Alterations in exhausted and classical memory B cells in lupus nephritis - Relationship with disease relapse.

INTRODUCTION: B cell exhaustion is a functional abnormality of B lymphocytes observed in chronic infections and shows association with autoreactivity. The role of exhausted and classical memory B cells in maintaining disease stability of lupus nephritis (LN) remains unclear. METHODS: We measured classical memory (CD19+CD21+CD27+), exhausted B cells (CD19+CD21-CD27-), and related cytokines in LN patients with multiple relapses (MR) (n = 15) and no relapse (NR) (n = 15) during disease remission. The expression of inhibitory/adhesion molecules, cell proliferation and calcium mobilization in classical memory and exhausted B cells were also assessed. RESULTS: The MR group had higher proportion of circulating exhausted and classical memory B cells compared to the NR group and healthy controls (HC) (p all <0.05 for MR vs. NR or HC). Blood levels of IL-6, BAFF, IL-21, CD62L, CXCR3 and Siglec-6 were all higher in the MR group (p < 0.05, for all). Exhausted B cells from the MR group showed higher FcRL4, CD22, CD85j and CD183 but lower CD62L expression than NR and HC groups. Exhausted B cells from MR patients exhibited reduced proliferation compared to NR patients and HC, while classical memory B cell proliferation in MR group was higher than the other two groups. Exhausted B cells from both MR and NR patients showed impaired calcium mobilization. CONCLUSION: Alterations in exhausted and classical memory B cells are related to disease relapse in LN. These findings may help devise new strategies for monitoring disease activity and preventing relapse in LN.

High recallability of memory B cells requires ZFP318-dependent transcriptional regulation of mitochondrial function.

Expression of the transcriptional regulator ZFP318 is induced in germinal center (GC)-exiting memory B cell precursors and memory B cells (MBCs). Using a conditional ZFP318 fluorescence reporter that also enables ablation of ZFP318-expressing cells, we found that ZFP318-expressing MBCs were highly enriched with GC-derived cells. Although ZFP318-expressing MBCs constituted only a minority of the antigen-specific MBC compartment, their ablation severely impaired recall responses. Deletion of Zfp318 did not alter the magnitude of primary responses but markedly reduced MBC participation in recall. CD40 ligation promoted Zfp318 expression, whereas B cell receptor (BCR) signaling was inhibitory. Enforced ZFP318 expression enhanced recall performance of MBCs that otherwise responded poorly. ZFP318-deficient MBCs expressed less mitochondrial genes, had structurally compromised mitochondria, and were susceptible to reactivation-induced cell death. The abundance of ZFP318-expressing MBCs, instead of the number of antigen-specific MBCs, correlated with the potency of prime-boost vaccination. Therefore, ZFP318 controls the MBC recallability and represents a quality checkpoint of humoral immune memory.

Cellular and humoral immunogenicity against SARS-CoV-2 vaccination or infection is associated with the memory phenotype of T- and B-lymphocytes in adult allogeneic hematopoietic cell transplant recipients.

We conducted a cross-sectional study to evaluate cellular and humoral immunogenicity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination or infection and examine how lymphocyte subpopulations in peripheral blood correlate with cellular and humoral immunogenicity in adult allogeneic hematopoietic cell transplantation (HCT) recipients. The median period from SARS-CoV-2 vaccination or infection to sample collection was 110.5 days (range, 6-345 days). The median SARS-CoV-2 spike-specific antibody level was 1761 binding antibody units (BAU)/ml (range, 0 to > 11,360 BAU/ml). Enzyme-linked immunosorbent spot (ELISpot) assay of T cells stimulated with SARS-CoV-2 spike antigens showed that interferon-gamma (IFN-γ)-, interleukin-2 (IL-2)-, and IFN-γ + IL-2-producing T cells were present in 68.9%, 62.0%, and 56.8% of patients, respectively. The antibody level was significantly correlated with frequency of IL-2-producing T cells (P = 0.001) and IFN-γ + IL-2-producing T cells (P = 0.006) but not IFN-γ-producing T cells (P = 0.970). Absolute counts of CD8+ and CD4+ central memory T cells were higher in both IL-2- and IFN-γ + IL-2-producing cellular responders compared with non-responders. These data suggest that cellular and humoral immunogenicity against SARS-CoV-2 vaccination or infection is associated with the memory phenotype of T cells and B cells in adult allogeneic HCT recipients.

