A triad of somatic mutagenesis converges in self-reactive B cells to cause a virus-induced autoimmune disease

The unexplained association between infection and autoimmune disease is strongest for hepatitis C virus-induced cryoglobulinemic vasculitis (HCV-cryovas). To analyze its origins, we traced the evolution of pathogenic rheumatoid factor (RF) autoantibodies in four HCV-cryovas patients by deep single-cell multi-omic analysis, revealing three sources of B cell somatic mutation converged to drive the accumulation of a large disease-causing clone. A method for quantifying low-affinity binding revealed recurring antibody variable domain combinations created by V(D)J recombination that bound self-immunoglobulin G (IgG) but not viral E2 antigen. Whole-genome sequencing revealed thousands of somatic mutations, numerically comparable to chronic lymphocytic leukemia and normal memory B cells, but with 1-2 corresponding to driver mutations found recurrently in B cell leukemia and lymphoma. V(D)J hypermutation created autoantibodies with compromised solubility in complex with self-IgG. In this virus-induced autoimmune disease, infection promotes a catastrophic confluence of somatic mutagenesis in the descendants of a single B cell.

Causal Mediation Analyses for the Natural Course of Hepatitis C: A Prospective Cohort Study

BACKGROUND

Hepatitis C virus (HCV) infection is a systemic disease. However, the relative contribution of intrahepatic and extrahepatic diseases to mediating HCV-induced mortality is unclear, albeit critical in resource allocation for reducing preventable deaths. To this end, this study comprehensively quantified the extent to which intrahepatic and extrahepatic diseases mediate HCV-induced mortality.

METHODS

A community-based cohort study with >25 years of follow-up was conducted in Taiwan. HCV infection was profiled by antibodies against HCV and HCV RNA in participants' serum samples. The cohort data were linked to Taiwan's National Health Insurance Research Database to determine the incidences of potential mediating diseases and mortality. We employed causal mediation analyses to estimate the mediation effects of HCV on mortality in relation to the incidences of 34 candidate diseases.

RESULTS

In 18,972 participants with 934 HCV infection, we observed that 54.1% of HCV-induced mortality was mediated by intrahepatic diseases, such as liver cirrhosis and liver cancer, and 45.9% of mortality was mediated by extrahepatic diseases. The major extrahepatic mediating diseases included septicemia (estimated proportion of HCV-induced mortality mediated through the disease: 25.2%), renal disease (16.7%), blood/immune diseases (12.2%), gallbladder diseases (9.7%), and endocrine diseases (9.6%). In women, hypertension (20.0%), metabolic syndrome (18.9%), and type 2 diabetes (17.0%) also mediated HCV-induced mortality. A dose-response relationship of HCV viral load was further demonstrated for the mediation effect.

CONCLUSION

Both intrahepatic and extrahepatic manifestations mediated approximately half of HCV-induced mortality. The mediation mechanisms are supported by a dose-response relationship of HCV viral load.

Longevity of antibody responses is associated with distinct antigen-specific B cell subsets early after infection

Introduction

Upon infection, T cell-driven B cell responses in GC reactions induce memory B cells and antibody-secreting cells that secrete protective antibodies. How formation of specifically long-lived plasma cells is regulated via the interplay between specific B and CD4+ T cells is not well understood. Generally, antibody levels decline over time after clearance of the primary infection.

Method

In this study, convalescent individuals with stable RBD antibody levels (n=14, "sustainers") were compared with donors (n=13) with the greatest antibody decline from a cohort of 132. To investigate the role of the cellular immune compartment in the maintenance of antibody levels, SARS-CoV-2-specific responses at 4 to 6 weeks post-mild COVID-19 infection were characterized using deep immune profiling.

Results

Both groups had similar frequencies of total SARS-CoV-2-specific B and CD4+ T cells. Sustainers had fewer Spike-specific IgG+ memory B cells early after infection and increased neutralizing capacity of RBD antibodies over time, unlike the declining group. However, declining IgG titers correlated with lower frequency of Spike-specific CD4+ T cells.

Conclusion

These data suggest that "sustainers" have unique dynamics of GC reactions, yield different outputs of terminally differentiating cells, and improve the quality of protective antibodies over time. This study helps identify factors controlling formation of long-lived PC and sustained antibody responses.

B-cell dynamics underlying poor response upon split-inactivated influenza virus vaccination

This investigation elucidated the differences in humoral and H1N1 HA-specific memory B-cells response in participants exhibiting distinct immune response patterns prior to and after vaccination with Fluzone, the quadrivalent split-inactivated seasonal influenza virus vaccine. Participants were categorized into persistent non-responders and persistent responders based on their hemagglutination-inhibition (HAI) antibody titers to the H1N1 component from each vaccine administered between the 2019-2020 to 2023-2024 seasons. Persistent responders had higher fold change in H1N1 HA-specific CD21 expressing B-cells, plasmablasts, and plasma cells. A significant increase in H1N1 HA-specific transitional B-cells in persistent non-responders was observed. The frequency and fold change of H1N1-specific IgM-expressing memory B-cells was higher in persistent non-responders. Dimensionality reduction analysis also demonstrated higher IgM expression for persistent non-responders than persistent responders. Furthermore, persistent non-responders had a significant fold change increase in IgA tissue-like memory, IgG exhausted tissue-like memory, and double negative (DN) activated memory cells. In contrast, persistent responders had increased frequency of IgG-activated memory B-cells, IgG resting B-cells and DN resting B-cells. Correlation analysis revealed a positive correlation between HAI titers and DN memory B-cells and a negative correlation between HAI titers and IgG-expressing memory B-cells in persistent non-responders. Conversely, persistent responders had a positive correlation between HAI titers and IgA resting memory B-cells and a negative correlation between IgG memory B-cells and DN memory B-cells. Overall, this study provided valuable insights into the differential immune memory B-cell responses following influenza virus vaccination and paves the way for future research to further unravel the complexities of vaccine-induced memory B-cells and ultimately improve vaccination strategies against influenza virus infection.

Cartilage destruction in early rheumatoid arthritis patients correlates with CD21-/low double-negative B cells

BACKGROUND

Involvement of B cells in the pathogenesis of rheumatoid arthritis (RA) is supported by the presence of disease-specific autoantibodies and the efficacy of treatment directed against B cells. B cells that express low levels of or lack the B cell receptor (BCR) co-receptor CD21, CD21-/low B cells, have been linked to autoimmune diseases, including RA. In this study, we characterized the CD21+ and CD21-/low B cell subsets in newly diagnosed, early RA (eRA) patients and investigated whether any of the B cell subsets were associated with autoantibody status, disease activity and/or joint destruction.

METHODS

Seventy-six eRA patients and 28 age- and sex-matched healthy donors were recruited. Multiple clinical parameters were assessed, including disease activity and radiographic joint destruction. B cell subsets were analysed in peripheral blood (PB) and synovial fluid (SF) using flow cytometry.

RESULTS

Compared to healthy donors, the eRA patients displayed an elevated frequency of naïve CD21+ B cells in PB. Amongst memory B cells, eRA patients had lower frequencies of the CD21+CD27+ subsets and CD21-/low CD27+IgD+ subset. The only B cell subset found to associate with clinical factors was the CD21-/low double-negative (DN, CD27-IgD-) cell population, linked with the joint space narrowing score, i.e. cartilage destruction. Moreover, in SF from patients with established RA, the CD21-/low DN B cells were expanded and these cells expressed receptor activator of the nuclear factor κB ligand (RANKL).

