Strength in diversity: Phenotypic, functional, and molecular heterogeneity within the memory B cell repertoire

Phenotypic heterogeneity defines B cell responses to repeated SARS-CoV-2 exposures through vaccination and infection

Long-lived humoral memory is key to durable immunity against pathogens yet remains challenging to define due to heterogeneity among antigen-reactive B cells. We addressed this gap through longitudinal sampling over the course of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccinations with or without breakthrough infection. High-dimensional phenotypic profiling performed on ∼72 million B cells showed that receptor-binding domain (RBD) reactivity was associated with five distinct immunoglobulin G (IgG) B cell populations. Two expressed the activation marker CD71, both correlated with neutralizing antibodies, yet the one lacking the memory marker CD27 was induced by vaccination and blunted by infection. Two were resting memory populations; one lacking CD73 arose early and contributed to cross-reactivity; the other, expressing CD73, arose later and correlated with neutralizing antibodies. The fifth, a rare germinal center-like population, contributed to recall responses and was highly cross reactive. Overall, robust and distinct responses to booster vaccination overcame the superiority of hybrid immunity provided by breakthrough infection.

Invariant NK T cells counteract HCC metastasis by mediating the migration of splenic CD4+ T cells into the white pulp and infiltration of B cells

Despite significant advances in the diagnosis and treatment of hepatocellular carcinoma (HCC), metastasis and recurrence remain two major obstacles to improving the clinical outcomes for HCC patients. Here, we demonstrate that splenic invariant natural killer T (iNKT) cells can significantly inhibit Hepa1-6-mediated intrahepatic HCC metastasis. Interestingly, in the HCC metastasis model, iNKT deficiency can result in a significant decrease in percentage and absolute number of CD4+ T cell and interleukin-4 level, thus suggesting the involvement of the cross-talk between iNKTs and CD4+ T cells in limiting HCC metastasis to the spleen. Transcriptional signatures of CD4+ T cells following iNKT deficiency displaying impairment of their cell migration function. During HCC metastasis, splenic iNKT rapidly secrete interferon-γ to promote the migration of CD4+ T cells from the marginal zone into the white pulp, thereby triggering subsequent migration of splenic B cells to the liver and exerting anti-tumor immune effects on Hepa1-6 cells. In conclusion, interactions between interferon-γ and its receptor on iNKT and CD4+ T cells can effectively coordinate immune activity between the marginal zone and the white pulp, thereby ultimately inhibiting intrahepatic HCC metastasis. These findings reveal the mechanism underlying the resistance of splenic iNKT to tumor metastasis.

Changes in and Potential Mechanisms of Circulating IgA+CD27-Class-Switched Memory B Cells in Patients With Allergic Rhinitis

Background

The role of memory B cells and their subgroups in allergic rhinitis (AR) and allergen immunotherapy (AIT) remains unclear. This study aimed to investigate the characteristics of memory B cells in the circulation of patients with AR and those undergoing AIT, as well as their clinical significance.

Methods

This study involved a cohort comprising 32 healthy control subjects, 39 individuals diagnosed with AR, and 31 AR patients who had received AIT for over one year. Visual analog scale (VAS) scores were used for symptom assessment, and the serum concentrations of immunoglobulins and cytokines were quantified. This study evaluated alterations in the proportions of peripheral blood memory B cells and their subpopulations, plasma cells, and various T-cell subsets across the three participant groups.

Results

The proportion of IgA+CD27- class-switched memory B cells in the AR group significantly decreased compared to the control group, but significantly increased following AIT (P < 0.05). In AR patients, circulating IgA+CD27- class-switched memory B cells were significantly positively correlated with Treg cells, IL-10, and IL-4 and significantly negatively correlated with IFN-γ, total IgE, sIgE, and VAS scores (P < 0.05). After AIT, the number of circulating IgA+CD27- class-switched memory B cells in AR patients was significantly positively correlated with the number of Treg cells and IL-10 and significantly negatively correlated with the VAS score (P < 0.05).

