A new memory CD27-IgG+ B cell population in peripheral blood expressing VH genes with low frequency of somatic mutation

Generation of circulating autoreactive pre-plasma cells fueled by naive B cells in celiac disease

Autoantibodies against the enzyme transglutaminase 2 (TG2) are characteristic of celiac disease (CeD), and TG2-specific immunoglobulin (Ig) A plasma cells are abundant in gut biopsies of patients. Here, we describe the corresponding population of autoreactive B cells in blood. Circulating TG2-specific IgA cells are present in untreated patients on a gluten-containing diet but not in controls. They are clonally related to TG2-specific small intestinal plasma cells, and they express gut-homing molecules, indicating that they are plasma cell precursors. Unlike other IgA-switched cells, the TG2-specific cells are negative for CD27, placing them in the double-negative (IgD-CD27-) category. They have a plasmablast or activated memory B cell phenotype, and they harbor fewer variable region mutations than other IgA cells. Based on their similarity to naive B cells, we propose that autoreactive IgA cells in CeD are generated mainly through chronic recruitment of naive B cells via an extrafollicular response involving gluten-specific CD4+ T cells.

B cell development and antibody responses in human immune system mice: current status and future perspective

Humanized immune system (HIS) mice have been developed and used as a small surrogate model to study human immune function under normal or disease conditions. Although variations are found between models, most HIS mice show robust human T cell responses. However, there has been unsuccessful in constructing HIS mice that produce high-affinity human antibodies, primarily due to defects in terminal B cell differentiation, antibody affinity maturation, and development of primary follicles and germinal centers. In this review, we elaborate on the current knowledge about and previous attempts to improve human B cell development in HIS mice, and propose a potential strategy for constructing HIS mice with improved humoral immunity by transplantation of human follicular dendritic cells (FDCs) to facilitate the development of secondary follicles.

Mice possess a more limited natural antihuman factor VIII antibody repertoire than humans that is produced disproportionately by marginal zone B cells

BACKGROUND

One-third of patients with severe hemophilia A develop neutralizing antibodies to the factor VIII (FVIII) protein in response to intravenous replacement therapy. Patients may also generate natural, nonneutralizing antibodies to FVIII before FVIII exposure. These patients are at increased risk of developing neutralizing antibodies to FVIII. However, natural anti-FVIII antibodies are also present in healthy human donors.

OBJECTIVES

To further characterize the natural antihuman (h) FVIII antibody repertoire in mice and humans.

METHODS

An in-house ELISA was developed using a purified polyclonal immunoglobulin (Ig) standard to quantify anti-hFVIII Ig in cell culture supernatant or plasma from mice (wild-type and FVIII-/-) and adult human donors.

RESULTS

All naïve wild-type and FVIII-/- mice, as well as healthy human donors, possess natural anti-hFVIII antibodies. Mice only have natural anti-hFVIII IgM, which is present in germ-free mice, suggesting that they are germline encoded. Although murine marginal zone B cells (MZBs) contribute 44% to all circulating natural IgM, they contribute disproportionately to the anti-hFVIII IgM repertoire (82%). This naturally occurring murine MZB-derived IgM is not B-domain specific and is reduced by intravenously administered hFVIII, suggesting that it may form immune complexes immediately upon hFVIII administration. Natural anti-hFVIII antibodies of IgG, IgM, and IgA isotypes can be detected in adult human donors. There were increased levels of B-domain-favoring anti-hFVIII IgG in 14% of healthy donors, which were markedly different from the rest of the "low-titer" population.

CONCLUSIONS

There is a preponderance of natural anti-hFVIII antibodies in both mice and healthy adult human donors.

Human IgM-expressing memory B cells

A hallmark of T cell dependent (TD) humoral immune responses is the generation of long-lived memory B cells. The generation of these cells occurs primarily in the germinal center (GC) reaction, where antigen-activated B cells undergo affinity maturation as a major consequence of the combined processes of proliferation, somatic hypermutation of their immunoglobulin V (IgV) region genes, and selection for improved affinity of their B-cell antigen receptors. As many B cells also undergo class-switching to IgG or IgA in these TD responses, there was traditionally a focus on class-switched memory B cells in both murine and human studies on memory B cells. However, it has become clear that there is also a large subset of IgM-expressing memory B cells, which have important phenotypic and functional similarities but also differences to class-switched memory B cells. There is an ongoing discussion about the origin of distinct subsets of human IgM+ B cells with somatically mutated IgV genes. We argue here that the vast majority of human IgM-expressing B cells with somatically mutated IgV genes in adults is indeed derived from GC reactions, even though a generation of some mostly lowly mutated IgM+ B cells from other differentiation pathways, mainly in early life, may exist.

Exploring Perturbations in Peripheral B Cell Memory Subpopulations Early after Kidney Transplantation Using Unsupervised Machine Learning

BACKGROUND

B cells have a significant role in transplantation. We examined the distribution of memory subpopulations (MBCs) and naïve B cell (NBCs) phenotypes in patients soon after kidney transplantation. Unsupervised machine learning cluster analysis is used to determine the association between the cellular phenotypes and renal function.

METHODS

MBC subpopulations and NBCs from 47 stable renal transplant recipients were characterized by flow cytometry just before (T0) and 6 months after (T6) transplantation. T0 and T6 measurements were compared, and clusters of patients with similar cellular phenotypic profiles at T6 were identified. Two clusters, clusters 1 and 2, were formed, and the glomerular filtration rate was estimated (eGFR) for these clusters.

RESULTS

A significant increase in NBC frequency was observed between T0 and T6, with no statistically significant differences in the MBC subpopulations. Cluster 1 was characterized by a predominance of the NBC phenotype with a lower frequency of MBCs, whereas cluster 2 was characterized by a high frequency of MBCs and a lower frequency of NBCs. With regard to eGFR, cluster 1 showed a higher value compared to cluster 2.

CONCLUSIONS

Transplanted kidney patients can be stratified into clusters based on the combination of heterogeneity of MBC phenotype, NBCs and eGFR using unsupervised machine learning.

Functions of double-negative B cells in autoimmune diseases, infections, and cancers

Most mature B cells can be divided into four subtypes based on the expression of the surface markers IgD and CD27: IgD+ CD27- naïve B cells, IgD+ CD27+ unswitched memory B cells, IgD- CD27+ switched memory B cells, and IgD- CD27- double-negative (DN) B cells. Despite their small population size in normal peripheral blood, DN B cells play integral roles in various diseases. For example, they generate autoimmunity in autoimmune conditions, while these cells may generate both autoimmune and antipathogenic responses in COVID-19, or act in a purely antipathogenic capacity in malaria. Recently, DN B cells have been identified in nasopharyngeal carcinoma and non-small-cell lung cancers, where they may play an immunosuppressive role. The distinct functions that DN B cells play in different diseases suggest that they are a heterogeneous B-cell population. Therefore, further study of the mechanisms underlying the involvement of DN B cells in these diseases is essential for understanding their pathogenesis and the development of therapeutic strategies. Further research is thus warranted to characterize the DN B-cell population in detail.

Investigation of the frequencies of various B cell populations in non-responder healthcare workers in comparison with responders to hepatitis B virus vaccination

BACKGROUND

Hepatitis B is a major global health problem. More than 90% of hepatitis B-vaccinated immunocompetent adults become fully immune. The main purpose of vaccination is immunization. Whether non-responders have a lower percentage of total or antigen-specific memory B cells in comparison with responders is still controversial. We aimed to assess and compare the frequency of various B cell subpopulations in non-responders and responders.

METHODS

Fourteen responders and 14 non-responders of hospital healthcare workers were enrolled in this study. We used flow cytometry to evaluate various CD19+ B cell subpopulations using fluorescent-labeled antibodies against CD19, CD10, CD21, CD27 and IgM and ELISA to evaluate total anti-HBs antibodies.

RESULTS

We found no significant differences in the frequency of various B cell subpopulations between the non-responder and responder groups. Furthermore, the frequency of the isotype-switched memory B cell population was significantly higher in the atypical memory B cell subset compared with the classical memory B cell subset in the responder and total groups (p=0.010 and 0.003, respectively).

CONCLUSIONS

Responders and non-responders to HBsAg vaccine had comparable memory B cell populations. Whether anti-HBs Ab production has a correlation with the level of class switching in B lymphocytes in healthy vaccinated individuals needs further investigation.

