Abstract
The origin and nature of age-associated B cells (ABCs) in mice are poorly understood. In this article, we show that their emergence required MHC class II and CD40/CD40L interactions. Young ...donor B cells were adoptively transferred into congenic recipients and allowed to remain for 1 mo in the absence of external Ag. B cells expressing the T-bet transcription factor, a marker for ABCs, were generated after multiple cell divisions from C57BL/6 donors but not from MHC class II– or CD40-deficient donors. Furthermore, old CD154 (CD40L)-deficient mice did not accrue ABCs, confirming that they arise primarily through T-dependent interactions. To determine what Igs ABCs express, we sequenced VH and Vκ rearranged genes from unimmunized 22-mo-old C57BL/6 mice and showed that they had a heterogeneous repertoire, which was comparable to that seen in old follicular and marginal zone B cell subsets. However, in contrast to the follicular and marginal zone cells, ABCs displayed significant somatic hypermutation. The mutation frequency was lower than found in germinal center cells after deliberate immunization, suggesting that ABCs have undergone mild stimulation from endogenous Ags over time. These observations show that quiescent ABCs are Ag-experienced cells that accumulate during T cell–dependent responses to diverse Ags during the life of an individual.
X-chromosome inactivation (XCI) in female lymphocytes is uniquely regulated, as the inactive X (Xi) chromosome lacks localized Xist RNA and heterochromatin modifications. Epigenetic profiling reveals ...that Xist RNA is lost from the Xi at the pro-B cell stage and that additional heterochromatic modifications are gradually lost during B cell development. Activation of mature B cells restores Xist RNA and heterochromatin to the Xi in a dynamic two-step process that differs in timing and pattern, depending on the method of B cell stimulation. Finally, we find that DNA binding domain of YY1 is necessary for XCI in activated B cells, as ex-vivo YY1 deletion results in loss of Xi heterochromatin marks and up-regulation of X-linked genes. Ectopic expression of the YY1 zinc finger domain is sufficient to restore Xist RNA localization during B cell activation. Together, our results indicate that Xist RNA localization is critical for maintaining XCI in female lymphocytes, and that chromatin changes on the Xi during B cell development and the dynamic nature of YY1-dependent XCI maintenance in mature B cells predisposes X-linked immunity genes to reactivation.
Summary
B cells expressing the transcription factor T‐bet have emerged as participants in a number of protective and pathogenic immune responses. T‐bet+ B cells characteristically differentiate in ...response to combined Toll‐like receptor and cytokine signaling, contribute to protective immunity against intracellular pathogens via IgG2a/c production and antibody‐independent mechanisms, and are prone to produce autoantibodies. Despite recent advances, a number of questions remain regarding the basic biology of T‐bet+ B cells and their functional niche within the immune system. Herein, we review the discovery and defining characteristics of the T‐bet+ B cell subset in both mice and humans. We further discuss their origins, the basis for their persistence, and their potential fate in vivo. Evidence indicates that T‐bet+ B cells represent a distinct, germinal center‐derived memory population that may serve as an important therapeutic target for the improvement of humoral immunity and prevention of autoimmunity.
Abstract
Exploiting mechanisms integrating antigen and cytokine signals to generate tumor-antigen specific CD8+ T cells that are durable and produce low proinflammatory profile can boost efficacy of ...adoptive cell therapy (ACT) of cancer. Herein, we show that IL-21 via STAT3 induces the atypical IKK family member, Bcl3, to dampen antigen driven NF-kB (p65/p50) activation. The IL-21 induced Bcl3 decreases antigen driven CD8+ proliferation as well as apoptosis to increase clonal expansion. Strikingly, Bcl3 skews expression of master transcriptional factors to facilitate transition of polyfunctional CD8+ effector cells to memory precursor cells (MPCs) with cytotoxicity but reduced IFNg production. The IL-21 conditioned CD8+ T cells are persistent and produce greater tumor efficacy upon adoptive transfer. These studies have revealed a role for NF-kB to serve as a node for integrating antigen and cytokine signals that determine fate of antigen stimulated CD8+ T cells and encourage development of new approaches to target NFkB for T cell mediated immunity.
Bacterial trigger possibly causes disease exacerbation in enthesitis-related arthritis (ERA) patients. Microbes initiate immune responses through Toll-like receptors (TLRs). We studied TLR expression ...on blood and SF monocytes and the effect of TLR ligands on peripheral blood (PB) mononuclear cells (PBMCs) in ERA patients.
PB from 26 ERA patients and 19 healthy subjects and paired SF from 13 patients were collected. Dual-colour flow cytometry was done for TLR and CD14 expression. Results are expressed as median fluorescence intensity (MFI). Real-time PCR was done for TLRs. PBMCs were stimulated with lipopolysaccharide (LPS) or peptidoglycan and levels of IL-6 and MMP-3 measured in the culture supernatants.
PBMCs from ERA patients had higher expression of TLR-2 MFI 295.5 (48.1-598) vs 179 (68.7-442); P < 0.05 and TLR-4 MFI 448 (178-2581) vs 402 (229-569); P < 0.05 as compared with controls. TLR-9 expression showed no significant difference between the two groups. In paired samples, SF mononuclear cells (SFMCs) had higher expression of both TLR-2 MFI 485 (141-1683) vs 353 (118-598); P < 0.05 and TLR-4 MFI 1016 (42.4-3159) vs 513 (193-2581); P < 0.05 as compared with PBMCs. Difference in TLR-9 expression was not significant. TLR RNA expression data were similar. Patients' PBMCs produced more IL-6 (13.51 vs 6.54 ng/ml) and MMP-3 (61 vs 32.9 ng/ml) as compared with those of the controls, on stimulation by LPS. With peptidoglycan also, IL-6 (30.58 vs 10.84) and MMP-3 (102.54 vs 49.45) were higher than in controls.
