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This post hoc analysis of the randomized, placebo-controlled N-MOmentum study (NCT02200770) of inebilizumab in neuromyelitis optica spectrum disorder (NMOSD) evaluated relationships between circulating B-cell subsets and aquaporin-4 immunoglobulin G (AQP4-lgG) titers and attacks. Among participants receiving placebo, CD20+ and CD27+ B-cell counts were modestly increased from the pre-attack visit to attack; plasmablast/plasma cell gene signature was increased from baseline to the pre-attack visit (p = 0.016) and from baseline to attack (p = 0.009). With inebilizumab treatment, B-cell subset counts decreased and did not increase with attacks. No difference in change of AQP4-IgG titers from baseline to time of attack was observed.

People living with HIV (PLWH) are at higher risk of developing lymphoma. In this study, we performed cytometry by time-of-flight (CyTOF) on peripheral blood mononuclear cells of cART-naïve HIV+ individuals and cART-naïve HIV+ individuals prior to AIDS-associated non-Hodgkin lymphoma (pre-NHL) diagnosis. Participants were enrolled in the Los Angeles site of the MACS/WIHS Combined Cohort Study (MWCCS). Uniform Manifold Approximation and Projection (UMAP) and unsupervised clustering analysis were performed to identify differences in the expression of B-cell activation markers and/or oncogenic markers associated with lymphomagenesis. CD10+CD27- B cells, CD20+CD27- B cells, and B-cell populations with aberrant features (CD20+CD27+CXCR4+CD71+ B cells and CD20+CXCR4+cMYC+ B cells) were significantly elevated in HIV+ cART-naïve compared to HIV-negative samples. CD20+CD27+CD24+CXCR4+CXCR5+ B cells, CD20+CD27+CD10+CD24+CXCR4+cMYC+ B cells, and a cluster of CD20+CXCR4hiCD27-CD24+CXCR5+CD40+CD4+AICDA+ B cells were significantly elevated in HIV+ pre-NHL (cART-naïve) compared to HIV+ cART-naïve samples. A potentially clonal cluster of CD20+CXCR4+CXCR5+cMYC+AICDA+ B cells and a cluster of germinal center B-cell-like cells (CD19-CD20+CXCR4+Bcl-6+PD-L1+cMYC+) were also found in the circulation of HIV+ pre-NHL (cART-naïve) samples. Moreover, significantly elevated clusters of CD19+CD24hiCD38hi cMYC+ AICDA+ B regulatory cells were identified in HIV+ pre-NHL (cART-naïve) compared to HIV+ cART-naïve samples. The present study identifies unique B-cell subsets in PLWH with potential pre-malignant features that may contribute to the development of pre-tumor B cells in PLWH and that may play a role in lymphomagenesis.

Background Thyroid autoantibody is a marker for the diagnosis of Hashimoto's thyroiditis (HT), and B cells are essential in the pathogenesis of HT. Enhancer of Zeste homolog 2 (EZH2), which is an important epigenetic regulator, plays an important role in the regulation of lymphocytes development and function. Objective To investigate EZH2 expression in plasmoblasts and plasma cells in HT, and further explore the therapeutic effect of EZH2 inhibitors in experimental autoimmune thyroiditis (EAT) model. Methods The thyroid tissues from 6 patients who underwent thyroidectomy (3 HT patients with PTC, 3 patients with PTC alone) in Peking University First Hospital between 2010 and 2020 were obtained from the contralateral lobe with thyroid cancer, and screened for the expression of B-lymphocyte-related genes by RNA-seq; thyroid tissues from 16 HT patients and 8 normal thyroid tissues were collected and verified for the the expression of EZH2 in B cells in HT thyroid tissues by immunohistochemistry or immunofluorescence, respectively. Fine-needle aspiration (FNA) samples from patients with HT (n=25), and peripheral blood from patients with HT (n=19) or healthy donors (n=12) were analyzed by flow cytometry to define altered EZH2 expression in plasmablasts and plasma cells. Fifteen seven-week-old NOD.H-2h4 mice were randomly divided into the control (n=5), EAT without injection group (n=5), and EZH2 inhibitor+ GSK126 injection group (10 mg/kg, intraperitoneal injection 3 times /week, n=5). The degree of thyroid inflammation and changes in TgAb levels were observed after 8 weeks. Results RNA sequencing analysis showed that EZH2 and genes associated with the B-cell phenotype such as CD19, CD27, CD38, CD52 were higher expressed in HT hyroid tissues compared with normal thyroid tissues. Immunohistochemical results showed that immunohistochemical staining for EZH2 in 16 HT thyroid tissue specimens was strongly positive with positive cells observed in the GC region, and no positive cells were observed in the staining of 8 normal thyroid tissues. EZH2 staining in HT thyroid tissue was highly expressed in the GC region, and EZH2 was specifically expressed in CD19+ B cells. The results of flow cytometry assay showed that the proportion of CD19+ B cells, plasmablasts and plasma cells in HT FNA samples was higher than that of HD peripheral blood and HT peripheral blood samples (P

Evolutionarily conserved, "natural" (n)IgM is broadly reactive to both self and foreign antigens. Its selective deficiency leads to increases in autoimmune diseases and infections. In mice, nIgM is secreted independent of microbial exposure to bone marrow (BM) and spleen B-1 cell-derived plasma cells (B-1PC), generating the majority of nIgM, or by B-1 cells that remain non-terminally differentiated (B-1sec). Thus, it has been assumed that the nIgM repertoire is broadly reflective of the repertoire of body cavity B-1 cells. Studies here reveal, however, that B-1PC generate a distinct, oligoclonal nIgM repertoire, characterized by short CDR3 variable immunoglobulin heavy chain regions, 7-8 amino acids in length, some public, many arising from convergent rearrangements, while specificities previously associated with nIgM were generated by a population of IgM-secreting B-1 (B-1sec). BM, but not spleen B-1PC, or B-1sec also required the presence of TCRαβ CD4 T cells for their development from fetal precursors. Together, the studies identify important previously unknown characteristics of the nIgM pool.

The complement system, a vital component of innate immunity, consists of various proteins and pathways crucial for the recognition and elimination of pathogens. In addition, it plays a major role in the initiation of adaptive response through the opsonization of antigens, contributing to B-cell activation and memory maintenance. Deficiencies in complement proteins, particularly C3, can lead to severe and recurrent infections as well as immune complex disorders. Here, we present a case report of two siblings with total C3 deficiency resulting from compound heterozygous mutations in C3 (NM_000064.4): c.305dup; [p.Asn103GlnfsTer66] and c.1269 + 5G>T, previously unreported in C3-related diseases. Both, the index case and her sister, presented a history of recurrent infections since early childhood and one of them developed hemolytic uremic syndrome (HUS). Immunological evaluation revealed absent plasma C3 levels, decreased memory B cells, hypogammaglobulinemia, and impaired response to polysaccharide antigens. The siblings showed partial responses to antimicrobial prophylaxis and vaccination, requiring intravenous immunoglobulin replacement therapy, resulting in clinical improvement. Genetic analysis identified additional risk polymorphisms associated with atypical HUS. This case highlights the importance of comprehensive genetic and immunological evaluations in complement deficiencies, along with the potential role of immunoglobulin replacement therapy in managing associated antibody defects.