Plasma cells are not restricted to the CD27+ phenotype: characterization of CD27-CD43+ antibody-secreting cells

Circulating antibody-secreting cells are present in the peripheral blood of healthy individuals reflecting the continued activity of the humoral immune system. Antibody-secreting cells typically express CD27. Here we describe and characterize a small population of antibody-secreting class switched CD19+CD43+ B cells that lack expression of CD27 in the peripheral blood of healthy subjects. In this study, we characterized CD27-CD43+ cells. We demonstrate that class-switched CD27-CD43+ B cells possess characteristics of conventional plasmablasts as they spontaneously secrete antibodies, are morphologically similar to antibody-secreting cells, show downregulation of B cell differentiation markers, and have a gene expression profile related to conventional plasmablasts. Despite these similarities, we observed differences in IgA and IgG subclass distribution, expression of homing markers, replication history, frequency of somatic hypermutation, immunoglobulin repertoire, gene expression related to Toll-like receptors, cytokines, and cytokine receptors, and antibody response to vaccination. Their frequency is altered in immune-mediated disorders.

Conclusion

we characterized CD27-CD43+ cells as antibody-secreting cells with differences in function and homing potential as compared to conventional CD27+ antibody-secreting cells.

IgD-CD27- double negative (DN) B cells: Origins and functions in health and disease

Human B cells can be divided into four main subsets based on differential expression of immunoglobulin (Ig)D and CD27. IgD^-CD27^- double negative (DN) B cells make up a heterogeneous group of B cells that have first been described in relation to aging and systemic lupus erythematosus but have been mostly disregarded in B cell research. Over the last few years, DN B cells have gained a lot of interest because of their involvement in autoimmune and infectious diseases. DN B cells can be divided into different subsets that originate via different developmental processes and have different functional properties. Further research into the origin and function of different DN subsets is needed to better understand the role of these B cells in normal immune responses and how they could be targeted in specific pathologies. In this review, we give an overview of both phenotypic and functional properties of DN B cells and provide insight into the currently proposed origins of DN B cells. Moreover, their involvement in normal aging and different pathologies is discussed.

B-Cell Responses to Sars-Cov-2 mRNA Vaccines

Most vaccines against viral pathogens protect through the acquisition of immunological memory from long-lived plasma cells that produce antibodies and memory B cells that can rapidly respond upon an encounter with the pathogen or its variants. The COVID-19 pandemic and rapid deployment of effective vaccines have provided an unprecedented opportunity to study the immune response to a new yet rapidly evolving pathogen. Here we review the scientific literature and our efforts to understand antibody and B-cell responses to SARS-CoV-2 vaccines, the effect of SARSCoV-2 infection on both primary and secondary immune responses, and how repeated exposures may impact outcomes.

Distinct and shared B cell responses of tuberculosis patients and their household contacts

This study was aimed at identifying the B cell responses which could distinguish between 'latent tuberculosis infection (LTBI)' and active TB disease. Study subjects were smear-positive TB patients (n = 54) and their disease-free household contacts (HHCs, n = 120). The sera were used for determination of antibody levels (ΔOD values) against Mycobacterium tuberculosis membrane (MtM) antigens by ELISA and for visualisation of seroreactive MtM antigens by immunoblotting. B cell subsets in whole blood samples were determined by flow cytometry. In TB sera, levels of IgG antibodies were significantly higher than IgM and IgA whereas IgM and IgA antibody levels were comparable. Conversely, HHC sera had significantly higher IgM antibody levels than IgG and IgA. The ratio of IgM to IgG antibodies in HHCs were also significantly higher than in patients. Immunoblotting revealed that some of the MtM antigens (<10, ~12 and ~25 kDa) reacted with TB as well as HHC sera whereas some other antigens (~16, ~36, ~45 and ~60 kDa) reacted with most of TB and a subset of HHC sera. Frequencies of classical memory B cells (cMBCs, CD19+CD27+) were significantly higher, and of IgG+ cMBCs were significantly lower in HHCs than in patients. Frequencies of IgA+ cMBCs in HHCs and patients were comparable but both were significantly higher than the corresponding frequencies of IgG+ cMBCs. Frequencies of IgA+ atypical MBCs (aMBCs, CD19+CD27-) in HHCs and patients were also comparable and significantly higher than the IgG+ aMBCs. The plasmablast (CD19+CD27++CD38++) frequencies in HHCs and patients were comparable. These results suggest that the IgM/IgG antibody ratio, antibody binding to selected MtM antigens and relative frequencies of MBC subsets could indicate protective or pathogenic immune responses following the primary infection with Mtb. Responses that orchestrate protection leading to a 'quiescent' LTBI may provide clues to an effective vaccination strategy against TB.

Improving naive B cell isolation by absence of CD45RB glycosylation and CD27 expression in combination with BCR isotype

In past years ex vivo and in vivo experimental approaches involving human naive B cells have proven fundamental for elucidation of mechanisms promoting B cell differentiation in both health and disease. For such studies, it is paramount that isolation strategies yield a population of bona fide naive B cells, i.e., B cells that are phenotypically and functionally naive, clonally non-expanded, and have non-mutated BCR variable regions. In this study different combinations of common as well as recently identified B cell markers were compared to isolate naive B cells from human peripheral blood. High-throughput BCR sequencing was performed to analyze levels of somatic hypermutation and clonal expansion. Additionally, contamination from mature mutated B cells intrinsic to each cell-sorting strategy was evaluated and how this impacts the purity of obtained populations. Our results show that current naive B cell isolation strategies harbor contamination from non-naive B cells, and use of CD27-IgD⁺ is adequate but can be improved by including markers for CD45RB glycosylation and IgM. The finetuning of naive B cell classification provided herein will harmonize research lines using naive B cells, and will improve B cell profiling during health and disease, e.g. during diagnosis, treatment, and vaccination strategies.

Persistent Maintenance of Intermediate Memory B Cells Following SARS-CoV-2 Infection and Vaccination Recall Response

Robust population-wide immunity will help to curb the SARS-CoV-2 pandemics. To maintain the immunity at protective levels, the quality and persistence of the immune response elicited by infection or vaccination must be determined. We analyzed the dynamics of B cell response during 12 months following SARS-CoV-2 infection on an individual level. In contrast to antibodies, memory B cells specific for the spike (S) protein persisted at high levels throughout the period. These cells efficiently secreted neutralizing antibodies and correlated with IFN-γ-secreting CD4⁺ T cells. Interestingly, the CD27⁻CD21⁺ intermediate memory B cell phenotype was associated with high B cell receptor avidity and the production of neutralizing antibodies. Vaccination of previously infected individuals triggered a recall response enhancing neutralizing antibody and memory B cell levels. Collectively, our findings provide a detailed insight into the longevity of SARS-CoV-2-infection-induced B cell immunity and highlight the importance of vaccination among previously infected.

IMPORTANCE To efficiently maintain immunity against SARS-CoV-2 infection, we must first determine the durability of the immune response following infection or vaccination. Here, we demonstrated that, unlike antibodies, virus-specific memory B cells persist at high levels for at least 12 months postinfection and successfully respond to a secondary antigen challenge. Furthermore, we demonstrated that vaccination of previously infected individuals significantly boosters B cell immunity.

Negative impact of HIV infection on broad-spectrum anti-HCV neutralizing antibody titers in HCV-infected patients with advanced HCV-related cirrhosis

OBJECTIVES

The current study aimed to assess the impact of HIV on the production of anti-HCV antibodies in HCV-infected individuals with advanced HCV-related cirrhosis before and 36 weeks after the sustained virological response (SVR) induced by direct-acting antivirals (DAAs) therapy.

METHODS

Prospective study on 62 patients (50 HIV/HCV-coinfected and 12 HCV-monoinfected). Plasma anti-E2 and HCV-nAbs were determined respectively by ELISA and microneutralization assays.