CONCLUSIONS

Cartilage destruction in eRA patients was associated with an expanded proportion of CD21-/low DN B cells in PB. The subset was also expanded in SF from established RA patients and expressed RANKL. Taken together, our results suggest a role for CD21-/low DN in RA pathogenesis.

Association Between Bruton's Tyrosine Kinase Gene Overexpression and Risk of Lymphoma in Primary Sjögren's Syndrome

OBJECTIVE

We undertook this study to analyze whole blood gene expression and to investigate the role of B cell genes in primary Sjögren's syndrome-related non-Hodgkin lymphoma (primary SS-NHL).

METHODS

Peripheral whole blood samples were collected from 345 well-phenotyped patients with primary SS enrolled in the prospective Assessment of Systemic Signs and Evolution in Sjögren's Syndrome (ASSESS) cohort. Transcriptomic analysis was performed using human Clariom S Arrays (Affymetrix). In our primary analysis, we considered patients with incident lymphoma (i-primary SS-NHL) as the case group and all patients without lymphoma as the comparison group. In our sensitivity analyses, we considered all patients with primary SS-NHL, including those with a history of lymphoma (h-primary SS-NHL), as the case group and primary SS patients without lymphoma, stratified on their risk factors of lymphoma, as the comparison group.

RESULTS

Twenty-one patients with primary SS-NHL (including 8 with i-primary SS-NHL and 13 h-primary SS-NHL) were eligible for transcriptomic analysis; we compared these patients to 324 primary SS controls without lymphoma, including 110 with moderate to severe disease activity and 61 with no risk factor of lymphoma. Functional clustering analyses revealed an enrichment of genes related to innate and adaptive immunity, including B cell-related genes. Bruton's tyrosine kinase (BTK) and a proliferation-inducing ligand (APRIL) genes were overexpressed before the occurrence of lymphoma in patients with incident lymphoma compared with patients without lymphoma. In sensitivity analyses, BTK was consistently up-regulated across all comparisons performed. BTK expression was associated with risk of lymphoma on multivariate analyses, which considered 9 validated predictors of lymphoma in primary SS.

CONCLUSION

BTK and APRIL were overexpressed in the peripheral blood of primary SS patients prior to lymphoma. The association between BTK, APRIL, and primary SS-NHL requires confirmation in other prospective cohorts.

Prevalence of hepatitis C virus among patients with arthralgia: is it logic for screening?

BACKGROUND

Hepatitis C virus (HCV) is well-known to be associated with multiple extrahepatic manifestations such as arthralgia, myalgia, arthritis, and vasculitis. Many studies reported frequent rheumatologic manifestations among patients infected by HCV. The purpose of this study was to determine the prevalence of HCV among chronic unexplained arthralgia patients in order to aid in the early detection and treatment of silent HCV infection.

METHODS

This study was a cross-sectional observational study conducted from July 2020 to May 2022. It included 145 individuals suffering from chronic unexplained arthralgia, with vast majority having oligoarticular joint pain (110, 75.9%). They were 103 (71%) females and 42 (29%) males. Serum samples from all patients were examined for the presence of anti-HCV antibodies using a rapid immunochromatographic assay. Seropositive samples were further examined using polymerase chain reaction (PCR) for detection of HCV RNA to confirm HCV infection.

RESULTS

Out of 145 patients who complained of arthralgia, seven patients tested positive for anti-HCV with a seroprevalence of 4.8% while five patients tested positive for HCV-RNA with a molecular prevalence of 3.4%. All positive patients were males (11.9%) with high statistical significance (χ² = 12.7 and p = 0.002). No association was found between HCV infection and age, blood transfusion, surgery, using personal shaving tools, or being a health-care worker.

CONCLUSIONS

The prevalence of HCV was high among males who complained of arthralgia. Patients with arthralgia, especially male patients, are recommended to perform HCV screening test.

Age-associated B cells predict impaired humoral immunity after COVID-19 vaccination in patients receiving immune checkpoint blockade

Age-associated B cells (ABC) accumulate with age and in individuals with different immunological disorders, including cancer patients treated with immune checkpoint blockade and those with inborn errors of immunity. Here, we investigate whether ABCs from different conditions are similar and how they impact the longitudinal level of the COVID-19 vaccine response. Single-cell RNA sequencing indicates that ABCs with distinct aetiologies have common transcriptional profiles and can be categorised according to their expression of immune genes, such as the autoimmune regulator (AIRE). Furthermore, higher baseline ABC frequency correlates with decreased levels of antigen-specific memory B cells and reduced neutralising capacity against SARS-CoV-2. ABCs express high levels of the inhibitory FcγRIIB receptor and are distinctive in their ability to bind immune complexes, which could contribute to diminish vaccine responses either directly, or indirectly via enhanced clearance of immune complexed-antigen. Expansion of ABCs may, therefore, serve as a biomarker identifying individuals at risk of suboptimal responses to vaccination.

Dual stimulation by autoantigen and CpG fosters the proliferation of exhausted rheumatoid factor-specific CD21low B cells in hepatitis C virus-cured mixed cryoglobulinemia

Introduction

Hepatitis C virus (HCV) causes mixed cryoglobulinemia (MC) by driving clonal expansion of B cells expressing B cell receptors (BCRs), often encoded by the VH1-69 variable gene, endowed with both rheumatoid factor (RF) and anti-HCV specificity. These cells display an atypical CD21low phenotype and functional exhaustion evidenced by unresponsiveness to BCR and Toll-like receptor 9 (TLR9) stimuli. Although antiviral therapy is effective on MC vasculitis, pathogenic B cell clones persist long thereafter and can cause virus-independent disease relapses.

Methods

Clonal B cells from patients with HCV-associated type 2 MC or healthy donors were stimulated with CpG or heath-aggregated IgG (as surrogate immune complexes) alone or in combination; proliferation and differentiation were then evaluated by flow cytometry. Phosphorylation of AKT and of the p65 NF-kB subunit were measured by flow cytometry. TLR9 was quantified by qPCR and by intracellular flow cytometry, and MyD88 isoforms were analyzed using RT-PCR.

Discussion

We found that dual triggering with autoantigen and CpG restored the capacity of exhausted VH1-69pos B cells to proliferate. The signaling mechanism for this BCR/TLR9 crosstalk remains elusive, since TLR9 mRNA and protein as well as MyD88 mRNA were normally expressed and CpG-induced phosphorylation of p65 NF-kB was intact in MC clonal B cells, whereas BCR-induced p65 NF-kB phosphorylation was impaired and PI3K/Akt signaling was intact. Our findings indicate that autoantigen and CpG of microbial or cellular origin may unite to foster persistence of pathogenic RF B cells in HCV-cured MC patients. BCR/TLR9 crosstalk might represent a more general mechanism enhancing systemic autoimmunity by the rescue of exhausted autoreactive CD21low B cells.