Conclusion

The IgA+CD27- class-switched memory cell subset in human peripheral blood may serve as a potential biomarker for evaluating AR symptoms and treatment efficacy. Its mechanism may be associated with interactions between T and B cells.

Cellular immune response to SARS-CoV-2 and clinical presentation in individuals exposed to endemic malaria

Ghana and other parts of West Africa have experienced lower COVID-19 mortality rates than other regions. This phenomenon has been hypothesized to be associated with previous exposure to infections such as malaria. This study investigated the immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the influence of previous malaria exposure. Blood samples were collected from individuals with asymptomatic or symptomatic COVID-19 (n = 217). A variety of assays were used to characterize the SARS-CoV-2-specific immune response, and malaria exposure was quantified using Plasmodium falciparum ELISA. The study found evidence of attenuated immune responses to COVID-19 among asymptomatic individuals, with elevated proportions of non-classical monocytes and greater memory B cell activation. Symptomatic patients displayed higher P. falciparum-specific T cell recall immune responses, whereas asymptomatic individuals demonstrated elevated P. falciparum antibody levels. Summarily, this study suggests that P. falciparum exposure-associated immune modulation may contribute to reduced severity of SARS-CoV-2 infection among people living in malaria-endemic regions.

Benchmarking and integrating human B-cell receptor genomic and antibody proteomic profiling

Immunoglobulins (Ig), which exist either as B-cell receptors (BCR) on the surface of B cells or as antibodies when secreted, play a key role in the recognition and response to antigenic threats. The capability to jointly characterize the BCR and antibody repertoire is crucial for understanding human adaptive immunity. From peripheral blood, bulk BCR sequencing (bulkBCR-seq) currently provides the highest sampling depth, single-cell BCR sequencing (scBCR-seq) allows for paired chain characterization, and antibody peptide sequencing by tandem mass spectrometry (Ab-seq) provides information on the composition of secreted antibodies in the serum. Yet, it has not been benchmarked to what extent the datasets generated by these three technologies overlap and complement each other. To address this question, we isolated peripheral blood B cells from healthy human donors and sequenced BCRs at bulk and single-cell levels, in addition to utilizing publicly available sequencing data. Integrated analysis was performed on these datasets, resolved by replicates and across individuals. Simultaneously, serum antibodies were isolated, digested with multiple proteases, and analyzed with Ab-seq. Systems immunology analysis showed high concordance in repertoire features between bulk and scBCR-seq within individuals, especially when replicates were utilized. In addition, Ab-seq identified clonotype-specific peptides using both bulk and scBCR-seq library references, demonstrating the feasibility of combining scBCR-seq and Ab-seq for reconstructing paired-chain Ig sequences from the serum antibody repertoire. Collectively, our work serves as a proof-of-principle for combining bulk sequencing, single-cell sequencing, and mass spectrometry as complementary methods towards capturing humoral immunity in its entirety.

B Cells Dynamic in Aging and the Implications of Nutritional Regulation

Aging negatively affects B cell production, resulting in a decrease in B-1 and B-2 cells and impaired antibody responses. Age-related B cell subsets contribute to inflammation. Investigating age-related alterations in the B-cell pool and developing targeted therapies are crucial for combating autoimmune diseases in the elderly. Additionally, optimal nutrition, including carbohydrates, amino acids, vitamins, and especially lipids, play a vital role in supporting immune function and mitigating the age-related decline in B cell activity. Research on the influence of lipids on B cells shows promise for improving autoimmune diseases. Understanding the aging B-cell pool and considering nutritional interventions can inform strategies for promoting healthy aging and reducing the age-related disease burden.