HIV-related immune activation attenuates polyfunctional IgG and memory B-cell responses to Tdap immunization during pregnancy.

BACKGROUND: Maternal pertussis vaccination with Tdap vaccine is recommended to protect newborns from severe postnatal infection. HIV-exposed uninfected (HEU) infants have a higher incidence of pertussis infection and may particularly benefit from maternal immunization. The impact of HIV infection on the quality of IgG and memory B cell (MBC) responses to Tdap vaccination in pregnant women (PW) living with HIV (PWH) is unknown. METHODS: In this observational study, humoral immune responses to Tdap vaccination, including IgG levels, Fc-dependent effector functions, and MBC frequencies, were measured before and after vaccination in 40 PWH and 42 HIV-uninfected PW. Placental transfer of IgG and avidity were assessed in cord blood (CB). Soluble and cellular immune activation markers were quantified at baseline. FINDINGS: One month after vaccination, PWH had lower frequencies of MBC compared with HIV-uninfected PW. At delivery, PWH had attenuated pertussis-specific IgG levels and Fc-dependent effector functions. Reduced levels of maternal vaccine polyfunctional IgG and IgG avidity were transferred to HEU as compared to HIV-unexposed newborns. After adjustment with ethnicity, maternal antibody levels and gestational age at vaccination, HIV infection was independently associated with decreased levels of PT specific-IgG in CB. Both maternal and neonatal pertussis-specific IgG responses as well as PT-specific IgG avidity were inversely correlated with maternal sCD14 levels before vaccination among PWH. INTERPRETATION: Maternal HIV infection is associated with attenuated humoral immune responses to Tdap vaccination that correlate with sCD14. Suboptimal transfer of maternal immunity may further increase the risk of severe pertussis infection in HEU infants. FUNDING: This work was supported by IRIS Fund managed by the Foundation Roi Baudouin [2017J1820690206902], Association Vésale pour la Recherche Médicale and the Medical Council of CHU Saint-Pierre and has been funded in part with Federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, US Department of Health and Human Services, under Award No. U19AI145825. N.D. is a clinical researcher and A.M. is Research Director at the Fonds de la Recherche Scientifique (F.R.S.-FNRS), Belgium. M.E.A. was partially supported by NIHNIAID1U19AI14825. This article is published with the support of the Fondation Universitaire of Belgium.

An Exploratory Approach of Clinically Useful Biomarkers of Cvid by Logistic Regression.

Despite advancements in genetic and functional studies, the timely diagnosis of common variable immunodeficiency (CVID) remains a significant challenge. This exploratory study was designed to assess the diagnostic performance of a novel panel of biomarkers for CVID, incorporating the sum of κ+λ light chains, soluble B-cell maturation antigen (sBCMA) levels, switched memory B cells (smB) and the VISUAL score. Comparative analyses utilizing logistic regression were performed against established gold-standard tests, specifically antibody responses. Our research encompassed 88 subjects, comprising 27 CVID, 23 selective IgA deficiency (SIgAD), 20 secondary immunodeficiency (SID) patients and 18 healthy controls. We established the diagnostic accuracy of sBCMA and the sum κ+λ, achieving sensitivity (Se) and specificity (Spe) of 89% and 89%, and 90% and 99%, respectively. Importantly, sBCMA showed strong correlations with all evaluated biomarkers (sum κ+λ, smB cell and VISUAL), whereas the sum κ+λ was uniquely independent from smB cells or VISUAL, suggesting its additional diagnostic value. Through a multivariate tree decision model, specific antibody responses and the sum κ+λ emerged as independent, signature biomarkers for CVID, with the model showcasing an area under the curve (AUC) of 0.946, Se 0.85, and Spe 0.95. This tree-decision model promises to enhance diagnostic efficiency for CVID, underscoring the sum κ+λ as a superior CVID classifier and potential diagnostic criterion within the panel.

Patients taking benralizumab, dupilumab, or mepolizumab have lower postvaccination SARS-CoV-2 immunity.