Burden, Outcome, and Comorbidities of Extrahepatic Manifestations in Hepatitis C Virus Infection

Hepatitis C virus (HCV) is a significant cause of chronic liver diseases worldwide and is associated with negative consequences, including cirrhosis, hepatic decompensation, hepatocellular carcinoma, and increased risk of mortality. In addition to liver-related morbidities, HCV is also associated with several extrahepatic manifestations, including mixed cryoglobulinemia, diabetes mellitus, cardiocerebrovascular disease, lymphoma, and autoimmune diseases. These non-liver-related complications of HCV increase the complexity of this disease and can contribute to the economic burden, morbidity, quality of life, and mortality throughout the world. Therefore, understanding how this virus can contribute to each extrahepatic manifestation is worth investigating. Currently, the advancement of HCV treatment with the advent of direct-acting anti-viral agents (DAAs) has led to a high cure rate as a result of sustained virologic response and tremendously reduced the burden of extrahepatic complications. However, HCV-associated extrahepatic manifestations remain a relevant concern, and this review aims to give an updated highlight of the prevalence, risk factors, associated burdens, and treatment options for these conditions.

Peripheral B cells from patients with hepatitis C virus-associated lymphoma exhibit clonal expansion and an anergic-like transcriptional profile

Chronic HCV infection remains a global health concern due to its involvement in hepatic and extrahepatic diseases, including B cell non-Hodgkin lymphoma (BNHL). Clinical and epidemiological evidence support a causal role for HCV in BNHL development, although mechanistic insight is lacking. We performed RNA-sequencing on peripheral B cells from patients with HCV alone, BNHL alone, and HCV-associated BNHL to identify unique and shared transcriptional profiles associated with transformation. In patients with HCV-associated BNHL, we observed the enrichment of an anergic-like gene signature and evidence of clonal expansion that was correlated with the expression of epigenetic regulatory genes. Our data support a role for viral-mediated clonal expansion of anergic-like B cells in HCV-associated BNHL development and suggest epigenetic dysregulation as a potential mechanism driving expansion. We propose epigenetic mechanisms may be involved in both HCV-associated lymphoma and regulation of B cell anergy, representing an attractive target for clinical interventions.

FcɣRIIB regulates autoantibody responses by limiting marginal zone B cell activation

FcɣRIIB is an inhibitory receptor expressed throughout B cell development. Diminished expression or function is associated with lupus in mice and humans, in particular through an effect on autoantibody production and plasma cell differentiation. Here, we analysed the effect of B cell-intrinsic FcɣRIIB expression on B cell activation and plasma cell differentiation. Loss of FcɣRIIB on B cells (Fcgr2b cKO mice) led to a spontaneous increase in autoantibody titers. This increase was most striking for IgG3, suggestive of increased extrafollicular responses. Marginal zone (MZ) B cells had the highest expression of FcɣRIIB in both mouse and human. This high expression of FcɣRIIB was linked to increased MZ B cell activation, Erk phosphorylation, and calcium fluxin the absence of FcɣRIIB triggering. Marked increases in IgG3+ plasma cells and B cells were observed during extrafollicular plasma cell responses in Fcgr2b cKO mice. The increased IgG3 response following immunization of Fcgr2b cKO mice was lost in MZ-deficient Notch2/Fcgr2b cKO mice. Importantly, SLE patients exhibited decreased expression of FcɣRIIB, most strongly in MZ B cells. Thus, we present a model where high FcɣRIIB expression in MZ B cells prevents their hyperactivation and ensuing autoimmunity.

Molecular mechanisms controlling age-associated B cells in autoimmunity

Age-associated B cells (ABCs) have emerged as critical components of immune responses. Their inappropriate expansion and differentiation have increasingly been linked to the pathogenesis of autoimmune disorders, aging-associated diseases, and infections. ABCs exhibit a distinctive phenotype and, in addition to classical B cell markers, often express the transcription factor T-bet and myeloid markers like CD11c; hence, these cells are also commonly known as CD11c+ T-bet+ B cells. Formation of ABCs is promoted by distinctive combinations of innate and adaptive signals. In addition to producing antibodies, these cells display antigen-presenting and proinflammatory capabilities. It is becoming increasingly appreciated that the ABC compartment exhibits a high degree of heterogeneity, plasticity, and sex-specific regulation and that ABCs can differentiate into effector progeny via several routes particularly in autoimmune settings. In this review, we will discuss the initial insights that have been obtained on the molecular machinery that controls ABCs and we will highlight some of the unique aspects of this control system that may enable ABCs to fulfill their distinctive role in immune responses. Given the expanding array of autoimmune disorders and pathophysiological settings in which ABCs are being implicated, a deeper understanding of this machinery could have important and broad therapeutic implications for the successful, albeit daunting, task of targeting these cells.

Marginal Zone B-Cell Populations and Their Regulatory Potential in the Context of HIV and Other Chronic Inflammatory Conditions

Inflammation in the context of Human Immunodeficiency Virus (HIV) establishes early and persists beyond antiretroviral therapy (ART). As such, we have shown excess B-cell activating factor (BAFF) in the blood of HIV-infected progressors, as soon as in the acute phase, and despite successful ART. Excess BAFF was associated with deregulation of the B-cell compartment; notably, with increased frequencies of a population sharing features of both transitional immature (TI) and marginal zone (MZ) B-cells, we termed Marginal Zone precursor-like (MZp). We have reported similar observations with HIV-transgenic mice, Simian Immunodeficiency Virus (SIV)-infected macaques, and more recently, with HIV-infected Beninese commercial sex workers, which suggests that excess BAFF and increased frequencies of MZp B-cells are reliable markers of inflammation in the context of HIV. Importantly, we have recently shown that in healthy individuals, MZps present an important regulatory B-cell (Breg) profile and function. Herein, we wish to review our current knowledge on MZ B-cell populations, especially their Breg status, and that of other B-cell populations sharing similar features. BAFF and its analog A Proliferation-Inducing Ligand (APRIL) are important in shaping the MZ B-cell pool; moreover, the impact that excess BAFF—encountered in the context of HIV and several chronic inflammatory conditions—may exert on MZ B-cell populations, Breg and antibody producing capacities is a threat to the self-integrity of their antibody responses and immune surveillance functions. As such, deregulations of MZ B-cell populations contribute to autoimmune manifestations and the development of MZ lymphomas (MZLs) in the context of HIV and other inflammatory diseases. Therefore, further comprehending the mechanisms regulating MZ B-cell populations and their functions could be beneficial to innovative therapeutic avenues that could be deployed to restore MZ B-cell immune competence in the context of chronic inflammation involving excess BAFF.

Immunophenotypic and functional analysis of lymphocyte subsets in common variable immunodeficiency patients without monogenic defects

Common variable immunodeficiency (CVID) is accompanied by various lymphocyte abnormalities believed to be mostly responsible for disease features in patients with no diagnosed monogenic defects. Here, we evaluated the association of B and T lymphocyte abnormalities with the incidence of CVID. Twenty-six genetically unsolved CVID patients were examined for B and T lymphocyte subsets by flow cytometry and CD4⁺ T cell proliferation by Carboxyfluorescein succinimidyl ester (CFSE) test. We detected a reduction in total, naive, memory B cells and plasmablasts, and also total, naive, central memory and regulatory CD4⁺ T cells, besides naive CD8⁺ T cells. There were an increase in CD21^low and transitional B cells, effector memory (EM) and terminally differentiated effector memory (T_EMRA ) CD4⁺ T cell subsets as well as total, EM, T_EMRA , activated and cytotoxic CD8⁺ T cells among non-monogenic CVID patients. CD4⁺ T cells proliferation response was reduced regarding both division index and percent divided. In conclusion, regarding the similarity of lymphocyte abnormalities between patients without genetic defects and those with monogenic defects, genetic mutations are not responsible for these specific lymphocyte changes. However, the novel correlations observed between lymphocyte alterations among genetically unsolved CVID patients may serve as a guide to predict the potential of future CVID development for hypogammaglobulinemia children.

