Oral bacteria induce IgA autoantibodies against a mesangial protein in IgA nephropathy model mice

IgA nephropathy (IgAN) is caused by deposition of IgA in the glomerular mesangium. The mechanism of selective deposition and production of IgA is unclear; however, we recently identified the involvement of IgA autoantibodies. Here, we show that CBX3 is another self-antigen for IgA in gddY mice, a spontaneous IgAN model, and in IgAN patients. A recombinant antibody derived from gddY mice bound to CBX3 expressed on the mesangial cell surface in vitro and to glomeruli in vivo. An elemental diet and antibiotic treatment decreased the levels of autoantibodies and IgAN symptoms in gddY mice. Serum IgA and the recombinant antibody from gddY mice also bound to oral bacteria of the mice and binding was competed with CBX3. One species of oral bacteria was markedly decreased in elemental diet-fed gddY mice and induced anti-CBX3 antibody in normal mice upon immunization. These data suggest that particular oral bacteria generate immune responses to produce IgA that cross-reacts with mesangial cells to initiate IgAN.

STIM-mediated calcium influx regulates maintenance and selection of germinal center B cells

Positive selection of high-affinity germinal center (GC) B cells is driven by antigen internalization through their B cell receptor (BCR) and presentation to follicular helper T cells. However, the requirements of BCR signaling in GC B cells remain poorly understood. Store-operated Ca2+ entry, mediated by stromal interacting molecule 1 (STIM1) and STIM2, is the main Ca2+ influx pathway triggered by BCR engagement. Here, we showed that STIM-deficient B cells have reduced B cell competitiveness compared with wild-type B cells during GC responses. B cell-specific deletion of STIM proteins decreased the number of high-affinity B cells in the late phase of GC formation. STIM deficiency did not affect GC B cell proliferation and antigen presentation but led to the enhancement of apoptosis due to the impaired upregulation of anti-apoptotic Bcl2a1. STIM-mediated activation of NFAT was required for the expression of Bcl2a1 after BCR stimulation. These findings suggest that STIM-mediated survival signals after antigen capture regulate the optimal selection and maintenance of GC B cells.

A B cell-driven EAE mouse model reveals the impact of B cell-derived cytokines on CNS autoimmunity

In multiple sclerosis (MS), pathogenic T cell responses are known to be important drivers of autoimmune inflammation. However, increasing evidence suggests an additional role for B cells, which may contribute to pathogenesis via antigen presentation and production of proinflammatory cytokines. However, these B cell effector functions are not featured well in classical experimental autoimmune encephalomyelitis (EAE) mouse models. Here, we compared properties of myelin oligodendrocyte glycoprotein (MOG)-specific and polyclonal B cells and developed an adjuvant-free cotransfer EAE mouse model, where highly activated, MOG-specific induced germinal center B cells provide the critical stimulus for disease development. We could show that high levels of MOG-specific immunoglobulin G (IgGs) are not required for EAE development, suggesting that antigen presentation and activation of cognate T cells by B cells may be important for pathogenesis. As our model allows for B cell manipulation prior to transfer, we found that overexpression of the proinflammatory cytokine interleukin (IL)-6 by MOG-specific B cells leads to an accelerated EAE onset accompanied by activation/expansion of the myeloid compartment rather than a changed T cell response. Accordingly, knocking out IL-6 or tumor necrosis factor α in MOG-specific B cells via CRISPR-Cas9 did not affect activation of pathogenic T cells. In summary, we generated a tool to dissect pathogenic B cell effector function in EAE development, which should improve our understanding of pathogenic processes in MS.

SpiB regulates the expression of B-cell-related genes and increases the longevity of memory B cells

Generation of memory B cells is one of the key features of adaptive immunity as they respond rapidly to re-exposure to the antigen and generate functional antibodies. Although the functions of memory B cells are becoming clearer, the regulation of memory B cell generation and maintenance is still not well understood. Here we found that transcription factor SpiB is expressed in some germinal center (GC) B cells and memory B cells and participates in the maintenance of memory B cells. Overexpression and knockdown analyses revealed that SpiB suppresses plasma cell differentiation by suppressing the expression of Blimp1 while inducing Bach2 in the in-vitro-induced germinal center B (iGB) cell culture system, and that SpiB facilitates in-vivo appearance of memory-like B cells derived from the iGB cells. Further analysis in IgG1+ cell-specific SpiB conditional knockout (cKO) mice showed that function of SpiB is critical for the generation of late memory B cells but not early memory B cells or GC B cells. Gene expression analysis suggested that SpiB-dependent suppression of plasma cell differentiation is independent of the expression of Bach2. We further revealed that SpiB upregulates anti-apoptosis and autophagy genes to control the survival of memory B cells. These findings indicate the function of SpiB in the generation of long-lasting memory B cells to maintain humoral memory.

DNASE1L3 enhances antitumor immunity and suppresses tumor progression in colon cancer

DNASE1L3, an enzyme highly expressed in DCs, is functionally important for regulating autoimmune responses to self-DNA and chromatin. Deficiency of DNASE1L3 leads to development of autoimmune diseases in both humans and mice. However, despite the well-established causal relationship between DNASE1L3 and immunity, little is known about the involvement of DNASE1L3 in regulation of antitumor immunity, the foundation of modern antitumor immunotherapy. In this study, we identify DNASE1L3 as a potentially new regulator of antitumor immunity and a tumor suppressor in colon cancer. In humans, DNASE1L3 is downregulated in tumor-infiltrating DCs, and this downregulation is associated with poor patient prognosis and reduced tumor immune cell infiltration in many cancer types. In mice, Dnase1l3 deficiency in the tumor microenvironment enhances tumor formation and growth in several colon cancer models. Notably, the increased tumor formation and growth in Dnase1l3-deficient mice are associated with impaired antitumor immunity, as evidenced by a substantial reduction of cytotoxic T cells and a unique subset of DCs. Consistently, Dnase1l3-deficient DCs directly modulate cytotoxic T cells in vitro. To our knowledge, our study unveils a previously unknown link between DNASE1L3 and antitumor immunity and further suggests that restoration of DNASE1L3 activity may represent a potential therapeutic approach for anticancer therapy.

Subcutaneous immunisation with zymosan generates mucosal IgA-eliciting memory and protects mice from heterologous influenza virus infection

Immunoglobulin A (IgA) is the most abundant isotype of antibodies and provides a first line of defense at the mucosa against pathogens invading the host. It has been widely accepted that the mucosal IgA response provided by vaccination requires mucosal inoculation, and intranasal inoculation has been proposed for vaccines against influenza virus. Considering the difficulty of intranasal vaccination in infants or elderly people, however, parenteral vaccination that provides the mucosal IgA response is desirable. Here, we demonstrate that subcutaneous immunisation with zymosan, a yeast cell wall constituent known to be recognised by Dectin-1 and TLR2, potentiates the production of antigen-specific IgA antibodies in the sera and airway mucosa upon intranasal antigen challenge. We confirmed that the antigen-specific IgA-secreting cells accumulated in the lung and nasal-associated lymphoid tissues after the antigen challenge. Such an adjuvant effect of zymosan in the primary immunisation for the IgA response depended on Dectin-1 signalling, but not on TLR2. The IgA response to the antigen challenge required both antigen-specific memory B and T cells, and the generation of memory T cells, but not memory B cells, depended on zymosan as an adjuvant. Finally, we demonstrated that subcutaneous inoculation of inactivated influenza virus with zymosan, but not with alum, mostly protected the mice from infection with a lethal dose of a heterologous virus strain. These data suggest that zymosan is a possible adjuvant for parenteral immunisation that generates memory IgA responses to respiratory viruses such as influenza virus.

