Transitional B cells commit to marginal zone B cell fate by Taok3-mediated surface expression of ADAM10

Glycan-Reactive Innate-like B Cells and Developmental Checkpoints

Using an Ig H chain conferring specificity for N-acetyl-d-glucosamine (GlcNAc), we developed transgenic (VHHGAC39 TG) mice to study the role of self-antigens in GlcNAc-reactive B-1 B cell development. In VHHGAC39 TG mice, GlcNAc-reactive B-1 B cell development during ontogeny and in adult bone marrow was normal. However, adult TG mice exhibited a block at transitional-2 immature B cell stages, resulting in impaired allelic exclusion and accumulation of a B cell subset coexpressing endogenous Ig gene rearrangements. Similarly, VHHGAC39 B cell fitness was impeded compared with non-self-reactive VHJ558 B TG cells in competitive mixed bone marrow chimeras. Nonetheless, adult VHHGAC39 mice immunized with Streptococcus pyogenes produce anti-GlcNAc Abs. Peritoneal cavity B cells transferred from VHHGAC39 TG mice into RAG-/- mice also exhibited robust expansion and anti-GlcNAc Ab production. However, chronic treatment of young VHHGAC39 mice with GlcNAc-specific mAbs leads to lower GlcNAc-binding B cell frequencies while increasing the proportion of GlcNAc-binding B1-a cells, suggesting that Ag masking or clearance of GlcNAc Ags impedes maturation of newly formed GlcNAc-reactive B cells. Finally, BCR H chain editing promotes expression of endogenous nontransgenic BCR alleles, allowing potentially self-reactive TG B cells to escape anergy or deletion at the transitional stage of precursor B cell development. Collectively, these observations indicate that GlcNAc-reactive B cell development is sensitive to the access of autologous Ags.

Notch2 controls developmental fate choices between germinal center and marginal zone B cells upon immunization

Sustained Notch2 signals induce trans-differentiation of Follicular B (FoB) cells into Marginal Zone B (MZB) cells in mice, but the physiology underlying this differentiation pathway is still elusive. Here, we demonstrate that most B cells receive a basal Notch signal, which is intensified in pre-MZB and MZB cells. Ablation or constitutive activation of Notch2 upon T-cell-dependent immunization reveals an interplay between antigen-induced activation and Notch2 signaling, in which FoB cells that turn off Notch2 signaling enter germinal centers (GC), while high Notch2 signaling leads to generation of MZB cells or to initiation of plasmablast differentiation. Notch2 signaling is dispensable for GC dynamics but appears to be re-induced in some centrocytes to govern expansion of IgG1+ GCB cells. Mathematical modelling suggests that antigen-activated FoB cells make a Notch2 dependent binary fate-decision to differentiate into either GCB or MZB cells. This bifurcation might serve as a mechanism to archive antigen-specific clones into functionally and spatially diverse B cell states to generate robust antibody and memory responses.

The induction of SHP-1 degradation by TAOK3 ensures the responsiveness of T cells to TCR stimulation

Thousand-and-one-amino acid kinase 3 (TAOK3) is a serine and threonine kinase that belongs to the STE-20 family of kinases. Its absence reduces T cell receptor (TCR) signaling and increases the interaction of the tyrosine phosphatase SHP-1, a major negative regulator of proximal TCR signaling, with the kinase LCK, a component of the core TCR signaling complex. Here, we used mouse models and human cell lines to investigate the mechanism by which TAOK3 limits the interaction of SHP-1 with LCK. The loss of TAOK3 decreased the survival of naïve CD4+ T cells by dampening the transmission of tonic and ligand-dependent TCR signaling. In mouse T cells, Taok3 promoted the secretion of interleukin-2 (IL-2) in response to TCR activation in a manner that depended on Taok3 gene dosage and on Taok3 kinase activity. TCR desensitization in Taok3-/- T cells was caused by an increased abundance of Shp-1, and pharmacological inhibition of Shp-1 rescued the activation potential of these T cells. TAOK3 phosphorylated threonine-394 in the phosphatase domain of SHP-1, which promoted its ubiquitylation and proteasomal degradation. The loss of TAOK3 had no effect on the abundance of SHP-2, which lacks a residue corresponding to SHP-1 threonine-394. Modulation of SHP-1 abundance by TAOK3 thus serves as a rheostat for TCR signaling and determines the activation threshold of T lymphocytes.

Pleiotropic functions of TAO kinases and their dysregulation in neurological disorders

Thousand and one amino acid kinases (TAOKs) are relatively understudied and functionally pleiotropic protein kinases that have emerged as important regulators of neurodevelopment. Through their conserved amino-terminal catalytic domain, TAOKs mediate phosphorylation at serine/threonine residues in their substrates, but it is their divergent regulatory carboxyl-terminal domains that confer both exquisite functional specification and cellular localization. In this Review, we discuss the physiological roles of TAOKs and the intricate signaling pathways, molecular interactions, and cellular behaviors they modulate-from cell stress responses, division, and motility to tissue homeostasis, immunity, and neurodevelopment. These insights are then integrated into an analysis of the known and potential impacts of disease-associated variants of TAOKs, with a focus on neurodevelopmental disorders, pain and addiction, and neurodegenerative diseases. Translating this foundation into clinical benefits for patients will require greater structural and functional differentiation of the TAOKs afforded by their individually specialized domains.

