IL-21, IL-22, and tissue-like B cells, were related to HCV infection but not type III asymptomatic MC. Higher frequencies of Th1 cells and activated memory B cells were associated with type III asymptomatic MC in HCV infection.

Skewed B cells in chronic hepatitis C virus infection maintain their ability to respond to virus-induced activation

Chronic hepatitis C virus (HCV) infection is characterized by persistent B-cell activation, with enhanced differentiation and reduced proliferative ability. To assess the possible role of HCV in altering B-cell subset distribution, we examined ex vivo frequencies and B-cell inhibitory receptor expression in 37 chronic HCV-infected patients and 25 healthy donors (HD). In addition, we determined whether short-term exposure to culture-derived HCV (HCVcc) resulted in B-cell subset skewing and/or activation. There was a statistically significant increase in the frequencies of immature transitional, activated memory and tissue-like memory (TLM) B cells in HCV-infected patients compared with HD. We also found that the frequency of memory B cells correlated with serum HCV RNA levels. The proportion of B cells expressing the marker of exhaustion Fc receptor-like 4 (FcRL4) was generally low even though significantly higher in the patients' memory B-cell compartment compared with HD, and a positive correlation was found between the frequencies of the patients' TLM FcRL4+ B cells and serum alanine aminotransferase and histological activity index at liver biopsy. Exposure to cell-free HCVcc in vitro did not result in B-cell skewing but induced significant activation of naïve, TLM and resting memory B cells in HCV-infected patients but not in HD, in whom cell-associated virus was an absolute requirement for activation of memory B cells. These findings provide corroborative evidence in favour of significant B-cell subset skewing in chronic HCV infection and in addition show that expression of exhaustion markers in selected B-cell subsets does not impair virus-induced B-cell activation.

CD4+ CXCR5+ T cells in chronic HCV infection produce less IL-21, yet are efficient at supporting B cell responses

BACKGROUND & AIMS

During chronic HCV infection, T cell dependent virus-specific antibodies are produced. However, the role of B-T cell interaction in chronic HCV is largely unknown. CD4(+)CXCR5(+) T follicular helper (TFH)-cells activate B cells and are important for clearance of various chronic viral infections. We investigated the function of TFH cells and B cells in liver and in peripheral blood of chronic HCV patients.

METHODS

T cells from chronic HCV patients and healthy individuals were analysed for expression of CXCR5, PD-1, ICOS, and IL-21 and IFN-γ production by flow cytometry. CD19(+) B cell subpopulations were identified on the basis of CD27 and IgD expression. In order to assess the frequency and function of T cells and B cells in liver follicles, immunohistochemistry was performed for CD3, CXCR5, Bcl6, IL-21, CD20, IgD, IgM, and IgG.

RESULTS

The frequency of IL-21-producing CXCR5(+)CD4(+) T cells in blood was lower in HCV patients compared to healthy individuals (p=0.002), which was reflected by lower serum IL-21 levels (p<0.001). Nonetheless, CXCR5(+)CD4(+) T cells from HCV patients and healthy individuals were equally capable to stimulate CD19(+)CD27(+) memory B cells into IgG and IgM-producing plasmablasts. Importantly, human intrahepatic TFH cells and their related function were identified by immunohistochemistry on liver biopsies for CD3, Bcl6, and CD20 within portal areas and follicles.

CONCLUSIONS

The specific localization of TFH cells and IgG and IgD/IgM-producing B cells suggests a functional B-T cell environment in liver follicles during HCV infection. The decreased frequency of IL-21-producing CXCR5(+)CD4(+) T cells and lower serum IL-21 levels in chronic HCV patients did not lead to an altered TFH-B cell interaction.

Adaptive immune response during hepatitis C virus infection

Hepatitis C virus (HCV) infection affects about 170 million people worldwide and it is a major cause of liver cirrhosis and hepatocellular carcinoma. HCV is a hepatotropic non-cytopathic virus able to persist in a great percentage of infected hosts due to its ability to escape from the immune control. Liver damage and disease progression during HCV infection are driven by both viral and host factors. Specifically, adaptive immune response carries out an essential task in controlling non-cytopathic viruses because of its ability to recognize infected cells and to destroy them by cytopathic mechanisms and to eliminate the virus by non-cytolytic machinery. HCV is able to impair this response by several means such as developing escape mutations in neutralizing antibodies and in T cell receptor viral epitope recognition sites and inducing HCV-specific cytotoxic T cell anergy and deletion. To impair HCV-specific T cell reactivity, HCV affects effector T cell regulation by modulating T helper and Treg response and by impairing the balance between positive and negative co-stimulatory molecules and between pro- and anti-apoptotic proteins. In this review, the role of adaptive immune response in controlling HCV infection and the HCV mechanisms to evade this response are reviewed.