Multi-faceted dysregulated immune response for COVID-19 infection explaining clinical heterogeneity

Clinical heterogeneity and varied prognosis are well noted for SARS-CoV-2 infection. Altered immune response is a major feature for the adverse prognosis however focus on altered immune response has been primarily limited to hyper-inflammatory responses like Cytokine storm. A deeper understanding of viral pathobiology and the interplay of innate and adaptive immune cells against SARS-CoV-2 infection is essential to optimize intervention strategy and future preparedness for SARS-CoV-2 or its related viral diseases. To uncover the immunological signatures driving the progression of SARS-CoV-2 infection, we performed an extensive immunophenotype on blood samples from 79 hospitalized patients with mild/moderate to severe infections as well as from healthy controls and recovered donors to understand the interplay between innate and adaptive responses impacting severity and prognosis. We observed multifarious immune dysregulation, varied across patients of the clinical spectrum. We observed 4 major dysregulations of immune phenotypes 1) depletion of M1φ (impaired antiviral response as APC), 2) immune suppression/exhaustion via activation of repressor like CD4+/CD8+PD1, TIM3, LAG3 3) inappropriate differentiation of lymphocyte (extreme elevated proportion of CD4 naive, memory B and T cells along with reduction of inflammatory activator like TLR2/4/TIGIT) and 4) cytokine storm. Our results show the identification of biomarkers to differentiate the different trajectories for SARS-CoV-2 infection.

Detection of Lymphocytic Choriomeningitis Virus-Specific Memory B Cells Using Antigen Tetramers

Memory B cells are central to the establishment of immunological memory, providing long-term protection against specific pathogens and playing a vital role in the efficacy of vaccines. Understanding how memory B cell formation is disrupted during persistent infection is essential for new therapeutics. Lymphocytic choriomeningitis virus (LCMV) is an ideal model for investigating memory B cells in acute versus chronic infection. This protocol details techniques to isolate, enrich, and examine LCMV-specific memory B cells in both acute and chronic LCMV infection. Using an antigen tetramer enrichment system and flow cytometry, this method assesses low-frequency, polyclonal antigen-specific memory B cells.

Requirements of IL-4 during the Generation of B Cell Memory

IL-4 has long been established as a key regulator of Th cells and for promoting effective B cell survival and isotype class switching. Yet, despite having been extensively studied, the specific role of IL-4 in generating humoral memory in vivo is unclear. In this review, we explore the recent studies that unravel the cellular sources and spatiotemporal production of IL-4, the relationship between IL-4 and IL-21 during germinal center responses and the formation of Ab-secreting cells, and the current understanding of whether IL-4 promotes or suppresses memory B cell generation in vitro and in vivo.

High-throughput spatiotemporal monitoring of single-cell secretions via plasmonic microwell arrays

Methods for the analysis of cell secretions at the single-cell level only provide semiquantitative endpoint readouts. Here we describe a microwell array for the real-time spatiotemporal monitoring of extracellular secretions from hundreds of single cells in parallel. The microwell array incorporates a gold substrate with arrays of nanometric holes functionalized with receptors for a specific analyte, and is illuminated with light spectrally overlapping with the device's spectrum of extraordinary optical transmission. Spectral shifts in surface plasmon resonance resulting from analyte-receptor bindings around a secreting cell are recorded by a camera as variations in the intensity of the transmitted light while machine-learning-assisted cell tracking eliminates the influence of cell movements. We used the microwell array to characterize the antibody-secretion profiles of hybridoma cells and of a rare subset of antibody-secreting cells sorted from human donor peripheral blood mononuclear cells. High-throughput measurements of spatiotemporal secretory profiles at the single-cell level will aid the study of the physiological mechanisms governing protein secretion.

Curcumin alleviates experimental colitis via a potential mechanism involving memory B cells and Bcl-6-Syk-BLNK signaling

BACKGROUND

Immune dysfunction is the crucial cause in the pathogenesis of inflammatory bowel disease (IBD), which is mainly related to lymphocytes (T or B cells, incl-uding memory B cells), mast cells, activated neutrophils, and macrophages. As the precursor of B cells, the activation of memory B cells can trigger and differentiate B cells to produce a giant variety of inducible B cells and tolerant B cells, whose dysfunction can easily lead to autoimmune diseases, including IBD.

AIM

To investigate whether or not curcumin (Cur) can alleviate experimental colitis by regulating memory B cells and Bcl-6-Syk-BLNK signaling.