BACKGROUND: Biologic therapies inhibiting the IL-4 or IL-5 pathways are very effective in the treatment of asthma and other related conditions. However, the cytokines IL-4 and IL-5 also play a role in the generation of adaptive immune responses. Although these biologics do not cause overt immunosuppression, their effect in primary severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunization has not been studied completely. OBJECTIVE: Our aim was to evaluate the antibody and cellular immunity after SARS-CoV-2 mRNA vaccination in patients on biologics (PoBs). METHODS: Patients with severe asthma or atopic dermatitis who were taking benralizumab, dupilumab, or mepolizumab and had received the initial dose of the 2-dose adult SARS-CoV-2 mRNA vaccine were enrolled in a prospective, observational study. As our control group, we used a cohort of immunologically healthy subjects (with no significant immunosuppression) who were not taking biologics (NBs). We used a multiplexed immunoassay to measure antibody levels, neutralization assays to assess antibody function, and flow cytometry to quantitate Spike-specific lymphocytes. RESULTS: We analyzed blood from 57 patients in the PoB group and 46 control subjects from the NB group. The patients in the PoB group had lower levels of SARS-CoV-2 antibodies, pseudovirus neutralization, live virus neutralization, and frequencies of Spike-specific B and CD8 T cells at 6 months after vaccination. In subgroup analyses, patients with asthma who were taking biologics had significantly lower pseudovirus neutralization than did subjects with asthma who were not taking biologics. CONCLUSION: The patients in the PoB group had reduced SARS-CoV-2-specific antibody titers, neutralizing activity, and virus-specific B- and CD8 T-cell counts. These results have implications when considering development of a more individualized immunization strategy in patients who receive biologic medications blocking IL-4 or IL-5 pathways.

Affinity alone does not drive long-lived plasma cell differentiation.

Long-lived plasma cells are important for preventing infection by maintaining baseline antibody titers. However, the cues leading to plasma cell differentiation remain unclear. In this article, we discuss recent work assessing the role of affinity on plasma cell differentiation.

Atypical memory B cells increase in the peripheral blood of patients with breast cancer regardless of lymph node involvement.

BACKGROUND: Breast cancer is the most common cancer in females. The immune system has a crucial role in the fight against cancer. B and T cells, the two main components of the adaptive immunity, are critical players that specifically target tumor cells. However, B cells, in contrast to T cells, and their role in cancer inhibition or progression is less investigated. Accordingly, in this study, we assessed and compared the frequency of naïve and different subsets of memory B cells in the peripheral blood of patients with breast cancer and healthy women. RESULTS: We found no significant differences in the frequencies of peripheral CD19+ B cells between the patients and controls. However, there was a significant decrease in the frequency of CD19+IgM+ B cells in patients compared to the control group (P=0.030). Moreover, the patients exhibited higher percentages of atypical memory B cells (CD19+CD27‒IgM‒, P=0.006) and a non-significant increasing trend in switched memory B cells (CD19+CD27+IgM‒, P=0.074). Further analysis revealed a higher frequency of atypical memory B cells (aMBCs) in the peripheral blood of patients without lymph node involvement as well as those with a tumor size greater than 2cm or with estrogen receptor (ER) negative/progesterone receptor (PR) negative tumors, compared with controls (P=0.030, P=0.040, P=0.031 and P=0.054, respectively). CONCLUSION: Atypical memory B cells (CD19+CD27‒IgM‒) showed a significant increase in the peripheral blood of patients with breast cancer compared to the control group. This increase seems to be associated with tumor characteristics. Nevertheless, additional research is necessary to determine the precise role of these cells during breast cancer progression.

Longitudinal Analysis of Humoral and Cellular Immune Response up to 6 Months after SARS-CoV-2 BA.5/BF.7/XBB Breakthrough Infection and BA.5/BF.7-XBB Reinfection.