Peripheral CD27-CD21- B-cells represent an exhausted lymphocyte population in hepatitis C cirrhosis

Hepatitis C cirrhosis is associated with a profound disappearance of memory B-cells. We sought to determine if this loss is associated with the expansion of the CD27(-)CD21(-) tissue-like memory B-cells with features of B-cell exhaustion. To this end, we quantified the frequency of CD27(-)CD21(-) B-cells in healthy, non-cirrhotic HCV-infected, and cirrhotic patients. We examined the expression of putative inhibitory receptors, the proliferative and immunoglobulin-secreting capacity of CD27/CD21-defined B-cell subsets upon B-cell receptor and/or CD40 stimulation. We found that CD27(-)CD21(-) B-cells are significantly increased in frequency relative to healthy donors in HCV-infected patients. CD27(-)CD21(-) B-cells were hypoproliferative relative to naïve and resting memory B-cells upon agonistic stimulation, but retained similar capacity for antibody secretion.

CONCLUSION

CD27(-)CD21(-) tissue-like memory B-cells with exhausted proliferation circulate at increased frequency in cirrhotic and non-cirrhotic HCV-infected patients. This B-cell subset does not appear anergic, exhibiting immunoglobulin-secreting capacity on CD40 agonism indistinguishable from other CD27/CD21-defined B-cell subsets.

Antiviral treatment improves disrupted peripheral B lymphocyte homeostasis in chronic hepatitis B virus-infected patients

Disruption of peripheral blood B-cell homeostasis and variation of surface receptors occur with certain infections and autoimmune diseases. However, the impact of antiviral therapy on B-cell alteration during chronic hepatitis B (CHB) infection remains unclear. Our study aims to document the effects of B-cell alteration in CHB patients treated with tenofovir or adefovir. A total of 21 CHB patients and 10 healthy donors were recruited into the study. We identified B-cell subsets by flow cytometry and observed changes in the B-cell repertoire of CHB patients upon tenofovir or adefovir antiviral treatment. The total and percent of B cells and CD5 + B-cell subsets were significantly increased in CHB patients compared to healthy donors. Total and percent of CD5 + B cells gradually decreased following the diminution of the HBV DNA load after tenofovir and adefovir treatment. Upon tenofovir treatment, the percent of memory CD27 + B cells was increased but the absolute number declined, whereas naïve CD27- B cells declined in both percent and absolute number. In the adefovir treatment group, neither naïve nor memory B cells were altered by the treatment. Furthermore, CHB patients displayed higher levels of activation markers (CD69 and CD24) and trended towards restored B-cell homeostasis after antiviral treatment. In conclusion, disrupted B-cell homeostasis is an important feature of CHB patients and is partially restored after control of viral replication by antiviral treatment. B-cell antiviral immunity is improved by restoring B-cell homeostasis and activation.

Immunity and hepatitis C: a review

Hepatitis C virus (HCV) is a major cause of chronic hepatitis and hepatocellular carcinoma worldwide. Due to shared transmission routes, the prevalence of HCV is especially high among individuals infected with HIV. HIV uninfected individuals spontaneously clear HCV approximately 30 % of the time, while the rate of control in HIV infected individuals who subsequently acquire HCV is substantially lower. In addition, complications of HCV are more frequent in those with HIV infection, making liver disease the leading cause of non-AIDS-related death in HIV infected individuals. This review summarizes recent advances in understanding the role of the innate and adaptive immune responses to HCV in those with and without HIV. Further defining the interaction between hepatitis C and the host immune system will potentially reveal insights into HCV pathogenesis and the host's ability to prevent persistent infection, as well as direct the development of vaccines.

Dynamics of memory B-cell populations in blood, lymph nodes, and bone marrow during antiretroviral therapy and envelope boosting in simian immunodeficiency virus SIVmac251-infected rhesus macaques

Human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) infection causes B-cell dysregulation and the loss of memory B cells in peripheral blood mononuclear cells (PBMC). These effects are not completely reversed by antiretroviral treatment (ART). To further elucidate B-cell changes during chronic SIV infection and treatment, we investigated memory B-cell subpopulations and plasma cells/plasmablasts (PC/PB) in blood, bone marrow, and lymph nodes of rhesus macaques during ART and upon release from ART. Macaques previously immunized with SIV recombinants and the gp120 protein were included to assess the effects of prior vaccination. ART was administered for 11 weeks, with or without gp120 boosting at week 9. Naïve and resting, activated, and tissue-like memory B cells and PC/PB were evaluated by flow cytometry. Antibody-secreting cells (ASC) and serum antibody titers were assessed. No lasting changes in B-cell memory subpopulations occurred in bone marrow and lymph nodes, but significant decreases in numbers of activated memory B cells and increases in numbers of tissue-like memory B cells persisted in PBMC. Macaque PC/PB were found to be either CD27(+) or CD27(-) and therefore were defined as CD19(+) CD38(hi) CD138(+). The numbers of these PC/PB were transiently increased in both PBMC and bone marrow following gp120 boosting of the unvaccinated and vaccinated macaque groups. Similarly, ASC numbers in PBMC and bone marrow of the two macaque groups also transiently increased following envelope boosting. Nevertheless, serum binding titers against SIVgp120 remained unchanged. Thus, even during chronic SIV infection, B cells respond to antigen, but long-term memory does not develop, perhaps due to germinal center destruction. Earlier and/or prolonged treatment to allow the generation of virus-specific long-term memory B cells should benefit ART/therapeutic vaccination regimens.