Increased TLR-2 and TLR-4 expression on PBMCs and SFMCs may recognize microbial/endogenous ligands and up-regulate IL-6 and MMP-3 leading to disease exacerbation.
•T-bet+ B cells can be protective in infections and pathogenic in autoimmunity.•T-bet+ B cells are antigen-experienced.•T-bet+ B cells may be plasmablast precursors or multipotent memory ...cells.•T-bet+ B cells are targets for vaccination and therapy.
T-bet+ B cells have emerged as a key component of the humoral immune response in both infections and autoimmune disorders, with many of their phenotypic and functional attributes conserved between mice and humans. They are protective (infections) and pathogenic (autoimmunity), although the associated commonalities and differences remain unclear. Heterogeneity within this pool, in terms of origin, fate and function may underlie these divergent roles. Their significance is context-dependent- they may constitute a persistent effector memory cell pool, or products of recent primary responses. In both cases however, T-bet+ cells likely represent antigen-experienced progenitors of antibody-secreting cells with multipotent properties. Given their key contributions to both immunity and disease, T-bet+ B cells are an attractive target for vaccination and therapeutic strategies.
B cell subsets expressing the transcription factor T-bet are associated with humoral immune responses and autoimmunity. Here, we examined the anatomic distribution, clonal relationships, and ...functional properties of T-bet+ and T-bet− memory B cells (MBCs) in the context of the influenza-specific immune response. In mice, both T-bet− and T-bet+ hemagglutinin (HA)-specific B cells arose in germinal centers, acquired memory B cell markers, and persisted indefinitely. Lineage tracing and IgH repertoire analyses revealed minimal interconversion between T-bet− and T-bet+ MBCs, and parabionts showed differential tissue residency and recirculation properties. T-bet+ MBCs could be subdivided into recirculating T-betlo MBCs and spleen-resident T-bethi MBCs. Human MBCs displayed similar features. Conditional gene deletion studies revealed that T-bet expression in B cells was required for nearly all HA stalk-specific IgG2c antibodies and for durable neutralizing titers to influenza. Thus, T-bet expression distinguishes MBC subsets that have profoundly different homing, residency, and functional properties, and mediate distinct aspects of humoral immune memory.
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•T-bet+ B cells are a separate and durable memory subset in mice and humans•T-bethi memory B cells are absent from the lymphatic circulation•Influenza-specific T-bethi memory B cells are spleen-resident in mice•B cell-intrinsic T-bet is required for >90% of flu- and HA stalk-specific antibodies
Johnson, Rosenthal, Knox, Myles, et al. find that differential T-bet expression marks subsets of memory B cells (MBCs) with distinct homing and tissue residency patterns and functional properties. Distinguishing features of T-bet−, T-bethi, and T-betlo MBCs are seen also in humans.
T-bet and CD11c expression in B cells is linked with IgG2c isotype switching, virus-specific immune responses, and humoral autoimmunity. However, the activation requisites and regulatory cues ...governing T-bet and CD11c expression in B cells remain poorly defined. In this article, we reveal a relationship among TLR engagement, IL-4, IL-21, and IFN-γ that regulates T-bet expression in B cells. We find that IL-21 or IFN-γ directly promote T-bet expression in the context of TLR engagement. Further, IL-4 antagonizes T-bet induction. Finally, IL-21, but not IFN-γ, promotes CD11c expression independent of T-bet. Using influenza virus and Heligmosomoides polygyrus infections, we show that these interactions function in vivo to determine whether T-bet(+) and CD11c(+) B cells are formed. These findings suggest that T-bet(+) B cells seen in health and disease share the common initiating features of TLR-driven activation within this circumscribed cytokine milieu.
•Signals that enable T-bet expression in B cells are reviewed.•Innate signals are necessary to poise B cells for Tbet expression.•Signals via the Jak/STAT axis govern Tbet expression in poised B ...cells.
Transcription factors regulate various developmental and functional aspects of B cells. T-bet is a recently appreciated transcription factor associated with “Age-associated B cells” or ABCs, the development of autoimmunity, and viral infections. T-bet expression is favored by nucleic acid-containing antigens and immune complexes and is regulated by interplay between various cytokines, notably, the TFH cytokines IL-21, IL-4 and IFNγ. Adaptive signals by themselves cannot upregulate T-bet; however, they have a synergistic effect on induction of T-bet by innate receptors. The functional role of T-bet+ B cells is unclear, although it is known that T-bet promotes class switching to IgG2a/c. It is likely T-bet serves dichotomous roles in B cells, promoting pathogenic autoreactive antibodies on one hand but mediating microbial immunity on the other, making it a target of interest in both therapeutic and prophylactic settings.
T follicular helper (Tfh) cells are required to develop germinal center (GC) responses and drive immunoglobulin class switch, affinity maturation, and long-term B cell memory. In this study, we ...characterize a recently developed vaccine platform, nucleoside-modified, purified mRNA encapsulated in lipid nanoparticles (mRNA-LNPs), that induces high levels of Tfh and GC B cells. Intradermal vaccination with nucleoside-modified mRNA-LNPs encoding various viral surface antigens elicited polyfunctional, antigen-specific, CD4
T cell responses and potent neutralizing antibody responses in mice and nonhuman primates. Importantly, the strong antigen-specific Tfh cell response and high numbers of GC B cells and plasma cells were associated with long-lived and high-affinity neutralizing antibodies and durable protection. Comparative studies demonstrated that nucleoside-modified mRNA-LNP vaccines outperformed adjuvanted protein and inactivated virus vaccines and pathogen infection. The incorporation of noninflammatory, modified nucleosides in the mRNA is required for the production of large amounts of antigen and for robust immune responses.
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