RESULTS

At baseline, the HCV-group had higher anti-E2 levels against Gt1a (p = 0.012), Gt1b (p = 0.023), and Gt4a (p = 0.005) than the HIV/HCV-group. After SVR, anti-E2 titers against Gt1a (p < 0.001), Gt1b (p = 0.001), and Gt4a (p = 0.042) were also higher in the HCV-group than HIV/HCV-group. At 36 weeks post-SVR, plasma anti-E2 titers decreased between 1.3 and 1.9-fold in the HIV/HCV-group (p < 0.001) and between 1.5 and 1.8-fold in the HCV-group (p ≤ 0.001). At baseline, the HCV-group had higher titers of HCV-nAbs against Gt1a (p = 0.022), Gt1b (p = 0.002), Gt2a (p < 0.001), and Gt4a (p < 0.001) than the HIV/HCV-group. After SVR, HCV-nAbs titers against Gt1a (p = 0.014), Gt1b (p < 0.001), Gt2a (p = 0.002), and Gt4a (p = 0.004) were also higher in the HCV-group. At 36 weeks post-SVR, HCV-nAbs decreased between 2.6 and 4.1-fold in the HIV/HCV-group (p < 0.001) and between 1.9 and 4.0-fold in the HCV-group (p ≤ 0.001).

CONCLUSIONS

HIV/HCV-coinfected patients produced lower levels of broad-spectrum anti-HCV antibodies than HCV-monoinfected patients.

Surface phenotypes of naive and memory B cells in mouse and human tissues

Memory B cells (MBCs) protect the body from recurring infections. MBCs differ from their naive counterparts (NBCs) in many ways, but functional and surface marker differences are poorly characterized. In addition, although mice are the prevalent model for human immunology, information is limited concerning the nature of homology in B cell compartments. To address this, we undertook an unbiased, large-scale screening of both human and mouse MBCs for their differential expression of surface markers. By correlating the expression of such markers with extensive panels of known markers in high-dimensional flow cytometry, we comprehensively identified numerous surface proteins that are differentially expressed between MBCs and NBCs. The combination of these markers allows for the identification of MBCs in humans and mice and provides insight into their functional differences. These results will greatly enhance understanding of humoral immunity and can be used to improve immune monitoring.

Patho-Physiology of Aging and Immune-Senescence: Possible Correlates With Comorbidity and Mortality in Middle-Aged and Old COVID-19 Patients

During the last 2 years, the entire world has been severely devastated by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic (COVID-19) as it resulted in several million deaths across the globe. While the virus infects people indiscriminately, the casualty risk is higher mainly in old, and middle-aged COVID-19 patients. The incidences of COVID-19 associated co-morbidity and mortality have a great deal of correlation with the weakened and malfunctioning immune systems of elderly people. Presumably, due to the physiological changes associated with aging and because of possible comorbidities such as diabetes, hypertension, obesity, cardiovascular, and lung diseases, which are more common in elderly people, may be considered as the reason making the elderly vulnerable to the infection on one hand, and COVID-19 associated complications on the other. The accretion of senescent immune cells not only contributes to the deterioration of host defense, but also results in elevated inflammatory phenotype persuaded immune dysfunction. In the present review, we envisage to correlate functioning of the immune defense of older COVID-19 patients with secondary/super infection, increased susceptibility or aggravation against already existing cancer, infectious, autoimmune, and other chronic inflammatory diseases. Moreover, we have discussed how age-linked modulations in the immune system affect therapeutic response against administered drugs as well as immunological response to various prophylactic measures including vaccination in the elderly host. The present review also provides an insight into the intricate pathophysiology of the aging and the overall immune response of the host to SARS-CoV-2 infection. A better understanding of age-related immune dysfunction is likely to help us in the development of targeted preemptive strategies for deadly COVID-19 in elderly patients.

The Tonsil Lymphocyte Landscape in Pediatric Tonsil Hyperplasia and Obstructive Sleep Apnea

Tonsil hyperplasia is the most common cause of pediatric obstructive sleep apnea (OSA). Despite the growing knowledge in tissue immunology of tonsils, the immunopathology driving tonsil hyperplasia and OSA remains unknown. Here we used multi-parametric flow cytometry to analyze the composition and phenotype of tonsillar innate lymphoid cells (ILCs), T cells, and B cells from pediatric patients with OSA, who had previous polysomnography. Unbiased clustering analysis was used to delineate and compare lymphocyte heterogeneity between two patient groups: children with small tonsils and moderate OSA (n = 6) or large tonsils and very severe OSA (n = 13). We detected disturbed ILC and B cell proportions in patients with large tonsils, characterized by an increase in the frequency of naïve CD27^-CD21^hi B cells and a relative reduction of ILCs. The enrichment of naïve B cells was not commensurate with elevated Ki67 expression, suggesting defective differentiation and/or migration rather than cellular proliferation to be the causative mechanism. Finally, yet importantly, we provide the flow cytometry data to be used as a resource for additional translational studies aimed at investigating the immunological mechanisms of pediatric tonsil hyperplasia and OSA.

Immunosenescence and inflammaging in the aging process: age-related diseases or longevity?

During aging the immune system (IS) undergoes remarkable changes that collectively are known as immunosenescence. It is a multifactorial and dynamic phenomenon that affects both natural and acquired immunity and plays a critical role in most chronic diseases in older people. For a long time, immunosenescence has been considered detrimental because it may lead to a low-grade, sterile chronic inflammation we proposed to call "inflammaging" and a progressive reduction in the ability to trigger effective antibody and cellular responses against infections and vaccinations. Recently, many scientists revised this negative meaning because it can be considered an essential adaptation/remodeling resulting from the lifelong immunological biography of single individuals from an evolutionary perspective. Inflammaging can be considered an adaptive process because it can trigger an anti-inflammatory response to counteract the age-related pro-inflammatory environment. Centenarians represent a valuable model to study the beneficial changes occurring in the IS with age. These extraordinary individuals reached the extreme limits of human life by slowing down the aging process and, in most cases, delaying, avoiding or surviving the major age-associated diseases. They indeed show a complex and heterogeneous phenotype determined by an improved ability to adapt and remodel in response to harmful stimuli. This review aims to point out the intimate relationship between immunosenescence and inflammaging and how these processes impact unsuccessful aging rather than longevity. We also describe the gut microbiota age-related changes as one of the significant triggers of inflammaging and the sex/gender differences in the immune system of the elderly, contributing to the sex/gender disparity in terms of epidemiology, pathophysiology, symptoms and severity of age-related diseases. Finally, we discuss how these phenomena could influence the susceptibility to COVID-19 infection.

B Cell Response Induced by SARS-CoV-2 Infection Is Boosted by the BNT162b2 Vaccine in Primary Antibody Deficiencies

Background: Patients with primary antibody deficiencies are at risk in the current COVID-19 pandemic due to their impaired response to infection and vaccination. Specifically, patients with common variable immunodeficiency (CVID) generated poor spike-specific antibody and T cell responses after immunization. Methods: Thirty-four CVID convalescent patients after SARS-CoV-2 infection, 38 CVID patients immunized with two doses of the BNT162b2 vaccine, and 20 SARS-CoV-2 CVID convalescents later and immunized with BNT162b2 were analyzed for the anti-spike IgG production and the generation of spike-specific memory B cells and T cells. Results: Spike-specific IgG was induced more frequently after infection than after vaccination (82% vs. 34%). The antibody response was boosted in convalescents by vaccination. Although immunized patients generated atypical memory B cells possibly by extra-follicular or incomplete germinal center reactions, convalescents responded to infection by generating spike-specific memory B cells that were improved by the subsequent immunization. Poor spike-specific T cell responses were measured independently from the immunological challenge. Conclusions: SARS-CoV-2 infection primed a more efficient classical memory B cell response, whereas the BNT162b2 vaccine induced non-canonical B cell responses in CVID. Natural infection responses were boosted by subsequent immunization, suggesting the possibility to further stimulate the immune response by additional vaccine doses in CVID.

SARS-CoV-2 Vaccine Induced Atypical Immune Responses in Antibody Defects: Everybody Does their Best

Background

Data on immune responses to SARS-CoV-2 in patients with Primary Antibody Deficiencies (PAD) are limited to infected patients and to heterogeneous cohorts after immunization.

Methods

Forty-one patients with Common Variable Immune Deficiencies (CVID), six patients with X-linked Agammaglobulinemia (XLA), and 28 healthy age-matched controls (HD) were analyzed for anti-Spike and anti-receptor binding domain (RBD) antibody production, generation of Spike-specific memory B-cells, and Spike-specific T-cells before vaccination and one week after the second dose of BNT162b2 vaccine.