BackgroundIL-6 receptor (IL-6R) signaling drives development of T cell populations important to type 1 diabetes pathogenesis. We evaluated whether blockade of IL-6R with monoclonal antibody tocilizumab would slow loss of residual β cell function in newly diagnosed type 1 diabetes patients.MethodsWe conducted a multicenter, randomized, placebo-controlled, double-blind trial with tocilizumab in new-onset type 1 diabetes. Participants were screened within 100 days of diagnosis. Eligible participants were randomized 2:1 to receive 7 monthly doses of tocilizumab or placebo. The primary outcome was the change from screening in the mean AUC of C-peptide collected during the first 2 hours of a mixed meal tolerance test at week 52 in pediatric participants (ages 6-17 years).ResultsThere was no statistical difference in the primary outcome between tocilizumab and placebo. Immunophenotyping showed reductions in downstream signaling of the IL-6R in T cells but no changes in CD4 memory subsets, Th17 cells, Tregs, or CD4+ T effector cell resistance to Treg suppression. A DC subset decreased during therapy but regressed to baseline once therapy stopped. Tocilizumab was well tolerated.ConclusionTocilizumab reduced T cell IL-6R signaling but did not modulate CD4+ T cell phenotypes or slow loss of residual β cell function in newly diagnosed individuals with type 1 diabetes.Trial RegistrationClinicalTrials.gov NCT02293837.FundingNIH National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and National Institute of Allergy and Infectious Diseases (NIAID) UM1AI109565, UL1TR000004 from NIH/National Center for Research Resources (NCRR) Clinical and Translational Science Award (CTSA), NIH/NIDDK P30DK036836, NIH/NIDDK U01DK103266, NIH/NIDDK U01DK103266, 1UL1TR000064 from NIH/NCRR CTSA, NIH/National Center for Advancing Translational Sciences (NCATS) UL1TR001878, UL1TR002537 from NIH/CTSA; National Health and Medical Research Council Practitioner Fellowship (APP1136735), NIH/NIDDK U01-DK085476, NIH/CTSA UL1-TR002494, Indiana Clinical and Translational Science Institute Award UL1TR002529, Vanderbilt Institute for Clinical and Translational Research UL1TR000445. NIH/NCATS UL1TR003142, NIH/CTSA program UL1-TR002494, Veteran Affairs Administration, and 1R01AI132774.

B cells within germinal centers (GCs) enter cycles of antibody affinity maturation or exit the GC as memory cells or plasma cells. Here, we examined the contribution of interleukin (IL)-4 on B cell fate decisions in the GC. Single-cell RNA-sequencing identified a subset of light zone GC B cells expressing high IL-4 receptor-a (IL4Ra) and CD23 and lacking a Myc-associated signature. These cells could differentiate into pre-memory cells. B cell-specific deletion of IL4Ra or STAT6 favored the pre-memory cell trajectory, and provision of exogenous IL-4 in a wild-type context reduced pre-memory cell frequencies. IL-4 acted during antigen-specific interactions but also influenced bystander cells. Deletion of IL4Ra from follicular dendritic cells (FDCs) increased the availability of IL-4 in the GC, impaired the selection of affinity-matured B cells, and reduced memory cell generation. We propose that GC FDCs establish a niche that limits bystander IL-4 activity, focusing IL-4 action on B cells undergoing selection and enhancing memory cell differentiation.

We report perhaps the most comprehensive study of subsets of CD4+ and CD8+ and subsets of B cells in a mild symptomatic SARS-CoV-2+ immunocompetent patient and a common variable immunodeficiency disease (CVID) patient who had normal absolute lymphocyte counts and remained negative for SARS-CoV-2 IgG antibodies. Naïve (TN), central memory (TCM), effector memory (TEM), and terminally differentiated effector memory (TEMRA) subsets of CD4+ and CD8+ T cells, subsets of T follicular helper cells (cTFH, TFH1, TFH2, TFH17, TFH1/TFH17, and TFR), CD4 Treg, CD8 Treg, mature B cells, transitional B cells, marginal zone B cells, germinal center (GC) B cells, CD21low B cells, antibody-secreting cells (plasmablasts), and Breg cells were examined in patients and age-matched controls with appropriate monoclonal antibodies and isotype controls using multicolor flow cytometry. Different patterns of abnormalities (often contrasting) were observed in the subsets of CD4+ T, CD8+ T, B-cell subsets, and regulatory lymphocytes among the immunocompetent patient and CVID patient as compared to corresponding healthy controls. Furthermore, when data were analyzed between the 2 patients, the immunocompetent patient demonstrated greater changes in various subsets as compared to the CVID patient. These data demonstrate different immunological responses to SARS-CoV-2 infection in an immunocompetent patient and the CVID patient. A marked decrease in GC B cells and plasmablasts may be responsible for failure to make SARS-CoV-2 antibodies. The lack of SARS-CoV-2 antibodies with mild clinical disease suggests an important role of T-cell response in defense against SARS-CoV-2 infection.

Circulating TFH (cTFH ) cells express CXCR5, PD-1, and, when activated, ICOS, and release IL-21. According to the production of IFN-γ, IL-4, and IL-17 and expression of FoxP3, these cells are also classified as cTFH 1, cTFH 2, cTFH 17, and cTFR cells, respectively. This CD4+ T-cell subset is pivotal to efficient humoral immunity, and pregnancy appears to favor IgG production. Here, not only pregnancy amplified the in vivo production of anti-HBsAg IgG in HBV immunized women, but the frequency of cTFH cells was directly correlated with estradiol levels. In vitro, pregnancy-related dose of 17-β-estradiol (E2) directly increased the percentage of different cTFH subsets. While E2 and progesterone (P4) increased the proportion of differentiated TFH cells derived from naïve CD4+ T-cells, only E2 amplified the release of IL-21 in those cell cultures. In addition, E2 and P4 increased the proportion of memory B cells and plasma cells, respectively. In SEB-activated B/TFH cell co-cultures, E2, in the presence of P4, increased the production of total IgG. Finally, among the hormones, P4 was stronger in upregulating the percentage of IL-10+ TFR cells. Collectively, our findings suggested that E2 and P4 cooperate in the humoral immune response by favoring the expansion of different cTFH and B cell subsets.

Kidney transplant recipients are patients at high risk for coronavirus disease 2019 (COVID-19) due to being on immunosuppressive therapy. B cell depletion therapy, including rituximab, is an important strategy for ABO-incompatible transplants. However, knowledge about the effect of B cell depletion therapy on COVID-19 is lacking. Thirty kidney transplant recipients who developed COVID-19 were included in this study. To examine the impact of B cell depletion therapy, we retrospectively investigated the relationship between the background of the patients and the clinical outcome. Of the 30 patients, 13 received B cell depletion therapy. The median time between transplant and onset of COVID-19 was 6.1 years after transplantation; however, nine cases remained markedly depleted of CD19(+) cells (<4.0%). The patients were assigned to the normal (n = 21) and depletion groups (n = 9). Progression rates in the depletion and normal groups were 55.6% and 9.5%, respectively (p = 0.014). Furthermore, the survival rate was significantly lower in the depletion group (100% in the normal group vs. 66.7% in the depletion group; p = 0.021). B cell depletion therapy may have long-term effects and increase the risk of COVID-19 in kidney transplant recipients. [ABSTRACT FROM AUTHOR]

Memory B cells (MBCs) are essential for long-lived humoral immunity. However, the transcription factors involved in MBC differentiation are poorly defined. Here, using single-cell RNA sequencing analysis, we identified a population of germinal center (GC) B cells in the process of differentiating into MBCs. Using an inducible CRISPR-Cas9 screening approach, we identified the hematopoietically expressed homeobox protein Hhex as a transcription factor regulating MBC differentiation. The corepressor Tle3 was also identified in the screen and was found to interact with Hhex to promote MBC development. Bcl-6 directly repressed Hhex in GC B cells. Reciprocally, Hhex-deficient MBCs exhibited increased Bcl6 expression and reduced expression of the Bcl-6 target gene Bcl2. Overexpression of Bcl-2 was able to rescue MBC differentiation in Hhex-deficient cells. We also identified Ski as an Hhex-induced transcription factor involved in MBC differentiation. These findings establish an important role for Hhex-Tle3 in regulating the transcriptional circuitry governing MBC differentiation.