Upregulated Expression of the IL-9 Receptor on TRAF3-Deficient B Lymphocytes Confers Ig Isotype Switching Responsiveness to IL-9 in the Presence of Antigen Receptor Engagement and IL-4

The pleiotropic cytokine IL-9 signals to target cells by binding to a heterodimeric receptor consisting of the unique subunit IL-9R and the common subunit γ-chain shared by multiple cytokines of the γ-chain family. In the current study, we found that the expression of IL-9R was strikingly upregulated in mouse naive follicular B cells genetically deficient in TNFR-associated factor 3 (TRAF3), a critical regulator of B cell survival and function. The highly upregulated IL-9R on Traf3-/- follicular B cells conferred responsiveness to IL-9, including IgM production and STAT3 phosphorylation. Interestingly, IL-9 significantly enhanced class switch recombination to IgG1 induced by BCR crosslinking plus IL-4 in Traf3-/- B cells, which was not observed in littermate control B cells. We further demonstrated that blocking the JAK-STAT3 signaling pathway abrogated the enhancing effect of IL-9 on class switch recombination to IgG1 induced by BCR crosslinking plus IL-4 in Traf3-/- B cells. Our study thus revealed, to our knowledge, a novel pathway that TRAF3 suppresses B cell activation and Ig isotype switching by inhibiting IL-9R-JAK-STAT3 signaling. Taken together, our findings provide (to our knowledge) new insights into the TRAF3-IL-9R axis in B cell function and have significant implications for the understanding and treatment of a variety of human diseases involving aberrant B cell activation such as autoimmune disorders.

Commensal Bacteria and the Lung Environment Are Responsible for Th2-Mediated Memory Yielding Natural IgE in MyD88-Deficient Mice

IgE Abs are a common mediator of allergic responses and are generally produced in type 2 immune responses to allergens. Allergen stimulation of IgE-bound FcεRI on mast cells or basophils induces the production of chemical mediators and cytokines. In addition, IgE binding to FcεRI without allergen promotes the survival or proliferation of these and other cells. Thus, spontaneously produced natural IgE can increase an individual's susceptibility to allergic diseases. Mice deficient in MyD88, a major TLR signaling molecule, have high serum levels of natural IgE, the mechanism for which remains unknown. In this study, we demonstrated that the high serum IgE levels were maintained from weaning by memory B cells (MBCs). IgE from plasma cells and sera from most Myd88-/- mice, but none of the Myd88+/- mice, recognized Streptococcus azizii, a commensal bacterium overrepresented in the lungs of Myd88-/- mice. IgG1+ MBCs from the spleen also recognized S. azizii. The serum IgE levels declined with the administration of antibiotics and were boosted by challenge with S. azizii in Myd88-/- mice, indicating the contribution of S. azizii-specific IgG1+ MBCs to the natural IgE production. Th2 cells were selectively increased in the lungs of Myd88-/- mice and were activated upon addition of S. azizii in the lung cells ex vivo. Finally, lung nonhematopoietic cells, and CSF1 overproduced therefrom, were responsible for natural IgE production in Myd88-/- mice. Thus, some commensal bacteria may prime the Th2 response and natural IgE production in the MyD88-defective lung environment in general.

Incomplete Atypical Femoral Fracture With Severe Bowing Treated by Intramedullary Nail and Corrective Osteotomy

We present the case of an 82-year-old female who had difficulty walking due to right thigh pain caused by incomplete atypical femoral fracture (AFF). The femoral bowing was so severe that intramedullary nail insertion was impossible, so we performed a corrective osteotomy of the femur and inserted the intramedullary nail. Postoperatively, the femoral pain disappeared, and bone fusion was achieved at one year and two months postoperatively. In cases of incomplete AFF with very severe femoral bowing, internal fixation with an intramedullary nail combined with corrective osteotomy of the femur is useful.

Identification of IgA autoantibodies targeting mesangial cells redefines the pathogenesis of IgA nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN) is the most common type of primary glomerulonephritis, often progressing to renal failure. IgAN is triggered by IgA deposition in the glomerular mesangium by an undefined mechanism. Here, we show that grouped ddY (gddY) mice, a spontaneous IgAN model, produce serum IgA against mesangial antigens, including βII-spectrin. Most patients with IgAN also have serum anti-βII-spectrin IgA. As in patients with IgAN, IgA⁺ plasmablasts accumulate in the kidneys of gddY mice. IgA antibodies cloned from the plasmablasts carry substantial V-region mutations and bind to βII-spectrin and the surface of mesangial cells. These IgAs recognize transfected and endogenous βII-spectrin exposed on the surface of embryonic kidney-derived cells. Last, we demonstrate that the cloned IgA can bind selectively to glomerular mesangial regions in situ. The identification of IgA autoantibody and its antigen in IgAN provides key insights into disease onset and redefines IgAN as a tissue-specific autoimmune disease.

B-cell-intrinsic DNase1L3 is essential for T-cell-independent type II response in mice

T-cell independent type II (TI-II) antigens, such as capsular polysaccharides, have multivalent epitope, which induce B cell activation, plasma cell differentiation and antibody production by strongly cross-linking B-cell receptors. However, the mechanism of B cell activation by TI-II antigens remains unclear. In this study, we demonstrate that DNA endonuclease DNase1L3 (also termed DNase γ) is required for the TI-II response. The production of antigen-specific antibodies was severely diminished in DNase1L3-deficient mice upon immunization with TI-II antigens, but not with TD antigens. Bone-marrow chimeric mice and B cell transfer experiments revealed that B-cell-intrinsic DNase1L3 was required for the TI-II response. DNase1L3-deficient B cells were defective in cell proliferation and plasma cell differentiation in the TI-II response in vivo as well as in vitro, which was not rescued by co-culture with DNase1L3-sufficient B cells in vitro, disproving an involvement of a secretory DNase1L3. In vitro stimulation with TI-II antigen transiently increased expression of DNase1L3 and its translocation into the nucleus. RNA-seq analysis of ex vivo B cells having been responded to TI-II antigen in vivo revealed a marked reduction of Myc-target gene sets in DNase1L3-deficient B cells. Expression of IRF4, the gene of which Myc targets, was diminished in the ex vivo DNase1L3-deficient B cells, in which forced expression of IRF4 restored the TI-II response in vivo. These data revealed an unexpected role of DNase1L3 in a missing link between B-cell receptor signaling and B cell activation in the TI-II response, giving a valuable clue to molecularly dissect this response.