[Cryoglobulinemic vasculitis]

Cryoglobulinemic vasculitis (CV) is a rare immune complex disease of small vessels (capillaries, venules or arterioles) with detection of cryoglobulins (CG). These are serum proteins that precipitate at temperatures below the normal body temperature. The laboratory diagnostics are logistically challenging because the temperature of the blood sample must be maintained continuously at 37 °C until arrival in the laboratory to prevent early precipitation of the proteins with adsorption to corpuscular blood components. Cryoglobulins can be divided into three classes (types I-III), with each class associated with specific underlying diseases and symptom complexes. Cryoglobulinemia can be caused by hematological, virological or autoimmune diseases and mixed forms also occur. The most common cause to date is a hepatitis C infection. Treatment of the underlying disease is obligatory, with antiviral treatment of hepatitis C offering the rare possibility of causal treatment. Depending on the severity of cryoglobulinemia, immunosuppressive therapy is indicated to prevent permanent damage caused by the inflammation.

Skewed peripheral B- and T-cell compartments in patients with ANCA-associated vasculitis

OBJECTIVES

To characterize lymphocytes dysregulation in patients with granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA).

METHODS

Using flow cytometry, we analysed B- and T-cell subsets in peripheral blood from 37 untreated patients with active disease (29 GPA and 8 MPA) and 22 healthy controls (HCs).

RESULTS

GPA patients had increased Th2 (1.8 vs 1.0%, P = 0.02), Th9 (1.1 vs 0.2%, P = 0.0007) and Th17 (1.4 vs 0.9%, P = 0.03) cells compared with HC. Patients with MPO-ANCAs had significantly more CD21- B cells than HC or PR3-ANCA patients (6.9 vs 3.3% and 4.4%, P = 0.01). CD69 expressing B cells were significantly higher in GPA and MPA (3.0 and 5.9 vs 1.4%, P = 0.02 and P = 0.03, respectively) compared with HC, whereas B-cell activating factor-receptor expression was decreased in GPA and MPA (median fluorescence intensity ratio 11.8 and 13.7 vs 45.1 in HC, P < 0.0001 and P = 0.003, respectively). Finally, IL-6-producing B cells were increased in GPA vs HC (25.8 vs 14.9%, P < 0.0001) and decreased in MPA vs HC (4.6 vs 14.9%, P = 0.005), whereas TNF-α-producing B cells were lower in both GPA and MPA patients compared with controls (15 and 8.4 vs 30%, P = 0.01 and P = 0.006, respectively).

CONCLUSION

Skewed T-cell polarization towards Th2, Th9 and Th17 responses characterizes GPA, whereas B-cell populations are dysregulated in both GPA and MPA with an activated phenotype and a decreased B-cell activating factor-receptor expression. Finally, inflammatory B cells producing IL-6 are dramatically increased in GPA, providing an additional mechanism by which rituximab could be effective.

Marginal zone B cells: From housekeeping function to autoimmunity?

Marginal zone (MZ) B cells comprise a subset of innate-like B cells found predominantly in the spleen, but also in lymph nodes and blood. Their principal functions are participation in quick responses to blood-borne pathogens and secretion of natural antibodies. The latter is important for housekeeping functions such as clearance of apoptotic cell debris. MZ B cells have B cell receptors with low poly-/self-reactivity, but they are not pathogenic at steady state. However, if simultaneously stimulated with self-antigen and pathogen- and/or damage-associated molecular patterns (PAMPs/DAMPs), MZ B cells may participate in the initial steps towards breakage of immunological tolerance. This review summarizes what is known about the role of MZ B cells in autoimmunity, both in mouse models and human disease. We cover factors important for shaping the MZ B cell compartment, how the functional properties of MZ B cells may contribute to breaking tolerance, and how MZ B cells are being regulated.

Naive- and Memory-like CD21low B Cell Subsets Share Core Phenotypic and Signaling Characteristics in Systemic Autoimmune Disorders

An expansion of CD21^low B cells has been described in a variety of diseases associated with persistent immune stimulation as in chronic infection, immunodeficiency, or autoimmunity. Different developmental stages of CD21^low B cells have been highlighted in specific diseases; however, a systematic comparison of distribution, phenotype, and signaling capacity of these populations has not yet been performed to delineate the pivotal character of this unusual B cell population. Screening of more than 200 patients with autoimmune disease demonstrated that the prevalence of patients with expanded CD21^low B cells varies between diseases. The expansion was frequent in patients with systemic lupus erythematosus, in which it correlated to relative B cell lymphopenia and duration of disease. Different proportions of distinct developmental stages of CD21^low B cells co-occur in nearly all patients with autoimmune disease. Although in most patients, naive-like and CD27^- switched memory B cells were the most prominent CD21^low subpopulations, there was no detectable association of the pattern with the underlying disease. Despite their distinct developmental stage, all CD21^low B cells share a common core phenotype including the increased expression of inhibitory receptors, associated with an elevated constitutive phosphorylation of proximal signaling molecules downstream of the BCR but impaired Ca²⁺ mobilization and NF-κB activation after BCR stimulation. Further, this was accompanied by impaired upregulation of CD69, although CD86 upregulation was preserved. Beyond maturation-associated differences, the common core characteristics of all CD21^low B cell populations suggests either a common ancestry or a shared sustained imprint by the environment they originated in.

E3 Ubiquitin Ligases as Immunotherapeutic Target in Atherosclerotic Cardiovascular Disease

Chronic low-grade inflammation drives atherosclerosis and despite optimal pharmacological treatment of classical cardiovascular risk factors, one third of the patients with atherosclerotic cardiovascular disease has elevated inflammatory biomarkers. Additional anti-inflammatory strategies to target this residual inflammatory cardiovascular risk are therefore required. T-cells are a dominant cell type in human atherosclerotic lesions. Modulation of T-cell activation is therefore a potential strategy to target inflammation in atherosclerosis. Ubiquitination is an important regulatory mechanism of T-cell activation and several E3 ubiquitin ligases, including casitas B-lineage lymphoma proto-oncogene B (Cbl-B), itchy homolog (Itch), and gene related to anergy in lymphocytes (GRAIL), function as a natural brake on T-cell activation. In this review we discuss recent insights on the role of Cbl-B, Itch, and GRAIL in atherosclerosis and explore the therapeutic potential of these E3 ubiquitin ligases in cardiovascular medicine.

CD21low B cells in systemic sclerosis: A possible marker of vascular complications

OBJECTIVES

To evaluate expansion of CD21^low B cells and their role in B cell homeostasis, apoptosis, clinical manifestations and serum vascular endothelial growth factor (VEGF) in systemic sclerosis (SSc).

MATERIALS AND METHODS

B-cells subpopulations and apoptosis have been assessed in 74 SSc patients and 20 healthy donors. Renal Doppler ultrasound, echocardiography, pulmonary function test and VEGF were performed.