Dynamic encounters with red blood cells trigger splenic marginal zone B cell retention and function

Spleen marginal zone (MZ) B cells are important for antibody responses against blood-borne antigens. The signals they use to detect exposure to blood are not well defined. Here, using intravital two-photon microscopy in mice, we observe transient contacts between MZ B cells and red blood cells that are in flow. We show that MZ B cells use adhesion G-protein-coupled receptor ADGRE5 (CD97) for retention in the spleen. CD97 function in MZ B cells depends on its ability to undergo autoproteolytic cleavage and signaling via Gα13 and ARHGEF1. Red blood cell expression of the CD97 ligand CD55 is required for MZ B cell homeostasis. Applying a pulling force on CD97-transfected cells using an optical C-trap and CD55+ beads leads to accumulation of active RhoA and membrane retraction. Finally, we show that CD97 deficiency leads to a reduced T cell-independent IgM response. Thus, our studies provide evidence that MZ B cells use mechanosensing to position in a manner that enhances antibody responses against blood-borne antigens.

Knockout of STE20-type kinase TAOK3 does not attenuate diet-induced NAFLD development in mice

OBJECTIVE

Non-alcoholic fatty liver disease (NAFLD), the primary hepatic consequence of obesity, is affecting about 25% of the global adult population. The aim of this study was to examine the in vivo role of STE20-type protein kinase TAOK3, which has been previously reported to regulate hepatocellular lipotoxicity in vitro, in the development of NAFLD and systemic insulin resistance in the context of obesity.

METHODS

Taok3 knockout mice and wild-type littermates were challenged with a high-fat diet. Various in vivo tests were performed to characterize the whole-body metabolism. NAFLD progression in the liver, and lipotoxic damage in adipose tissue, kidney, and skeletal muscle were compared between the genotypes by histological assessment, immunofluorescence microscopy, protein and gene expression profiling, and biochemical assays. Intracellular lipid accumulation and oxidative/ER stress were analyzed in cultured human and mouse hepatocytes where TAOK3 was knocked down by small interfering RNA. The expression of TAOK3-related STE20-type kinases was quantified in different organs from high-fat diet-fed Taok3-/- and wild-type mice.

RESULTS

TAOK3 deficiency had no impact on body weight or composition, food consumption, locomotor activity, or systemic glucose or insulin homeostasis in obese mice. Consistently, Taok3-/- mice and wild-type littermates developed a similar degree of high-fat diet-induced liver steatosis, inflammation, and fibrosis, and we detected no difference in lipotoxic damage of adipose tissue, kidney, or skeletal muscle when comparing the two genotypes. In contrast, the silencing of TAOK3 in vitro markedly suppressed ectopic lipid accumulation and metabolic stress in mouse and human hepatocytes. Interestingly, the hepatic mRNA abundance of several TAOK3-related kinases, which have been previously implicated to increase the risk of NAFLD susceptibility, was significantly elevated in Taok3-/- vs. wild-type mice.

CONCLUSIONS

In contrast to the in vitro observations, genetic deficiency of TAOK3 in mice failed to mitigate the detrimental metabolic consequences of chronic exposure to dietary lipids, which may be partly attributable to the activation of liver-specific compensation response for the genetic loss of TAOK3 by related STE20-type kinases.

STE20 kinase TAOK3 regulates type 2 immunity and metabolism in obesity

Healthy adipose tissue (AT) contains ST2+ Tregs, ILC2s, and alternatively activated macrophages that are lost in mice or humans on high caloric diet. Understanding how this form of type 2 immunity is regulated could improve treatment of obesity. The STE20 kinase Thousand And One amino acid Kinase-3 (TAOK3) has been linked to obesity in mice and humans, but its precise function is unknown. We found that ST2+ Tregs are upregulated in visceral epididymal white AT (eWAT) of Taok3-/- mice, dependent on IL-33 and the kinase activity of TAOK3. Upon high fat diet feeding, metabolic dysfunction was attenuated in Taok3-/- mice. ST2+ Tregs disappeared from eWAT in obese wild-type mice, but this was not the case in Taok3-/- mice. Mechanistically, AT Taok3-/- Tregs were intrinsically more responsive to IL-33, through higher expression of ST2, and expressed more PPARγ and type 2 cytokines. Thus, TAOK3 inhibits adipose tissue Tregs and regulates immunometabolism under excessive caloric intake.