ObjectiveTo investigate the effect of cholecalciferol (vitamin D3) supplementation on peripheral immune cell frequency and N-glycan branching in patients with relapsing-remitting multiple sclerosis (RRMS).MethodsExploratory analysis of high-dose (20 400 IU) and low-dose (400 IU) vitamin D3 supplementation taken every other day of an 18-month randomized controlled clinical trial including 38 RRMS patients on stable immunomodulatory therapy (NCT01440062). We investigated cholecalciferol treatment effects on N-glycan branching using L-PHA stain (phaseolus vulgaris leukoagglutinin) at 6 months and frequencies of T-, B-, and NK-cell subpopulations at 12 months with flow cytometry.ResultsHigh-dose supplementation did not change CD3+ T cell subsets, CD19+ B cells subsets, and NK cells frequencies, except for CD8+ T regulatory cells, which were reduced in the low-dose arm compared to the high-dose arm at 12 months. High-dose supplementation decreased N-glycan branching on T and NK cells, measured as L-PHA mean fluorescence intensity (MFI). A reduction of N-glycan branching in B cells was not significant. In contrast, low-dose supplementation did not affect N-glycan branching. Changes in N-glycan branching did not correlate with cell frequencies.InterpretationImmunomodulatory effect of vitamin D may involve regulation of N-glycan branching in vivo. Vitamin D3 supplementation did at large not affect the frequencies of peripheral immune cells.

BACKGROUND:CD8+ regulatory T cells (CD8+ Tregs) are relatively recently described T cell subsets that have been shown to regulate various T cell responses and appear to play a role in autoimmunity. However, their effects on B cells have not been explored. OBJECTIVES:In this investigation we examine the effect of CD8+ Tregs on various subsets of peripheral B cells include naïve B cells, transitional B cells, marginal zone B cells, IgM memory B cells, class switched memory B cells, and plasmablasts, and on the expression of B cell-activating factor receptor (BAFF-R). METHODS:CD8+ T cells were first purified and then activated with anti-CD3/CD28 beads to generate CD8+ Tregs. Purified CD19+ B cells were cultured alone or with sorted CD8+ Tregs (CD8+CD183+CCR7+CD45RA-) and activated with anti-CD40 monoclonal antibody and CpG. B cell subsets and the expression of BAFF-R on naïve and memory B cells were analyzed using various monoclonal antibodies and corresponding control isotypes. Ten thousand cells were acquired and analyzed by FACSCalibur using the FlowJo software. RESULTS:CD8+ Tregs selectively and significantly suppressed plasmablasts without any significant effect on other B cell subsets or on the expression of BAFF-R. CONCLUSION:CD8+ Tregs may play a role in autoimmunity by regulating antibody production via suppression of plasmablasts.

Calcium (Ca2+) flux acts as a central signaling pathway in B cells, and its alterations are associated with autoimmune dysregulation and B-cell malignancies. We standardized a flow-cytometry-based method using various stimuli to investigate the Ca2+ flux characteristics of circulating human B lymphocytes from healthy individuals. We found that different activating agents trigger distinct Ca2+ flux responses and that B-cell subsets show specific developmental-stage dependent Ca2+ flux response patterns. Naive B cells responded with a more substantial Ca2+ flux to B cell receptor (BCR) stimulation than memory B cells. Non-switched memory cells responded to anti-IgD stimulation with a naive-like Ca2+ flux pattern, whereas their anti-IgM response was memory-like. Peripheral antibody-secreting cells retained their IgG responsivity but showed reduced Ca2+ responses upon activation, indicating their loss of dependence on Ca2+ signaling. Ca2+ flux is a relevant functional test for B cells, and its alterations could provide insight into pathological B-cell activation development. [ABSTRACT FROM AUTHOR]

RATIONALE:B-1 cell-derived natural IgM antibodies against oxidation-specific epitopes on low-density lipoprotein are anti-inflammatory and atheroprotective. Bone marrow (BM) B-1a cells contribute abundantly to IgM production, yet the unique repertoire of IgM antibodies generated by BM B-1a and the factors maintaining the BM B-1a population remain unexplored. CXCR4 (C-X-C motif chemokine receptor 4) has been implicated in human cardiovascular disease and B-cell homeostasis, yet the role of B-1 cell CXCR4 in regulating atheroprotective IgM levels and human cardiovascular disease is unknown. OBJECTIVE:To characterize the BM B-1a IgM repertoire and to determine whether CXCR4 regulates B-1 production of atheroprotective IgM in mice and humans. METHODS AND RESULTS:Single-cell sequencing demonstrated that BM B-1a cells from aged ApoE-/- mice with established atherosclerosis express a unique repertoire of IgM antibodies containing increased nontemplate-encoded nucleotide additions and a greater frequency of unique heavy chain complementarity determining region 3 sequences compared with peritoneal cavity B-1a cells. Some complementarity determining region 3 sequences were common to both compartments suggesting B-1a migration between compartments. Indeed, mature peritoneal cavity B-1a cells migrated to BM in a CXCR4-dependent manner. Furthermore, BM IgM production and plasma IgM levels were reduced in ApoE-/- mice with B-cell-specific knockout of CXCR4, and overexpression of CXCR4 on B-1a cells increased BM localization and plasma IgM against oxidation specific epitopes, including IgM specific for malondialdehyde-modified LDL (low-density lipoprotein). Finally, in a 50-subject human cohort, we find that CXCR4 expression on circulating human B-1 cells positively associates with plasma levels of IgM antibodies specific for malondialdehyde-modified LDL and inversely associates with human coronary artery plaque burden and necrosis. CONCLUSIONS:These data provide the first report of a unique BM B-1a cell IgM repertoire and identifies CXCR4 expression as a critical factor selectively governing BM B-1a localization and production of IgM against oxidation specific epitopes. That CXCR4 expression on human B-1 cells was greater in humans with low coronary artery plaque burden suggests a potential targeted approach for immune modulation to limit atherosclerosis.

Secreted IgM (sIgM) is a multifunctional evolutionary conserved antibody that is critical for the maintenance of tissue homeostasis as well as the development of fully protective humoral responses to pathogens. Constitutive secretion of self- and polyreactive natural IgM, produced mainly by B-1 cells, provides a circulating antibody that engages with autoantigens as well as invading pathogens, removing apoptotic and other cell debris and initiating strong immune responses. Pathogen-induced IgM production by B-1 and conventional B-2 cells strengthens this early, passive layer of IgM-mediated immune defense and regulates subsequent IgG production. The varied effects of secreted IgM on immune homeostasis and immune defense are facilitated through its binding to numerous different cell types via different receptors. Recent studies identified a novel function for pentameric IgM, namely as a transporter for the effector protein ″apoptosis-inhibitor of macrophages″ (AIM/CD5L). This review aims to provide a summary of the known functions and effects of sIgM on immune homeostasis and immune defense, and its interaction with its various receptors, and to highlight the many critical immune regulatory functions of this ancient and fascinating immunoglobulin.

In mice, neonatally-developing, self-reactive B-1 cells generate steady levels of natural antibodies throughout life. B-1 cells can, however, also rapidly respond to infections with increased local antibody production. The mechanisms regulating these two seemingly very distinct functions are poorly understood, but have been linked to expression of CD5, an inhibitor of BCR-signaling. Here we demonstrate that TLR-mediated activation of CD5+ B-1 cells induced the rapid reorganization of the IgM-BCR complex, leading to the eventual loss of CD5 expression, and a concomitant increase in BCR-downstream signaling, both in vitro and in vivo after infections of mice with influenza virus and Salmonella typhimurium. Both, initial CD5 expression and TLR-mediated stimulation, were required for the differentiation of B-1 cells to IgM-producing plasmablasts after infections. Thus, TLR-mediated signals support participation of B-1 cells in immune defense via BCR-complex reorganization.