METHODS

Colitis was induced in mice with a dextran sulphate sodium (DSS) solution in drinking water. Colitis mice were given Cur (100 mg/kg/d) orally for 14 con-secutive days. The colonic weight, colonic length, intestinal weight index, occult blood scores, and histological scores of mice were examined to evaluate the curative effect. The levels of memory B cells in peripheral blood of mice were measured by flow cytometry, and IL-1β, IL-6, IL-10, IL-7A, and TNF-α expression in colonic tissue homogenates were analyzed by enzyme-linked immunosorbent assay. Western blot was used to measure the expression of Bcl-6, BLNK, Syk, and other signaling pathway related proteins.

RESULTS

After Cur treatment for 14 d, the body weight, colonic weight, colonic length, colonic weight index, and colonic pathological injury of mice with colitis were ameliorated. The secretion of IL-1β, IL-6, TNF-α, and IL-7A was statistically decreased, while the IL-35 and IL-10 levels were considerably increased. Activation of memory B cell subsets in colitis mice was confirmed by a remarkable reduction in the expression of IgM, IgG, IgA, FCRL5, CD103, FasL, PD-1, CD38, and CXCR3 on the surface of CD19+ CD27+ B cells, while the number of CD19+ CD27+ IL-10+ and CD19+ CD27+ Tim-3+ B cells increased significantly. In addition, Cur significantly inhibited the protein levels of Syk, p-Syk, Bcl-6, and CIN85, and increased BLNK and p-BLNK expression in colitis mice.

CONCLUSION

Cur could effectively alleviate DSS-induced colitis in mice by regulating memory B cells and the Bcl-6-Syk-BLNK signaling pathway.

STAT5B restrains human B-cell differentiation to maintain humoral immune homeostasis

BACKGROUND

Lymphocyte differentiation is regulated by coordinated actions of cytokines and signaling pathways. IL-21 activates STAT1, STAT3, and STAT5 and is fundamental for the differentiation of human B cells into memory cells and antibody-secreting cells. While STAT1 is largely nonessential and STAT3 is critical for this process, the role of STAT5 is unknown.

OBJECTIVES

This study sought to delineate unique roles of STAT5 in activation and differentiation of human naive and memory B cells.

METHODS

STAT activation was assessed by phospho-flow cytometry cell sorting. Differential gene expression was determined by RNA-sequencing and quantitative PCR. The requirement for STAT5B in B-cell and CD4+ T-cell differentiation was assessed using CRISPR-mediated STAT5B deletion from B-cell lines and investigating primary lymphocytes from individuals with germline STAT5B mutations.

RESULTS

IL-21 activated STAT5 and strongly induced SOCS3 in human naive, but not memory, B cells. Deletion of STAT5B in B-cell lines diminished IL-21-mediated SOCS3 induction. PBMCs from STAT5B-null individuals contained expanded populations of immunoglobulin class-switched B cells, CD21loTbet+ B cells, and follicular T helper cells. IL-21 induced greater differentiation of STAT5B-deficient B cells into plasmablasts in vitro than B cells from healthy donors, correlating with higher expression levels of transcription factors promoting plasma cell formation.

CONCLUSIONS

These findings reveal novel roles for STAT5B in regulating IL-21-induced human B-cell differentiation. This is achieved by inducing SOCS3 to attenuate IL-21 signaling, and BCL6 to repress class switching and plasma cell generation. Thus, STAT5B is critical for restraining IL-21-mediated B-cell differentiation. These findings provide insights into mechanisms underpinning B-cell responses during primary and subsequent antigen encounter and explain autoimmunity and dysfunctional humoral immunity in STAT5B deficiency.

Spatial determinates of effector and memory CD8+ T cell fates

The lymph node plays a critical role in mounting an adaptive immune response to infection, clearance of foreign pathogens, and cancer immunosurveillance. Within this complex structure, intranodal migration is vital for CD8⁺ T cell activation and differentiation. Combining tissue clearing and volumetric light sheet fluorescent microscopy of intact lymph nodes has allowed us to explore the spatial regulation of T cell fates. This has determined that short-lived effector (T_SLEC ) are imprinted in peripheral lymph node interfollicular regions, due to CXCR3 migration. In contrast, stem-like memory cell (T_SCM ) differentiation is determined in the T cell paracortex. Here, we detail the inflammatory and chemokine regulators of spatially restricted T cell differentiation, with a focus on how to promote T_SCM . We propose a default pathway for T_SCM differentiation due to CCR7-directed segregation of precursors away from the inflammatory effector niche. Although volumetric imaging has revealed the consequences of intranodal migration, we still lack knowledge of how this is orchestrated within a complex chemokine environment. Toward this goal, we highlight the potential of combining microfluidic chambers with pre-determined complexity and subcellular resolution microscopy.