The rapid mutation of SARS-CoV-2 has led to multiple rounds of large-scale breakthrough infection and reinfection worldwide. However, the dynamic changes of humoral and cellular immunity responses to several subvariants after infection remain unclear. In our study, a 6-month longitudinal immune response evaluation was conducted on 118 sera and 50 PBMC samples from 49 healthy individuals who experienced BA.5/BF.7/XBB breakthrough infection or BA.5/BF.7-XBB reinfection. By studying antibody response, memory B cell, and IFN-γ secreting CD4+/CD8+ T cell response to several SARS-CoV-2 variants, we observed that each component of immune response exhibited distinct kinetics. Either BA.5/BF.7/XBB breakthrough infection or BA.5/BF.7-XBB reinfection induces relatively high level of binding and neutralizing antibody titers against Omicron subvariants at an early time point, which rapidly decreases over time. Most of the individuals at 6 months post-breakthrough infection completely lost their neutralizing activities against BQ.1.1, CH.1.1, BA.2.86, JN.1 and XBB subvariants. Individuals with BA.5/BF.7-XBB reinfection exhibit immune imprinting shifting and recall pre-existing BA.5/BF.7 neutralization antibodies. In the BA.5 breakthrough infection group, the frequency of BA.5 and XBB.1.16-RBD specific memory B cells, resting memory B cells, and intermediate memory B cells gradually increased over time. On the other hand, the frequency of IFN-γ secreting CD4+/CD8+ T cells induced by WT/BA.5/XBB.1.16 spike trimer remains stable over time. Overall, our research indicates that individuals with breakthrough infection have rapidly declining antibody levels but have a relatively stable cellular immunity that can provide some degree of protection from future exposure to new antigens.

Intrahepatic plasma cells, but not atypical memory B cells, associate with clinical phases of chronic hepatitis B.

Studies have traditionally focused on the role of T cells in chronic hepatitis B (CHB), but recent evidence supports a role for B cells. The enrichment of so-called atypical memory (AtM) B cells, which show reduced signaling and impaired differentiation, is believed to be a characteristic feature of CHB, potentially contributing to the observed dysfunctional anti-HBsAg B-cell responses. Our study, involving 62 CHB patients across clinical phases, identified AtM B cells expressing IFNLR1 and interferon-stimulated genes. Contrary to previous reports, we found relatively low frequencies of AtM B cells in the liver, comparable to peripheral blood. However, liver plasma cell frequencies were significantly higher, particularly during phases with elevated viral loads and liver enzyme levels. Liver plasma cells exhibited signs of active proliferation, especially in the immune active phase. Our findings suggest a potential role for plasma cells, alongside potential implications and consequences of local proliferation, within the livers of CHB patients. While the significance of AtM B cells remains uncertain, further investigation is warranted to determine their responsiveness to interferons and their role in CHB.

Type I interferons induce an epigenetically distinct memory B cell subset in chronic viral infection.

Memory B cells (MBCs) are key providers of long-lived immunity against infectious disease, yet in chronic viral infection, they do not produce effective protection. How chronic viral infection disrupts MBC development and whether such changes are reversible remain unknown. Through single-cell (sc)ATAC-seq and scRNA-seq during acute versus chronic lymphocytic choriomeningitis viral infection, we identified a memory subset enriched for interferon (IFN)-stimulated genes (ISGs) during chronic infection that was distinct from the T-bet+ subset normally associated with chronic infection. Blockade of IFNAR-1 early in infection transformed the chromatin landscape of chronic MBCs, decreasing accessibility at ISG-inducing transcription factor binding motifs and inducing phenotypic changes in the dominating MBC subset, with a decrease in the ISG subset and an increase in CD11c+CD80+ cells. However, timing was critical, with MBCs resistant to intervention at 4 weeks post-infection. Together, our research identifies a key mechanism to instruct MBC identity during viral infection.

Poly I:C elicits broader and stronger humoral and cellular responses to a Plasmodium vivax circumsporozoite protein malaria vaccine than Alhydrogel in mice.

Malaria remains a global health challenge, necessitating the development of effective vaccines. The RTS,S vaccination prevents Plasmodium falciparum (Pf) malaria but is ineffective against Plasmodium vivax (Pv) disease. Herein, we evaluated the murine immunogenicity of a recombinant PvCSP incorporating prevalent polymorphisms, adjuvanted with Alhydrogel or Poly I:C. Both formulations induced prolonged IgG responses, with IgG1 dominance by the Alhydrogel group and high titers of all IgG isotypes by the Poly I:C counterpart. Poly I:C-adjuvanted vaccination increased splenic plasma cells, terminally-differentiated memory cells (MBCs), and precursors relative to the Alhydrogel-combined immunization. Splenic B-cells from Poly I:C-vaccinated mice revealed an antibody-secreting cell- and MBC-differentiating gene expression profile. Biological processes such as antibody folding and secretion were highlighted by the Poly I:C-adjuvanted vaccination. These findings underscore the potential of Poly I:C to strengthen immune responses against Pv malaria.