B-1 cells represent an innate-like early-developing B cell population, whose existence as an independent lymphocyte subset has been questioned in the past. Recent molecular and lineage tracing studies have not only confirmed their unique origins and differentiation paths, they have also provided a rationale for their distinctive functionalities compared to conventional B cells. This review summarizes our current understanding of B-1 cell development, and the activation events that regulate B-1 cell responses to self and foreign antigens. We discuss the unresolved question to what extent BCR engagement, that is, antigen-specificity versus innate signaling contributes to B-1 cell's participation in tissue homeostasis and immune defense as providers of 'natural' and antigen-induced antibody responses, and as cytokine-producing immune regulators.

B cells are key contributors to chronic autoimmune pathology in multiple sclerosis (MS). Clonally related B cells exist in the cerebrospinal fluid (CSF), meninges, and CNS parenchyma of MS patients. We sought to investigate the presence of clonally related B cells over time by performing Ig heavy chain variable region repertoire sequencing on B cells from longitudinally collected blood and CSF samples of MS patients (n = 10). All patients were untreated at the time of the initial sampling; the majority (n = 7) were treated with immune-modulating therapies 1.2 (±0.3 SD) years later during the second sampling. We found clonal persistence of B cells in the CSF of 5 patients; these B cells were frequently Ig class-switched and CD27+. Specific blood B cell subsets appear to provide input into CNS repertoires over time. We demonstrate complex patterns of clonal B cell persistence in CSF and blood, even in patients on immune-modulating therapy. Our findings support the concept that peripheral B cell activation and CNS-compartmentalized immune mechanisms can in part be therapy resistant.

Abstract Background The role of B cell subsets remained to be elucidated in a variety of immune diseases, though which was used as an effective biomarker for anti-inflammatory or antiviral response. This study aimed to evaluate the early changes of B cell subtypes distribution in elderly patients with community acquired pneumonia (CAP), as well as the association between B cell subtypes and prognosis. Methods This prospective study included elderly patients with CAP, severe CAP (sCAP) and healthy elderly subjects between April 2016 and March 2018. Flow cytometry was used to detect CD3, CD20, HLA-DR, CD24, CD27, CD38, IgM, and IgD. CD20+ B cells were further divided into naïve B cells (Bn), IgM/D+ memory B cells (IgM+ Bm), switched B cells (SwB), and transitional B cells (Btr). Results A total of 22 healthy controls, 87 patients with CAP and 58 patients with sCAP were included in the study. Compared to CAP, sCAP was characterized by significantly lower absolute number of B cells, Bn and Btr, significantly lower Btr and Bn subset percentage, while percentage of IgM+ Bm was significantly higher. Heat map showed Bn and Btr on day 3 and day 7 was negatively correlated with activated partial prothrombin time (APTT), international normalized ratio (INR), sequential organ failure assessment score (SOFA) and Acute Physiology and Chronic Health Evaluation II (APACHE II). After 28-day follow-up, Btr percentage in survival group was significantly higher. Receiver operator characteristic (ROC) curve analysis found that Btr count showed sensitivity of 48.6% and specificity of 87.0% for predicting the 28-day survival, with an area under the ROC curves of 0.689 (p = 0.019). Conclusions Severity and prognosis of CAP in elderly people is accompanied by changes in the B cell subsets. Btr subsets could play prognostic role for a short-term mortality of elderly CAP patients.

Effector-triggered immunity (ETI) in plants involves a large family of nucleotide-binding leucine-rich repeat (NLR) immune receptors, including Toll/IL-1 receptor-NLRs (TNLs) and coiled-coil NLRs (CNLs). Although various NLR immune receptors are known, a mechanistic understanding of NLR function in ETI remains unclear. The TNL Recognition of XopQ 1 (Roq1) recognizes the effectors XopQ and HopQ1 from Xanthomonas and Pseudomonas, respectively, which activates resistance to Xanthomonas euvesicatoria and Xanthomonas gardneri in an Enhanced Disease Susceptibility 1 (EDS1)-dependent way in Nicotiana benthamiana In this study, we found that the N. benthamiana N requirement gene 1 (NRG1), a CNL protein required for the tobacco TNL protein N-mediated resistance to tobacco mosaic virus, is also essential for immune signaling [including hypersensitive response (HR)] triggered by the TNLs Roq1 and Recognition of Peronospora parasitica 1 (RPP1), but not by the CNLs Bs2 and Rps2, suggesting that NRG1 may be a conserved key component in TNL signaling pathways. Besides EDS1, Roq1 and NRG1 are necessary for resistance to Xanthomonas and Pseudomonas in N. benthamiana NRG1 functions downstream of Roq1 and EDS1 and physically associates with EDS1 in mediating XopQ-Roq1-triggered immunity. Moreover, RNA sequencing analysis showed that XopQ-triggered gene-expression profile changes in N. benthamiana were almost entirely mediated by Roq1 and EDS1 and were largely regulated by NRG1. Overall, our study demonstrates that NRG1 is a key component that acts downstream of EDS1 to mediate various TNL signaling pathways, including Roq1 and RPP1-mediated HR, resistance to Xanthomonas and Pseudomonas, and XopQ-regulated transcriptional changes in N. benthamiana.

Many immune receptors transduce activation across the plasma membrane through their clustering. With Fcγ receptors (FcγRs), this clustering is driven by binding to antibodies of differing affinities that are in turn bound to multivalent antigen. As a consequence of this activation mechanism, accounting for and rationally manipulating immunoglobulin (Ig)G effector function is complicated by, among other factors, differing affinities between FcγR species and changes in the valency of antigen binding. In this study, we show that a model of multivalent receptor-ligand binding can effectively account for the contribution of IgG-FcγR affinity and immune complex valency. This model in turn enables us to make specific predictions about the effect of immune complexes of defined composition. In total, these results enable both rational immune complex design for a desired IgG effector function and the deconvolution of effector function by immune complexes.

OBJECTIVES:Infants exposed to combination therapy with anti-tumor necrosis factor (anti-TNF) agents and thiopurines may exhibit increased infections at 1 year of age compared to unexposed infants. We hypothesized that this increased risk of infection is due to abnormal development of the newborn immune system. METHODS:We immunophenotyped B-cell and T-cell subsets using multiparameter flow cytometry in 1-year-old infants whose mothers were exposed to therapeutic agents for IBD. We analyzed samples from infants exposed to infliximab (IFX) or adalimumab (ADA) monotherapy (IFX/ADA, n = 11), certolizumab pegol (CZP) monotherapy (CZP, n = 4), IFX or ADA plus thiopurine combination therapy (IFX/ADA + IM, n = 4), and CZP plus thiopurine combination therapy (CZP + IM, n = 2). RESULTS:Percentages of B cells, CD4+ T helper cells, T regulatory cells (Tregs), and CD8+ cytotoxic T cells, were similar among the groups. Infants exposed to combination therapy (IFX/ADA + IM) exhibited trends toward fewer CD27+ B cells, switched memory B cells, plasmablasts, interferon gamma (IFNγ)-producing CD4+ and CD8+ T cells, and CCR5+CD4+ T cells, but these did not reach statistical significance. CONCLUSIONS:Multiparameter immunophenotyping of major B-cell and T-cell subsets suggests that the adaptive newborn immune system develops largely unaltered after exposure to combination therapy as compared to anti-TNF monotherapy.