RESULTS

SSc patients with expanded CD21^low B cells (SSc-CD21^low) show a distinct B cell profile with increased memory B cells compared to patients without CD21^low B cells (SSc-CD21⁺). Renal resistive index, systolic pulmonary arterial pressure and FVC/DLCO ratio were significantly higher in SSc-CD21^low group than SSc-CD21⁺, DLCO was lower in SSc-CD21^low group than SSc-CD21⁺. We found a positive linear correlation between CD21^low and sPAP, RI and FVC/DLCO ratio whereas a negative correlation was observed between CD21^low and DLCO and VEGF levels.

CONCLUSIONS

CD21^low B cells are increased in SSc patients with visceral vascular manifestations.

TLR9 signalling in HCV-associated atypical memory B cells triggers Th1 and rheumatoid factor autoantibody responses

BACKGROUND & AIMS

Hepatitis C virus (HCV) infection contributes to the development of autoimmune disorders such as cryoglobulinaemia vasculitis (CV). However, it remains unclear why only some individuals with HCV develop HCV-associated CV (HCV-CV). HCV-CV is characterized by the expansion of anergic CD19⁺CD27⁺CD21^low/- atypical memory B cells (AtMs). Herein, we report the mechanisms by which AtMs participate in HCV-associated autoimmunity.

METHODS

The phenotype and function of peripheral AtMs were studied by multicolour flow cytometry and co-culture assays with effector T cells and regulatory T cells in 20 patients with HCV-CV, 10 chronicallyHCV-infected patients without CV and 8 healthy donors. We performed gene expression profile analysis of AtMs stimulated or not by TLR9. Immunoglobulin gene repertoire and antibody reactivity profiles of AtM-expressing IgM antibodies were analysed following single B cell FACS sorting and expression-cloning of monoclonal antibodies.

RESULTS

The Tbet⁺CD11c⁺CD27⁺CD21^- AtM population is expanded in patients with HCV-CV compared to HCV controls without CV. TLR9 activation of AtMs induces a specific transcriptional signature centred on TNFα overexpression, and an enhanced secretion of TNFα and rheumatoid factor-type IgMs in patients with HCV-CV. AtMs stimulated through TLR9 promote type 1 effector T cell activation and reduce the proliferation of CD4⁺CD25^hiCD127^-/lowFoxP3⁺ regulatory T cells. AtM expansions display intraclonal diversity with immunoglobulin features of antigen-driven maturation. AtM-derived IgM monoclonal antibodies do not react against ubiquitous autoantigens or HCV antigens including NS3 and E2 proteins. Rather, AtM-derived antibodies possess rheumatoid factor activity and target unique epitopes on the human IgG-Fc region.

CONCLUSION

Our data strongly suggest a central role for TLR9 activation of AtMs in driving HCV-CV autoimmunity through rheumatoid factor production and type 1 T cell responses.

LAY SUMMARY

B cells are best known for their capacity to produce antibodies, which often play a deleterious role in the development of autoimmune diseases. During chronic hepatitis C, self-reactive B cells proliferate and can be responsible for autoimmune symptoms (arthritis, purpura, neuropathy, renal disease) and/or lymphoma. Direct-acting antiviral therapy clears the hepatitis C virus and eliminates deleterious B cells.

Autoimmune complications of cancer immunotherapy

Immunotherapy of cancer with blockade of inhibitory immune checkpoints and adoptive cell therapies have led to impressive clinical responses in several cancers. However, with increasing utilization of these therapies, immune-related adverse events have emerged as a major obstacle. Herein I discuss recent insights into the immunobiology of these toxicities. Deeper understanding of the underlying pathogenic mechanisms, cellular and molecular pathways involved, similarities and differences with spontaneous autoimmunity, and identification of clinically relevant predictive biomarkers is needed to develop optimal approaches to prevent and treat these toxicities, without compromising the therapeutic benefit from these immune therapies. These events may also provide a unique window into mechanisms underlying spontaneous autoimmunity.

New insights in cryoglobulinemic vasculitis

Cryoglobulins are antibodies that precipitate at low temperatures and dissolve after rewarming. Cryoglobulinemia refers to the presence of circulating cryoglobulins and generally leads to a systemic inflammatory syndrome characterized by fatigue, arthralgia, purpura, ulcers, neuropathy and/or glomerulonephritis. The disease mainly involves small to medium-sized blood vessels and causes vasculitis due to cryoglobulin-containing immune complexes. Cryoglobulinemia is classified into three types (I, II and III) on the basis of immunoglobulin composition. Predisposing conditions include lymphoproliferative, autoimmune diseases and hepatitis C virus infection. The diagnosis of cryoglobulinemic syndrome is predominantly based on the presence of clinical features and laboratorial demonstration of serum cryoglobulins. The treatment strategy depends on the cause of cryoglobulinemia. For patients with chronic HCV infection, antiviral therapy is indicated. Immunosuppressive or immunomodulatory therapy, including steroids, plasmapheresis and cytotoxic agents, is reserved for organ-threatening manifestations. In this review, we discuss the main clinical presentations, diagnostic approach and treatment options.

Skewed Lymphocyte Subpopulations and Associated Phenotypes in Patients with Mastocytosis

BACKGROUND

Mastocytosis is a clonal mast cell disorder associated with elevated mast cell mediators, which themselves have been reported to affect lymphocyte function. However, the impact of an expanded mast cell compartment on lymphocyte subpopulations, and their correlation with clinical phenotypes in patients with indolent systemic mastocytosis (ISM), has not been explored.

OBJECTIVE

To examine the immunophenotype of circulating lymphocytes in patients with ISM compared with healthy adult controls and examine relationships with aspects of clinical disease.

METHODS

We examined lymphocyte subsets in 20 adult patients with ISM and 40 healthy adult volunteers by multiparameter flow cytometry. Results were correlated with clinical characteristics.

RESULTS

Patients with ISM exhibited a significantly lower median frequency and absolute cell count of both circulating CD8⁺ T cells and natural killer cells accompanying a significantly increased ratio of CD4⁺/CD8⁺ T cells when compared with healthy volunteers. Stratification of our ISM patient cohort according to clinical manifestations revealed that CD19⁺CD21^lowCD38^low B cells were significantly higher in patients with a history of autoimmune disease and counts of terminally differentiated CD4⁺ T cells were significantly higher in patients with osteoporosis or osteopenia.

CONCLUSIONS

Several circulating lymphocyte subpopulations in patients with ISM were significantly different when compared with healthy controls; in specific lymphocyte subsets, this lymphocyte skewing correlated with clinical observations including osteoporosis and autoimmune disease. These data suggest the need for further studies on abnormalities in lymphocyte subsets and the attendant clinical consequences in both mast cell proliferative and activation disorders.

Widespread B cell perturbations in HIV-1 infection afflict naive and marginal zone B cells

Liechti et al. demonstrate severe B cell perturbations in HIV-1 infection beyond described effects on memory B cells. Naive and marginal zone B cells down-regulate CD21 and display chemokine receptor and activation marker signatures associated with inflammation and diminished response to stimulation.

Perturbations in B cells are a hallmark of HIV-1 infection. This is signified by increased numbers of exhausted CD21^neg memory B cells, driven by continuous antigen-specific and bystander activation. Using high-dimensional flow cytometry, we demonstrate that this exhausted phenotype is also prevalent among peripheral antigen-inexperienced naive and marginal zone (MZ) B cells in acute and chronic HIV-1 infection. A substantial fraction of naive and MZ B cells exhibit down-regulated CD21 levels and diminished response to B cell receptor (BCR)–dependent stimulation. Compared with CD21^pos subsets, the CD21^neg naive and MZ B cells differ in the expression of chemokine receptors and activation markers. Effective antiretroviral treatment normalizes peripheral naive and MZ B cell populations. Our results emphasize a more widely spread impairment of B cells in HIV-1 infection than previously appreciated, including antigen-inexperienced cells. This highlights the importance of monitoring functional capacities of naive B cells in HIV-1 infection, as exhausted CD21^neg naive B cells may severely impair induction of novel B cell responses.