RelB contributes to the survival, migration and lymphomagenesis of B cells with constitutively active CD40 signaling

Activation of CD40-signaling contributes to the initiation, progression and drug resistance of B cell lymphomas. We contributed to this knowledge by showing that constitutive CD40-signaling in B cells induces B cell hyperplasia and finally B cell lymphoma development in transgenic mice. CD40 activates, among others, the non-canonical NF-ĸB signaling, which is constitutively activated in several human B cell lymphomas and is therefore presumed to contribute to lymphopathogenesis. This prompted us to study the regulatory role of the non-canonical NF-ĸB transcription factor RelB in lymphomagenesis. To this end, we crossed mice expressing a constitutively active CD40 receptor in B cells with conditional RelB-KO mice. Ablation of RelB attenuated pre-malignant B cell expansion, and resulted in an impaired survival and activation of long-term CD40-stimulated B cells. Furthermore, we found that hyperactivation of non-canonical NF-кB signaling enhances the retention of B cells in the follicles of secondary lymphoid organs. RNA-Seq-analysis revealed that several genes involved in B-cell migration, survival, proliferation and cytokine signaling govern the transcriptional differences modulated by the ablation of RelB in long-term CD40-stimulated B cells. Inactivation of RelB did not abrogate lymphoma development. However, lymphomas occurred with a lower incidence and had a longer latency period. In summary, our data suggest that RelB, although it is not strictly required for malignant transformation, accelerates the lymphomagenesis of long-term CD40-stimulated B cells by regulating genes involved in migration, survival and cytokine signaling.

Mouse pulmonary interstitial macrophages mediate the pro-tumorigenic effects of IL-9

Although IL-9 has potent anti-tumor activity in adoptive cell transfer therapy, some models suggest that it can promote tumor growth. Here, we show that IL-9 signaling is associated with poor outcomes in patients with various forms of lung cancer, and is required for lung tumor growth in multiple mouse models. CD4+ T cell-derived IL-9 promotes the expansion of both CD11c+ and CD11c- interstitial macrophage populations in lung tumor models. Mechanistically, the IL-9/macrophage axis requires arginase 1 (Arg1) to mediate tumor growth. Indeed, adoptive transfer of Arg1+ but not Arg1- lung macrophages to Il9r-/- mice promotes tumor growth. Moreover, targeting IL-9 signaling using macrophage-specific nanoparticles restricts lung tumor growth in mice. Lastly, elevated expression of IL-9R and Arg1 in tumor lesions is associated with poor prognosis in lung cancer patients. Thus, our study suggests the IL-9/macrophage/Arg1 axis is a potential therapeutic target for lung cancer therapy.

An IL-9-pulmonary macrophage axis defines the allergic lung inflammatory environment

Despite IL-9 functioning as a pleiotropic cytokine in mucosal environments, the IL-9-responsive cell repertoire is still not well defined. Here, we found that IL-9 mediates proallergic activities in the lungs by targeting lung macrophages. IL-9 inhibits alveolar macrophage expansion and promotes recruitment of monocytes that develop into CD11c+ and CD11c- interstitial macrophage populations. Interstitial macrophages were required for IL-9-dependent allergic responses. Mechanistically, IL-9 affected the function of lung macrophages by inducing Arg1 activity. Compared with Arg1-deficient lung macrophages, Arg1-expressing macrophages expressed greater amounts of CCL5. Adoptive transfer of Arg1+ lung macrophages but not Arg1- lung macrophages promoted allergic inflammation that Il9r-/- mice were protected against. In parallel, the elevated expression of IL-9, IL-9R, Arg1, and CCL5 was correlated with disease in patients with asthma. Thus, our study uncovers an IL-9/macrophage/Arg1 axis as a potential therapeutic target for allergic airway inflammation.

Integrin CD11b provides a new marker of pre-germinal center IgA + B cells in murine Peyer's patches

Activated B cells can enter germinal centers (GCs) for affinity maturation to produce high-affinity antibodies. However, which activated B cells will enter GCs remains unknown. Here, we found a small population of CD11b⁺IgA⁺ B cells located outside of GCs in murine Peyer’s patches (PPs). After injection of the CD11b⁺IgA⁺ PP B cells into a PP of a recipient mouse, they entered GCs forty hours later. They expressed GC surface markers and pre-GC B cell genes, suggesting that CD11b provides a novel surface marker of pre-GC IgA⁺ B cells in murine PPs. Furthermore, independently of dendritic cell activation, CD11b expression on B cells can be induced by bacterial antigens, such as pam3CSK4 and heat-killed Escherichia coli in vitro. In addition, mice orally administered with pam3CSK4 or heat-killed E. coli increased the number of PP GC B cells within two days, and enhanced the mucosal antigen-specific IgA response. Our results demonstrate that the induction of CD11b on B cells is a promising marker for selecting an effective mucosal vaccine adjuvant.

MicroRNA-directed pathway discovery elucidates an miR-221/222-mediated regulatory circuit in class switch recombination

MicroRNAs (miRNAs, miRs) regulate cell fate decisions by post-transcriptionally tuning networks of mRNA targets. We used miRNA-directed pathway discovery to reveal a regulatory circuit that influences Ig class switch recombination (CSR). We developed a system to deplete mature, activated B cells of miRNAs, and performed a rescue screen that identified the miR-221/222 family as a positive regulator of CSR. Endogenous miR-221/222 regulated B cell CSR to IgE and IgG1 in vitro, and miR-221/222-deficient mice exhibited defective IgE production in allergic airway challenge and polyclonal B cell activation models in vivo. We combined comparative Ago2-HITS-CLIP and gene expression analyses to identify mRNAs bound and regulated by miR-221/222 in primary B cells. Interrogation of these putative direct targets uncovered functionally relevant downstream genes. Genetic depletion or pharmacological inhibition of Foxp1 and Arid1a confirmed their roles as key modulators of CSR to IgE and IgG1.

Protein kinase Cδ is essential for the IgG response against T-cell-independent type 2 antigens and commensal bacteria

Antigens (Ags) with multivalent and repetitive structure elicit IgG production in a T-cell-independent manner. However, the mechanisms by which such T-cell-independent type-2 (TI-2) Ags induce IgG responses remain obscure. Here, we report that B-cell receptor (BCR) engagement with a TI-2 Ag but not with a T-cell-dependent (TD) Ag was able to induce the transcription of Aicda encoding activation-induced cytidine deaminase (AID) and efficient class switching to IgG3 upon costimulation with IL-1 or IFN-α in mouse B cells. TI-2 Ags strongly induced the phosphorylation of protein kinase C (PKC)δ and PKCδ mediated the Aicda transcription through the induction of BATF, the key transcriptional regulator of Aicda. In PKCδ-deficient mice, production of IgG was intact against TD Ag but abrogated against typical TI-2 Ags as well as commensal bacteria, and experimental disruption of the gut epithelial barrier resulted in fatal bacteremia. Thus, our results have revealed novel molecular requirements for class switching in the TI-2 response and highlighted its importance in homeostatic commensal-specific IgG production.

When the human body faces a potentially harmful microorganism, the immune system responds by finding and destroying the pathogen. This involves the coordination of several different parts of the immune system. B cells are a type of white blood cell that is responsible for producing antibodies: large proteins that bind to specific targets such as pathogens. B cells often need help from other immune cells known as T cells to complete antibody production.

However, T cells are not required for B cells to produce antibodies against some bacteria. For example, when certain pathogenic bacteria coated with a carbohydrate called a capsule – such as pneumococcus, which causes pneumonia, or salmonella – invade our body, B cells recognize a repetitive structure of the capsule using a B-cell antigen receptor. This recognition allows B cells to produce antibodies independently of T cells. It is unclear how B cells produce antibodies in this situation or what proteins are required for this activity.

To understand this process, Fukao et al. used genetically modified mice and their B cells to study how they produce antibodies independently of T cells. They found that a protein called PKCδ is critical for B cells to produce antibodies, especially of an executive type called IgG, in the T-cell-independent response. PKCδ became active when B cells were stimulated with the repetitive antigen present on the surface of bacteria like salmonella or pneumococcus. Mice that lack PKCδ were unable to produce IgG independently of T cells, leading to fatal infections when bacteria reached the tissues and blood.