B-1 cells are a unique subset of B cells that are positively selected for expressing autoreactive BCRs. We isolated RNA from peritoneal (B-1a, B-1b, B-2) and splenic (B-1a, marginal zone, follicular) B cells from C57BL/6 mice and used 5'-RACE to amplify the IgH V region using massively parallel sequencing. By analyzing 379,000 functional transcripts, we demonstrate that B-1a cells use a distinct and restricted repertoire. All B-1 cell subsets, especially peritoneal B-1a cells, had a high proportion of sequences without N additions, suggesting predominantly prenatal development. Their transcripts differed markedly and uniquely contained VH11 and VH12 genes, which were rearranged only with a restricted selection of D and J genes, unlike other V genes. Compared to peritoneal B-1a, the peritoneal B-1b repertoire was larger, had little overlap with B-1a, and most sequences contained N additions. Similarly, the splenic B-1a repertoire differed from peritoneal B-1a sequences, having more unique sequences and more frequent N additions, suggesting influx of B-1a cells into the spleen from nonperitoneal sites. Two CDR3s, previously described as Abs to bromelain-treated RBCs, comprised 43% of peritoneal B-1a sequences. We show that a single-chain variable fragment designed after the most prevalent B-1a sequence bound oxidation-specific epitopes such as the phosphocholine of oxidized phospholipids. In summary, we provide the IgH V region library of six murine B cell subsets, including, to our knowledge for the first time, a comparison between B-1a and B-1b cells, and we highlight qualities of B-1 cell Abs that indicate unique selection processes.

We investigated if differentially expressed mRNA targets could be used as surrogate markers for circulating B cells and subsets. In paired blood samples from patients with untreated, anti-CD20-treated, fingolimod-treated, and natalizumab-treated multiple sclerosis, whole blood expression of CD19 correlated with B cell counts determined by flow cytometry, ROR1 with transitional B cells, TCL1A and ZNF727 with naïve B cells, NEXMIF with memory B cells and BCMA with plasmablasts. CD19 expression distinguished patients with B cell repletion and may be used as an alternative to flow cytometry, but NEXMIF was unsuitable for memory B cell monitoring in rituximab-treated patients., Competing Interests: Declaration of competing interest SEM has received speaker honoraria and non-financial support for conference participation from Merck. MRvE has received speaker honoraria from Merck. MH has received non-financial support for conference participation from Merck and Sanofi. JRC has received speaker honoraria from Biogen. FS has served on scientific advisory boards for, served as consultant for, received support for congress participation or received speaker honoraria from Alexion, Biogen, Bristol Myers Squibb, Lundbeck, Merck, Novartis, Roche and Sanofi Genzyme. His laboratory has received research support from Biogen, Merck, Novartis, Roche and Sanofi Genzyme. HBS reports no conflicts of interest., (Copyright © 2024. Published by Elsevier B.V.)

Kidney transplant recipients are patients at high risk for coronavirus disease 2019 (COVID-19) due to being on immunosuppressive therapy. B cell depletion therapy, including rituximab, is an important strategy for ABO-incompatible transplants. However, knowledge about the effect of B cell depletion therapy on COVID-19 is lacking. Thirty kidney transplant recipients who developed COVID-19 were included in this study. To examine the impact of B cell depletion therapy, we retrospectively investigated the relationship between the background of the patients and the clinical outcome. Of the 30 patients, 13 received B cell depletion therapy. The median time between transplant and onset of COVID-19 was 6.1 years after transplantation; however, nine cases remained markedly depleted of CD19(+) cells (n = 21) and depletion groups (n = 9). Progression rates in the depletion and normal groups were 55.6% and 9.5%, respectively (p = 0.014). Furthermore, the survival rate was significantly lower in the depletion group (100% in the normal group vs. 66.7% in the depletion group; p = 0.021). B cell depletion therapy may have long-term effects and increase the risk of COVID-19 in kidney transplant recipients.

Several studies have identified main changes in T- and B-lymphocyte subsets during chronic HIV infection, but few data exist on how these subsets behave during the initial phase of HIV infection. We enrolled 22 HIV-infected patients during the acute stage of infection before the initiation of antiretroviral therapy (ART). Patients had blood samples drawn previous to ART initiation (T0), and at 2 (T1) and 12 (T2) months after ART initiation. We quantified cellular HIV-DNA content in sorted naïve and effector memory CD4 T cells and identified the main subsets of T- and B-lymphocytes using an 18-parameter flow cytometry panel. We identified correlations between the patients' clinical and immunological data using PCA. Effective HIV treatment reduces integrated HIV DNA in effector memory T cells after 12 months (T2) of ART. The main changes in CD4+ T cells occurred at T2, with a reduction of activated memory, cytolytic and activated/exhausted stem cell memory T (TSCM) cells. Changes were present among CD8+ T cells since T1, with a reduction of several activated subsets, including activated/exhausted TSCM. At T2 a reduction of plasmablasts and exhausted B cells was also observed. A negative correlation was found between the total CD4+ T-cell count and IgM-negative plasmablasts. In patients initiating ART immediately following acute/early HIV infection, the fine analysis of T- and B-cell subsets has allowed us to identify and follow main modifications due to effective treatment, and to identify significant changes in CD4+ and CD8+ T memory stem cells. [ABSTRACT FROM AUTHOR]

A small population of B cells exists in lymphoid tissues and body cavities of mice that is distinct in development, phenotype, and function from the majority (B-2) B cell population. This population, originally termed "Ly-1" and now "B-1," has received renewed interest as an innate-like B cell population of fetal-derived hematopoiesis, responsible for natural Ab production and rapid immune responses. Molecular analyses have begun to define fetal and adult hematopoiesis, while cell-fate mapping studies have revealed complex developmental origins of B-1 cells. Together the studies provide a more detailed understanding of B-1 cell regulation and function. This review outlines studies that defined B-1 cells as natural Ab- and cytokine-producing B cells of fetal origin, with a focus on work conducted by R.R. Hardy, an early pioneer and codiscoverer of B-1 cells, whose seminal contributions enhanced our understanding of this enigmatic B cell population.

Tissue inflammation is a key component of obesity-induced insulin resistance, with a variety of immune cell types accumulating in adipose tissue. Here, we have demonstrated increased numbers of B2 lymphocytes in obese adipose tissue and have shown that high-fat diet-induced (HFD-induced) insulin resistance is mitigated in B cell-deficient (Bnull) mice. Adoptive transfer of adipose tissue B2 cells (ATB2) from wild-type HFD donor mice into HFD Bnull recipients completely restored the effect of HFD to induce insulin resistance. Recruitment and activation of ATB2 cells was mediated by signaling through the chemokine leukotriene B4 (LTB4) and its receptor LTB4R1. Furthermore, the adverse effects of ATB2 cells on glucose homeostasis were partially dependent upon T cells and macrophages. These results demonstrate the importance of ATB2 cells in obesity-induced insulin resistance and suggest that inhibition of the LTB4/LTB4R1 axis might be a useful approach for developing insulin-sensitizing therapeutics.

Aging and certain viral infections can negatively impact humoral responses in humans. To further develop the nonhuman primate (NHP) model for investigating B cell dynamics in human aging and infectious disease, a flow cytometric panel was developed to characterize circulating rhesus B cell subsets. Significant differences between human and macaque B cells included the proportions of cells within IgD+ and switched memory populations and a prominent CD21-CD27+ unswitched memory population detected only in macaques. We then utilized the expanded panel to analyze B cell alterations associated with aging and acute simian immunodeficiency virus (SIV) infection in the NHP model. In the aging study, distinct patterns of B cell subset frequencies were observed for macaques aged one to five years compared to those between ages 5 and 30 years. In the SIV infection study, B cell frequencies and absolute number were dramatically reduced following acute infection, but recovered within four weeks of infection. Thereafter, the frequencies of activated memory B cells progressively increased; these were significantly correlated with the magnitude of SIV-specific IgG responses, and coincided with impaired maturation of anti-SIV antibody avidity, as previously reported for HIV-1 infection. These observations further validate the NHP model for investigation of mechanisms responsible for B cells alterations associated with immunosenescence and infectious disease.