Results

The vaccine induced Spike-specific IgG and IgA antibody responses in all HD and in 20% of SARS-CoV-2 naive CVID patients. Anti-Spike IgG were detectable before vaccination in 4 out 7 CVID previously infected with SARS-CoV-2 and were boosted in six out of seven patients by the subsequent immunization raising higher levels than patients naïve to infection. While HD generated Spike-specific memory B-cells, and RBD-specific B-cells, CVID generated Spike-specific atypical B-cells, while RBD-specific B-cells were undetectable in all patients, indicating the incapability to generate this new specificity. Specific T-cell responses were evident in all HD and defective in 30% of CVID. All but one patient with XLA responded by specific T-cell only.

Conclusion

In PAD patients, early atypical immune responses after BNT162b2 immunization occurred, possibly by extra-follicular or incomplete germinal center reactions. If these responses to vaccination might result in a partial protection from infection or reinfection is now unknown. Our data suggests that SARS-CoV-2 infection more effectively primes the immune response than the immunization alone, possibly suggesting the need for a third vaccine dose for patients not previously infected.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10875-021-01133-0.

Characterising the Phenotypic Diversity of Antigen-Specific Memory B Cells Before and After Vaccination

The diversity of B cell subsets and their contribution to vaccine-induced immunity in humans are not well elucidated but hold important implications for rational vaccine design. Prior studies demonstrate that B cell subsets distinguished by immunoglobulin (Ig) isotype expression exhibit divergent activation-induced fates. Here, the antigen-specific B cell response to tetanus toxoid (TTd) booster vaccination was examined in healthy adults, using a dual-TTd tetramer staining flow cytometry protocol. Unsupervised analyses of the data revealed that prior to vaccination, IgM-expressing CD27⁺ B cells accounted for the majority of TTd-binding B cells. 7 days following vaccination, there was an acute expansion of TTd-binding plasmablasts (PB) predominantly expressing IgG, and a minority expressing IgA or IgM. Frequencies of all PB subsets returned to baseline at days 14 and 21. TTd-binding IgG⁺ and IgA⁺ memory B cells (MBC) exhibited a steady and delayed maximal expansion compared to PB, peaking in frequencies at day 14. In contrast, the number of TTd-binding IgM⁺IgD⁺CD27⁺ B cells and IgM-only CD27⁺ B cells remain unchanged following vaccination. To examine TTd-binding capacity of IgG⁺ MBC and IgM⁺IgD⁺CD27⁺ B cells, surface TTd-tetramer was normalised to expression of the B cell receptor-associated CD79b subunit. CD79b-normalised TTd binding increased in IgG⁺ MBC, but remained unchanged in IgM⁺IgD⁺CD27⁺ B cells, and correlated with the functional affinity index of plasma TTd-specific IgG antibodies, following vaccination. Finally, frequencies of activated (PD-1⁺ICOS⁺) circulating follicular helper T cells (cT_FH), particularly of the CXCR3^-CCR6^- cT_FH2 cell phenotype, at their peak expansion, strongly predicted antigen-binding capacity of IgG⁺ MBC. These data highlight the phenotypic and functional diversity of the B cell memory compartment, in their temporal kinetics, antigen-binding capacities and association with cT_FH cells, and are important parameters for consideration in assessing vaccine-induced immune responses.

BAFF, involved in B cell activation through the NF-κB pathway, is related to disease activity and bone destruction in rheumatoid arthritis

B cell activating factor of TNF family (BAFF) is a member of TNF ligand superfamily and plays a key role in B cell homeostasis, proliferation, maturation, and survival. In this study, we detected BAFF level, the expressions of BAFF receptors and important molecules in NF-κB pathway in rheumatoid arthritis (RA) patients and analyzed the correlation between BAFF level and clinical variables, laboratory parameters or X-ray scores in order to elucidate the roles of BAFF in RA. A total of 50 RA patients and 50 healthy controls (HCs) were enrolled. We showed that the serum BAFF level in RA patients was significantly higher than that of HCs, and the percentages of B cell subsets (CD19⁺ B cells, CD19⁺CD27⁺ B cells, CD19⁺CD20⁺CD27⁺ B cells, and CD19⁺CD20^-CD27⁺ B cells) in the serum of RA patients were significantly increased compared with those of HCs. The percentages of CD19⁺BAFFR⁺ B cells, CD19⁺ BCMA⁺ B cells, and CD19⁺ TACI⁺ B cells in RA patients were significantly increased compared with those in HCs. The expression of important molecules in the NF-κB pathway (MKK3, MKK6, p-P38, p-P65, TRAF2, and p52) was significantly higher in RA patients than in HCs, but p100 level in RA patients was lower than that in HCs. The serum BAFF level was positively correlated with C-reactive protein, rheumatoid factor, disease activity score (in 28 joints), swollen joint counts, tender joint counts, and X-ray scores. When normal B cells were treated with BAFF in vitro, the percentages of the B cell subset and the expression of BAFF receptors were significantly upregulated. BAFF also promoted the expression of MKK3, MKK6, p-P38, p-P65, TRAF2, and p52. In conclusion, this study demonstrates that BAFF level is correlated with the disease activity and bone destruction of RA. BAFF is involved in the differentiation, proliferation, and activation of B cells in RA through NF-κB signaling pathway, suggesting that BAFF might be an ideal therapeutic target for RA.

The Role of B Cells in Adult and Paediatric Liver Injury

B lymphocytes are multitasking cells that direct the immune response by producing pro- or anti-inflammatory cytokines, by presenting processed antigen for T cell activation and co-stimulation, and by turning into antibody-secreting cells. These functions are important to control infection in the liver but can also exacerbate tissue damage and fibrosis as part of persistent inflammation that can lead to end stage disease requiring a transplant. In transplantation, immunosuppression increases the incidence of lymphoma and often this is of B cell origin. In this review we bring together information on liver B cell biology from different liver diseases, including alcohol-related and metabolic fatty liver disease, autoimmune hepatitis, primary biliary and primary sclerosing cholangitis, viral hepatitis and, in infants, biliary atresia. We also discuss the impact of B cell depletion therapy in the liver setting. Taken together, our analysis shows that B cells are important in the pathogenesis of liver diseases and that further research is necessary to fully characterise the human liver B cell compartment.

Memory B cells and plasma cells: The differentiative continuum of humoral immunity

Immunological memory is a composite of lasting antibody titers maintained by plasma cells in conjunction with memory T and B cells. Memory B cells are a critical reservoir for plasma cell generation in the secondary response. Identification of memory B cells requires that they be distinguished from naïve, activated, and germinal center precursors and from plasma cells. Memory B cells are heterogeneous in isotype usage, immunoglobulin mutational content, and phenotypic marker expression. Phenotypic subsets of memory B cells are defined by PD-L2, CD80, and CD73 expression in mice, by CD27 and FCRL4 expression in humans and by T-bet in both mice and humans. These subsets display marked functional heterogeneity, including the ability to rapidly differentiate into plasma cells versus seed germinal centers in the secondary response. Memory B cells are located in the spleen, blood, other lymphoid organs, and barrier tissues, and recent evidence indicates that some memory B cells may be dedicated tissue-resident populations. Open questions about memory B cell longevity, renewal and progenitor-successor relationships with plasma cells are discussed.

Generation of plasma cells and CD27-IgD- B cells during hantavirus infection is associated with distinct pathological findings

OBJECTIVE

Human hantavirus infections can cause haemorrhagic fever with renal syndrome (HFRS). The pathogenic mechanisms are not fully understood, nor if they affect the humoral immune system. The objective of this study was to investigate humoral immune responses to hantavirus infection and to correlate them to the typical features of HFRS: thrombocytopenia and transient kidney dysfunction.

METHODS

We performed a comprehensive characterisation of longitudinal antiviral B-cell responses of 26 hantavirus patients and combined this with paired clinical data. In addition, we measured extracellular adenosine triphosphate (ATP) and its breakdown products in circulation and performed in vitro stimulations to address its effect on B cells.

RESULTS

We found that thrombocytopenia was correlated to an elevated frequency of plasmablasts in circulation. In contrast, kidney dysfunction was indicative of an accumulation of CD27-IgD- B cells and CD27-/low plasmablasts. Finally, we provide evidence that high levels of extracellular ATP and matrix metalloproteinase 8 can contribute to shedding of CD27 during human hantavirus infection.