Molecular signatures of hepatitis C virus (HCV)-induced type II mixed cryoglobulinemia (MCII)

The role of hepatitis C virus (HCV) infection in the induction of type II mixed cryoglobulinemia (MCII) and the possible establishment of related lymphoproliferative disorders, such as B-cell non-Hodgkin lymphoma (B-NHL), is well ascertained. However, the molecular pathways involved and the factors predisposing to the development of these HCV-related extrahepatic complications deserve further consideration and clarification. To date, several host- and virus-related factors have been implicated in the progression to MCII, such as the virus-induced expansion of selected subsets of B-cell clones expressing discrete immunoglobulin variable (IgV) gene subfamilies, the involvement of complement factors and the specific role of some HCV proteins. In this review, we will analyze the host and viral factors taking part in the development of MCII in order to give a general outlook of the molecular mechanisms implicated.

B cell homeostasis in chronic hepatitis C virus-related mixed cryoglobulinemia is maintained through naïve B cell apoptosis

Mixed cryoglobulinemia (MC) is the most common extrahepatic manifestation of chronic hepatitis C virus (HCV) infection. Although the formation of inflammation-triggering immune complexes is driven by clonal expansions of autoreactive B cells, we found total B cell numbers paradoxically reduced in HCV-infected patients with MC. HCV patients with MC (n = 17) also displayed a reduced number and a reduced frequency of naïve B cells compared with HCV-infected patients without MC (n = 19), hepatitis B virus-infected patients (n = 10), and uninfected controls (n = 50). This was due to an increased sensitivity of naïve B cells to apoptosis resulting in a reduction in the size of the naïve B cell subset. In addition, 4-fold expansion and skewing (lower T1/T2-ratio) of the immature B cell subset was noted in MC patients, suggesting that apoptosis of naïve B cells triggered the release of B cell precursors from bone marrow in an attempt to maintain normal B cell numbers. Following treatment of MC with the B cell-depleting antibody rituximab, the size of all B cell subsets, the T1/T2-ratio, and the cyroglobulin levels all normalized. Cryoglobulin levels correlated with in vivo proliferation of T2 B cells, suggesting a link between the skewing of the T1/T2 ratio and the formation of immune complexes.

CONCLUSION

This study provides insight into the mechanisms maintaining B cell homeostasis in HCV-induced MC and the ability of rituximab therapy to restore normal B cell compartments. (HEPATOLOGY 2012;56:1602-1610).

May viral (antigen) load be the real crucial tool leading to anergy in a "micro-evolutionary" model of host/virus interaction?

HYPOTHESIS

The hypothesis in the present work is that in host/virus/tumor (antigens) interactions, leading to anergy of the immune system, the Viral (antigen) load plays a crucial and central role, which all interactions turn around.

BACKGROUND

Notwithstanding apparent strong favorable evidences, the still prevailing concept of "active virus strategies to escape" may be misleading, since it might hide the cited pivotal role in a wide number of researches. This concept could be easily substituted by a microevolutionary model explaining many unresolved questions and allowing to emerge the role of antigen load conditioned reactions of the host's immune system as motivated choices. EVIDENCES: An anergy induced condition can be detected not only in HCV, but also in the course of persistent viral (e.g. HBV, HIV) and non viral parasitic infections (e.g. Leishmania and Helminths) which share the same host's reactions leading to anergy, independently on the infecting agents. The starting point of those reactions is always time elapsing from the primary infection after a short early (often undetected) period of high viral(antigen) load in the lack of clearance. This latter seems then the only conceivable link between such so different infections determining, as far as HBV and HCV are concerned, also Hepatocarcinoma under indirect facilitating conditions. In a wide majority of studies it seems clearly evident that viral load exerts a main role which contributes to determine host chosen reactions aimed at avoiding dangerous outcomes while controlling viral load. Strong clinical (i.e. both HIV infected patients treated with HAART, and helminths infected people with deworming drugs acting directly on viral and parasitic loads) and experimental studies (i.e. chimpanzees (the only animal model of HCV infection) infected with HBV inocula of different size) are here reported or cited to highlight the crucial role of antigen load also on HIV infection transmission, seroconversion, disease progression, treatment initiation and efficacy.