Background: The role of B cell subsets remained to be elucidated in a variety of immune diseases, though which was used as an effective biomarker for anti-inflammatory or antiviral response. This study aimed to evaluate the early changes of B cell subtypes distribution in elderly patients with community acquired pneumonia (CAP), as well as the association between B cell subtypes and prognosis.Methods: This prospective study included elderly patients with CAP, severe CAP (sCAP) and healthy elderly subjects between April 2016 and March 2018. Flow cytometry was used to detect CD3, CD20, HLA-DR, CD24, CD27, CD38, IgM, and IgD. CD20+ B cells were further divided into naïve B cells (Bn), IgM/D+ memory B cells (IgM+ Bm), switched B cells (SwB), and transitional B cells (Btr).Results: A total of 22 healthy controls, 87 patients with CAP and 58 patients with sCAP were included in the study. Compared to CAP, sCAP was characterized by significantly lower absolute number of B cells, Bn and Btr, significantly lower Btr and Bn subset percentage, while percentage of IgM+ Bm was significantly higher. Heat map showed Bn and Btr on day 3 and day 7 was negatively correlated with activated partial prothrombin time (APTT), international normalized ratio (INR), sequential organ failure assessment score (SOFA) and Acute Physiology and Chronic Health Evaluation II (APACHE II). After 28-day follow-up, Btr percentage in survival group was significantly higher. Receiver operator characteristic (ROC) curve analysis found that Btr count showed sensitivity of 48.6% and specificity of 87.0% for predicting the 28-day survival, with an area under the ROC curves of 0.689 (p = 0.019).Conclusions: Severity and prognosis of CAP in elderly people is accompanied by changes in the B cell subsets. Btr subsets could play prognostic role for a short-term mortality of elderly CAP patients. [ABSTRACT FROM AUTHOR]

IgMFcR (FcμR) are expressed on B cell and B cell subsets. Mice deficient in secreted IgM and FcμR share properties of impaired specific antibody response and autoimmunity with patient with selective IgM deficiency (SIGMD). Intravenous immunoglobulin (IGIV) regulates immune response, including modulation of IgGFc receptors. However, there are no data on the expression of FcμR in patients with SIGMD, and the effects of IGIV on FcμR. In this study, we investigated FcμR expression in naïve marginal zone (MZ), IgM memory, and class-switched memory B cells in patients with selective IgM deficiency and healthy controls. Furthermore, we examined the direct effect of IGIV on FcμR expression and on the upregulation of FcμR by TLR2 agonist (Pam3). Finally, we examined the effect of IVIG on spontaneously produced IgM and natural IgM anti-phosphorylcholine (PC) antibodies by B cells and B1 cells. FcμR expression is significantly decreased in MZ B cells in patients with SIGMD as compared to control. IGIV, at immunomodulatory concentrations, inhibited FcμR upregulation by Pam3 in MZ B cells, and IgM-depleted IGIV inhibited spontaneous secretion of natural IgM anti-PC antibodies and not total IgM by B1 cells. These data suggest that decreased FcμR expression on MZ B cells may play a role in the pathogenesis of SIGMD, and an inhibition of TLR-2-induced upregulation of FcμR by IGIV may be one of the mechanisms of its anti-inflammatory action. IGIV-induced inhibition of natural IgM antibodies may be one of the mechanisms of IGIV-induced immunoregulation.

B1 and B2 B cells differ in their ability to respond to T-cell-independent (TI) antigens. Here we report that the Src-family kinase (SFK) regulator CD148 has a unique and critical role in the initiation of B1 but not B2 cell antigen receptor signaling. CD148 loss-of-function mice were found to have defective B1 B-cell-mediated antibody responses against the T-cell-independent antigens NP-ficoll and Pneumovax 23 and had impaired selection of the B1 B cell receptor (BCR) repertoire. These deficiencies were associated with a decreased ability of B1 B cells to induce BCR signaling downstream of the SFK Lyn. Notably, Lyn appeared to be selectively regulated by CD148 and loss of this SFK resulted in opposite signaling phenotypes in B1 and B2 B cells. These findings reveal that the function and regulation of Lyn during B1 cell BCR signaling is distinct from other B cell subsets.

B cell development is often depicted as a linear process initiating in the fetus and continuing postnatally. Using a PU.1 hypomorphic mouse model, we found that B-1 and B-2 lymphopoiesis occurred in distinct fetal and adult waves differentially dependent on the Sfpi1 14 kB upstream regulatory element. The initial wave of fetal B-1 development was absent in PU.1 hypomorphic mice, while subsequent fetal and adult waves emerged. In contrast, B-2 lymphopoiesis occurred in distinct fetal and adult waves. Whole-transcriptome profiling of fetal and adult B cell progenitors supported the existence of three waves of B-1 and two waves of B-2 development and revealed that the network of transcription factors governing B lineage specification and commitment was highly divergent between B-1 and B-2 progenitors. These findings support the view that the B-1 and B-2 lineages are distinct and provide a genetic basis for layering of immune system development.

The complement system, a vital component of innate immunity, consists of various proteins and pathways crucial for the recognition and elimination of pathogens. In addition, it plays a major role in the initiation of adaptive response through the opsonization of antigens, contributing to B-cell activation and memory maintenance. Deficiencies in complement proteins, particularly C3, can lead to severe and recurrent infections as well as immune complex disorders. Here, we present a case report of two siblings with total C3 deficiency resulting from compound heterozygous mutations in C3 (NM&#95;000064.4): c.305dup; [p.Asn103GlnfsTer66] and c.1269 + 5G>T, previously unreported in C3-related diseases. Both, the index case and her sister, presented a history of recurrent infections since early childhood and one of them developed hemolytic uremic syndrome (HUS). Immunological evaluation revealed absent plasma C3 levels, decreased memory B cells, hypogammaglobulinemia, and impaired response to polysaccharide antigens. The siblings showed partial responses to antimicrobial prophylaxis and vaccination, requiring intravenous immunoglobulin replacement therapy, resulting in clinical improvement. Genetic analysis identified additional risk polymorphisms associated with atypical HUS. This case highlights the importance of comprehensive genetic and immunological evaluations in complement deficiencies, along with the potential role of immunoglobulin replacement therapy in managing associated antibody defects., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2024 Bernacchia, Ginaca, Rotondo, Tejada and Di Giovanni.)

Mouse B-1 cells are not only major producers of steady-state natural antibodies but also rapid responders to infections and inflammation. These discrete functions may be the outcomes of distinct environmental or developmental triggers that drive B-1 cells toward IgM production or an effector cell fate. Alternatively, distinct B-1 cell subsets may exist, which differ in their functional plasticity. In this paper, we summarize existing data suggesting that B-1 cells form a heterogeneous group of cells with distinct developmental requirements and nonoverlapping functions. Most spleen B-1 cells differ in development from that of bone marrow and peritoneal cavity B-1 cells, in that they develop in the absence of natural IgM. Functional heterogeneity is revealed by findings that B-1 cells in the bone marrow and spleen, but not the peritoneal cavity, generate natural serum IgM, while the latter are rapid responders to inflammatory and infectious insults, resulting in their relocation to secondary lymphoid tissues. A clearer understanding of the developmental and functional differences within the B-1 cell pool may reveal how they might be harnessed for prophylaxis or therapy.

Natural IgM plays a critical role in protection from pathogens and the prevention of autoimmunity. While its importance has been shown in many different settings, its origins are incompletely understood. This review focuses on the properties of the natural IgM antibody-secreting cells (ASCs), which arise mainly from the B-1 cell lineage. B-1 cells are generated in multiple waves during development, mostly in the fetal and early postfetal periods. The developmental time points can affect their repertoire: prenatal B-1 cells express a mainly germ line-encoded repertoire, while postnatally developing B-1 cells can express Ig with a greater degree of variation. Spleen and bone marrow, but not the body cavities, are primary sites of natural IgM secretion. Within these tissues heterogeneous populations of IgM ASCs can be found. While some ASCs express classical markers of B-1 lymphocytes, others express those of terminally differentiated plasma cells. A better understanding of the properties of these different natural IgM ASCs could aid their future therapeutic exploitation.