GPR182 is a broadly scavenging atypical chemokine receptor influencing T-independent immunity

Immune responses highly depend on the effective trafficking of immune cells into and within secondary lymphoid organs (SLOs). Atypical chemokine receptors (ACKRs) scavenge chemokines to eliminate them from the extracellular space, thereby generating gradients that guide leukocytes. In contrast to canonical chemokine receptors, ACKRs do not induce classical intracellular signaling that results in cell migration. Recently, the closest relative of ACKR3, GPR182, has been partially deorphanized as a potential novel ACKR. We confirm and extend previous studies by identifying further ligands that classify GPR182 as a broadly scavenging chemokine receptor. We validate the "atypical" nature of the receptor, wherein canonical G-protein-dependent intracellular signaling is not activated following ligand stimulation. However, β-arrestins are required for ligand-independent internalization and chemokine scavenging whereas the C-terminus is in part dispensable. In the absence of GPR182 in vivo, we observed elevated chemokine levels in the serum but also in SLO interstitium. We also reveal that CXCL13 and CCL28, which do not bind any other ACKR, are bound and efficiently scavenged by GPR182. Moreover, we found a cooperative relationship between GPR182 and ACKR3 in regulating serum CXCL12 levels, and between GPR182 and ACKR4 in controlling CCL20 levels. Furthermore, we unveil a new phenotype in GPR182-KO mice, in which we observed a reduced marginal zone (MZ), both in size and in cellularity, and thus in the T-independent antibody response. Taken together, we and others have unveiled a novel, broadly scavenging chemokine receptor, which we propose should be named ACKR5.

TAOK3 limits age-associated inflammation by negatively modulating macrophage differentiation and their production of TNFα

BACKGROUND

Human aging is characterized by a state of chronic inflammation, termed inflammaging, for which the causes are incompletely understood. It is known, however, that macrophages play a driving role in establishing inflammaging by promoting pro-inflammatory rather than anti-inflammatory responses. Numerous genetic and environmental risk factors have been implicated with inflammaging, most of which are directly linked to pro-inflammatory mediators IL-6, IL1Ra, and TNFα. Genes involved in the signaling and production of those molecules have also been highlighted as essential contributors. TAOK3 is a serine/threonine kinase of the STE-20 kinase family that has been associated with an increased risk of developing auto-immune conditions in several genome-wide association studies (GWAS). Yet, the functional role of TAOK3 in inflammation has remained unexplored.

RESULTS

We found that mice deficient in the serine/Threonine kinase Taok3 developed severe inflammatory disorders with age, which was more pronounced in female animals. Further analyses revealed a drastic shift from lymphoid to myeloid cells in the spleens of those aged mice. This shift was accompanied by hematopoietic progenitor cells skewing in Taok3^-/- mice that favored myeloid lineage commitment. Finally, we identified that the kinase activity of the enzyme plays a vital role in limiting the establishment of proinflammatory responses in macrophages.

CONCLUSIONS

Essentially, Taok3 deficiency promotes the accumulation of monocytes in the periphery and their adoption of a pro-inflammatory phenotype. These findings illustrate the role of Taok3 in age-related inflammation and highlight the importance of genetic risk factors in this condition.

Gene expression analysis of the Tao kinase family of Ste20p-like map kinase kinase kinases during early embryonic development in Xenopus laevis

Development of the vertebrate embryo requires strict coordination of a highly complex series of signaling cascades, that drive cell proliferation, differentiation, migration, and the general morphogenetic program. Members of the Map kinase signaling pathway are repeatedly required throughout development to activate the downstream effectors, ERK, p38, and JNK. Regulation of these pathways occurs at many levels in the signaling cascade, with the Map3Ks playing an essential role in target selection. The thousand and one amino acid kinases (Taoks) are Map3Ks that have been shown to activate both p38 and JNK and are linked to neurodevelopment in both invertebrate and vertebrate organisms. In vertebrates, there are three Taok paralogs (Taok1, Taok2, and Taok3) which have not yet been ascribed a role in early development. Here we describe the spatiotemporal expression of Taok1, Taok2, and Taok3 in the model organism Xenopus laevis. The X. laevis Tao kinases share roughly 80% identity to each other, with the bulk of the conservation in the kinase domain. Taok1 and Taok3 are highly expressed in pre-gastrula and gastrula stage embryos, with initial expression localized to the animal pole and later expression in the ectoderm and mesoderm. All three Taoks are expressed in the neural and tailbud stages, with overlapping expression in the neural tube, notochord, and many anterior structures (including branchial arches, brain, otic vesicles, and eye). The expression patterns described here provide evidence that the Tao kinases may play a central role in early development, in addition to their function during neural development, and establish a framework to better understand the developmental roles of Tao kinase signaling.

AKT activity orchestrates marginal zone B cell development in mice and humans

The signals controlling marginal zone (MZ) and follicular (FO) B cell development remain incompletely understood. Here, we show that AKT orchestrates MZ B cell formation in mice and humans. Genetic models that increase AKT signaling in B cells or abolish its impact on FoxO transcription factors highlight the AKT-FoxO axis as an on-off switch for MZ B cell formation in mice. In humans, splenic immunoglobulin (Ig) D+CD27+ B cells, proposed as an MZ B cell equivalent, display higher AKT signaling than naive IgD+CD27- and memory IgD-CD27+ B cells and develop in an AKT-dependent manner from their precursors in vitro, underlining the conservation of this developmental pathway. Consistently, CD148 is identified as a receptor indicative of the level of AKT signaling in B cells, expressed at a higher level in MZ B cells than FO B cells in mice as well as humans.