CONCLUSION

Our findings demonstrate that thrombocytopenia and kidney dysfunction associate with distinctly different effects on the humoral immune system. Moreover, hantavirus-infected individuals have significantly elevated levels of extracellular ATP in circulation.

B-cell compartment abnormalities are associated with ACLF and mortality in patients with liver cirrhosis

BACKGROUND

Liver cirrhosis profoundly affects the immune system, leading to an immunological imbalance known as cirrhosis-associated immune dysfunction.

AIMS

This study aimed to investigate B-cell disturbances in patients with acute decompensation (AD) of cirrhosis and assess relationships with prognosis and mortality.

METHODS

The study included 39 patients with AD of cirrhosis, 29 patients with stable cirrhosis (SC), and 30 healthy controls (CTR). Circulating B-cell subsets and cytokine plasma levels were determined by flow cytometry.

RESULTS

Cirrhotic groups showed higher percentages of naïve B cells, and lower percentages of CD27⁺ memory B cells (MBCs) than CTR. Further analysis comparing SC and AD revealed that the latter had higher frequencies of double-negative (DN) B cells and plasmablasts. Patients with more advanced liver disease exhibited a B-cell maturation shift toward MBCs and plasmablasts. Acute-on-chronic liver failure (ACLF) was associated with higher DN frequency. The Kaplan-Meier one-year survival probability was 92.9% in patients with >1.3% of transitional B cells and 27.3% in patients with <1.3%.

CONCLUSIONS

B-cell subsets are markedly altered in cirrhotic patients, and cell profiles differ between stable and decompensated liver disease. Increased frequencies of DN B cells and reduced proportions of transitional B cells may be of great relevance in predicting ACLF and mortality, respectively.

Memory B Cells in Multiple Sclerosis: Emerging Players in Disease Pathogenesis

Multiple Sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system. Once thought to be primarily driven by T cells, B cells are emerging as central players in MS immunopathogenesis. Interest in multiple B cell phenotypes in MS expanded following the efficacy of B cell-depleting agents targeting CD20 in relapsing-remitting MS and inflammatory primary progressive MS patients. Interestingly, these therapies primarily target non-antibody secreting cells. Emerging studies seek to explore B cell functions beyond antibody-mediated roles, including cytokine production, antigen presentation, and ectopic follicle-like aggregate formation. Importantly, memory B cells (Bmem) are rising as a key B cell phenotype to investigate in MS due to their antigen-experience, increased lifespan, and rapid response to stimulation. Bmem display diverse effector functions including cytokine production, antigen presentation, and serving as antigen-experienced precursors to antibody-secreting cells. In this review, we explore the cellular and molecular processes involved in Bmem development, Bmem phenotypes, and effector functions. We then examine how these concepts may be applied to the potential role(s) of Bmem in MS pathogenesis. We investigate Bmem both within the periphery and inside the CNS compartment, focusing on Bmem phenotypes and proposed functions in MS and its animal models. Finally, we review how current immunomodulatory therapies, including B cell-directed therapies and other immunomodulatory therapies, modify Bmem and how this knowledge may be harnessed to direct therapeutic strategies in MS.

Double-negative (DN) B cells: an under-recognized effector memory B cell subset in autoimmunity

Human B cells could be divided into four classical subsets based on CD27 and immunoglobulin (Ig)D expression. Distinct from the other three well-studied subsets, CD27^- IgD^- B cells, also termed as double-negative (DN) B cells, have long been neglected. However, in recent years emerging evidence shows that DN B cells are unique memory B cells with important functions. They are expanded in a variety of diseases, especially in autoimmune diseases, contributing to the disease pathogenesis. Here, we briefly review the studies on DN B cells, including their origins, characteristics, subsets and roles in diseases, to try to bring new insights into this under-recognized B cell subset.

Potential Relevance of B-cell Maturation Pathways in Defining the Cell(s) of Origin for Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a common, incurable disease of undefined cause. Notably, the normal cell equivalents of CLL cells remain elusive, and it is possible that the disease emanates from several normal B-cell subsets. This article reviews the literature relating to this issue, focusing on recent findings, in particular made through epigenetic analyses that strongly support the disease developing from a normal Ag-experienced and memory cell-like B lymphocyte. It also reports the known pathways whereby normal B lymphocytes mature after antigenic challenge and proposes that this information is relevant in defining the cells of origin of this disease.

Post-Transformation IGHV-IGHD-IGHJ Mutations in Chronic Lymphocytic Leukemia B Cells: Implications for Mutational Mechanisms and Impact on Clinical Course

Analyses of IGHV gene mutations in chronic lymphocytic leukemia (CLL) have had a major impact on the prognostication and treatment of this disease. A hallmark of IGHV-mutation status is that it very rarely changes clonally over time. Nevertheless, targeted and deep DNA sequencing of IGHV-IGHD-IGHJ regions has revealed intraclonal heterogeneity. We used a DNA sequencing approach that achieves considerable depth and minimizes artefacts and amplification bias to identify IGHV-IGHD-IGHJ subclones in patients with prolonged temporal follow-up. Our findings extend previous studies, revealing intraclonal IGHV-IGHD-IGHJ diversification in almost all CLL clones. Also, they indicate that some subclones with additional IGHV-IGHD-IGHJ mutations can become a large fraction of the leukemic burden, reaching numerical criteria for monoclonal B-cell lymphocytosis. Notably, the occurrence and complexity of post-transformation IGHV-IGHD-IGHJ heterogeneity and the expansion of diversified subclones are similar among U-CLL and M-CLL patients. The molecular characteristics of the mutations present in the parental, clinically dominant CLL clone (CDC) differed from those developing post-transformation (post-CDC). Post-CDC mutations exhibit significantly lower fractions of mutations bearing signatures of activation induced deaminase (AID) and of error-prone repair by Polη, and most of the mutations were not ascribable to those enzymes. Additionally, post-CDC mutations displayed a lower percentage of nucleotide transitions compared with transversions that was also not like the action of AID. Finally, the post-CDC mutations led to significantly lower ratios of replacement to silent mutations in VH CDRs and higher ratios in VH FRs, distributions different from mutations found in normal B-cell subsets undergoing an AID-mediated process. Based on these findings, we propose that post-transformation mutations in CLL cells either reflect a dysfunctional standard somatic mutational process or point to the action of another mutational process not previously associated with IG V gene loci. If the former option is the case, post-CDC mutations could lead to a lesser dependence on antigen dependent BCR signaling and potentially a greater influence of off-target, non-IG genomic mutations. Alternatively, the latter activity could add a new stimulatory survival/growth advantage mediated by the BCR through structurally altered FRs, such as that occurring by superantigen binding and stimulation.

High-Throughput Detection of Autoantigen-Specific B Cells Among Distinct Functional Subsets in Autoimmune Donors

Antigen-specific B cells (ASBCs) can drive autoimmune disease by presenting autoantigen to cognate T cells to drive their activation, proliferation, and effector cell differentiation and/or by differentiating into autoantibody-secreting cells. Autoantibodies are frequently used to predict risk and diagnose several autoimmune diseases. ASBCs can drive type 1 diabetes even when immune tolerance mechanisms block their differentiation into antibody-secreting cells. Furthermore, anti-histidyl tRNA synthetase syndrome patients have expanded IgM⁺ Jo-1-binding B cells, which clinically diagnostic IgG Jo-1 autoantibodies may not fully reflect. Given the potential disconnect between the pathologic function of ASBCs and autoantibody secretion, direct study of ASBCs is a necessary step towards developing better therapies for autoimmune diseases, which often have no available cure. We therefore developed a high-throughput screening pipeline to 1) phenotypically identify specific B cell subsets, 2) expand them in vitro, 3) drive them to secrete BCRs as antibody, and 4) identify wells enriched for ASBCs through ELISA detection of antibody. We tested the capacity of several B cell subset(s) to differentiate into antibody-secreting cells following this robust stimulation. IgM⁺ and/or IgD⁺, CD27^- memory, memory, switched memory, and B_ND B cells secreted B cell receptor (BCR) as antibody following in vitro stimulation, whereas few plasmablasts responded. Bimodal responses were observed across autoimmune donors for IgM⁺ CD21^lo and IgM^- CD21^lo B cells, consistent with documented heterogeneity within the CD21^lo subset. Using this approach, we detected insulin-binding B cell bias towards CD27^- memory and CD27⁺ memory subsets in pre-symptomatic type 1 diabetes donors. We took advantage of routine detection of Jo-1-binding B cells in Jo-1+ anti-histidyl tRNA synthetase syndrome patients to show that Jo-1-binding B cells and total B cells expanded 20-30-fold using this culture system. Overall, these studies highlight technology that is amenable to small numbers of cryopreserved peripheral blood mononuclear cells that enables interrogation of phenotypic and repertoire attributes of ASBCs derived from autoimmune patients.