CONCLUDING SUGGESTIONS

The new era for antiviral drugs like protease and polymerase inhibitors that seem to be more efficacious and less toxic than Ribavirin, may open the possibility to verify, when administered during the early phase of HCV infection (eventually helped by an immune-stimulant cytokine as IL-2), whether a precocious significant reduction of viral load (threshold) may allow the host to sustain his strong reactions and clear the virus within the due time, confirming the hypothesis about the crucial role of this tool which may be extended to all the cited infections.

SERPINB3 expression on B-cell surface in autoimmune diseases and hepatitis C virus-related chronic liver infection

SERPINB3 is a serine protease inhibitor with pleiotropic functions. It is involved in several physiological and pathological processes, where it appears to exert antiapoptotic effects. Little is known about its expression on immune system cells, the major players in mechanisms of viral defense and autoimmune disorders. The aim of this study was to characterize the expression of SERPINB3 on the surface of peripheral blood mononuclear cell subsets in both normal subjects and in patients with chronic viral infections and autoimmune diseases. Sixty-two patients were analyzed by flow cytometric analysis, including 45 with hepatitis C virus (HCV)-related chronic liver disease and 17 with systemic lupus erythematosus (SLE). SERPINB3 was expressed on B lymphocytes in 79% of the controls, in 32% of the HCV-infected patients and in none of the SLE patients. Surface localization of SERPINB3 was confirmed by confocal microscopy. SERPINB3 positivity was associated with CD27 reactivity (r = 0.98), but not to other activation molecules (CD69, CD71, CD86 and CXCR3). SERPINB3 is physiologically expressed on the surface of CD27(+) B lymphocytes, but its expression is reduced in HCV viral infection and not detectable in SLE patients. These results may suggest a role for SERPINB3 in B-cell defects typically found in viral infections and autoimmune disorders.

Direct phenotypical and functional dysregulation of primary human B cells by human immunodeficiency virus (HIV) type 1 in vitro

Background

Human immunodeficiency virus type 1 (HIV-1) induces a general dysregulation of immune system. Dysregulation of B cell compartment is generally thought to be induced by HIV-related immune activation and lymphopenia. However, a direct influence of HIV-1 particles on B cells was recently proposed as the third pathway of B cells dysregulation.

Methods/Principal Findings

We evaluated the direct and specific consequences of HIV-1 contact on activation, survival, proliferation and phenotype of primary B cells in vitro. Moreover, we examined expression of activation-induced cytidine deaminase (AID) mRNA that is responsible for class switch recombination (CSR) and somatic hypermutation (SHM). Here, we report that changes observed in cellular proliferation, phenotypes and activation of B cells could be caused by direct contact between HIV-1 particles and primary B cells in vitro. Finally, direct HIV-1-derived B cells activation led to the increase of AID mRNA expression and its subsequent CSR function was detected in vitro.

Conclusion/Significance

We showed that HIV-1 could directly induce primary B cells dysregulation triggering phenotypical and functional abilities of B cells in vitro that could explain in some extent early B-cell abnormalities in HIV disease.

Chronic hepatitis C virus infection breaks tolerance and drives polyclonal expansion of autoreactive B cells

Chronic Hepatitis C virus (HCV) infection has been linked with B cell lymphoproliferative disorders and several autoimmune-related diseases. The mechanisms of how chronic viral infection affects B cell development and predisposes the patients to autoimmune manifestations are poorly understood. In this study, we established an experimental system to probe the B cell responses and characterize the antibodies from chronic-HCV-infected individuals. We identified an unusual polyclonal expansion of the IgM memory B cell subset in some patients. This B cell subset is known to be tightly regulated, and autoreactive cells are eliminated by tolerance mechanisms. Genetic analysis of the immunoglobulin (Ig) heavy chain variable gene (V(H)) sequences of the expanded cell population showed that the levels of somatic hypermutation (SHM) correlate with the extent of cell expansion in the patients and that the V(H) genes exhibit signs of antigen-mediated selection. Functional analysis of the cloned B cell receptors demonstrated autoreactivity in some of the expanded IgM memory B cells in the patients which is not found in healthy donors. In summary, this study demonstrated that, in some patients, chronic HCV infection disrupts the tolerance mechanism that normally deletes autoreactive B cells, therefore increasing the risk of developing autoimmune antibodies. Long-term follow-up of this expanded B cell subset within the infected individuals will help determine whether these cells are predictors of more-serious clinical manifestations.