CD21-/low B cells associate with joint damage in rheumatoid arthritis patients

Depletion of B cells is beneficial in rheumatoid arthritis (RA) patients with autoantibodies to citrullinated proteins (ACPA) and/or the Fc portion of immunoglobulins (rheumatoid factor [RF]), suggesting a role for B cells in disease pathogenesis. To date, however, the identity of specifically pathogenic B cell subsets has not been discovered. One candidate population is identified by the low expression or absence of complement receptor 2 (CD21^-/low B cells). In this study, we sought to determine whether there was any correlation between CD21^-/low B cells and clinical outcome in patients with established RA, either ACPA⁺ /RF⁺ (n = 27) or ACPA^- /RF^- (n = 10). Healthy donors (n = 17) were included as controls. The proportion of the CD21^-/low CD27^- IgD^- memory B cell subset in peripheral blood (PB) was significantly increased in ACPA⁺ /RF⁺ RA patients compared with healthy donors, and the frequency of this subset correlated with joint destruction (r = 0.57, P < 0.04). The levels of the chemokines CXCL-9 and CXCL-10 were higher in synovial fluid than in plasma, and PB CD21^-/low cells expressed the receptor, CXCR3. In synovial fluid, most of the B cells were CD21^-/low , approximately 40% of that population was CD27^- IgD^- , and a third of those expressed the pro-osteoclastogenic factor receptor activator of the nuclear factor κB ligand (RANKL). This subset also secreted RANKL, in addition to other factors such as IL-6, even in the absence of stimulation. We interpret these data as reason to propose the hypothesis that the CD27^- IgD^- subset of CD21^-/low B cells may mediate joint destruction in patients with ACPA⁺ /RF⁺ RA.

B cell profiling in malaria reveals expansion and remodelling of CD11c+ B cell subsets

Humoral immunity is important in limiting clinical disease in malaria, yet the longitudinal B cell response to infection remains unclear. We performed a 1-year prospective study in patients treated for acute P. falciparum malaria for the first time, or with previous exposure to the disease. Using an unbiased exploratory approach with mass cytometry, followed by targeted flow cytometry, we found that ~80% of mature B cells that proliferated in response to acute infection expressed CD11c. Only ~40% of CD11c+ B cells displayed an atypical B cell phenotype, with the remaining cells primarily made up of activated- and resting memory B cells. The CD11c+ B cells expanded rapidly following infection, with previous exposure to malaria resulting in a significantly larger increase compared to individuals with primary infection. This was attributed to an expansion of switched CD11c+ B cells that was absent in primary infected individuals. The rate of contraction of the CD11c+ B cell compartment was independent of previous exposure to malaria and displayed a slow decay with a half-life of ~300 days. Collectively, these results identify CD11c as a marker of B cells responding to malaria and further highlight differences in primary- and secondary B cell responses during infection.

Long-lasting persistence of large B-cell clones in hepatitis C virus-cured patients with complete response of mixed cryoglobulinaemia vasculitis

BACKGROUND & AIMS

Hepatitis C virus (HCV)-related mixed cryoglobulinaemia vasculitis (MCV) is characterized by the expansion of rheumatoid factor-producing B-cell clones. The aim of this study was to assess whether B-cell clones may persist in these patients after the clearance of the virus with antiviral therapy, and whether their persistence influences clinical outcomes.

METHODS

Forty-five HCV-cured MCV patients were followed up for a median of 18.5 (range 9-38) months after the clearance of HCV. Circulating B-cell clones were detected using flow cytometry either by the skewing of kappa/lambda ratio or by the expression of a V_H 1-69-encoded idiotype.

RESULTS

The clinical response of vasculitis was 78% complete, 18% partial and 4% null. However, cryoglobulins remained detectable in 42% of patients for more than 12 months. Circulating B-cell clones were detected in 18 of 45 patients, and in 17 of them persisted through the follow-up; nine of the latter patients cleared cryoglobulins and had complete response of vasculitis. Several months later, two of these patients had relapse of MCV.

CONCLUSIONS

B-cell clones persist in MCV patients long after HCV infection has been cleared but halt the production of pathogenic antibody. These 'dormant' cells may be reactivated by events that perturb B-cell homeostasis and can give rise to the relapse of cryoglobulinaemic vasculitis.

Considering hepatitis C virus infection as a systemic disease

Hepatitis C virus (HCV) infection has been demonstrated to result in several adverse hepatic outcomes and has been associated with a number of important extrahepatic manifestations. The scope of extrahepatic clinical possibilities includes systemic diseases such as vasculitis and lymphoproliferative disorders, cardiovascular disease, myalgia, arthritis, and sicca syndrome. These end-organ effects of HCV may dominate the clinical course beyond the hepatic complications and significantly worsen the long-term prognosis of infected patients. Until several years ago, the standard of care for the treatment of HCV infection had been interferon-alpha-based regimens, which not only had limited effectiveness in achieving a cure but were often poorly tolerated, especially in patients with kidney disease. In those HCV-infected patients with significant systemic manifestations, the interferon-based regimens were problematic given their association with a wide variety of toxicities. The development of highly effective direct-acting antiviral agents to treat HCV infection presented an opportunity to improve the HCV care cascade with the eradication of HCV in most infected patients and by reducing the burden of both hepatic and extrahepatic complications.

Update on Fc receptor-like (FCRL) family: new immunoregulatory players in health and diseases

INTRODUCTION

Fc receptor-like (FCRL) molecules, as recently identified members of the immunoglobulin superfamily (IgSF), are preferentially expressed by B-cells. They have variable number of extracellular immunoglobulin-like domains and cytoplasmic activating ITAMs and/or inhibitory ITIMs. FCRL1-5 are dominantly expressed in different stages of B-cells development. But, FCRL6 is preferentially expressed in different subsets of T-cells and NK cells. FCRL1-5 could regulate different features of B-cell evolution such as development, differentiation, activation, antibody secretion and isotype switching. Areas covered: Improved understanding of FCRL expression may grant B-cells and finally its signaling pathways, alone or in cooperation with other signaling molecules, as interesting new targets for diagnostic, monitoring and immunotherapeutic modalities; although further investigations remain to be defined. Recent investigations on different family members of FCRL proteins have substantiated their differential expression on different tissues, malignancies, immune related disease and infectious diseases. Expert opinion: FCRLs restricted expressions in normal B-cells and T-cell subsets accompanied with their overexpression in B-cell malignancies introduce them as logical candidates for the development of antibody- and cell-based immunotherapy approaches in B-cell malignancies, immune-mediated and infectious diseases. FCRLs would be applied as attractive and specific targets for immunodiagnostic approaches, clinical prognosis as well as disease monitoring of relevant patients.