Immunomodulatory role of metalloproteases in cancers: Current progress and future trends

Metalloproteinases (MPs) is a large family of proteinases with metal ions in their active centers. According to the different domains metalloproteinases can be divided into a variety of subtypes mainly including Matrix Metalloproteinases (MMPs), A Disintegrin and Metalloproteases (ADAMs) and ADAMs with Thrombospondin Motifs (ADAMTS). They have various functions such as protein hydrolysis, cell adhesion and remodeling of extracellular matrix. Metalloproteinases expressed in multiple types of cancers and participate in many pathological processes involving tumor genesis and development, invasion and metastasis by regulating signal transduction and tumor microenvironment. In this review, based on the current research progress, we summarized the structure of MPs, their expression and especially immunomodulatory role and mechanisms in cancers. Additionally, a relevant and timely update of recent advances and future directions were provided for the diagnosis and immunotherapy targeting MPs in cancers.

Hypoxia and hypoxia-inducible factor signals regulate the development, metabolism, and function of B cells

Hypoxia is a common hallmark of healthy tissues in physiological states or chronically inflamed tissues in pathological states. Mammalian cells sense and adapt to hypoxia mainly through hypoxia-inducible factor (HIF) signaling. Many studies have shown that hypoxia and HIF signaling play an important regulatory role in development and function of innate immune cells and T cells, but their role in B cell biology is still controversial. B cells experience a complex life cycle (including hematopoietic stem cells, pro-B cells, pre-B cells, immature B cells, mature naïve B cells, activated B cells, plasma cells, and memory B cells), and the partial pressure of oxygen (PO₂) in the corresponding developmental niche of stage-specific B cells is highly dynamic, which suggests that hypoxia and HIF signaling may play an indispensable role in B cell biology. Based on the fact that hypoxia niches exist in the B cell life cycle, this review focuses on recent discoveries about how hypoxia and HIF signaling regulate the development, metabolism, and function of B cells, to facilitate a deep understanding of the role of hypoxia in B cell-mediated adaptive immunity and to provide novel strategies for vaccine adjuvant research and the treatment of immunity-related or infectious diseases.

CD20+CD22+ADAM28+ B Cells in Tertiary Lymphoid Structures Promote Immunotherapy Response

Background

As the indication for immunotherapy is rapidly expanding, it is crucial to accurately identify patients who are likely to respond. Infiltration of B cells into many tumor types correlates with a good response to immune checkpoint inhibitor (ICI) therapy. However, B cells' roles in the anti-tumor response are far from clear.

Methods

Based on single-cell transcriptomic data for ICI-treated patients, we identified a B-cell cluster [B_IR (ICI-Responsive B) cells] and described the phenotype, cell-cell communication, biological processes, gene signature, and prognosis value of B_IR cells through bioinformatic analysis, tissue immunofluorescence, and animal experiments. Surgery samples from 12 non-small cell lung carcinoma (NSCLC) patients with adjuvant checkpoint blockade were evaluated as external validation.

Results

B_IR cells were identified as a subset of CD20⁺CD22⁺ADAM28⁺ B cells with a memory phenotype. Bioinformatic analysis revealed that B_IR cells had enhanced cell viability and epigenetic regulation, and that ALOX5AP, MIF, and PTPRC/CD45 expressed by myeloid cells may be critical coordinators of diverse biological processes of B_IR cells. Immunofluorescence confirmed the presence of B_IR cells in tertiary lymphoid structures (TLSs) in skin SCC, RCC, CRC, and breast cancer. B_IR-associated gene signatures correlate with positive outcomes in patients with melanoma, glioblastoma, NSCLC, HNSCC, or RCC treated with ICI therapy, and B_IR-cell density predicted NSCLC patients' response to checkpoint immunotherapy. In line with this, melanoma-bearing mice depleted of B_IR cells were resistant to ICIs.

Conclusions

CD20⁺CD22⁺ADAM28⁺ B_IR cells were present in cancer-associated TLS and promoted the response to ICI therapy.

A MZB Cell Activation Profile Present in the Lacrimal Glands of Sjögren's Syndrome-Susceptible C57BL/6.NOD-Aec1Aec2 Mice Defined by Global RNA Transcriptomic Analyses