Metformin and insulin-resistant related diseases: Emphasis on the role of microRNAs

Metformin is one of the most prescribed drugs in type II diabetes (T2DM) which has recently found new applications in the prevention and treatment of various illnesses, from metabolic disorders to cardiovascular and age-related diseases. Metformin improves insulin resistance (IR) by modulating metabolic mechanisms and mitochondrial biogenesis. Alternation of microRNAs (miRs) in the treatment of IR-related illnesses has been observed by metformin therapy. MiRs are small non-coding RNAs that play important roles in RNA silencing, targeting the 3'untranslated region (3'UTR) of most mRNAs and inhibiting the translation of related proteins. As a result, their dysregulation is associated with many diseases. Metformin may alter miRs levels in the treatment of various diseases by AMPK-dependent or AMPK-independent mechanisms. Here, we summarized the therapeutic role of metformin by modifying the aberrant expression of miRs as potential biomarkers or therapeutic targets in diseases in which IR plays a key role.

Role of Circulating T Follicular Helper Cells and Stem-Like Memory CD4+ T Cells in the Pathogenesis of HIV-2 Infection and Disease Progression

CD4⁺ T cells are critical players in the host adaptive immune response. Emerging evidence suggests that certain CD4⁺ T cell subsets contribute significantly to the production of neutralizing antibodies and help in the control of virus replication. Circulating T follicular helper cells (Tfh) constitute a key T cell subset that triggers the adaptive immune response and stimulates the production of neutralizing antibodies (NAbs). T cells having stem cell-like property, called stem-like memory T cells (Tscm), constitute another important subset of T cells that play a critical role in slowing the rate of disease progression through the differentiation and expansion of different types of memory cell subsets. However, the role of these immune cell subsets in T cell homeostasis, CD4⁺ T cell proliferation, and progression of disease, particularly in HIV-2 infection, has not yet been elucidated. The present study involved a detailed evaluation of the different CD4⁺ T cell subsets in HIV-2 infected persons with a view to understanding the role of these immune cell subsets in the better control of virus replication and delayed disease progression that is characteristic of HIV-2 infection. We observed elevated levels of CD4⁺ Tfh and CD4⁺ Tscm cells along with memory and effector T cell abundance in HIV-2 infected individuals. We also found increased frequencies of CXCR5⁺ CD8⁺ T cells and CD8⁺ Tscm cells, as well as memory B cells that are responsible for NAb development in HIV-2 infected persons. Interestingly, we found that the frequency of memory CD4⁺ T cells as well as memory B cells correlated significantly with neutralizing antibody titers in HIV-2 infected persons. These observations point to a more robust CD4⁺ T cell response that supports B cell differentiation, antibody production, and CD8⁺ T cell development in HIV-2 infected persons and contributes to better control of the virus and slower rate of disease progression in these individuals.

Single-Cell Transcriptomic Analyses Define Distinct Peripheral B Cell Subsets and Discrete Development Pathways

Separation of B cells into different subsets has been useful to understand their different functions in various immune scenarios. In some instances, the subsets defined by phenotypic FACS separation are relatively homogeneous and so establishing the functions associated with them is straightforward. Other subsets, such as the “Double negative” (DN, CD19+CD27-IgD-) population, are more complex with reports of differing functionality which could indicate a heterogeneous population. Recent advances in single-cell techniques enable an alternative route to characterize cells based on their transcriptome. To maximize immunological insight, we need to match prior data from phenotype-based studies with the finer granularity of the single-cell transcriptomic signatures. We also need to be able to define meaningful B cell subsets from single cell analyses performed on PBMCs, where the relative paucity of a B cell signature means that defining B cell subsets within the whole is challenging. Here we provide a reference single-cell dataset based on phenotypically sorted B cells and an unbiased procedure to better classify functional B cell subsets in the peripheral blood, particularly useful in establishing a baseline cellular landscape and in extracting significant changes with respect to this baseline from single-cell datasets. We find 10 different clusters of B cells and applied a novel, geometry-inspired, method to RNA velocity estimates in order to evaluate the dynamic transitions between B cell clusters. This indicated the presence of two main developmental branches of memory B cells. A T-independent branch that involves IgM memory cells and two DN subpopulations, culminating in a population thought to be associated with Age related B cells and the extrafollicular response. The other, T-dependent, branch involves a third DN cluster which appears to be a precursor of classical memory cells. In addition, we identify a novel DN4 population, which is IgE rich and closely linked to the classical/precursor memory branch suggesting an IgE specific T-dependent cell population.

Atypical B cells are part of an alternative lineage of B cells that participates in responses to vaccination and infection in humans

The diversity of circulating human B cells is unknown. We use single-cell RNA sequencing (RNA-seq) to examine the diversity of both antigen-specific and total B cells in healthy subjects and malaria-exposed individuals. This reveals two B cell lineages: a classical lineage of activated and resting memory B cells and an alternative lineage, which includes previously described atypical B cells. Although atypical B cells have previously been associated with disease states, the alternative lineage is common in healthy controls, as well as malaria-exposed individuals. We further track Plasmodium-specific B cells after malaria vaccination in naive volunteers. We find that alternative lineage cells are primed after the initial immunization and respond to booster doses. However, alternative lineage cells develop an atypical phenotype with repeated boosts. The data highlight that atypical cells are part of a wider alternative lineage of B cells that are a normal component of healthy immune responses.

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Single-cell RNA-seq reveals two distinct B cell lineages

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An alternative lineage contains CXCR3⁺ and atypical B cells

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Alternative B cells are primed after primary vaccination and respond to boosters

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Alternative B cells adopt a more atypical phenotype following repeated antigen exposure

FcγRIIb Expression Is Decreased on Naive and Marginal Zone-Like B Cells From Females With Multiple Sclerosis

B cells are critical to the development of multiple sclerosis (MS), but the mechanisms by which they contribute to the disease are poorly defined. We hypothesised that the expression of CD32b (FcγRIIb), a receptor for the Fc region of IgG with inhibitory activities in B cells, is lower on B cell subsets from people with clinically isolated syndrome (CIS) or MS. CD32b expression was highest on post-naive IgM⁺ B cell subsets in healthy controls. For females with MS or CIS, significantly lower CD32b expression was identified on IgM⁺ B cell subsets, including naive and IgM^hi MZ-like B cells, when compared with control females. Lower CD32b expression on these B cell subsets was associated with detectable anti-Epstein Barr Virus viral capsid antigen IgM antibodies, and higher serum levels of B cell activating factor. To investigate the effects of lower CD32b expression, B cells were polyclonally activated in the presence of IgG immune complexes, with or without a CD32b blocking antibody, and the expression of TNF and IL-10 in B cell subsets was assessed. The reduction of TNF but not IL-10 expression in controls mediated by IgG immune complexes was reversed by CD32b blockade in naive and IgM^hi MZ-like B cells only. However, no consequence of lower CD32b expression on these cells from females with CIS or MS was detected. Our findings highlight a potential role for naive and marginal zone-like B cells in the immunopathogenesis of MS in females, which requires further investigation.

B cell depletion therapies in autoimmune disease: advances and mechanistic insights

In the past 15 years, B cells have been rediscovered to be not merely bystanders but rather active participants in autoimmune aetiology. This has been fuelled in part by the clinical success of B cell depletion therapies (BCDTs). Originally conceived as a method of eliminating cancerous B cells, BCDTs such as those targeting CD20, CD19 and BAFF are now used to treat autoimmune diseases, including systemic lupus erythematosus and multiple sclerosis. The use of BCDTs in autoimmune disease has led to some surprises. For example, although antibody-secreting plasma cells are thought to have a negative pathogenic role in autoimmune disease, BCDT, even when it controls the disease, has limited impact on these cells and on antibody levels. In this Review, we update our understanding of B cell biology, review the results of clinical trials using BCDT in autoimmune indications, discuss hypotheses for the mechanism of action of BCDT and speculate on evolving strategies for targeting B cells beyond depletion.