Innate and Adaptive Immune Responses in Chronic HCV Infection

Hepatitis C virus (HCV) remains a public health problem of global importance, even in the era of potent directly-acting antiviral drugs. In this chapter, I discuss immune responses to acute and chronic HCV infection. The outcome of HCV infection is influenced by viral strategies that limit or delay the initiation of innate antiviral responses. This delay may enable HCV to establish widespread infection long before the host mounts effective T and B cell responses. HCV's genetic agility, resulting from its high rate of replication and its error prone replication mechanism, enables it to evade immune recognition. Adaptive immune responses fail to keep up with changing viral epitopes. Neutralizing antibody epitopes may be hidden by decoy structures, glycans, and lipoproteins. T cell responses fail due to changing epitope sequences and due to exhaustion, a phenomenon that may have evolved to limit immune-mediated pathology. Despite these difficulties, innate and adaptive immune mechanisms do impact HCV replication. Immune-mediated clearance of infection is possible, occurring in 20-50% of people who contract the disease. New developments raise hopes for effective immunological interventions to prevent or treat HCV infection.

DEC1/STRA13 is a key negative regulator of activation-induced proliferation of human B cells highly expressed in anergic cells

The transcription factor DEC1/STRA13 (also known as BHLHE40 and SHARP2) is involved in a number of processes including inhibition of cell proliferation and delay of cell cycle, and is a negative regulator of B cell activation and development in mice. We show here that, unlike in mice, DEC1/STRA13 expression is induced in human naïve and memory resting B cells by activation through the B-cell receptor (BCR) or Toll-like receptor 9 (TLR9). siRNA silencing of DEC1/STRA13 increases the capacity of activated B cells to perform a high number of divisions after TLR9 ligation. This identifies DEC1/STRA13 as a critical negative regulator of clonal expansion of activated human B cells. We also show that DEC1/STRA13 is upregulated in human anergic CD21^low B cells clonally expanded in patients with HCV-associated mixed cryoglobulinemia, which fail to proliferate in response to BCR or TLR9 ligation. siRNA knockdown of DEC1/STRA13, however, fails to restore responsiveness to stimuli in these cells, although it might improve the proliferative capacity in a subset of anergic cells with less pronounced proliferative defect.

Tailoring Immune Responses toward Autoimmunity: Transcriptional Regulators That Drive the Creation and Collusion of Autoreactive Lymphocytes

T-dependent humoral immune responses to infection involve a collaboration between B and CD4 T cell activation, migration, and co-stimulation, thereby culminating in the formation of germinal centers (GCs) and eventual differentiation into memory cells and long-lived plasma cells (PCs). CD4 T cell-derived signals drive the formation of a tailored B cell response. Downstream of these signals are transcriptional regulators that are the critical enactors of immune cell programs. In particular, a core group of transcription factors regulate both B and T cell differentiation, identity, and function. The timing and expression levels of these transcription factors are tightly controlled, with dysregulated expression correlated to immune cell dysfunction in autoimmunity and lymphomagenesis. Recent studies have significantly advanced our understanding of both extrinsic and intrinsic regulators of autoreactive B cells and antibody-secreting PCs in systemic lupus erythematosus, rheumatoid arthritis, and other autoimmune conditions. Yet, there are still gaps in our understanding of the causative role these regulators play, as well as the link between lymphoid responses and peripheral damage. This review will focus on the genesis of immunopathogenic CD4 helper and GC B cells. In particular, we will detail the transcriptional regulation of cytokine and chemokine receptor signaling during the pathogenesis of GC-derived autoimmune conditions in both murine models and human patients.

Evidence for B Cell Exhaustion in Chronic Graft-versus-Host Disease

Chronic graft-versus-host disease (cGvHD) remains a major complication of allogeneic hematopoietic stem cell transplantation (HSCT). A number of studies support a role for B cells in the pathogenesis of cGvHD. In this study, we report the presence of an expanded population of CD19+CD21- B cells with features of exhaustion in the peripheral blood of patients with cGvHD. CD21- B cells were significantly increased in patients with active cGvHD compared to patients without cGvHD and healthy controls (median 12.2 versus 2.12 versus 3%, respectively; p < 0.01). Compared with naïve (CD27-CD21+) and classical memory (CD27+CD21+) B cells, CD19+CD21- B cells in cGvHD were CD10 negative, CD27 negative and CD20hi, and exhibited features of exhaustion, including increased expression of multiple inhibitory receptors such as FCRL4, CD22, CD85J, and altered expression of chemokine and adhesion molecules such as CD11c, CXCR3, CCR7, and CD62L. Moreover, CD21- B cells in cGvHD patients were functionally exhausted and displayed poor proliferative response and calcium mobilization in response to B-cell receptor triggering and CD40 ligation. Finally, the frequencies of circulating CD21- B cells correlated with cGvHD severity in patients after HSCT. Our study further characterizes B cells in chronic cGVHD and supports the use of CD21-CD27-CD10- B cell frequencies as a biomarker of disease severity.

Dysregulation of Innate Lymphoid Cells in Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is the most prevalent symptomatic primary immune deficiency. With widespread use of immunoglobulin replacement therapy, non-infectious complications, such as autoimmunity, chronic intestinal inflammation, and lung disease, have replaced infections as the major cause of morbidity and mortality in this immune deficiency. The pathogenic mechanisms that underlie the development of these complications in CVID are not known; however, there have been numerous associated laboratory findings. Among the most intriguing of these associations is elevation of interferon signature genes in CVID patients with inflammatory/autoimmune complications, as a similar gene expression profile is found in systemic lupus erythematosus and other chronic inflammatory diseases. Linked with this heightened interferon signature in CVID is an expansion of circulating IFN-γ-producing innate lymphoid cells. Innate lymphoid cells are key regulators of both protective and pathogenic immune responses that have been extensively studied in recent years. Further exploration of innate lymphoid cell biology in CVID may uncover key mechanisms underlying the development of inflammatory complications in these patients and may inspire much needed novel therapeutic approaches.

From the pathogenesis to the cure of indolent B-cell lymphoproliferative disorders associated with hepatitis C virus infection: which role for direct-acting antivirals?

INTRODUCTION

Hepatitis C virus (HCV) causes monoclonal B cell lymphoproliferative disorders ranging from benign, such as in mixed cryoglobulinemia (MC), to indolent or aggressive lymphomas. MC and indolent lymphomas commonly regress when HCV is eradicated with interferon (IFN) therapy; however, sustained virologic response (SVR) to IFN is achieved only in ~50% of patients. The new all oral direct-acting antivirals (DAA), yielding nearly 100% SVR, promise a breakthrough in the treatment of HCV-associated lymphoproliferative disorders, but experience is still scanty. Areas covered: A literature search was performed to summarize current pathogenetic hypotheses in HCV-associated indolent lymphoproliferative disorders and to identify clinical trials focused on the use of antiviral therapy. Hematological outcomes of IFN-based and IFN-free DAA-based regimens were compared. Expert commentary: While MC appears to regress in most patients after DAA therapy, the still very limited experience with indolent lymphomas suggests that hematologic responses might be less than those observed with IFN. Furthermore, anecdotal observations of early progression to aggressive lymphoma after DAA are disquieting. Large studies are needed to determine the values and limits of DAA for treating HCV-associated indolent lymphomas and to identify subgroups at risk of non-response.

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.

Reversion of anergy signatures in clonal CD21low B cells of mixed cryoglobulinemia after clearance of HCV viremia

Anergic features of B cells of MC rapidly reverse after eradication of HCV with DAAs. Phenotypic and functional features of virus-specific B-cell exhaustion persist for several months after HCV eradication.