Engraving our first B cell memories into the repertoire

Memory B cells are central to effective protection against reinfection. Glaros et al. used single-cell techniques to illuminate how activated mouse B cells are diverted into forming memory cells a few days post-immunogenic exposure. Early memory subsets contribute to a crucial goal: building a diverse and agile humoral defense system.

Advances in understanding the formation and fate of B-cell memory in response to immunization or infection

Immunological memory has the potential to provide lifelong protection against recurrent infections. As such, it has been crucial to the success of vaccines. Yet, the recent pandemic has illuminated key gaps in our knowledge related to the factors influencing effective memory formation and the inability to predict the longevity of immune protection. In recent decades, researchers have acquired a number of novel and powerful tools with which to study the factors underpinning humoral memory. These tools have been used to study the B-cell fate decisions that occur within the germinal centre (GC), a site where responding B cells undergo affinity maturation and are one of the major routes for memory B cell and high-affinity long-lived plasma cell formation. The advent of single-cell sequencing technology has provided an enhanced resolution for studying fate decisions within the GC and cutting-edge techniques have enabled researchers to model this reaction with more accuracy both in vitro and in silico. Moreover, modern approaches to studying memory B cells have allowed us to gain a better appreciation for the heterogeneity and adaptability of this vital class of B cells. Together, these studies have facilitated important breakthroughs in our understanding of how these systems operate to ensure a successful immune response. In this review, we describe recent advances in the field of GC and memory B-cell biology in order to provide insight into how humoral memory is formed, as well as the potential for generating lasting immunity to novel pathogens such as severe acute respiratory syndrome coronavirus 2.

Circulating IgA/IgG memory B cells against Mycobacterium tuberculosis dormancy-associated antigens Rv2659c and Rv3128c in active and latent tuberculosis

OBJECTIVE

To elucidate the antigenic potential of dormancy-associated antigens Rv2659c and Rv3128c of Mycobacterium tuberculosis by examining the persistence of specific IgG and IgA memory B cells (MBCs) among patients with active tuberculosis (TB), household contacts with latent tuberculosis (LTBI), and an endemic healthy control group.

METHODS

Fresh peripheral blood mononuclear cells from the three study groups were used to enumerate the numbers of IgG and IgA MBCs specific to recombinant protein Rv2659c and Rv3128c by ELISpot assay. The composition of MBC subsets IgA⁺ and IgG ⁺ was analyzed by flow cytometry.

RESULTS

The number of IgA MBCs specific to antigen Rv2659c was significantly higher in the LTBI group than the TB group. In contrast, no significant difference was found in IgA or IgG MBCs against antigen Rv3128c. The number of IgA⁺ MBCs was significantly higher than that of IgG⁺ MBCs in the classical MBC subset of the LTBI group.

CONCLUSION

The results indicated that the dormancy-associated antigen Rv2659c induced an IgA MBCs response in individuals with latent TB, and IgA⁺ classical MBCs formed a major portion of the MBCs subset. This new knowledge will be beneficial for the development of novel TB vaccines and their control of latent TB.

Immunity to Influenza Infection in Humans

This review discusses the human immune responses to influenza infection with some insights from studies using animal models, such as experimental infection of mice. Recent technological advances in the study of human immune responses have greatly added to our knowledge of the infection and immune responses, and therefore much of the focus is on recent studies that have moved the field forward. We consider the complexity of the adaptive response generated by many sequential encounters through infection and vaccination.