Spike-Specific Memory B Cell Response in Hematopoietic Cell Transplantation Recipients following Multiple mRNA-1273 Vaccinations: A Longitudinal Observational Study.

Preventing SARS-CoV-2 infection is of utmost importance in allogeneic hematopoietic cell transplantation patients (allo-HCT), given their heightened susceptibility to adverse outcomes associated with SARS-CoV-2 infection. However, limited data are available regarding the immune response to COVID-19 vaccines in these subjects, particularly concerning the generation and persistence of spike-specific memory response. Here, we analyzed the spike-specific memory B cells in a cohort of allo-HCT recipients vaccinated with multiple doses of the mRNA-1273 vaccine and monitored the spike-specific antibody response from baseline up to one month after the fourth dose. After the primary vaccine series, the frequency of spike-specific B cells, detected within the pool of Ig-switched CD19+ cells, significantly increased. The booster dose further induced a significant expansion, reaching up to 0.28% of spike-specific B cells. The kinetics of this expansion were slower in the allo-HCT recipients compared to healthy controls. Spike-specific IgG and ACE2/RBD binding inhibition activity were observed in 80% of the allo-HCT recipients after the first two doses, with a significant increase after the third and fourth booster doses, including in the subjects who did not respond to the primary vaccine series. Additionally, 87% of the allo-HCT recipients exhibited positive cross-inhibition activity against the BA.1 variant. Our findings provide evidence that allo-HCT recipients need repeated doses of the mRNA-1273 vaccine to induceSARS-CoV-2 specific immune response similar to that observed in healthy individuals. This is particularly crucial for vulnerable individuals who may exhibit a limited response to the primary series of SARS-CoV-2 vaccination.

Abnormal frequency of the memory B cell subsets and plasmablasts in patients with congenital severe hemophilia A: correlation with "Inhibitor" formation.

BACKGROUND: Development of antibodies against infused Factor VIII (FVIII) or "inhibitors" represents a major challenge following FVIII replacement therapy in patients with hemophilia A (HA). Recent studies have shown that certain cellular compartments of the immune system contribute to the production of such antibodies. Herein, we determined the frequency of class-switched CD19+IgD-CD27+/non-class-switched CD19+IgD+CD27+ memory B cell subsets and CD19+CD27hiCD38hi plasmablasts in patients with severe HA and their association with the development of inhibitors in these patients. METHODS: This cross-sectional case-control study enrolled 32 patients with severe HA, including 8 with and 24 without inhibitors, and 24 healthy individuals. The frequencies of the memory B cell subsets and plasmablasts were determined using flow cytometry. RESULTS: The frequency of CD19+IgD+CD27+ non-class-switched memory B cells was significantly lower in patients with HA (including both patients with and without inhibitors) than in healthy controls. The percentages of both CD19+IgD-CD27+ class-switched and CD19+IgD+CD27+ non-class-switched memory B cells did not differ significantly between patients with and without inhibitors. HA patients with inhibitors had significantly higher proportions of CD19+CD27hiCD38hi plasmablasts than the control group as well as the inhibitor (-) ones. No significant correlation was observed between the inhibitor levels with the percentages of memory B cell subsets and plasmablasts. CONCLUSION: This study is the first to demonstrate a dysregulated proportion of CD19+IgD+CD27+ non-class-switched memory B cells and CD19+CD27hiCD38hi plasmablasts in patients with severe HA. Therefore, strategies targeting memory B-cell/plasmablast differentiation may have promising outcomes in the management of inhibitor formation in patients with severe HA.

Memory B-cell derived donor-specific antibodies do not predict outcome in sensitized kidney transplant recipients: a retrospective single-center study.