The C57BL/6.NOD-Aec1Aec2 mouse has been extensively studied to define the underlying cellular and molecular basis for the onset and development of Sjögren's syndrome (SS), a human systemic autoimmune disease characterized clinically as the loss of normal lacrimal and salivary gland functions leading respectively to dry eye and dry mouth pathologies. While an overwhelming majority of SS studies in both humans and rodent models have long focused primarily on pathophysiological events and the potential role of T lymphocytes in these events, recent studies in our murine models have indicated that marginal zone B (MZB) lymphocytes are critical for both development and onset of SS disease. Although migration and function of MZB cells are difficult to study in vivo and in vitro, we have carried out ex vivo investigations that use temporal global RNA transcriptomic analyses to track early cellular and molecular events in these exocrine glands of C57BL/6.NOD-Aec1Aec2 mice. In the present report, genome-wide transcriptome analyses of lacrimal glands indicate that genes and gene-sets temporally upregulated during early onset of disease define the Notch2/NF-kβ14 and Type1 interferon signal transduction pathways, as well as identify chemokines, especially Cxcl13, and Rho-GTPases, including DOCK molecules, in the cellular migration of immune cells to the lacrimal glands. We discuss how the current results compare with our recently published salivary gland data obtained from similar studies carried out in our C57BL/6.NOD-Aec1Aec2 mice, pointing out both similarities and differences in the etiopathogeneses underlying the autoimmune response within the two glands. Overall, this study uses the power of transcriptomic analyses to identify temporal molecular bioprocesses activated during the preclinical covert pathogenic stage(s) of SS disease and how these findings may impact future intervention therapies as the disease within the two exocrine glands may not be identical.

Marginal Zone B-Cell Populations and Their Regulatory Potential in the Context of HIV and Other Chronic Inflammatory Conditions

Inflammation in the context of Human Immunodeficiency Virus (HIV) establishes early and persists beyond antiretroviral therapy (ART). As such, we have shown excess B-cell activating factor (BAFF) in the blood of HIV-infected progressors, as soon as in the acute phase, and despite successful ART. Excess BAFF was associated with deregulation of the B-cell compartment; notably, with increased frequencies of a population sharing features of both transitional immature (TI) and marginal zone (MZ) B-cells, we termed Marginal Zone precursor-like (MZp). We have reported similar observations with HIV-transgenic mice, Simian Immunodeficiency Virus (SIV)-infected macaques, and more recently, with HIV-infected Beninese commercial sex workers, which suggests that excess BAFF and increased frequencies of MZp B-cells are reliable markers of inflammation in the context of HIV. Importantly, we have recently shown that in healthy individuals, MZps present an important regulatory B-cell (Breg) profile and function. Herein, we wish to review our current knowledge on MZ B-cell populations, especially their Breg status, and that of other B-cell populations sharing similar features. BAFF and its analog A Proliferation-Inducing Ligand (APRIL) are important in shaping the MZ B-cell pool; moreover, the impact that excess BAFF—encountered in the context of HIV and several chronic inflammatory conditions—may exert on MZ B-cell populations, Breg and antibody producing capacities is a threat to the self-integrity of their antibody responses and immune surveillance functions. As such, deregulations of MZ B-cell populations contribute to autoimmune manifestations and the development of MZ lymphomas (MZLs) in the context of HIV and other inflammatory diseases. Therefore, further comprehending the mechanisms regulating MZ B-cell populations and their functions could be beneficial to innovative therapeutic avenues that could be deployed to restore MZ B-cell immune competence in the context of chronic inflammation involving excess BAFF.

IRF4 Has a Unique Role in Early B Cell Development and Acts Prior to CD21 Expression to Control Marginal Zone B Cell Numbers

Strict control of B lymphocyte development is required for the ability to mount humoral immune responses to diverse foreign antigens while remaining self-tolerant. In the bone marrow, B lineage cells transit through several developmental stages in which they assemble a functional B cell receptor in a stepwise manner. The immunoglobulin heavy chain gene is rearranged at the pro-B stage. At the large pre-B stage, cells with a functional heavy chain expand in response to signals from IL-7 and the pre-BCR. Cells then cease proliferation at the small pre-B stage and rearrange the immunoglobulin light chain gene. The fully formed BCR is subsequently expressed on the surface of immature B cells and autoreactive cells are culled by central tolerance mechanisms. Once in the periphery, transitional B cells develop into mature B cell subsets such as marginal zone and follicular B cells. These developmental processes are controlled by transcription factor networks, central to which are IRF4 and IRF8. These were thought to act redundantly during B cell development in the bone marrow, with their functions diverging in the periphery where IRF4 limits the number of marginal zone B cells and is required for germinal center responses and plasma cell differentiation. Because of IRF4's unique role in mature B cells, we hypothesized that it may also have functions earlier in B cell development that cannot be compensated for by IRF8. Indeed, we find that IRF4 has a unique role in upregulating the pre-B cell marker CD25, limiting IL-7 responsiveness, and promoting migration to CXCR4 such that IRF4-deficient mice have a partial block at the pre-B cell stage. We also find that IRF4 acts in early transitional B cells to restrict marginal zone B cell development, as deletion of IRF4 in mature B cells with CD21-cre impairs plasma cell differentiation but has no effect on marginal zone B cell numbers. These studies highlight IRF4 as the dominant IRF family member in early B lymphopoiesis.

Multi-ancestral GWAS identifies shared and Asian-specific loci for SLE and links type III interferon signaling and lysosomal function to the disease

OBJECTIVES

Systemic lupus erythematosus (SLE) is a prototype autoimmune disease with differences in prevalence and severity among ancestral groups. This study aims to identify novel genetic components either shared or distinct between Asian and European populations.