Immunoglobulins concentration and B cell counts as severity markers in adult community-acquired pneumonia: Cross sectional study

Community-acquired pneumonia (CAP) is a worldwide cause of morbidity and mortality. Immunoglobulins (Igs) and B cells quantification studies in CAP are few and show discrepancies. Serum IgA acts as a powerful natural anti-inflammatory factor, but its role in the CAP has not yet been defined. The highly sensitive xMAP Luminex technique allows better immunoglobulins quantification. The aim of this study was to analyze the relation between clinical severity and circulating Igs and B cells in adults with CAP.Igs (M, A, G1, G2, G3, and G4) and B cells were quantified in peripheral blood of 190 Chilean patients ≥18 years old hospitalized for CAP and in 21 adults without respiratory disease, using xMAP Luminex and flow cytometry, respectively. Clinical history was recorded and PSI and CURB-65 scores were calculated for evaluation of clinical severity.The total IgM, IgG2 and total IgG levels were lower in CAP than in asymptomatic adults (P < .05). No significant differences of Igs levels were found between patients classified as severe and mild by PSI and CURB-65 scores. Fatal cases had higher levels of IgA (P < .05). No differences in CD19 B cells frequency was found between CAP and asymptomatic adults (P = .40). In PSI severe cases, CD19 B cells were significantly lower than in mild cases (P = .008). No differences were found in CURB-65 severe and mild groups (P = .11). In fatal cases (11/82) group, CD19 B cells frequency was lower than in 71 survivors (P = .2). No differences in memory B lymphocytes were detected between asymptomatic and CAP adults, severe and mild patients, survivors and fatal cases (P > .05).Serum IgA levels were significantly higher in fatal CAP cases, raising it as a potential biomarker for severe disease considering its relatively universal availability. In PSI severe patients, B cells showed lower levels and could have a role on its physiopathology. Finding new markers rooted in physiopathology could improve the possibility of scoring severe CAP cases. Luminex technology showed promising quantification serum Igs.

Maturation of the Human Immunoglobulin Heavy Chain Repertoire With Age

B cells play a central role in adaptive immune processes, mainly through the production of antibodies. The maturation of the B cell system with age is poorly studied. We extensively investigated age-related alterations of naïve and antigen-experienced immunoglobulin heavy chain (IgH) repertoires. The most significant changes were observed in the first 10 years of life, and were characterized by altered immunoglobulin gene usage and an increased frequency of mutated antibodies structurally diverging from their germline precursors. Older age was associated with an increased usage of downstream IgH constant region genes and fewer antibodies with self-reactive properties. As mutations accumulated with age, the frequency of germline-encoded self-reactive antibodies decreased, indicating a possible beneficial role of self-reactive B cells in the developing immune system. Our results suggest a continuous process of change through childhood across a broad range of parameters characterizing IgH repertoires and stress the importance of using well-selected, age-appropriate controls in IgH studies.

Deficits in the IgG+ memory B-cell recovery after anthracycline treatment is confined to the spleen of rhesus macaques

Objectives

Loss of vaccine‐induced antibodies (Abs) after chemotherapy against paediatric acute lymphoblastic leukaemia (ALL) is common and often necessitates re‐immunisation after cessation of treatment. Even so, some ALL survivors fail to mount or to maintain protective Abs. Germinal centres (GCs) are clusters of proliferating B cells in follicles of secondary lymphoid tissues (SLTs) formed during adaptive immune responses and the origins of long‐lived memory B and plasma cells that are the source of Abs. Furthermore, productive GC reactions depend on T follicular helper (T_FH) cells. To understand why chemotherapy induces deficits in Ab responses, we examined how SLTs were affected by chemotherapy.

Methods

Rhesus macaques were infused with either three cycles of the anthracycline doxorubicin or saline, followed by immunisation with a de novo and booster antigen. Spleen and lymph nodes were removed, and memory B, bulk T and T_FH cells were examined.

Results

Despite adequate GC morphology, a diminished memory and IgG⁺ B‐cell population along with diminished total and booster vaccine‐specific IgG‐producing memory B cells were noted in the spleens of macaques with past doxorubicin exposure compared to the saline‐treated controls (P < 0.05). Intact bulk T and T_FH cells were found in the SLTs of treated macaques, which displayed higher CD40L upregulation capacity by their splenic CXCR5⁺ helper T cells (P < 0.01). In contrast to the spleen, the immune cell populations studied were comparable between the lymph nodes of both saline‐ and doxorubicin‐treated macaques.

Conclusion

Our findings suggest that the splenic memory B‐cell subset, compared to its lymph node counterpart, is more severely altered by anthracycline treatment.

Double Negative B Cell Is Associated With Renal Impairment in Systemic Lupus Erythematosus and Acts as a Marker for Nephritis Remission

Objective: Recent studies on double negative B cells (DN B cells) suggested that they have potential pathogenic roles in systemic lupus erythematosus (SLE). This study aimed to determine the circulating DN B cells in SLE patients and analyzed the clinical significance of this cell subset. Methods: Fifty-seven SLE patients and fifty healthy controls (HCs) were recruited in this study. Among the 57 SLE patients, 25 had lupus nephritis (LN). All patients were followed up for 24 weeks. Peripheral B cell subsets were analyzed by flow cytometry. Results: DN B cells were significantly elevated in the SLE patients, especially in the patients with LN (p < 0.01). DN B showed a positive correlation with 24-h urine protein excretion (24 h-UPE) levels (r = 0.444, p = 0.034) in LN patients, and inversely correlated with evaluated glomerular filtration rate (eGFR) (r = -0.351, p = 0.011). DN B cells had a positive correlation with plasma cells (r = 0.484, p < 0.001) and memory B cells (r = 0.703, p < 0.001). After treatment, decreased DN B cells were associated with LN alleviation (p = 0.002). In the follow-up, the remission rate of LN patients with decreased DN B cells was significantly higher than LN patients with increased DN B cells (83.33 vs. 25.00%, p = 0.030) at week 24. Conclusions: This study suggests that the peripheral DN B cells are positively correlated with the severity of renal damage in LN patients and may potentially be used as a prognostic marker in LN.

Peripheral B Cell Subsets in Autoimmune Diseases: Clinical Implications and Effects of B Cell-Targeted Therapies

Antibody-secreting cells (ASCs) play a fundamental role in humoral immunity. The aberrant function of ASCs is related to a number of disease states, including autoimmune diseases and cancer. Recent insights into activated B cell subsets, including naïve B cell to ASC stages and their resultant cellular disturbances, suggest that aberrant ASC differentiation occurs during autoimmune diseases and is closely related to disease severity. However, the mechanisms underlying highly active ASC differentiation and the B cell subsets in autoimmune patients remain undefined. Here, we first review the processes of ASC generation. From the perspective of novel therapeutic target discovery, prediction of disease progression, and current clinical challenges, we further summarize the aberrant activity of B cell subsets including specialized memory CD11c^hiT-bet⁺ B cells that participate in the maintenance of autoreactive ASC populations. An improved understanding of subgroups may also enhance the knowledge of antigen-specific B cell differentiation. We further discuss the influence of current B cell therapies on B cell subsets, specifically focusing on systemic lupus erythematosus, rheumatoid arthritis, and myasthenia gravis.