Background: Repeated exposure to sensitizing events can activate HLA-specific memory B cells, leading to the production of donor-specific memory B cell antibodies (DSAm) that pose a risk for antibody-mediated rejection (ABMR) in kidney transplant recipients (KTRs). This single-center retrospective study aimed to identify DSAm and assess their association with outcomes in a cohort of KTRs with pretransplant serum donor-specific antibodies (DSA). Methods: We polyclonally activated pretransplant peripheral blood mononuclear cells (PBMCs) from 60 KTRs in vitro, isolated and quantified IgG from the culture supernatant using ELISA, and analyzed the HLA antibodies of eluates with single antigen bead (SAB) assays, comparing them to the donor HLA typing for potential DSAm. Biopsies from 41 KTRs were evaluated for rejection based on BANFF 2019 criteria. Results: At transplantation, a total of 37 DSAm were detected in 26 of 60 patients (43%), of which 13 (35%) were found to be undetectable in serum. No significant association was found between pretransplant DSAm and ABMR (P=0.53). Similar results were observed in a Kaplan-Meier analysis for ABMR within the first year posttransplant (P=0.29). Additionally, MFI levels of DSAm showed no significant association with ABMR (P=0.28). Conclusion: This study suggests no significant association between DSAm and biopsy-proven clinical ABMR. Further prospective research is needed to determine whether assessing DSAm could enhance existing immunological risk assessment methods for monitoring KTRs, particularly in non-sensitized KTRs.

Interleukin-4 downregulates transcription factor BCL6 to promote memory B cell selection in germinal centers.

Germinal center (GC)-derived memory B cells (MBCs) are critical for humoral immunity as they differentiate into protective antibody-secreting cells during re-infection. GC formation and cellular interactions within the GC have been studied in detail, yet the exact signals that allow for the selection and exit of MBCs are not understood. Here, we showed that IL-4 cytokine signaling in GC B cells directly downregulated the transcription factor BCL6 via negative autoregulation to release cells from the GC program and to promote MBC formation. This selection event required additional survival cues and could therefore result in either GC exit or death. We demonstrate that both increasing IL-4 bioavailability or limiting IL-4 signaling disrupted MBC selection stringency. In this way, IL-4 control of BCL6 expression serves as a tunable switch within the GC to tightly regulate MBC selection and affinity maturation.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine response in adults with predominantly antibody deficiency.

Background: Patients with predominantly antibody deficiency (PAD) have lower anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike antibody levels after initial 2-dose SARS-CoV-2 vaccination than healthy controls do; however, the anti-spike antibody responses and neutralization function in patients with PAD following subsequent immunizations remain understudied. Objective: We sought to characterize anti-spike antibody responses in adults with PAD over the course of 5 SARS-CoV-2 vaccine doses and identify diagnostic and immunophenotypic risk factors for low antibody response. Methods: We evaluated anti-spike antibody levels in 117 adult patients with PAD and 192 adult healthy controls following a maximum of 5 SARS-CoV-2 immunizations. We assessed neutralization of the SARS-CoV-2 wild-type strain and the Omicron BA.5 variant and analyzed infection outcomes. Results: The patients with PAD had significantly lower mean anti-spike antibody levels after 3 SARS-CoV-2 vaccine doses than the healthy controls did (1,439.1 vs 21,890.4 U/mL [P < .0001]). Adults with secondary PAD, severe primary PAD, and high-risk immunophenotypes had lower mean anti-spike antibody levels following vaccine doses 2, 3, and/or 4 but not following vaccine dose 5. Compared with patients with mild and moderate PAD, patients with severe PAD had a higher rate of increase in anti-spike antibody levels over 5 immunizations. A strong positive correlation was observed between anti-spike antibody levels and neutralization of both the SARS-CoV-2 wild-type strain and the Omicron BA.5 variant. Most infections were managed on an outpatient basis. Conclusions: In all of the patients with PAD, anti-spike antibody levels increased with successive SARS-CoV-2 immunizations and were correlated with neutralization of both the SARS-CoV-2 wild-type strain and the Omicron BA.5 variant. Secondary PAD, severe primary PAD, and high-risk immunophenotypes were correlated with lower mean anti-spike antibody levels following vaccine doses 2 through 4. Patients with severe PAD had the highest rate of increase in anti-spike antibody levels over 5 immunizations. These data suggest a clinical benefit to sequential SARS-CoV-2 immunizations, particularly among high-risk patients with PAD.

Migration Inhibition Factor Secreted by Peripheral Blood Memory B Cells Binding to CD74-CD44 Receptor Complex Drives Macrophage Behavior in Alzheimer's Disease.