METHODS

Both trans-ancestral and ancestry-specific meta-analyses of genome-wide association studies (GWAS) for SLE were performed, involving 30,604 participants of European, Chinese or Thai origin. Using public epigenomic data and expression quantitative trait loci, fine-mapping analyses were conducted to identify putative causal variants and genes for the newly identified loci. Performance of polygenic risk scores (PRS) for the Thai cohort was evaluated comparing different training data.

RESULTS

We identified ten novel SLE susceptibility loci, four of which were found by Asian-specific meta-analyses. A 1bp deletion upstream of IFNLR1 was found associated with SLE, with the risk allele correlated with increased expression of IFNLR1. This gene encodes interferon lambda receptor 1, pointing to the role of type III interferon signaling in SLE. An intronic variant in SLC29A3 was found associated with SLE only in Asians. The putative risk variant may modulate SLC29A3 expression in a monocyte-specific manner. SLC29A3 encodes a lysosomal nucleoside transporter, and subsequent analyses suggest reduced lysosomal function and phagocytosis might be the mechanism underlying this association. In addition, trans-ancestral meta-analysis was proved to be valuable in risk prediction for individuals without ancestry-matched data.

CONCLUSION

Multi-ancestral GWAS identified both shared and Asian-specific loci for SLE, and functional annotation pointed to the involvement of increased type III interferon signaling and reduced lysosomal function in SLE.

Thymic B Cells as a New Player in the Type 1 Diabetes Response

Type 1 diabetes (T1d) results from a sustained autoreactive T and B cell response towards insulin-producing β cells in the islets of Langerhans. The autoreactive nature of the condition has led to many investigations addressing the genetic or cellular changes in primary lymphoid tissues that impairs central tolerance- a key process in the deletion of autoreactive T and B cells during their development. For T cells, these studies have largely focused on medullary thymic epithelial cells (mTECs) critical for the effective negative selection of autoreactive T cells in the thymus. Recently, a new cellular player that impacts positively or negatively on the deletion of autoreactive T cells during their development has come to light, thymic B cells. Normally a small population within the thymus of mouse and man, thymic B cells expand in T1d as well as other autoimmune conditions, reside in thymic ectopic germinal centres and secrete autoantibodies that bind selective mTECs precipitating mTEC death. In this review we will discuss the ontogeny, characteristics and functionality of thymic B cells in healthy and autoimmune settings. Furthermore, we explore how in silico approaches may help decipher the complex cellular interplay of thymic B cells with other cells within the thymic microenvironment leading to new avenues for therapeutic intervention.

STE20-type kinase TAOK3 regulates hepatic lipid partitioning

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD), defined by excessive lipid storage in hepatocytes, has recently emerged as a leading global cause of chronic liver disease. The aim of this study was to examine the role of STE20-type protein kinase TAOK3, which has previously been shown to associate with hepatic lipid droplets, in the initiation and aggravation of human NAFLD.

METHODS

The correlation between TAOK3 mRNA expression and the severity of NAFLD was investigated in liver biopsies from 62 individuals. In immortalized human hepatocytes, intracellular fat deposition, lipid metabolism, and oxidative and endoplasmic reticulum stress were analyzed when TAOK3 was overexpressed or knocked down by small interfering RNA. Subcellular localization of TAOK3 was characterized in human and mouse hepatocytes by immunofluorescence microscopy.

RESULTS

We found that the TAOK3 transcript levels in human liver biopsies were positively correlated with the key lesions of NAFLD (i.e., hepatic steatosis, inflammation, and ballooning). Overexpression of TAOK3 in cultured human hepatocytes exacerbated lipid storage by inhibiting β-oxidation and triacylglycerol secretion while enhancing lipid synthesis. Conversely, silencing of TAOK3 attenuated lipid deposition in human hepatocytes by stimulating mitochondrial fatty acid oxidation and triacylglycerol efflux while suppressing lipogenesis. We also found aggravated or decreased oxidative/endoplasmic reticulum stress in human hepatocytes with increased or reduced TAOK3 levels, respectively. The subcellular localization of TAOK3 in human and mouse hepatocytes was confined to intracellular lipid droplets.

CONCLUSIONS

This study provides the first evidence that hepatic lipid droplet-coating kinase TAOK3 is a critical regulatory node controlling liver lipotoxicity and susceptibility to NAFLD.

The STE20 kinase TAOK3 controls the development house dust mite-induced asthma in mice

BACKGROUND

The most common endotype of asthma is type 2-high asthma, which is sometimes driven by adaptive allergen-specific T_H2 lymphocytes that react to allergens presented by dendritic cells (DCs), or sometimes by an innate immune response dominated by type 2 innate lymphocytes (ILC2s). Understanding the underlying pathophysiology of asthma is essential to improve patient-tailored therapy. The STE20 kinase thousand-and-one kinase 3 (TAOK3) controls key features in the biology of DCs and lymphocytes, but to our knowledge, its potential usefulness as a target for asthma therapy has not yet been addressed.