Direct-Acting Antiviral Therapy Restores Immune Tolerance to Patients With Hepatitis C Virus-Induced Cryoglobulinemia Vasculitis

BACKGROUND & AIMS

Interferon-free direct-acting antiviral (DAA) therapies are effective in patients with hepatitis C virus-induced cryoglobulinemia vasculitis (HCV-CV). We analyzed blood samples from patients with HCV-CV before and after DAA therapy to determine mechanisms of these drugs and their effects on cellular immunity.

METHODS

We performed a prospective study of 27 consecutive patients with HCV-CV (median age, 59 y) treated with DAA therapy (21 patients received sofosbuvir plus ribavirin for 24 weeks, 4 patients received sofosbuvir plus daclatasvir for 12 weeks, and 2 patients received sofosbuvir plus simeprevir for 12 weeks) in Paris, France. Blood samples were collected from these patients before and after DAA therapy, and also from 12 healthy donors and 12 individuals with HCV infection without CV. HCV load, cryoglobulins, and cytokines were quantified by flow cytometry, cytokine multiplex assays, and enzyme-linked immunosorbent assay.

RESULTS

Twenty-four patients (88.9%) had a complete clinical response of CV to DAA therapy at week 24, defined by improvement of all the affected organs and the absence of relapse. Compared with healthy donors and patients with HCV infection without CV, patients with HCV-CV, before DAA therapy, had a lower percentage of CD4+CD25hiFoxP3+ regulatory T cells (P < .01), but higher proportions of IgM+CD21-/low memory B cells (P < .05), CD4+IFNγ+ cells (P < .01), CD4+IL17A+ cells (P < .01), and CD4+CXCR5+interleukin 21+ follicular T-helper (Tfh) cells (P < .01). In patients with HCV-CV, there was a negative correlation between numbers of IgM+CD21-/low memory B cells and T-regulatory cells (P = .03), and positive correlations with numbers of Tfh cells (P = .03) and serum levels of cryoglobulin (P = .01). DAA therapy increased patients' numbers of T-regulatory cells (1.5% ± 0.18% before therapy vs 2.1% ± 0.18% after therapy), decreased percentages of IgM+CD21-/low memory B cells (35.7% ± 6.1% before therapy vs 14.9% ± 3.8% after therapy), and decreased numbers of Tfh cells (12% ± 1.3% before therapy vs 8% ± 0.9% after therapy). Expression levels of B lymphocyte stimulator receptor 3 and programmed cell death 1 on B cells increased in patients with HCV-CV after DAA-based therapy (mean fluorescence units, 37 ± 2.4 before therapy vs 47 ± 2.6 after therapy, P < .01; and 29 ± 7.3 before therapy vs 48 ± 9.3 after therapy, P < .05, respectively).

CONCLUSIONS

In a prospective clinical trial of patients with HCV-CV, DAA-based therapy restored disturbances in peripheral B- and T-cell homeostasis.

The TH1 phenotype of follicular helper T cells indicates an IFN-γ-associated immune dysregulation in patients with CD21low common variable immunodeficiency

BACKGROUND

A subgroup of patients with common variable immunodeficiency (CVID) experience immune dysregulation manifesting as autoimmunity, lymphoproliferation, and organ inflammation and thereby increasing morbidity and mortality. Therefore treatment of these complications demands a deeper comprehension of their cause and pathophysiology.

OBJECTIVES

On the basis of the identification of an interferon signature in patients with CVID with secondary complications and a skewed follicular helper T-cell differentiation in defined monogenic immunodeficiencies, we sought to determine the profile of CD4 memory T cells in blood and secondary lymphatic tissues of these patients.

METHODS

We quantified T_H1/T_H2/T_H17 CD4 memory T cells in blood and lymph nodes of patients with CVID using flow cytometry, analyzed their function, and correlated all findings to the burden of immune dysregulation.

RESULTS

Patients with CVID with immune dysregulation had a skewed memory CD4 T-cell differentiation toward a CXCR3⁺CCR6^- T_H1 phenotype both in blood and lymph nodes. Consistent with our phenotypic findings, we observed a higher IFN-γ production in peripheral CD4 memory T cells and lymph node-derived follicular helper T cells of patients with CVID compared with those of healthy control subjects. Increased IFN-γ production was accompanied by a poor germinal center output, an accumulation of T-box transcription factor (T-bet)⁺ B cells in lymph nodes, and an accumulation of T-bet⁺CD21^low B cells in peripheral blood of affected patients.

CONCLUSION

Identification of excessive IFN-γ production by blood and lymph node-derived T cells of patients with CVID with immune dysregulation will offer new therapeutic avenues for this subgroup. CD21^low B cells might serve as a marker of this IFN-γ-associated dysregulation.

High SYK Expression Drives Constitutive Activation of CD21low B Cells

Human CD21^low B cells present with an activated phenotype and accumulate in distinct disorders connected with chronic immune stimulation. Signaling studies had revealed an increased basal phosphorylation of spleen tyrosine kinase (SYK) and phospholipase Cγ2. Additional BCR stimulation of these constitutively active cells, however, led to reduced activation of these signaling molecules and subsequently NF-κB and Ca²⁺ activation. In this article, we demonstrate that high SYK expression is a common feature of CD21^low B cells independent of the underlying disorder, and that this high expression is sufficient to drive constitutive phosphorylation of SYK and its immediate targets Bruton's tyrosine kinase and phospholipase Cγ2. Inhibition of SYK activity eliminated features of the constitutive activation in these cells and partly restored BCR signaling. High SYK expression is especially induced by CpG or CD40L in combination with IL-21, but not BCR stimulation, suggesting the importance of the immune-stimulatory context for the induction of this B cell phenotype. In summary, high SYK expression is a common feature of human CD21^low B cells and presumably results from chronic activation in inflammatory environments present in a subgroup of patients with heterogeneous disorders like chronic infection, autoimmunity, and immunodeficiency. High SYK expression by itself drives the constitutive activation observed in these B cells, which in turn may contribute to the hyporesponsiveness upon BCR stimulation. Given the high prevalence of autoreactive clones among CD21^low B cells in autoimmune disorders, the dominant role of SYK in CD21^low B cells may provide a new option for therapeutic interventions in patients with expanded CD21^low B cells and humoral autoimmunity.

An antigen to remember: regulation of B cell memory in health and disease

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IgM⁺ MBCs are early responders in malaria and may be vital in parasite clearance.

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MBC heterogeneity may be expanded to tackle varying antigen in chronic infection.

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Atypical MBCs, CD21^neg and T-bet⁺CD11c⁺ B cells may share transcriptional programs.

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In vivo studies will allow insight into intrinsic and extrinsic regulators of MBCs.

Vaccine success relies on the formation of immunity. Humoral immunity is critical and is mediated by long-lived antibody-secreting cells and memory B cells (MBCs). Chronic infectious diseases cause a significant global burden of disease; pathogens that evade the immune system can cause phenotypical and functional changes to immune memory populations. Thus, recent studies have focused on MBC subset function. IgM⁺ MBCs have emerged as important early responders in malaria. Atypical MBCs have functional qualities associated with exhaustion in chronic infectious diseases, but the requirements for their formation and where they localize remains unknown. Similarly, the T-bet-driven transcriptional program drives formation of MBCs phenotypically similar to atypical MBCs. Identifying protective or detrimental roles of MBC subsets, and their regulators, will be important for clinical intervention.