Dysfunctional B-cell activation in cirrhosis resulting from hepatitis C infection associated with disappearance of CD27-positive B-cell population

Chronic hepatitis C virus (HCV) infection is a leading cause of cirrhosis and hepatocellular carcinoma (HCC). Both advanced solid tumors and HCV have previously been associated with memory B-cell dysfunction. In this study, we sought to dissect the effect of viral infection, cirrhosis, and liver cancer on memory B-cell frequency and function in the spectrum of HCV disease. Peripheral blood from healthy donors, HCV-infected patients with F1-F2 liver fibrosis, HCV-infected patients with cirrhosis, patients with HCV-related HCC, and non-HCV-infected cirrhotics were assessed for B-cell phenotype by flow cytometry. Isolated B cells were stimulated with anti-cluster of differentiation (CD)40 antibodies and Toll-like receptor (TLR)9 agonist for assessment of costimulation marker expression, cytokine production, immunoglobulin (Ig) production, and CD4(+) T-cell allostimulatory capacity. CD27(+) memory B cells and, more specifically, CD27(+) IgM(+) B cells were markedly less frequent in cirrhotic patients independent of HCV infection. Circulating B cells in cirrhotics were hyporesponsive to CD40/TLR9 activation, as characterized by CD70 up-regulation, tumor necrosis factor beta secretion, IgG production, and T-cell allostimulation. Last, blockade of TLR4 and TLR9 signaling abrogated the activation of healthy donor B cells by cirrhotic plasma, suggesting a role for bacterial translocation in driving B-cell changes in cirrhosis.

CONCLUSION

Profound abnormalities in B-cell phenotype and function occur in cirrhosis independent of HCV infection. These B-cell defects may explain, in part, the vaccine hyporesponsiveness and susceptibility to bacterial infection in this population.

Enhancement of humoral immunity in mice by coupling pUCpGs10 and aluminium to the HCV recombinant immunogen

Aim

To investigate the enhancement of humoral immunity when CpG ODN (cytidine phosphate guanosine oligodeoxynucleotides) and aluminium adjuvants are complexed with the HCV (Hepatitis C virus) recombinant immunogen in mice.

Methods

After immunizing Balb/c mice with the recombination HCV antigen adjuvanted with pUCpGs10 and/or aluminium(antigen+CpG+alum, antigen+CpG, antigen+alum, antigen+PBS), enzyme-linked immunosorbent assay (ELISA) was used to measure the specific serum antibody titers of IgG, to determine the neutralization response to various peptide genotypes, and to determine the concentration of IL-6 and IL-10 in supernatants of in vitro cultured splenic lymphocytes. Enzyme-linked immunospot assay (ELISPOT) was used to quantify the non-specific and specific splenic antibody-secreting cells (ASCs), and flow cytometry (FCM) determined the ratio of different splenic lymphocytes. The serum of rabbits immunized with the recombinant pBVGST/HVR1 antigen immunoprecipitated the HCV isolated from 12 patients' serum.

Results

The sera antibody titers were 1:51200, 1:9051, 1:18102, 1:6400 respectively after the final immunization and demonstrated good neutralization responses to the six gene peptide containing 1a, 1b, 2a, 3a, 4a and 6a. The aluminum adjuvant increased the population of both specific ASCs (P < 0.01) and total ASCs(P < 0.05), with a proportional rise in concentrations of CD19⁺CD27⁺ (P < 0.05), as well as levels of IL-6, IL-10 (P < 0.05) in splenic lymphocytes. The results clearly indicated a significantly higher number of CD19⁺CD38⁺ splenic lymphocytes with the aluminum and pUCpGs10 adjuvant present compared to the control group(P < 0.05). Anti-HVR1 antibody in induced mice can cross-reactively capture HCV particles (10/12).

Conclusions

1. The aluminum adjuvant induces a potent Th2-biased immune response by increasing both the populations of specific and total ASCs and the ratio of CD19⁺CD27⁺ cells. 2. The pUCpGs10 complexed with the aluminum adjuvant boosts the population of plasma cells and increase the efficiency of the immune response. 3. The two adjuvants have synergistic effects on humoral immunity. 4. The recombinant HVR1 protein has the possibility of generating broadly reactive anti-HVR1 antibody.

Antibody V(h) repertoire differences between resolving and chronically evolving hepatitis C virus infections

Despite the production of neutralizing antibodies to hepatitis C virus (HCV), many patients fail to clear the virus and instead develop chronic infection and long-term complications. To understand how HCV infection perturbs the antibody repertoire and to identify molecular features of antibody genes associated with either viral clearance or chronic infection, we sequenced the V(D)J region of naïve and memory B cells of 6 persons who spontaneously resolved an HCV infection (SR), 9 patients with a newly diagnosed chronically evolving infection (CE), and 7 healthy donors. In both naïve and memory B cells, the frequency of use of particular antibody gene subfamilies and segments varied among the three clinical groups, especially between SR and CE. Compared to CE, SR antibody genes used fewer VH, D and JH gene segments in naïve B cells and fewer VH segments in memory B cells. SR and CE groups significantly differed in the frequency of use of 7 gene segments in naïve B cell clones and 3 gene segments in memory clones. The nucleotide mutation rates were similar among groups, but the pattern of replacement and silent mutations in memory B cell clones indicated greater antigen selection in SR than CE. Greater clonal evolution of SR than CE memory B cells was revealed by analysis of phylogenetic trees and CDR3 lengths. Pauciclonality of the peripheral memory B cell population is a distinguishing feature of persons who spontaneously resolved an HCV infection. This finding, previously considered characteristic only of patients with HCV-associated lymphoproliferative disorders, suggests that the B cell clones potentially involved in clearance of the virus may also be those susceptible to abnormal expansion.