OBJECTIVE

We examined if and how loss of Taok3 affects the development of house dust mite (HDM)-driven allergic asthma in an in vivo mouse model.

METHODS

Wild-type Taok3^+/+ and gene-deficient Taok3^-/- mice were sensitized and challenged with HDM, and bronchoalveolar lavage fluid composition, mediastinal lymph node cytokine production, lung histology, and bronchial hyperreactivity measured. Conditional Taok3^fl/fl mice were crossed to tissue- and cell-specific specific deletor Cre mice to understand how Taok3 acted on asthma susceptibility. Kinase-dead (KD) Taok3^KD mice were generated to probe for the druggability of this pathway. Activation of HDM-specific T cells was measured in adoptively transferred HDM-specific T-cell receptor-transgenic CD4⁺ T cells. ILC2 biology was assessed by in vivo and in vitro IL-33 stimulation assays in Taok3^-/- and Taok3^+/+, Taok3^KD, and Red5-Cre Taok3^fl/fl mice.

RESULTS

Taok3^-/- mice failed to mount salient features of asthma, including airway eosinophilia, T_H2 cytokine production, IgE secretion, airway goblet cell metaplasia, and bronchial hyperreactivity compared to controls. This was due to intrinsic loss of Taok3 in hematopoietic and not epithelial cells. Loss of Taok3 resulted in hampered HDM-induced lung DC migration to the draining lymph nodes and defective priming of HDM-specific T_H2 cells. Strikingly, HDM and IL-33-induced ILC2 proliferation and function were also severely affected in Taok3-deficient and Taok3^KD mice.

CONCLUSIONS

Absence of Taok3 or loss of its kinase activity protects from HDM-driven allergic asthma as a result of defects in both adaptive DC-mediated T_H2 activation and innate ILC2 function. This identifies Taok3 as an interesting drug target, justifying further testing as a new treatment for type 2-high asthma.

RHO GTPases: from new partners to complex immune syndromes

Ras homology (RHO) GTPases are signalling proteins that have crucial roles in triggering multiple immune functions. Through their interactions with a broad range of effectors and kinases, they regulate cytoskeletal dynamics, cell polarity and the trafficking and proliferation of immune cells. The activity and localization of RHO GTPases are highly controlled by classical families of regulators that share consensus motifs. In this Review, we describe the recent discovery of atypical modulators and partners of RHO GTPases, which bring an additional layer of regulation and plasticity to the control of RHO GTPase activities in the immune system. Furthermore, the development of large-scale genetic screening has now enabled researchers to identify dysregulation of RHO GTPase signalling pathways as a cause of many immune system-related diseases. We discuss the mutations that have been identified in RHO GTPases and their signalling circuits in patients with rare diseases. The discoveries of new RHO GTPase partners and genetic mutations in RHO GTPase signalling hubs have uncovered unsuspected layers of crosstalk with other signalling pathways and may provide novel therapeutic opportunities for patients affected by complex immune or broader syndromes.

Protein Kinase CK2 Regulates B Cell Development and Differentiation

Protein kinase CK2 (also known as Casein Kinase 2) is a serine/threonine kinase composed of two catalytic subunits (CK2α and/or CK2α') and two regulatory CK2β subunits. CK2 is overexpressed and overactive in B cell acute lymphoblastic leukemia and diffuse large B cell lymphomas, leading to inappropriate activation of the NF-κB, JAK/STAT, and PI3K/AKT/mTOR signaling pathways and tumor growth. However, whether CK2 regulates normal B cell development and differentiation is not known. We generated mice lacking CK2α specifically in B cells (using CD19-driven Cre recombinase). These mice exhibited cell-intrinsic expansion of marginal zone B cells at the expense of transitional B cells, without changes in follicular B cells. Transitional B cells required CK2α to maintain adequate BCR signaling. In the absence of CK2α, reduced BCR signaling and elevated Notch2 signaling activation increased marginal zone B cell differentiation. Our results identify a previously unrecognized function for CK2α in B cell development and differentiation.

Marginal Zone Formation Requires ACKR3 Expression on B Cells

The marginal zone (MZ) contributes to the highly organized spleen microarchitecture. We show that expression of atypical chemokine receptor 3 (ACKR3) defines two equal-sized populations of mouse MZ B cells (MZBs). ACKR3 is required for development of a functional MZ and for positioning of MZBs. Deletion of ACKR3 on B cells distorts the MZ, and MZBs fail to deliver antigens to follicles, reducing humoral responses. Reconstitution of MZ-deficient CD19^ko mice shows that ACKR3^- MZBs can differentiate into ACKR3⁺ MZBs, but not vice versa. The lack of a MZ is rescued by adoptive transfer of ACKR3-sufficient, and less by ACKR3-deficient, follicular B cells (FoBs); hence, ACKR3 expression is crucial for establishment of the MZ. The inability of CD19^ko mice to respond to T-independent antigen is rescued when ACKR3-proficient, but not ACKR3-deficient, FoBs are transferred. Accordingly, ACKR3-deficient FoBs are able to reconstitute the MZ if the niche is pre-established by ACKR3-proficient MZBs.