Rheumatoid arthritis patients display B-cell dysregulation already in the naïve repertoire consistent with defects in B-cell tolerance

B cells are postulated to be central in seropositive rheumatoid arthritis (RA). Here, we use exploratory mass cytometry (n = 23) and next-generation sequencing (n = 19) to study B-cell repertoire shifts in RA patients. Expression of several B-cell markers were significantly different in ACPA⁺ RA compared to healthy controls, including an increase in HLA-DR across subsets, CD22 in clusters of IgM⁺ B cells and CD11c in IgA⁺ memory. Moreover, both IgA⁺ and IgG⁺ double negative (IgD⁻ CD27⁻) CD11c⁺ B cells were increased in ACPA⁺ RA, and there was a trend for elevation in a CXCR5/CCR6^high transitional B-cell cluster. In the RA BCR repertoire, there were significant differences in subclass distribution and, notably, the frequency of VH with low somatic hypermutation (SHM) was strikingly higher, especially in IgG1 (p < 0.0001). Furthermore, both ACPA⁺ and ACPA⁻ RA patients had significantly higher total serum IgA and IgM compared to controls, based on serology of larger cohorts (n = 3494 IgA; n = 397 IgM). The observed elevated Ig-levels, distortion in IgM⁺ B cells, increase in double negative B cells, change in B-cell markers, and elevation of unmutated IgG⁺ B cells suggests defects in B-cell tolerance in RA. This may represent an underlying cause of increased polyreactivity and autoimmunity in RA.

2019 Russell Ross Memorial Lecture in Vascular Biology: B Lymphocyte-Mediated Protective Immunity in Atherosclerosis

Atherosclerosis-the major underlying pathology of cardiovascular disease-is characterized by accumulation and subsequent oxidative modification of lipoproteins within the artery wall, leading to inflammatory cell infiltration and lesion formation that can over time result in arterial stenosis, ischemia, and downstream adverse events. The contribution of innate and adaptive immunity to atherosclerosis development is well established, and B cells have emerged as important modulators of both pro- and anti-inflammatory effects in atherosclerosis. Murine B cells can broadly be divided into 2 subsets: (1) B-2 cells, which are bone marrow derived and include conventional follicular and marginal zone B cells, and (2) B-1 cells, which are largely fetal liver derived and persist in adults through self-renewal. B-cell subsets are developmentally, functionally, and phenotypically distinct with unique subset-specific contributions to atherosclerosis development. Mechanisms whereby B cells regulate vascular inflammation and atherosclerosis will be discussed with a particular emphasis on B-1 cells. B-1 cells have a protective role in atherosclerosis that is mediated in large part by IgM antibody production. Accumulating evidence over the last several years has pointed to a previously underappreciated heterogeneity in B-1 cell populations, which may have important implications for understanding atherosclerosis development and potential targeted therapeutic approaches. This heterogeneity within atheroprotective innate B-cell subsets will be highlighted.

Aging and the Immune System: the Impact of Immunosenescence on Viral Infection, Immunity and Vaccine Immunogenicity

Immunosenescence is characterized by a progressive deterioration of the immune system associated with aging. Multiple components of both innate and adaptive immune systems experience aging-related changes, such as alterations in the number of circulating monocytic and dendritic cells, reduced phagocytic activities of neutrophils, limited diversity in B/T cell repertoire, T cell exhaustion or inflation, and chronic production of inflammatory cytokines known as inflammaging. The elderly are less likely to benefit from vaccinations as preventative measures against infectious diseases due to the inability of the immune system to mount a successful defense. Therefore, aging is thought to decrease the efficacy and effectiveness of vaccines, suggesting aging-associated decline in the immunogenicity induced by vaccination. In this review, we discuss aging-associated changes in the innate and adaptive immunity and the impact of immunosenescence on viral infection and immunity. We further explore recent advances in strategies to enhance the immunogenicity of vaccines in the elderly. Better understanding of the molecular mechanisms underlying immunosenescence-related immune dysfunction will provide a crucial insight into the development of effective elderly-targeted vaccines and immunotherapies.

Memory B Cells and Long-lived Plasma Cells

The importance of B cell and antibody-mediated immune response in the acute and long-term persistence of transplanted solid organs has become increasingly evident in recent years. A variety of therapeutic innovations target antibodies directed toward HLA or blood groups (ABO) to allow better allocation and posttransplant longevity of organs. Antibodies originate from plasma cells (PCs), which are terminally differentiated B cells. Long-term production and persistence of these antibodies is partly due to fast reactivation of previously generated memory B cells; however, there is increasing evidence that some differentiated PCs can persist independently in the bone marrow for years or even decades, producing specific antibodies or even experiencing regeneration without proliferation without need to be replaced by newly differentiating B cells. This review outlines the currently presumed pathways of differentiation, antibody, and memory generation on both B-cell and PC levels. On this background, current therapeutic concepts for antibody reduction before and after solid organ transplantation are considered, to better understand their mechanisms, possible synergisms, and specific risks. Specific differences in regards to ABO versus HLA antibodies as well as practical relevance for generation of desensitization and posttransplant antibody-directed therapy protocols are discussed.

Challenges and Opportunities for Consistent Classification of Human B Cell and Plasma Cell Populations

The increasingly recognized role of different types of B cells and plasma cells in protective and pathogenic immune responses combined with technological advances have generated a plethora of information regarding the heterogeneity of this human immune compartment. Unfortunately, the lack of a consistent classification of human B cells also creates significant imprecision on the adjudication of different phenotypes to well-defined populations. Additional confusion in the field stems from: the use of non-discriminatory, overlapping markers to define some populations, the extrapolation of mouse concepts to humans, and the assignation of functional significance to populations often defined by insufficient surface markers. In this review, we shall discuss the current understanding of human B cell heterogeneity and define major parental populations and associated subsets while discussing their functional significance. We shall also identify current challenges and opportunities. It stands to reason that a unified approach will not only permit comparison of separate studies but also improve our ability to define deviations from normative values and to create a clean framework for the identification, functional significance, and disease association with new populations.

Rapid decrease in titer and breadth of neutralizing anti-HCV antibodies in HIV/HCV-coinfected patients who achieved SVR

The main targets for neutralizing anti-hepatitis C virus (HCV) antibodies (HCV-nAbs) are the E1 and E2 envelope glycoproteins. We have studied the characteristics of HCV-nAbs through a retrospective study involving 29 HIV/HCV-coinfected patients who achieved sustained virological response (SVR) with peg-IFNα + ribavirin anti-HCV therapy. Plasma samples at baseline and week 24 after SVR were used to perform neutralization assays against five JFH1-based HCV recombinant viruses coding for E1 and E2 from genotypes 1a (H77), 1b (J4), 2a (JFH1), 3a (S52) and 4a (ED43). At baseline, the majority of plasma samples neutralized 1a, 1b, 2a, and 4a, but not 3a, genotypes. Twenty-four weeks following SVR, most neutralizing titers declined substantially. Furthermore, titers against 3a and 2a were not detected in many patients. Plasma samples with high HCV-nAb titers neutralized all genotypes, and the highest titers at the starting point correlated with the highest titers at week 24 after SVR. In conclusion, high titers of broad-spectrum HCV-nAbs were detected in HIV/HCV-coinfected individuals, however, those titers declined soon after SVR.

Phenotypic and Ig Repertoire Analyses Indicate a Common Origin of IgD-CD27- Double Negative B Cells in Healthy Individuals and Multiple Sclerosis Patients

IgD^-CD27^- double negative (DN) B cells with proinflammatory characteristics are abnormally elevated in a proportion of multiple sclerosis (MS) patients. In this study, the origin and selection characteristics of DN B cells were studied in MS patients and healthy controls (HC). Expression of developmental markers on peripheral blood DN, IgD^-CD27⁺ class-switched memory (CSM) and IgD⁺CD27^- naive B cells of HC (n = 48) and MS patients (n = 96) was determined by flow cytometry. High-throughput adaptive immune receptor repertoire sequencing was performed on peripheral blood DN and CSM B cells of HC and MS patients (n = 3 each). DN B cells from HC and MS patients showed similar phenotypic and Ig repertoire characteristics. Phenotypic analysis indicated a mature state of DN B cells by low CD5, CD10, and CD38 expression. However, the frequency of CD95⁺ and IgA⁺ cells was lower in DN versus CSM B cells. DN B cells are Ag experienced, as shown by somatic hypermutation of their Ig genes in adaptive immune receptor repertoire sequencing, although they showed a lower mutation load than CSM B cells. Shared clones were found between DN and CSM B cells, although >95% of the clones were unique to each population, and differences in V(D)J usage and CDR3 physicochemical properties were found. Thus, DN B cells arise in HC and MS patients via a common developmental pathway that is probably linked to immune aging. However, DN and CSM B cells develop through unique differentiation pathways, with most DN B cells representing an earlier maturation state.