Understanding the mechanism behind the T cell-independent B cell response could lead to more effective antibody production, potentially paving the way for new vaccines to prevent fatal diseases caused by pathogenic bacteria.

C/EBPβ induces B-cell acute lymphoblastic leukemia and cooperates with BLNK mutations

BLNK (BASH/SLP‐65) encodes an adaptor protein that plays an important role in B‐cell receptor (BCR) signaling. Loss‐of‐function mutations in this gene are observed in human pre‐B acute lymphoblastic leukemia (ALL), and a subset of Blnk knock‐out (KO) mice develop pre‐B‐ALL. To understand the molecular mechanism of the Blnk mutation‐associated pre‐B‐ALL development, retroviral tagging was applied to KO mice using the Moloney murine leukemia virus (MoMLV). The Blnk mutation that significantly accelerated the onset of MoMLV‐induced leukemia and increased the incidence of pre‐B‐ALL Cebpb was identified as a frequent site of retroviral integration, suggesting that its upregulation cooperates with Blnk mutations. Transgenic expression of the liver‐enriched activator protein (LAP) isoform of Cebpb reduced the number of mature B‐lymphocytes in the bone marrow and inhibited differentiation at the pre‐BI stage. Furthermore, LAP expression significantly accelerated leukemogenesis in Blnk KO mice and alone acted as a B‐cell oncogene. Furthermore, an inverse relationship between BLNK and C/EBPβ expression was also noted in human pre‐B‐ALL cases, and the high level of CEBPB expression was associated with short survival periods in patients with BLNK‐downregulated pre‐B‐ALL. These results indicate the association between the C/EBPβ transcriptional network and BCR signaling in pre‐B‐ALL development and leukemogenesis. This study gives insight into ALL progression and suggests that the BCR/C/EBPβ pathway can be a therapeutic target.

Mechanisms for the regulation of memory B-cell recall responses in mice

Upon infection by pathogens or vaccination, the adaptive immune system rapidly but transiently produces antibodies. Some weeks later, however, long-lasting immunity is established that protects the host against the same pathogens almost for life through continuous production of antibodies on one hand and the maintenance of cytotoxic T cells on the other, collectively called immunological memory. The antibody-mediated arm, also called serological memory, is mainly exerted by long-lived plasma cells and memory B cells (MBCs). MBCs express receptors for the specific pathogens and circulate to survey the body for almost a life-long period. Upon recognizing the pathogen, MBCs clonally expand and produce a large amount of the specific antibodies to stop the infection, the process called a (memory) recall response. Although such a function of MBCs has long been known, the mechanism of how their performance is regulated has been obscure. This is due to their paucity in the body, lack of definitive surface markers and obscure ontogeny. However, recent studies have revealed the multifold mechanisms by which the recall response of MBCs is regulated: Rapid and enhanced antibody production is due to a mechanism intrinsic to MBCs; namely, upregulated expression levels of surface molecules interacting with T cells and the property of IgG-class antigen receptors; to a property of the responsible subset of MBCs; and to co-stimulation through innate receptors and cytokines. It has also been unveiled that the recall response is negatively regulated by an inhibitory receptor on MBCs and by antigens with repetitive epitopes.

Metabolic Reprogramming Induces Germinal Center B Cell Differentiation through Bcl6 Locus Remodeling

The germinal center (GC) reaction is essential for long-lived humoral immunity. However, molecular requirements for the induction of Bcl6, the master regulator for GC B cell differentiation, remain unclear. Through screening for cytokines and other stimuli that regulate Bcl6 expression, we identify IL-4 as the strongest inducer. IL-4 signaling alters the metabolomic profile in activated B cells and induces accumulation of the TCA cycle intermediate α-ketoglutarate (αKG), which is required for activation of the Bcl6 gene locus. Mechanistically, after IL-4 treatment, STAT6 bound to the known enhancers in the Bcl6 locus recruits UTX, a demethylase for the repressive histone mark H3K27me3 that requires αKG as a cofactor. In turn, the H3K27me3 demethylation activates the enhancers and transcription of the Bcl6 gene. We propose that IL-4-mediated metabolic reprogramming in B cells is pivotal for epigenomic activation of Bcl6 expression to promote GC B cell differentiation.

Multi-faceted regulation of IgE production and humoral memory formation

IgE antibodies play a protective role against parasites and environmental toxins by its strong effector functions. However, aberrant IgE production can contribute to the development of allergic disorders, and thus is tightly regulated. Beside its very short half-life, IgE is normally produced only transiently and its affinity maturation is limited under physiological immune responses. Although such distinct characteristics of IgE among Ig classes are well-known, the underlying molecular mechanisms have not been understood until recently. Somatic or genetic defects of such mechanisms can lead to pathogenesis of allergic diseases. In this review, we summarize recent advances in our understanding of the mechanisms that control the production of IgE and formation of IgE-type humoral memory, focusing on the B cell immune responses.

Tracing Self-Reactive B Cells in Normal Mice

BCR transgenic mice dominate studies of B cell tolerance; consequently, tolerance in normal mice expressing diverse sets of autoreactive B cells is poorly characterized. We have used single B cell cultures to trace self-reactivity in BCR repertoires across the first and second tolerance checkpoints and in tolerized B cell compartments of normal mice. This approach reveals affinity "setpoints" that define each checkpoint and a subset of tolerized, autoreactive B cells that is long-lived. In normal mice, the numbers of B cells avidly specific for DNA fall significantly as small pre-B become immature and transitional-1 B cells, revealing the first tolerance checkpoint. By contrast, DNA reactivity does not significantly change when immature and transitional-1 B cells become mature follicular B cells, showing that the second checkpoint does not reduce DNA reactivity. In the spleen, autoreactivity was high in transitional-3 (T3) B cells, CD93⁺IgM^-/loIgD^hi anergic B cells, and a CD93^- anergic subset. Whereas splenic T3 and CD93⁺ anergic B cells are short-lived, CD93^-IgM^-/loIgD^hi B cells have half-lives comparable to mature follicular B cells. B cell-specific deletion of proapoptotic genes, Bak and Bax, resulted in increased CD93^-IgM^-/loIgD^hi B cell numbers but not T3 B cell numbers, suggesting that apoptosis regulates differently persistent and ephemeral autoreactive B cells. The self-reactivity and longevity of CD93^-IgM^-/loIgD^hi B cells and their capacity to proliferate and differentiate into plasmacytes in response to CD40 activation in vitro lead us to propose that this persistent, self-reactive compartment may be the origin of systemic autoimmunity and a potential target for vaccines to elicit protective Abs cross-reactive with self-antigens.