Analysis of Antigen-Specific Human Memory B Cell Populations Based on In Vitro Polyclonal Stimulation

Antigen-specific memory B cell (MBC) populations mediate the rapid, strong, and high-affinity secondary antibody responses that play a key role in combating infection and generating protective responses to vaccination. Recently, cell staining with fluorochrome-labeled antigens together with sequencing methods such as Drop-seq and CITE-seq have provided information on the specificity, phenotype, and transcriptome of single MBCs. However, characterization of MBCs at the level of antigen-reactive populations remains an important tool for assessing an individual's B cell immunity and responses to antigen exposure. This is readily performed using a long-established method based on in vitro polyclonal stimulation of MBCs to induce division and differentiation into antibody-secreting cells (ASCs). Post-stimulation antigen-specific measurement of the MBC-derived ASCs (or the secreted antibodies) indicates the size of precursor MBC populations. Additional information about the character of antigen-reactive MBC populations is provided by analysis of MBC-derived antibodies of particular specificities for binding avidity and functionality. This article outlines a simple and reliable strategy for efficient in vitro MBC stimulation and use of the ELISpot assay as a post-stimulation readout to determine the size of antigen-specific MBC populations. Other applications of the in vitro stimulation technique for MBC analysis are discussed. The following protocols are included. © 2020 Wiley Periodicals LLC Basic Protocol 1: Polyclonal stimulation of memory B cells using unfractionated PBMCs Alternate Protocol: Stimulation of small PBMC numbers using 96-well plates with U-bottom wells Basic Protocol 2: ELISpot assay for enumeration of memory B cell-derived antibody-secreting cells.

The Histone Methyltransferase DOT1L Is Essential for Humoral Immune Responses

Histone modifiers are essential for the ability of immune cells to reprogram their gene expression during differentiation. The recruitment of the histone methyltransferase DOT1L (disruptor of telomeric silencing 1-like) induces oncogenic gene expression in a subset of B cell leukemias. Despite its importance, its role in the humoral immune system is unclear. Here, we demonstrate that DOT1L is a critical regulator of B cell biology. B cell development is defective in Dot1l^f/fMb1^Cre/+ mice, culminating in a reduction of peripheral mature B cells. Upon immunization or influenza infection of Dot1l^f/fCd23^Cre/+ mice, class-switched antibody-secreting cells are significantly attenuated and germinal centers fail to form. Consequently, DOT1L is essential for B cell memory formation. Transcriptome, pathway, and histological analyses identified a role for DOT1L in reprogramming gene expression for appropriate localization of B cells during the initial stage of the response. Together, these results demonstrate an essential role for DOT1L in generating an effective humoral immune response.

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.

Dysregulation of humoral immunity in chronic infection

Chronic viral infections disrupt the ability of the humoral immune response to produce neutralizing antibody or form effective immune memory, preventing viral clearance and making vaccine design difficult. Multiple components of the B-cell response are affected by pathogens that are not cleared from the host. Changes in the microenvironment shift production of B cells to short-lived plasma cells early in the response. Polyclonal B cells are recruited into both the plasma cell and germinal center compartments, inhibiting the formation of a targeted, high-affinity response. Finally, memory B cells shift toward an "atypical" phenotype, which may in turn result in changes to the functional properties of this population. While similar properties of B-cell dysregulation have been described across different types of persistent infections, key questions about the underlying mechanisms remain. This review will discuss the recent advances in this field, as well as highlight the critical questions about the interplay between viral load, microenvironment, the polyclonal response and atypical memory B cells that are yet to be answered. Design of new preventative treatments will rely on identifying the extrinsic and intrinsic modulators that push B cells toward an ineffective response, and thus identify new ways to guide them back onto the best path for clearance of virus and formation of effective immune memory.

Epigenetic regulation of B cell fate and function during an immune response

The humoral immune response requires coordination of molecular programs to mediate differentiation into unique B cell subsets that help clear the infection and form immune memory. Epigenetic modifications are crucial for ensuring that the appropriate genes are transcribed or repressed during B cell differentiation. Recent studies have illuminated the changes in DNA methylation and histone post-translational modifications that accompany the formation of germinal center and antibody-secreting cells during an immune response. In particular, the B cell subset-specific expression and function of DNA methyltransferases and histone-modifying complexes that mediate epigenome changes have begun to be unravelled. This review will discuss the recent advances in this field, as well as highlight critical questions about the relationship between epigenetic regulation and B cell fate and function that are yet to be answered.