HIV-specific antibodies (Abs) can reduce viral burden by blocking new rounds of infection or by destroying infected cells via activation of effector cells through Fc–FcR interaction. This latter process, referred to as antibody-dependent cellular cytotoxicity (ADCC), has been associated with viral control and improved clinical outcome following both HIV and SIV infections. Here we describe an HIV viral-like particle (VLP)-based sorting strategy that led to identification of HIV-specificmemory B cells encoding Abs that mediate ADCC froma subtype A-infected Kenyan woman at 914 days post-infection. Using this strategy, 12 HIV-envelope-specific monoclonal antibodies (mAbs) were isolated and three mediated potent ADCC activitywhen compared to well-characterized ADCC mAbs. The ADCC-mediating Abs also mediated antibody-dependent cell-mediated virus inhibition (ADCVI), which provides a net measure of Fc receptor-triggered effects against replicating virus. Two of the three ADCC-mediating Abs targeted a CD4-induced (CD4i) epitope also bound by the mAb C11; the third antibody targeted the N-terminus of V3. Both CD4i Abs identified here demonstrated strong cross-clade breadth with activity against 10 of 11 envelopes tested, including those from clades A, B, C, A/D and C/D, whereas the V3-specific antibody showed more limited breadth. Variants of these CD4i, C11-like mAbs engineered to interrupt binding to FcγRs inhibited a measurable percentage of the donor's ADCC activity starting as early as 189 days post-infection. C11-like antibodies also accounted for between 18–78% of ADCC activity in 9 chronically infected individuals from the same cohort study. Further, the two CD4i Abs originated from unique B cells, suggesting that antibodies targeting this epitope can be commonly produced. Taken together, these data provide strong evidence that CD4i, C11-like antibodies develop within the first 6 months of infection and they can arise fromunique B-cell lineages in the same individual. Further, thesemAbsmediate potent plasma IgG-specificADCC breadth and potency and contribute to ADCC activity in other HIV-infected individuals.

ObjectivesIn antiretroviral therapy (ART)-treated patients, to determine if AIDS-related non-Hodgkin lymphoma (AIDS-NHL) is preceded by: elevated frequency of potentially malignant abnormal activated/germinal center-like B cells, elevated serum prevalence of B-cell stimulatory Toll-like receptor (TLR) ligands resulting from HIV infection-associated microbial translocation, dysregulated B-cell TLR expression/signaling, and perturbations in the frequency of immunoregulatory cells.DesignA case-control study nested with a cohort study of HIV-infected women.MethodsPrediagnostic AIDS-NHL cases (n = 12, collected 1-12 months before diagnosis) and controls (n = 42) from the Women's Interagency HIV Study cohort, were matched for HIV and ART status, age, race, and CD4 lymphocyte count. Serum levels of TLR ligands, the prevalence of malignancy-associated abnormal activated/germinal center-like (CD19CD10CD71CD86AID) B cells, TLR2 expression on B cells, expression of TLR2-modulating micro-RNA, and the frequency of regulatory T and B cells were assessed.ResultsDiagnosis of AIDS-NHL was preceded by a significantly elevated frequency of activated/germinal center-like CD19CD10CD71CD86AID B cells (P = 0.0072), elevated serum prevalence of the TLR2 ligand, and significantly elevated B-cell TLR2 expression (P = 0.0015), positively correlating with the frequency of activated/germinal center-like B cells (rho = 0.7273, P = 0.0144). In cases, a purified subset of activated/germinal center-like B cells exhibited decreased expression of microRNAs that modulate TLR2 signaling, including miR-21, 146a, 146b, and 155. Finally, cases also exhibited significantly elevated frequencies of antitumor immunity inhibitory regulatory B cells (P = 0.0024), but not regulatory T cells.ConclusionsOur findings suggest that increased microbial translocation and dysregulated TLR expression/signaling, coupled with an elevated frequency of regulatory B cells, precede the diagnosis of AIDS-NHL in HIV-infected ART-treated patients.

It is unclear why selective deficiency in secreted (s)IgM causes Ab-mediated autoimmunity. We demonstrate that sIgM is required for normal B cell development and selection. The CD5(+) B cells that were previously shown to accumulate in body cavities of sIgM(-/-) mice are not B-1a cells, but CD19(int), CD43(-), short-lived, BCR signaling-unresponsive anergic B-2 cells. Body cavity B-1 cells were >10-fold reduced, including VH11(+) and phosphotidylcholine-specific B-1a cells, whereas splenic B-1 cells were unaffected and marginal zone B cells increased. Follicular B cells had higher turnover rates, survived poorly after adoptive transfer, and were unresponsiveness to BCR stimulation in vitro. sIgM bound to B cell precursors and provided a positive signal to overcome a block at the pro/pre-B stage and during IgVH repertoire selection. Polyclonal IgM rescued B cell development and returned autoantibody levels to near normal. Thus, natural IgM deficiency causes primary autoimmune disease by altering B cell development, selection, and central tolerance induction.

Innate-like B-1a lymphocytes rapidly redistribute to regional mediastinal lymph nodes (MedLNs) during influenza infection to generate protective IgM. Here we demonstrate that influenza infection-induced type I interferons directly stimulate body cavity B-1 cells and are a necessary signal required for B-1 cell accumulation in MedLNs. Vascular mimetic flow chamber studies show that type I interferons increase ligand-mediated B-1 cell adhesion under shear stress by inducing high-affinity conformation shifts of surface-expressed integrins. In vivo trafficking experiments identify CD11b as the non-redundant, interferon-activated integrin required for B-1 cell accumulation in MedLNs. Thus, CD11b on B-1 cells senses infection-induced innate signals and facilitates their rapid sequester into secondary lymphoid tissues, thereby regulating the accumulation of polyreactive IgM producers at sites of infection.

Hematopoiesis occurs in a complex bone marrow microenvironment in which bone marrow stromal cells provide critical support to the process through direct cell contact and indirectly through the secretion of cytokines and growth factors. We report that connective tissue growth factor (Ctgf, also known as Ccn2) is highly expressed in murine bone marrow stromal cells. In contrast, connective tissue growth factor is barely detectable in unfractionated adult bone marrow cells. While connective tissue growth factor has been implicated in hematopoietic malignancies, and is known to play critical roles in skeletogenesis and regulation of bone marrow stromal cells, its role in hematopoiesis has not been described. Here we demonstrate that the absence of connective tissue growth factor in mice results in impaired hematopoiesis. Using a chimeric fetal liver transplantation model, we show that absence of connective tissue growth factor has an impact on B-cell development, in particular from pro-B to more mature stages, which is linked to a requirement for connective tissue growth factor in bone marrow stromal cells. Using in vitro culture systems, we demonstrate that connective tissue growth factor potentiates B-cell proliferation and promotes pro-B to pre-B differentiation in the presence of interleukin-7. This study provides a better understanding of the functions of connective tissue growth factor within the bone marrow, showing the dual regulatory role of the growth factor in skeletogenesis and in stage-specific B lymphopoiesis.

Salmonella are a common source of food- or water-borne infection and cause a wide range of clinical disease in human and animal hosts. Salmonella are relatively easy to culture and manipulate in a laboratory setting, and the infection of laboratory animals induces robust innate and adaptive immune responses. Thus, immunologists have frequently turned to Salmonella infection models to expand understanding of host immunity to intestinal pathogens. In this review, I summarize current knowledge of innate and adaptive immunity to Salmonella and highlight features of this response that have emerged from recent studies. These include the heterogeneity of the antigen-specific T-cell response to intestinal infection, the prominence of microbial mechanisms to impede T- and B-cell responses, and the contribution of non-cognate pathways for elicitation of T-cell effector functions. Together, these different issues challenge an overly simplistic view of host-pathogen interaction during mucosal infection, but also allow deeper insight into the real-world dynamic of protective immunity to intestinal pathogens.