Ubiquitination of IgG1 cytoplasmic tail modulates B-cell signalling and activation

Upon antigen stimulation, IgG+ B cells rapidly proliferate and differentiate into plasma cells, which has been attributed to the characteristics of membrane-bound IgG (mIgG), but the underlying molecular mechanisms remain elusive. We have found that a part of mouse mIgG1 is ubiquitinated through the two responsible lysine residues (K378 and K386) in its cytoplasmic tail and this ubiquitination is augmented upon antigen stimulation. The ubiquitination of mIgG1 involves its immunoglobulin tail tyrosine (ITT) motif, Syk/Src-family kinases and Cbl proteins. Analysis of a ubiquitination-defective mutant of mIgG1 revealed that ubiquitination of mIgG1 facilitates its ligand-induced endocytosis and intracellular trafficking from early endosome to late endosome, and also prohibits the recycling pathway, thus attenuating the surface expression level of mIgG1. Accordingly, ligation-induced activation of B-cell receptor (BCR) signalling molecules is attenuated by the mIgG1 ubiquitination, except MAP kinase p38 whose activation is up-regulated due to the ubiquitination-mediated prohibition of mIgG1 recycling. Adaptive transfer experiments demonstrated that ubiquitination of mIgG1 facilitates expansion of germinal centre B cells. These results indicate that mIgG1-mediated signalling and cell activation is regulated by ubiquitination of mIgG1, and such regulation may play a role in expansion of germinal centre B cells.

Cross-Reactivity to Kynureninase Tolerizes B Cells That Express the HIV-1 Broadly Neutralizing Antibody 2F5

2F5 is an HIV-1 broadly neutralizing Ab that also binds the autoantigens kynureninase (KYNU) and anionic lipids. Generation of 2F5-like Abs is proscribed by immune tolerance, but it is unclear which autospecificity is responsible. We sampled the BCR repertoire of 2F5 knock-in mice before and after the first and second tolerance checkpoints. Nearly all small pre-B (precheckpoint) and 35-70% of anergic peripheral B cells (postcheckpoint) expressed the 2F5 BCR and maintained KYNU, lipid, and HIV-1 gp41 reactivity. In contrast, all postcheckpoint mature follicular (MF) B cells had undergone L chain editing that purged KYNU and gp41 binding but left lipid reactivity largely intact. We conclude that specificity for KYNU is the primary driver of tolerization of 2F5-expressing B cells. The MF and anergic B cell populations favored distinct collections of editor L chains; surprisingly, however, MF and anergic B cells also frequently expressed identical BCRs. These results imply that BCR autoreactivity is the primary determinant of whether a developing B cell enters the MF or anergic compartments, with a secondary role for stochastic factors that slightly mix the two pools. Our study provides mechanistic insights into how immunological tolerance impairs humoral responses to HIV-1 and supports activation of anergic B cells as a potential method for HIV-1 vaccination.

Molecular Design, Optimization, and Genomic Integration of Chimeric B Cell Receptors in Murine B Cells

Immune cell therapies based on the integration of synthetic antigen receptors comprise a powerful strategy for the treatment of diverse diseases, most notably T cells engineered to express chimeric antigen receptors (CAR) for targeted cancer therapy. In addition to T lymphocytes, B lymphocytes may also represent valuable immune cells that can be engineered for therapeutic purposes such as protein replacement therapy or recombinant antibody production. In this article, we report a promising concept for the molecular design, optimization, and genomic integration of a novel class of synthetic antigen receptors, chimeric B cell receptors (CBCR). We initially optimized CBCR expression and detection by modifying the extracellular surface tag, the transmembrane regions and intracellular signaling domains. For this purpose, we stably integrated a series of CBCR variants using CRISPR-Cas9 into immortalized B cell hybridomas. Subsequently, we developed a reliable and consistent pipeline to precisely introduce cassettes of several kb size into the genome of primary murine B cells also using CRISPR-Cas9 induced HDR. Finally, we were able to show the robust surface expression and antigen recognition of a synthetic CBCR in primary B cells. We anticipate CBCRs and our approach for engineering primary B cells will be a valuable tool for the advancement of future B cell- based immune cell therapies.

The quantity of CD40 signaling determines the differentiation of B cells into functionally distinct memory cell subsets

In mice, memory B (B_mem) cells can be divided into two subpopulations: CD80^hi B_mem cells, which preferentially differentiate into plasma cells; and CD80^lo B_mem cells, which become germinal center (GC) B cells during a recall response. We demonstrate that these distinct responses can be B-cell-intrinsic and essentially independent of B-cell receptor (BCR) isotypes. Furthermore, we find that the development of CD80^hi B_mem cells in the primary immune response requires follicular helper T cells, a relatively strong CD40 signal and a high-affinity BCR on B cells, whereas the development of CD80^lo B_mem cells does not. Quantitative differences in CD40 stimulation were enough to recapitulate the distinct B cell fate decisions in an in vitro culture system. The quantity of CD40 signaling appears to be translated into NF-κB activation, followed by BATF upregulation that promotes B_mem cell differentiation from GC B cells.

DNA immunization using in vivo electroporation for generating monoclonal antibodies Against Mouse IL-9R

Membrane proteins such as cytokine receptors and G protein-coupled receptors can be drug targets. Recently, we have generated specific monoclonal antibodies (mAbs) against the mouse IL-9 receptor (IL-9R) and found that IL-9R on memory B cells have critical roles in T-dependent immune response. So far, most antibodies against cell surface proteins have been generated by immunization of animals with recombinant proteins produced in Escherichia coli (E. coli) or peptides derived from the protein. However, such antibodies often fail to recognize native proteins on cell surfaces because these antigens lack posttranslational modification and natural protein conformations. To circumvent such problems, we have developed a mouse immunization method, the DNA-immunization utilizing hyaluronidase and E. coli GroEL. Herein, we report an application of the original mouse immunization method in rats to generate anti-mouse IL-9R mAbs which could react with the native form of mouse IL-9R on cell surfaces. Thus, we suggest that the DNA-immunization method is feasible for generating monoclonal antibodies against cell surface proteins in rats.

Induced Germinal Center B Cell Culture System

The germinal center (GC) is the site where B cells undergo clonal expansion, affinity-based selection, and differentiation into memory B cells or plasma cells. It has been difficult to elucidate regulatory mechanisms for the dynamic GC B cell maturation and differentiation, partly because experimental manipulation of GC B cells in vivo has been limited and no in vitro system has been available that resembles B cell reaction in GC. Here we describe the protocol for a culture system named "induced GC B (iGB) culture system" which can induce massive expansion of B cells that exhibit GC B cell-like phenotype, and thus it mimics the GC reaction. This protocol can be useful to elucidate the molecular mechanisms of GC B cell differentiation.

Transcription Factor STAT3 Serves as a Negative Regulator Controlling IgE Class Switching in Mice

A mutation in STAT3 has been linked to the incidence of autosomal dominant hyper IgE syndrome, a disease characterized by elevated serum IgE Ab. However, how this genetic mutation leads to the phenotype has not been fully understood. We investigated the specific role of STAT3 in the germinal center (GC) B cells and plasma cells for IgE class switching. Through the use of STAT3 conditional knockout (cKO) mice in a Th2-type immunization model, we demonstrated that CD2-Cre-driven STAT3 cKO mice showed elevated IgE and decreased IgG₁ in the serum and a reduction in GC formation. Within the GC, IgG₁ ⁺ GC B cells were decreased, whereas IgE⁺ GC B cells were more prevalent. Additionally, these mice exhibited reduced IgG₁ and elevated IgE populations of Ab-producing plasma cells. Subsequent experiments using a CD19-Cre cKO mouse established this effect to be B cell-intrinsic. Transcription factors critical for GC and plasma cell differentiation, including Bcl-6 and Aicda, were shown to function as downstream signals of STAT3 regulation. Chromatin immunoprecipitation sequencing analysis revealed that many genes, including Bcl3 and Crtc2, were among the direct STAT3 regulated targets. Mice with STAT3 deficiency in B cells also demonstrated an increase in lung inflammation when used in an asthma-like disease model. This model suggests a negative role for STAT3 in regulating class switching of the GC B cells from the IgG₁ to the IgE producing state, which may serve as a therapeutic target for treatment of autosomal dominant hyper IgE syndrome and other immune disorders.