Enhanced B-cell differentiation and reduced proliferative capacity in chronic hepatitis C and chronic hepatitis B virus infections

BACKGROUND & AIMS

Chronic microbial infections are frequently associated with B-cell activation and polyclonal proliferation, potentially leading to autoimmunity and lymphoproliferative disorders. We assessed B-cell phenotype and function in chronic hepatitis B (HBV) and chronic hepatitis C (HCV) virus infection.

METHODS

We studied 70 patients with chronic HCV infection, 34 with chronic HBV infection and 54 healthy controls. B-cell phenotype was assessed by flow cytometry using monoclonal antibodies specific for CD27, the CD69, CD71, and CD86 activation markers and the chemokine receptor CXCR3. Differentiation into immunoglobulin-producing cells (IPC) was analysed by ELISpot upon stimulation and with CD40 ligand±IL-10 as surrogate bystander T-cell help or CpG oligodeoxynucleotide±IL-2, as innate immunity signal. Proliferation was examined by flow cytometry using carboxyfluorescein diacetate succinimidyl ester (CFSE) after stimulation with CpG.

RESULTS

A significantly higher proportion of B cells from both HCV- and HBV-infected patients expressed activation markers compared with controls and a positive correlation was found between CXCR3(+) B cells and HCV RNA values. Memory B cells from patients with chronic HCV and HBV infections showed enhanced differentiation into IPC compared with controls, although this was restricted to IgG and at a lower level in HCV-compared with HBV-infected patients. Moreover, patients' activated B cells displayed significantly lower proliferative ability compared to healthy donors despite low expression of the FcRL4 exhaustion marker.

CONCLUSIONS

B-cell activation, but not exhaustion, is common in chronic viral hepatitis. However, enhanced B-cell differentiation and deficient proliferative capacity were not associated with commitment to terminal differentiation.

Clonal B cells in patients with hepatitis C virus-associated mixed cryoglobulinemia contain an expanded anergic CD21low B-cell subset

Hepatitis C virus (HCV) is associated with the B-cell lymphoproliferative disorders mixed cryoglobulinemia (MC) and non-Hodgkin lymphoma. We have previously reported that HCV(+)MC(+) patients have clonal expansions of hypermutated, rheumatoid factor-bearing marginal zone-like IgM(+)CD27(+) peripheral B cells using the V(H)1-69 gene. Here we coupled transcriptional profiling with immunophenotypic and functional studies to ascertain these cells' role in MC pathogenesis. Despite their fundamental role in MC disease, these B cells have overall transcriptional features of anergy and apoptosis instead of neoplastic transformation. Highly up-regulated genes include SOX5, CD11C, galectin-1, and FGR, similar to a previously described FCRL4(+) memory B-cell subset and to an "exhausted," anergic CD21(low) memory B-cell subset in HIV(+) patients. Moreover, HCV(+)MC(+) patients' clonal peripheral B cells are enriched with CD21(low), CD11c(+), FCRL4(high), IL-4R(low) memory B cells. In contrast to the functional, rheumatoid factor-secreting CD27(+)CD21(high) subset, the CD27(+)CD21(low) subpopulation exhibits decreased calcium mobilization and does not efficiently differentiate into rheumatoid factor-secreting plasmablasts, suggesting that a large proportion of HCV(+)MC(+) patients' clonally expanded peripheral B cells is prone to anergy and/or apoptosis. Down-regulation of multiple activation pathways may represent a homeostatic mechanism attenuating otherwise uncontrolled stimulation of circulating HCV-containing immune complexes.

Human herpesvirus-8 infection leads to expansion of the preimmune/natural effector B cell compartment

Background

Human herpesvirus-8 (HHV-8) is the etiological agent of Kaposi's sarcoma (KS) and of some lymphoproliferative disorders of B cells. Most malignancies develop after long-lasting viral dormancy, and a preventing role for both humoral and cellular immune control is suggested by the high frequency of these pathologies in immunosuppressed patients. B cells, macrophages and dendritic cells of peripheral lymphoid organs and blood represent the major reservoir of HHV-8. Due to the dual role of B cells in HHV-8 infection, both as virus reservoir and as agents of humoral immune control, we analyzed the subset distribution and the functional state of peripheral blood B cells in HHV-8-infected individuals with and without cKS.