B-1 and B-2 B cells derive from distinct progenitors that emerge in overlapping waves of development. The number of murine B-1 progenitors peaks during fetal development whereas B-2 B cell production predominates in adult bone marrow. Many genetic mutations that underlie B-acute lymphoblastic leukemia (B-ALL) occur in the fetus, at which time B-1 progenitor numbers are high. However, whether B-ALL can initiate in B-1 progenitors is unknown. In the present study, we report that BCR-ABL-transformed murine B-1 progenitors can be B-ALL cells of origin and demonstrate that they initiate disease more rapidly than do oncogene-expressing B-2 progenitors. We further demonstrate that B-1 progenitors exhibit relative resistance to apoptosis and undergo significant growth following oncogene expression, and we propose that these properties underlie the accelerated kinetics with which they initiate leukemia. These results provide a developmental perspective on the origin of B-ALL and indicate B cell lineage as a factor influencing disease progression.

Viral entry targets with therapeutic neutralizing potential are subject to multiple escape mechanisms, including antigenic drift, immune dominance of functionally irrelevant epitopes, and subtle variations in host cell mechanisms. A surprising finding of recent years is that potent neutralizing antibodies to viral epitopes independent of strain exist, but are poorly represented across the diverse human population. Identifying these antibodies and understanding the biology mediating the specific immune response is thus difficult. An effective strategy for meeting this challenge is to incorporate multiplexed antigen screening into a high throughput survey of the memory B cell repertoire from immune individuals. We used this approach to discover suites of cross-clade antibodies directed to conformational epitopes in the stalk region of the influenza A hemagglutinin (HA) protein and to select high-affinity anti-peptide antibodies to the glycoprotein B (gB) of human cytomegalovirus. In each case, our screens revealed a restricted VH and VL germline usage, including published and previously unidentified gene families. The in vivo evolution of paratope specificity with optimal neutralizing activity was understandable after correlating biological activities with kinetic binding and epitope recognition. Iterative feedback between antigen probe design based on structure and function information with high throughput multiplexed screening demonstrated a generally applicable strategy for efficient identification of safe, native, finely tuned antibodies with the potential for high genetic barriers to viral escape.

Objective To investigate the clinical significance of peripheral B-cell subsets with CD27 and CD38 phenotypes in myasthenia gravis (MG) patients. Methods Peripheral blood samples of 43 MG patients and 38 health controls (HC) from January 2016 to Decamber 2018 were collected in this study. Peripheral CD27+CD38- , CD27+CD38+ , CD27-CD38+ and CD27-CD38- B-cell subsets were detected through flow cytometer and tricolor fluorescence labeling. Results Percentages of CD27+CD38- and CD27+CD38+ B lymphocytes were increased but CD27-CD38+B-cell percentage was decreased in MG patients compared with those in HC (P = 0.000; P = 0.000; P = 0.001). Elevated percentages of CD27+CD38-B cells were found in MG patients compared with MG patients (P = 0.031). However, patients with thymoma demonstrated had lower CD27-CD38+B-cell percentages than patients with normal thymus (P = 0.026). CD27+CD38- and CD27+CD38+ B cells were enriched in patients with myasthenic crisis compared with patients without crisis (P = 0.017; P = 0.011). In addition, after the treatment of methylprednisolone, the Quantitative Myasthenia Gravis Score (QMGS) was decreased (P = 0.012), the CD27+CD38+ B cells reduced (P = 0.034) and CD27+CD38- B celsl elevated (P = 0.006). Meanwhile, percentages of CD27+CD38- B cells were significantly correlated with disease severities in MG patients (rs = 0.394, P = 0.009). Conclusions Abnormal changes of B-cell subsets with CD27 and CD38 phenotypes were observed and closely associated with disease severities in MG patients. These findings suggested that aberrancy of B-cell subsets may be involved in the progression of MG. DOI：10.3969/j.issn.1672⁃6731.2019.11.013

Several studies have identified main changes in T- and B-lymphocyte subsets during chronic HIV infection, but few data exist on how these subsets behave during the initial phase of HIV infection. We enrolled 22 HIV-infected patients during the acute stage of infection before the initiation of antiretroviral therapy (ART). Patients had blood samples drawn previous to ART initiation (T0), and at 2 (T1) and 12 (T2) months after ART initiation. We quantified cellular HIV-DNA content in sorted naïve and effector memory CD4 T cells and identified the main subsets of T- and B-lymphocytes using an 18-parameter flow cytometry panel. We identified correlations between the patients’ clinical and immunological data using PCA. Effective HIV treatment reduces integrated HIV DNA in effector memory T cells after 12 months (T2) of ART. The main changes in CD4+ T cells occurred at T2, with a reduction of activated memory, cytolytic and activated/exhausted stem cell memory T (TSCM) cells. Changes were present among CD8+ T cells since T1, with a reduction of several activated subsets, including activated/exhausted TSCM. At T2 a reduction of plasmablasts and exhausted B cells was also observed. A negative correlation was found between the total CD4+ T-cell count and IgM-negative plasmablasts. In patients initiating ART immediately following acute/early HIV infection, the fine analysis of T- and B-cell subsets has allowed us to identify and follow main modifications due to effective treatment, and to identify significant changes in CD4+ and CD8+ T memory stem cells.

Influenza virus infection induces robust and highly protective B-cell responses. Knowledge gained from the analysis of such protective humoral responses can provide important clues for the design of successful vaccines and vaccination approaches and also provides a window into the regulation of fundamental aspects of B-cell responses that may not be at play when responses to non-replicating agents are studied. Here, I review features of the B-cell response to viruses, with emphasis on influenza virus infection, a highly localized infection of respiratory tract epithelial cells, and a response that is directed against a virus that continuously undergoes genetic changes to its surface spike protein, a major target of neutralizing antibodies. Two aspects of the B-cell response to influenza are discussed here, namely polyreactive natural antibodies and the role and function of germinal center responses. Both these features of the B-cell response raise the question of how important antibody fine-specificity is for long-term protection from infection. As outlined, the pathogenesis of influenza virus and the nature of the antiviral B-cell response seem to emphasize repertoire diversity over affinity maturation as driving forces behind the influenza-specific B-cell immunity.

CD45 is a receptor-like tyrosine phosphatase that positively regulates BCR signaling by dephosphorylating the inhibitory tyrosine of the Src family kinases. We showed previously that a single point mutation, E613R, introduced into the cytoplasmic membrane-proximal "wedge" domain of CD45 is sufficient to drive a lupus-like autoimmune disease on a susceptible genetic background. To clarify the molecular mechanism of this disease, we took advantage of a unique allelic series of mice in which the expression of CD45 is varied across a broad range. Although both E613R B cells and those with supraphysiologic CD45 expression exhibited hyperresponsive BCR signaling, they did so by opposite regulation of the Src family kinase Lyn. We demonstrated that the E613R allele of CD45 does not function as a hyper- or hypomorphic allele but rather alters the substrate specificity of CD45 for Lyn. Despite similarly enhancing BCR signaling, only B cells with supraphysiologic CD45 expression became anergic, whereas only mice harboring the E613R mutation developed frank autoimmunity on a susceptible genetic background. We showed that selective impairment of a Lyn-dependent negative-regulatory circuit in E613R B cells drove autoimmunity in E613R mice. This demonstrates that relaxing negative regulation of BCR signaling, rather than enhancing positive regulation, is critical for driving autoimmunity in this system.