Cbl Ubiquitin Ligases Control B Cell Exit from the Germinal-Center Reaction

Selective expansion of high-affinity antigen-specific B cells in germinal centers (GCs) is a key event in antibody affinity maturation. GC B cells with improved affinity can either continue affinity-driven selection or exit the GC to differentiate into plasma cells (PCs) or memory B cells. Here we found that deleting E3 ubiquitin ligases Cbl and Cbl-b (Cbls) in GC B cells resulted in the early exit of high-affinity antigen-specific B cells from the GC reaction and thus impaired clonal expansion. Cbls were highly expressed in GC light zone (LZ) B cells, where they promoted the ubiquitination and degradation of Irf4, a transcription factor facilitating PC fate choice. Strong CD40 and BCR stimulation triggered the Cbl degradation, resulting in increased Irf4 expression and exit from GC affinity selection. Thus, a regulatory cascade that is centered on the Cbl ubiquitin ligases ensures affinity-driven clonal expansion by connecting BCR affinity signals with differentiation programs.

IL-9 receptor signaling in memory B cells regulates humoral recall responses

Memory B cells (B_mem cells) are the basis of long-lasting humoral immunity. They respond to re-encountered antigens by rapidly producing specific antibodies and forming germinal centers (GCs), a recall response that has been known for decades but remains poorly understood. We found that the receptor for the cytokine IL-9 (IL-9R) was induced selectively on B_mem cells after primary immunization and that IL-9R-deficient mice exhibited a normal primary antibody response but impaired recall antibody responses, with attenuated population expansion and plasma-cell differentiation of B_mem cells. In contrast, there was augmented GC formation, possibly due to defective downregulation of the ligand for the co-stimulatory receptor ICOS on B_mem cells. A fraction of B_mem cells produced IL-9. These findings indicate that IL-9R signaling in B_mem cells regulates humoral recall responses.

A splenic IgM memory subset with antibacterial specificities is sustained from persistent mucosal responses

Le Gallou et al. use an AID fate-mapping model to identify an IgM memory population in the spleen of unimmunized mice, originating from persistent gut immune responses and endowed with cross-reactivity against bacteria.

To what extent immune responses against the gut flora are compartmentalized within mucosal tissues in homeostatic conditions remains a much-debated issue. We describe here, based on an inducible AID fate-mapping mouse model, that systemic memory B cell subsets, including mainly IgM⁺ B cells in spleen, together with IgA⁺ plasma cells in spleen and bone marrow, are generated in mice in the absence of deliberate immunization. While the IgA component appears dependent on the gut flora, IgM memory B cells are still generated in germ-free mice, albeit to a reduced extent. Clonal relationships and renewal kinetics after anti-CD20 treatment reveal that this long-lasting splenic population is mainly sustained by output of B cell clones persisting in mucosal germinal centers. IgM-secreting hybridomas established from splenic IgM memory B cells showed reactivity against various bacterial isolates and endogenous retroviruses. Ongoing activation of B cells in gut-associated lymphoid tissues thus generates a diversified systemic compartment showing long-lasting clonal persistence and protective capacity against systemic bacterial infections.

Tracing self-reactive B cells in normal mice

Self-tolerance removes or inactivates autoreactive B cells in primary and secondary lymphoid organs. Studies have used transgenic mouse models or characterizing recombinant antibodies from single B cells to study B-cell tolerance. These approaches are limited, however, by the restricted diversity of transgenic B-cell repertoires or the effort necessary to generate significant numbers of recombinant antibodies. To overcome these difficulties, we used a single-cell culture approach, which supports high-throughput analysis of the B-cell repertoire in pre-tolerance, post-tolerance, and tolerizing anergic B-cell compartments. This approach revealed the affinity “setpoints” of the tolerance checkpoints, the stochastic nature of B-cell tolerance, and subsets of autoreactive B cells that are persistent in periphery. We propose that these anergic compartments may be the origin of systemic autoimmunity and a potential target for HIV-1 vaccines that elicit neutralizing antibodies cross-reactive with self-antigens.

Host DNases prevent vascular occlusion by neutrophil extracellular traps

Platelet and fibrin clots occlude blood vessels in hemostasis and thrombosis. Here we report a noncanonical mechanism for vascular occlusion based on neutrophil extracellular traps (NETs), DNA fibers released by neutrophils during inflammation. We investigated which host factors control NETs in vivo and found that two deoxyribonucleases (DNases), DNase1 and DNase1-like 3, degraded NETs in circulation during sterile neutrophilia and septicemia. In the absence of both DNases, intravascular NETs formed clots that obstructed blood vessels and caused organ damage. Vascular occlusions in patients with severe bacterial infections were associated with a defect to degrade NETs ex vivo and the formation of intravascular NET clots. DNase1 and DNase1-like 3 are independently expressed and thus provide dual host protection against deleterious effects of intravascular NETs.

BCR and Endosomal TLR Signals Synergize to Increase AID Expression and Establish Central B Cell Tolerance

Activation-induced cytidine deaminase (AID) is required to purge autoreactive immature and transitional-1 (immature/T1) B cells at the first tolerance checkpoint, but how AID selectively removes self-reactive B cells is unclear. We now show that B cell antigen receptor (BCR) and endosomal Toll-like receptor (TLR) signals synergize to elicit high levels of AID expression in immature/T1 B cells. This synergy is restricted to ligands for endocytic TLR and requires phospholipase-D activation, endosomal acidification, and MyD88. The first checkpoint is significantly impaired in AID- or MyD88-deficient mice and in mice doubly heterozygous for AID and MyD88, suggesting interaction of these factors in central B cell tolerance. Moreover, administration of chloroquine, an inhibitor of endosomal acidification, results in a failure to remove autoreactive immature/T1 B cells in mice. We propose that a BCR/TLR pathway coordinately establishes central tolerance by hyper-activating AID in immature/T1 B cells that bind ligands for endosomal TLRs.

In Vitro-Induced Germinal Center B Cell Culture System

In germinal centers (GCs), B cells undergo repeated cycles of proliferation and affinity-based selection, and differentiate into memory B cells or long-lived plasma cells. It has been difficult to elucidate regulatory mechanisms for the dynamic GC B cell maturation and differentiation, partly because experimental manipulation of GC B cells has been limited. Here we describe a culture system in which we can induce massive expansion of naive B cells that exhibit GC B cell-like phenotype and acquire abilities to differentiate into memory B cells or bone marrow plasma cells depending on cytokine conditions. This system will allow us to elucidate the molecular mechanisms of GC B cell differentiation.

The AID-Cre-ERT2 Model: A Tool for Monitoring B Cell Immune Responses and Generating Selective Hybridomas

Expression of activation-induced cytidine deaminase (AID) is the hallmark of B cells engaged in an immune response in germinal centers. We designed an inducible fate-mapping reporter mouse in which AID-expressing B cells could be timely and irreversibly marked, by knockin at the Aicda locus of a tamoxifen-inducible Cre recombinase. This mouse model allows notably for the long-term follow-up of memory B cells and plasma cells engaged in an immune response. We describe here a protocol to generate hybridomas from small memory subsets that can be easily traced and identified in this mouse line through Cre-activated fluorescent reporters.