Methodology/Principal Findings

Circulating B cells and their subsets were analyzed by 6-color flow cytometry in the following groups: 1- patients HHV-8 positive with classic KS (cKS) (n = 47); 2- subjects HHV-8 positive and cKS negative (HSP) (n = 10); 3- healthy controls, HHV-8 negative and cKS negative (HC) (n = 43). The number of B cells belonging to the preimmune/natural effector compartment, including transitional, pre-naïve, naïve and MZ-like subsets, was significantly higher among HHV-8 positive subjects, with or without cKS, while was comparable to healthy controls in the antigen-experienced T-cell dependent compartment. The increased number of preimmune/natural effector B cells was associated with increased resistance to spontaneous apoptosis, while it did not correlate with HHV-8 viral load.

Conclusions/Significance

Our results indicate that long-lasting HHV-8 infection promotes an imbalance in peripheral B cell subsets, perturbing the equilibrium between earlier and later steps of maturation and activation processes. This observation may broaden our understanding of the complex interplay between viral and immune factors leading HHV-8-infected individuals to develop HHV-8-associated malignancies.

Peripheral blood memory B cells are resistant to apoptosis in chronic hepatitis C patients

Our recent study indicated that peripheral B cells in chronic hepatitis C (CHC) patients were infected with hepatitis C virus (HCV). It was also demonstrated that the frequency of CD27(+) B cells, i.e. memory phenotype, was significantly reduced in the peripheral blood of CHC patients. An assumption was made by these findings that the CD27(+) B cells are susceptible to apoptosis when infected with HCV. Therefore, in this study, the susceptibility of CD27(+) B cells to apoptosis in CHC patients was analyzed. Contrary to our assumption, it was found that CD27(+) B cells are more resistant to apoptosis than the counterpart subset, i.e. CD27(-) B cells. The rationale for this finding is discussed with regard to the possible role for memory B cells as an HCV reservoir for persistent infection in CHC patients.

Possible recruitment of peripheral blood CXCR3+ CD27+ CD19+ B cells to the liver of chronic hepatitis C patients

It has been suggested that hepatitis C virus (HCV) infects not only hepatocytes but also immune cells, including B cells. HCV infection of B cells is the likely cause of B-cell dysregulation disorders such as mixed cryoglobulinemia, rheumatoid factor production, and B-cell lymphoproliferative disorders that may evolve into non-Hodgkin's lymphoma. To clarify the effects of chronic HCV infection on B-cell dynamics, peripheral B cells from chronic hepatitis C patients (CHC) were characterized. We found that the frequency of CD27(+) B cells, that is memory phenotype, was significantly reduced in the peripheral blood of CHC. At the same time, the amount of IFN-gamma-inducible protein-10 (IP-10), a CXCR3 ligand, was markedly elevated in the plasma of CHC. Furthermore, the CD27(+) B-cell population was found to highly express CXCR3 in CHC, thus suggesting that the CD27(+) B-cell population was recruited from peripheral blood to the inflammatory site of the liver of CHC, where IP-10 is produced. Immunohistochemical analyses of intrahepatic lymphocytes indicated that CXCR3(+) B cells were infiltrated in the liver of CHC. Our results thus offer new insight into the role of memory B cells in the HCV pathogenesis.

Peripheral blood B cell subset skewing is associated with altered cell cycling and intrinsic resistance to apoptosis and reflects a state of immune activation in chronic hepatitis C virus infection

Chronic hepatitis C virus (HCV) infection is associated with B cell activation, although underlying mechanisms are unclear. To investigate B cell regulation during HCV infection, we measured bulk B cell CpG and Staphylococcus aureus Cowan-induced IgG Ab-secreting cell (ASC) frequency, HCV and tetanus-specific ASC frequency, BCR- and CD40L-dependent CD80/CD86 expression, and activation of memory CD4 cells. Immature transitional, naive, resting memory, mature activated, tissue-like memory, and plasma B cell subset frequencies, cell cycling, and intrinsic apoptosis were quantified. We observed intact or enhanced tetanus-specific and total IgG ASC frequency, serum IgG, BCR- and CD40L-dependent CD80/CD86 expression, and CD40L-dependent bulk B cell activation of memory CD4 cells in HCV infection. HCV-specific ASCs were observed in HCV-infected but not control subjects, although frequencies were lower compared with tetanus-specific cells. Immature transitional and mature activated B cell subset frequencies were increased in HCV-infected subjects, with immature transitional frequency associated with liver inflammation and serum B cell-activating factor. Mature activated B cells less commonly expressed Ki67, more commonly expressed Bcl2, and were more intrinsically resistant to apoptosis, whereas immature transitional B cells more commonly expressed Ki67, the latter associated with plasma HCV level. Taken together, these results indicate that in the setting of chronic HCV infection, a state of activation results in B cell subset skewing that is likely the result of alterations in homeostasis, cell cycling, and intrinsic resistance to apoptosis and that results in an overall intact or enhanced B cell response to BCR and CD40L.