Overexpression of T-bet in HIV infection is associated with accumulation of B cells outside germinal centers and poor affinity maturation

Nearly all chronic human infections are associated with alterations in the memory B cell (MBC) compartment, including a large expansion of CD19hiT-bethi MBC in the peripheral blood of HIV-infected individuals with chronic viremia. Despite their prevalence, it is unclear how these B cells arise and whether they contribute to the inefficiency of antibody-mediated immunity in chronic infectious diseases. We addressed these questions by characterizing T-bet-expressing B cells in lymph nodes (LN) and identifying a strong T-bet signature among HIV-specific MBC associated with poor immunologic outcome. Confocal microscopy and quantitative imaging revealed that T-bethi B cells in LN of HIV-infected chronically viremic individuals distinctly accumulated outside germinal centers (GC), which are critical for optimal antibody responses. In single-cell analyses, LN T-bethi B cells of HIV-infected individuals were almost exclusively found among CD19hi MBC and expressed reduced GC-homing receptors. Furthermore, HIV-specific B cells of infected individuals were enriched among LN CD19hiT-bethi MBC and displayed a distinct transcriptome, with features similar to CD19hiT-bethi MBC in blood and LN GC B cells (GCBC). LN CD19hiT-bethi MBC were also related to GCBC by B cell receptor (BCR)-based phylogenetic linkage but had lower BCR mutation frequencies and reduced HIV-neutralizing capacity, consistent with diminished participation in GC-mediated affinity selection. Thus, in the setting of chronic immune activation associated with HIV viremia, failure of HIV-specific B cells to enter or remain in GC may help explain the rarity of high-affinity protective antibodies.

The Importance of Vaccinating Children and Pregnant Women against Influenza Virus Infection

Influenza virus infection is responsible for significant morbidity and mortality in the pediatric and pregnant women populations, with deaths frequently caused by severe influenza-associated lower respiratory tract infection and acute respiratory distress syndrome (ARDS). An appropriate immune response requires controlling the viral infection through activation of antiviral defenses, which involves cells of the lung and immune system. High levels of viral infection or high levels of inflammation in the lower airways can contribute to ARDS. Pregnant women and young children, especially those born prematurely, may develop serious complications if infected with influenza virus. Vaccination against influenza will lead to lower infection rates and fewer complications, even if the vaccine is poorly matched to circulating viral strains, with maternal vaccination offering infants protection via antibody transmission through the placenta and breast milk. Despite the health benefits of the influenza vaccine, vaccination rates around the world remain well below targets. Trust in the use of vaccines among the public must be restored in order to increase vaccination rates and decrease the public health burden of influenza.

Role of Memory B Cells in Hemagglutinin-Specific Antibody Production Following Human Influenza A Virus Infection

When influenza A virus infects an immune individual, preexisting memory B cell (MBC) activation and rapid anamnestic antibody production plays a key role in viral clearance. The most effective neutralizing antibodies target the antigenically variable head of the viral hemagglutinin (HA); antibodies against the conserved HA stalk provide broader but less potent protection. In this review, we provide a comprehensive picture of an adult's HA-specific antibody response to influenza virus infection. The process is followed from preexisting HA-specific MBC activation and rapid production of anti-HA antibodies, through to germinal center seeding and adaptation of the response to novel features of the HA. A major focus of the review is the role of competition between preexisting MBCs in determining the character of the HA-reactive antibody response. HA novelty modifies this competition and can shift the response from the immunodominant head to the stalk. We suggest that antibodies resulting from preexisting MBC activation are important regulators of anti-HA antibody production and play a role in positive selection of germinal center B cells reactive to novel HA epitopes. Our review also considers the role of MBCs in the effects of early-life imprinting on HA head- and stalk-specific antibody responses to influenza infection. An understanding of the processes described in this review will guide development of vaccination strategies that provide broadly effective protection.