Differing Requirements for MALT1 Function in Peripheral B Cell Survival and Differentiation

During a T cell-dependent immune response, formation of the germinal center (GC) is essential for the generation of high-affinity plasma cells and memory B cells. The canonical NF-κB pathway has been implicated in the initiation of GC reaction, and defects in this pathway have been linked to immune deficiencies. The paracaspase MALT1 plays an important role in regulating NF-κB activation upon triggering of Ag receptors. Although previous studies have reported that MALT1 deficiency abrogates the GC response, the relative contribution of B cells and T cells to the defective phenotype remains unclear. We used chimeric mouse models to demonstrate that MALT1 function is required in B cells for GC formation. This role is restricted to BCR signaling where MALT1 is critical for B cell proliferation and survival. Moreover, the proapoptotic signal transmitted in the absence of MALT1 is dominant to the prosurvival effects of T cell-derived stimuli. In addition to GC B cell differentiation, MALT1 is required for plasma cell differentiation, but not mitogenic responses. Lastly, we show that ectopic expression of Bcl-2 can partially rescue the GC phenotype in MALT1-deficient animals by prolonging the lifespan of BCR-activated B cells, but plasma cell differentiation and Ab production remain defective. Thus, our data uncover previously unappreciated aspects of MALT1 function in B cells and highlight its importance in humoral immunity.

IFN-γ receptor and STAT1 signaling in B cells are central to spontaneous germinal center formation and autoimmunity

Spontaneously developed germinal centers (GCs [Spt-GCs]) harbor autoreactive B cells that generate somatically mutated and class-switched pathogenic autoantibodies (auto-Abs) to promote autoimmunity. However, the mechanisms that regulate Spt-GC development are not clear. In this study, we report that B cell-intrinsic IFN-γ receptor (IFN-γR) and STAT1 signaling are required for Spt-GC and follicular T helper cell (Tfh cell) development. We further demonstrate that IFN-γR and STAT1 signaling control Spt-GC and Tfh cell formation by driving T-bet expression and IFN-γ production by B cells. Global or B cell-specific IFN-γR deficiency in autoimmune B6.Sle1b mice leads to significantly reduced Spt-GC and Tfh cell responses, resulting in diminished antinuclear Ab reactivity and IgG2c and IgG2b auto-Ab titers compared with B6.Sle1b mice. Additionally, we observed that the proliferation and differentiation of DNA-reactive B cells into a GC B cell phenotype require B cell-intrinsic IFN-γR signaling, suggesting that IFN-γR signaling regulates GC B cell tolerance to nuclear self-antigens. The IFN-γR deficiency, however, does not affect GC, Tfh cell, or Ab responses against T cell-dependent foreign antigens, indicating that IFN-γR signaling regulates autoimmune, but not the foreign antigen-driven, GC and Tfh cell responses. Together, our data define a novel B cell-intrinsic IFN-γR signaling pathway specific to Spt-GC development and autoimmunity. This novel pathway can be targeted for future pharmacological intervention to treat systemic lupus erythematosus.

Interferon-γ receptor and STAT1 signaling in B cells are central to spontaneous germinal center formation and autoimmunity

In Systemic Lupus Erythematosus (SLE), spontaneously developed germinal centers (Spt-GCs) harbor AutoAb-producing B cells that promote disease, but the mechanisms that control Spt-GC development are not clear. Here we report that B cell-intrinsic IFNγR and STAT1 signaling are essential for Spt-GC formation. The IFNγR deficiency, however, does not significantly affect foreign Ag-induced GC and Tfh responses, suggesting that two distinct mechanisms regulate foreign-Ag vs Spt-GC responses. We also demonstrate that IFNγR-mediated STAT1 signaling drives T-bet expression, pro-GC gene expression and IFNγ production by B cells, which are critical for Spt-GC and Tfh development. To understand how IFNγ signaling regulates the Spt-GC response and associated AutoAb production in SLE, we utilized B6.Sle1b mice that harbor the lupus-prone NZM2410 strain-derived SLAM locus. B6.Sle1b mice exhibit elevated Spt-GC and follicular helper T cell (Tfh) responses that associate with impaired B cell selection in GCs. B6.Sle1b mice with B cell intrinsic IFNγR deficiency have significantly reduced Spt-GC and Tfh responses resulting in a markedly lower number of IgG-producing antibody forming cells and diminished IgG2c and IgG2b autoantibody titers compared to B6.Sle1b mice. Additionally, the proliferation and differentiation of DNA-reactive B cells into a GC B cell phenotype require B cell-intrinsic IFNγR signaling. Together, our data define a novel B cell-intrinsic IFNγR signaling pathway in Spt-GC development and autoimmunity.

How Tolerance Shapes the Development of the HIV-1 Broadly Neutralizing Antibody 2F5

An effective HIV-1 vaccine is likely to require induction of broadly neutralizing antibodies (bnAbs), which neutralize multiple HIV-1 strains. Generating HIV-1 bnAbs has been challenging due partly to a number of viral immune evasion mechanisms, including viral molecular mimicry of host in order to exploit immunological tolerance. Indeed, generation of neutralizing antibodies to the 2F5 epitope of HIV-1 gp41 is proscribed by immune tolerance. However, the specific mechanisms by which tolerance relieves the autoreactivity of B cells expressing the VH and VL regions (dKI) or the VH region (sKI) of the 2F5 bnAb are not well understood. To compare the reactivity and repertoire of 2F5 dKI and sKI B cells before and after immune tolerance checkpoints, we used a newly developed in vitro single B cell culture system that induces B cell expansion and differentiation into Ab-secreting plasmacytes. The reactivities of expanded B cell clones were determined by ELISA, while repertoire was determined by recovering the V(D)J rearrangements using RT-PCR and Sanger sequencing. In 2F5 dKI mice, the great majority of cells in the small-pre-B compartment express the knock in heavy- and light-chains, and maintain HIV-1 gp41-reactivity. However, 2F5 dKI B cells that survive tolerance checkpoints to become mature B cells have undergone extensive light-chain editing and are purged of gp41- and KYNU-reactivity. Importantly, the peripheral 2F5 dKI IgM−IgD+ (anergic) B cell subset retains a substantial fraction of HIV-1- and KYNU-reactive cells. In conclusion, our study provides mechanistic insights into how immunological tolerance impairs humoral responses to HIV-1, and suggests activation of anergic B cells as a potential target for HIV-1 vaccination.

B-Cell Selection in Germinal Centers Elicited by Complex Antigens

Germinal center (GC) B cells evolve towards increased affinity by a Darwinian process studied intensively in genetically restricted, hapten-specific responses. While experimentally tractable, genetically restricted humoral responses are atypical as antibodies to complex protein antigens represent genetically diverse, polyclonal humoral responses driven by various epitopes arrayed across the antigen. We have developed a single B-cell culture method that supports the proliferation and plasmacytic differentiation of mature and GC B cells. With this tool, we explore the population dynamics of genetically diverse GC responses to two complex antigens – protective antigen of Bacillus anthracis and influenza hemagglutinin – in which B cells compete both intra- and interclonally for distinct epitopes. Our characterizations begin with antigen-binding, mature naïve B cells and follow clonal selection and affinity maturation in GCs. Preferred VH rearrangements among antigen-binding, naïve B cells were similarly abundant in early GCs but, unlike restricted responses to haptens, clonal diversity increased in GC B cells as early “winners” were replaced by rarer, high affinity clones. Despite affinity maturation, half of GC B cells did not detectably bind immunogen but exhibited genetic selection comparable to antigen-binding cells, as determined by VH usage, mutations, and clonal expansion. In GCs elicited by rPA or rHA, interclonal BCR avidities can differ 100-fold and intraclonal avidity by as much as 40-fold. We propose that intraclonal selection in GCs is permissive for a wide range of BCR affinities and that lower affinity/less fit GC B cells may remain viable in GCs for substantially longer periods than generally thought.