Rotavirus differentially infects and polyclonally stimulates human B cells depending on their differentiation state and tissue of origin

We have shown previously that rotavirus (RV) can infect murine intestinal B220(+) cells in vivo (M. Fenaux, M. A. Cuadras, N. Feng, M. Jaimes, and H. B. Greenberg, J. Virol. 80:5219-5232, 2006) and human blood B cells in vitro (M. C. Mesa, L. S. Rodriguez, M. A. Franco, and J. Angel, Virology 366:174-184, 2007). However, the effect of RV on B cells, especially those present in the human intestine, the primary site of RV infection, is unknown. Here, we compared the effects of the in vitro RV infection of human circulating (CBC) and intestinal B cells (IBC). RV infected four times more IBC than CBC, and in both types of B cells the viral replication was highly restricted to the memory subset. RV induced cell death in 30 and 3% of infected CBC and IBC, respectively. Moreover, RV induced activation and differentiation into antibody-secreting cells (ASC) of CBC but not IBC when the B cells were present with other mononuclear cells. However, RV did not induce these effects in purified CBC or IBC, suggesting the participation of other cells in activating and differentiating CBC. RV infection was associated with enhanced interleukin-6 (IL-6) production by CBC independent of viral replication. The infection of the anti-B-cell receptor, lipopolysaccharide, or CpG-stimulated CBC reduced the secretion of IL-6 and IL-8 and decreased the number of ASC. These inhibitory effects were associated with an increase in viral replication and cell death and were observed in polyclonally stimulated CBC but not in IBC. Thus, RV differentially interacts with primary human B cells depending on their tissue of origin and differentiation stage, and it affects their capacity to modulate the local and systemic immune responses.

An optimized assay for the enumeration of antigen-specific memory B cells in different compartments of the human body

OBJECT

In the framework of our current study we set out to develop an optimized assay for the quantification of antigen-specific B cells in different compartments of the human body.

METHODS

Mononuclear cells (MNC) derived from the peripheral blood, bone marrow (BM), or human tonsils were incubated with different combinations of stimuli. The stimulated cells and culture supernatants were then applied to IgG-ELISPOT and ELISA read-out assays and tetanus toxoid (TT)-specific B cell responses were quantified.

RESULTS

We found that a combination of CD40L, CpG, and IL21 was optimal for the induction of TT-specific IgG-producing cells from memory B cell (mBc) precursors. This cocktail of stimuli led to a proliferation-dependent induction of CD19(intermediate)CD38(high)CD138(high)IgD(negative) terminally differentiated plasma cells. Applying our optimized methodology we were also able to quantify mBc specific for cytomegalovirus and influenza virus A. Most importantly, the same method proved useful for the comparison of mBc frequencies between different compartments of the body and, accordingly, we were able to demonstrate that TT-specific mBc preferably reside within tonsillar tissue.

CONCLUSION

Here, we optimized an assay for the quantification of antigen-specific B cells in different human tissues demonstrating, for example, that TT-specific mBc preferably reside in human tonsils but not in the BM or the peripheral blood. We suggest that our approach can be used for the enumeration of mBc specific for a wide variety of Ag (microbial, tumor-related, auto-antigens), which will lead to significant improvements regarding our knowledge about the biology of humoral immunity.

Clonal CD27+ CD19+ B cell expansion through inhibition of FC gammaIIR in HCV(+) cryoglobulinemic patients

Persistent HCV infection may be associated with extrahepatic manifestations such as type II mixed cryoglobulinemia (II-MC), a clonal B cell proliferative disorder. In persistent HCV infection without II-MC, an increase in serum immunoglobulins (Ig) is commonly observed. This increase is polyclonal and is determined primarily by increased levels of IgG which include both HCV-specific and nonspecific antibodies. Nonetheless, memory CD27(+) B cells do not accumulate. This paradoxical phenomenon depends on heightened sensitivity of memory B cells to BCR-independent noncognate T cell help, which speeds up their terminal differentiation into antibody-secreting cells and makes them more prone to apoptosis. In persistent HCV infection with II-MC, serum Ig elevation is also a general occurrence, and characteristically includes IgM antibodies with rheumatoid factor activity, which are essential for the development of circulating, cryoprecipitable immune complexes. Hypergammaglobulinemia is sustained by a peripheral expansion of IgM(+)k(+)IgD(low/neg)CD21(low)CD27(+) B cells. These cells exhibit marked V(H), J(H), and V(K) gene segment usage restriction, indicating that a limited number of antigens drive their proliferation through BCR interaction. Recently, two epitopes, one of the human IgG and the second of the HCV(NS3) protein, had been identified and demonstrated able to link the BCR exposed on II-MC subjects. Based on the above findings, we propose a model whereby BCR binding the IgM/IgG/HCV(NS3) immune complexes deprives Fc gammaIIR of its natural ligand. This takes the brake off RF(+)CD27(+) B cell proliferation and promotes their selective accumulation, which is otherwise prevented by increased apoptosis susceptibility in persistent HCV infection without II-MC.