Dysregulation of the peripheral immune system is be involved in the neuroinflammation in Alzheimer disease (AD) and accelerate the disease progression. The contribution of immune cells, particularly B cells, to AD pathogenesis has gained attention in recent research. In this study, we investigated the role of Peripheral Blood Memory B cells (PBMBs) and their secreted Migration Inhibition Factor (MIF) in driving macrophage behavior in AD based on the scRNA-seq technique, immunofluorescence and flow cytometry. We discovered that MIF binds to the CD74-CD44 receptor complex on macrophages, influencing their behavior. The dysregulated macrophage response hampers the clearance of amyloid-beta (Aß) plaques, exacerbating AD pathology. Targeting the MIF-CD74-CD44 signal pathway may hold therapeutic potential in modulating macrophage activity and mitigating neuroinflammation in AD. This study provides a further understanding of peripheral immune cells dysregulated in AD.

A comprehensive method for the phenotypical and functional characterization of recalled human memory B and T cells specific to vaccine antigens.

Current methodologies for assessing vaccine effectiveness and longevity primarily center on measuring vaccine-induced neutralizing antibodies in serum or plasma. However, these methods overlook additional parameters such as the presence of memory B cells, even as antibody levels wane, and the pivotal role played by memory T cells in shaping antigen-specific memory B cell responses. Several studies have employed a combination of polyclonal activators, such as CpG and R848, along with various cytokines to provoke the recall of memory B cells from peripheral blood mononuclear cells (PBMCs) into antibody-secreting cells (ASCs). Other studies have examined the use of live attenuated viruses to stimulate antigen-specific memory T cells within PBMCs into effector T cells that produce Th1/Th2 cytokines. However, these studies have not fully elucidated the distinct effects of these polyclonal activators on individual subsets, nor have they evaluated whether the vaccine antigen alone is sufficient to trigger the recall of memory T cells. Thus, in this study, we directly compared the capacity of two B cell polyclonal activators to induce the transition of existing vaccine-specific memory cells present in peripheral blood samples into ASCs. Simultaneously, we also assessed the transition of existing memory T cells into effector subsets in response to vaccine antigens. Our findings demonstrate that both polyclonal activator combinations, CpG with IL-6 and IL-15, as well as R848 with IL-2, effectively induce the terminal differentiation of memory B cells into ASCs. Notably, CpG treatment preferentially expanded naïve and non-class-switched B cells, while R848 expanded class-switched memory cells, plasmablasts, and plasma cells. Consequently, R848 treatment led to a greater overall production of total and antigen-specific IgG immunoglobulins. Additionally, the exposure of isolated PBMCs to vaccine antigens alone proved sufficient for recalling the rare antigen-specific memory T cells into effector subsets, predominantly consisting of IFN-γ-producing CD4 T cells and TNF-ß-producing CD8 T cells. This study not only establishes a rationale for the selection of methods to expand and detect antigen-specific lymphocyte subsets but also presents a means to quantify vaccine effectiveness by correlating serum antibody levels with preexisting memory cells within peripheral blood samples.

Isotype switching in human memory B cells sets intrinsic antigen-affinity thresholds that dictate antigen-driven fates.

Memory B cells (MBCs) play a critical role in protection against homologous and variant pathogen challenge by either differentiating to plasma cells (PCs) or to germinal center (GC) B cells. The human MBC compartment contains both switched IgG+ and unswitched IgM+ MBCs; however, whether these MBC subpopulations are equivalent in their response to B cell receptor cross-linking and their resulting fates is incompletely understood. Here, we show that IgG+ and IgM+ MBCs can be distinguished based on their response to κ-specific monoclonal antibodies of differing affinities. IgG+ MBCs responded only to high-affinity anti-κ and differentiated almost exclusively toward PC fates. In contrast, IgM+ MBCs were eliminated by apoptosis by high-affinity anti-κ but responded to low-affinity anti-κ by differentiating toward GC B cell fates. These results suggest that IgG+ and IgM+ MBCs may play distinct yet complementary roles in response to pathogen challenge ensuring the immediate production of high-affinity antibodies to homologous and closely related challenges and the generation of variant-specific MBCs through GC reactions.