Complex Antigens Drive Permissive Clonal Selection in Germinal Centers

Germinal center (GC) B cells evolve toward increased affinity by a Darwinian process that has been studied primarily in genetically restricted, hapten-specific responses. We explored the population dynamics of genetically diverse GC responses to two complex antigens-Bacillus anthracis protective antigen and influenza hemagglutinin-in which B cells competed both intra- and interclonally for distinct epitopes. Preferred VH rearrangements among antigen-binding, naive B cells were similarly abundant in early GCs but, unlike responses to haptens, clonal diversity increased in GC B cells as early "winners" were replaced by rarer, high-affinity clones. Despite affinity maturation, inter- and intraclonal avidities varied greatly, and half of GC B cells did not bind the immunogen but nonetheless exhibited biased VH use, V(D)J mutation, and clonal expansion comparable to antigen-binding cells. GC reactions to complex antigens permit a range of specificities and affinities, with potential advantages for broad protection.

GIMAP1 Is Essential for the Survival of Naive and Activated B Cells In Vivo

An effective immune system depends upon regulation of lymphocyte function and homeostasis. In recent years, members of the GTPases of the immunity associated protein (GIMAP) family were proposed to regulate T cell homeostasis. In contrast, little is known about their function and mode of action in B cells. We used a combination of transgenic mice and in vivo and in vitro techniques to conditionally and electively ablate GIMAP1 in resting and activated peripheral B cells. Our data suggest that GIMAP1 is absolutely essential for the survival of peripheral B cells, irrespective of their activation state. Together with recent data showing increased expression of GIMAP1 in B cell lymphomas, our work points to the possible potential of GIMAP1 as a target for manipulation in a variety of B cell-mediated diseases.

Acrolein, a highly toxic aldehyde generated under oxidative stress in vivo, aggravates the mouse liver damage after acetaminophen overdose

Although acetaminophen-induced liver injury in mice has been extensively studied as a model of human acute drug-induced hepatitis, the mechanism of liver injury remains unclear. Liver injury is believed to be initiated by metabolic conversion of acetaminophen to the highly reactive intermediate N-acetyl p-benzoquinoneimine, and is aggravated by subsequent oxidative stress via reactive oxygen species (ROS), including hydrogen peroxide (H2O2) and the hydroxyl radical (•OH). In this study, we found that a highly toxic unsaturated aldehyde acrolein, a byproduct of oxidative stress, has a major role in acetaminophen-induced liver injury. Acetaminophen administration in mice resulted in liver damage and increased acrolein-protein adduct formation. However, both of them were decreased by treatment with N-acetyl-L-cysteine (NAC) or sodium 2-mercaptoethanesulfonate (MESNA), two known acrolein scavengers. The specificity of NAC and MESNA was confirmed in cell culture, because acrolein toxicity, but not H2O2 or •OH toxicity, was inhibited by NAC and MESNA. These results suggest that acrolein may be more strongly correlated with acetaminophen-induced liver injury than ROS, and that acrolein produced by acetaminophen-induced oxidative stress can spread from dying cells at the primary injury site, causing damage to the adjacent cells and aggravating liver injury.

Concurrent spinal schwannoma and meningioma mimicking a single cervical dumbbell-shaped tumor: case report

Dumbbell-shaped tumors consisting of 2 different tumors are extremely rare. Herein, the authors present a case of concurrent spinal schwannoma and meningioma mimicking a single cervical dumbbell-shaped tumor. A 64-year-old man presented with a 5-year history of gradually exacerbating left occipital pain without clinical evidence of neurofibromatosis. Magnetic resonance imaging showed an extradural tumor along the left C-2 nerve root with a small intradural component. The tumor was approached via a C-1 hemilaminectomy. The intradural tumor was resected together with the extradural tumor after opening the dura mater. The intradural tumor was attached to the dura mater around the exit point of the C-2 nerve root. Intraoperative biopsy revealed that the extradural tumor was a schwannoma and that the intradural tumor was a meningioma. The dura mater adjacent to the tumor was then coagulated and resected. Postoperative pathological examination confirmed the same diagnoses with no evidence of continuity between the intra- and extradural components. The patient's postoperative clinical course was uneventful. Clinicians should be aware that cervical dumbbell-shaped tumors can consist of 2 different tumors.

Ex vivo engineered immune organoids for controlled germinal center reactions

Ex vivo engineered three-dimensional organotypic cultures have enabled the real-time study and control of biological functioning of mammalian tissues. Organs of broad interest where its architectural, cellular, and molecular complexity has prevented progress in ex vivo engineering are the secondary immune organs. Ex vivo immune organs can enable mechanistic understanding of the immune system and more importantly, accelerate the translation of immunotherapies as well as a deeper understanding of the mechanisms that lead to their malignant transformation into a variety of B and T cell malignancies. However, till date, no modular ex vivo immune organ has been developed with an ability to control the rate of immune reaction through tunable design parameter. Here we describe a B cell follicle organoid made of nanocomposite biomaterials, which recapitulates the anatomical microenvironment of a lymphoid tissue that provides the basis to induce an accelerated germinal center (GC) reaction by continuously providing extracellular matrix (ECM) and cell-cell signals to naïve B cells. Compared to existing co-cultures, immune organoids provide a control over primary B cell proliferation with ∼100-fold higher and rapid differentiation to the GC phenotype with robust antibody class switching.

JNK regulatory molecule G5PR induces IgG autoantibody-producing plasmablasts from peritoneal B1a cells

Peritoneal B1a cells expressing CD5 and CD11b generate autoantibody-producing precursors in autoimmune-prone mice. Previous studies show reduced JNK signaling in peritoneal B1a cells of female New Zealand Black mice and an abnormal increase of protein phosphatase 2A subunit G5PR that regulates BCR-mediated JNK signaling as a cause of autoimmunity. To investigate the mechanism regulating B1a differentiation into autoantibody-secreting plasmablasts (PBs), we applied an in vitro culture system that supports long-term growth of germinal center (GC) B cells (iGB) with IL-4, CD40L, and BAFF. Compared with spleen B2 cells, B1a cells differentiated into GC-like B cells, but more markedly into PBs, and underwent class switching toward IgG1. During iGB culture, B1a cells expressed GC-associated aicda, g5pr, and bcl6, and markedly PB-associated prdm1, irf4, and xbp1. B1a-derived iGB cells from New Zealand Black × New Zealand White F1 mice highly differentiated into autoantibody-secreting PBs in vitro and localized to the GC area in vivo. In iGB culture, JNK inhibitor SP600125 augmented the differentiation of C57BL/6 B1a cells into PBs. Furthermore, B1a cells from G5PR transgenic mice markedly differentiated into IgM and IgG autoantibody-secreting PBs. In conclusion, JNK regulation is critical to suppress autoantibody-secreting PBs from peritoneal B1a cells.