Human marginal zone B cell development from early T2 progenitors

B cells emerge from the bone marrow as transitional (TS) B cells that differentiate through T1, T2, and T3 stages to become naive B cells. We have identified a bifurcation of human B cell maturation from the T1 stage forming IgMhi and IgMlo developmental trajectories. IgMhi T2 cells have higher expression of α4β7 integrin and lower expression of IL-4 receptor (IL4R) compared with the IgMlo branch and are selectively recruited into gut-associated lymphoid tissue. IgMhi T2 cells also share transcriptomic features with marginal zone B cells (MZBs). Lineage progression from T1 cells to MZBs via an IgMhi trajectory is identified by pseudotime analysis of scRNA-sequencing data. Reduced frequency of IgMhi gut-homing T2 cells is observed in severe SLE and is associated with reduction of MZBs and their putative IgMhi precursors. The collapse of the gut-associated MZB maturational axis in severe SLE affirms its existence in health.

Marginal zone B cells: From housekeeping function to autoimmunity?

Marginal zone (MZ) B cells comprise a subset of innate-like B cells found predominantly in the spleen, but also in lymph nodes and blood. Their principal functions are participation in quick responses to blood-borne pathogens and secretion of natural antibodies. The latter is important for housekeeping functions such as clearance of apoptotic cell debris. MZ B cells have B cell receptors with low poly-/self-reactivity, but they are not pathogenic at steady state. However, if simultaneously stimulated with self-antigen and pathogen- and/or damage-associated molecular patterns (PAMPs/DAMPs), MZ B cells may participate in the initial steps towards breakage of immunological tolerance. This review summarizes what is known about the role of MZ B cells in autoimmunity, both in mouse models and human disease. We cover factors important for shaping the MZ B cell compartment, how the functional properties of MZ B cells may contribute to breaking tolerance, and how MZ B cells are being regulated.

Notch2-mediated plasticity between marginal zone and follicular B cells

Follicular B (FoB) and marginal zone B (MZB) cells are functionally and spatially distinct mature B cell populations in the spleen, originating from a Notch2-dependent fate decision after splenic influx of immature transitional B cells. In the B cell follicle, a Notch2-signal is provided by DLL-1-expressing fibroblasts. However, it is unclear whether FoB cells, which are in close contact with these DLL-1 expressing fibroblasts, can also differentiate to MZB cells if they receive a Notch2-signal. Here, we show induced Notch2IC-expression in FoB cells re-programs mature FoB cells into bona fide MZB cells as is evident from the surface phenotype, localization, immunological function and transcriptome of these cells. Furthermore, the lineage conversion from FoB to MZB cells occurs in immunocompetent wildtype mice. These findings demonstrate plasticity between mature FoB and MZB cells that can be driven by a singular signaling event, the activation of Notch2.

Early Covert Appearance of Marginal Zone B Cells in Salivary Glands of Sjögren's Syndrome-Susceptible Mice: Initiators of Subsequent Overt Clinical Disease

The C57BL/6.NOD-Aec1Aec2 mouse model has been extensively studied to define the underlying cellular and molecular bioprocesses critical in the onset of primary Sjögren’s Syndrome (pSS), a human systemic autoimmune disease characterized clinically as the loss of lacrimal and salivary gland functions leading to dry eye and dry mouth pathologies. This mouse model, together with several gene knockout mouse models of SS, has indicated that B lymphocytes, especially marginal zone B (MZB) cells, are necessary for development and onset of clinical manifestations despite the fact that destruction of the lacrimal and salivary gland cells involves a classical T cell-mediated autoimmune response. Because migrations and functions of MZB cells are difficult to study in vivo, we have carried out ex vivo investigations that use temporal global RNA transcriptomic analyses to profile autoimmunity as it develops within the salivary glands of C57BL/6.NOD-Aec1Aec2 mice. Temporal profiles indicate the appearance of Notch2-positive cells within the salivary glands of these SS-susceptible mice concomitant with the early-phase appearance of lymphocytic foci (LF). Data presented here identify cellular bioprocesses occurring during early immune cell migrations into the salivary glands and suggest MZB cells are recruited to the exocrine glands by the upregulated Cxcl13 chemokine where they recognize complement (C’)-decorated antigens via their sphingosine-1-phosphate (S1P) and B cell (BC) receptors. Based on known MZB cell behavior and mobility, we propose that MZB cells activated in the salivary glands migrate to splenic follicular zones to present antigens to follicular macrophages and dendritic cells that, in turn, promote a subsequent systemic cell-mediated and autoantibody-mediated autoimmune T cell response that targets exocrine gland cells and functions. Overall, this study uses the power of transcriptomic analyses to provide greater insight into several molecular events defining cellular bioprocesses underlying SS that can be modelled and more thoroughly studied at the cellular level.

Notch Signaling in B Cell Immune Responses

The Notch signaling pathway is highly evolutionarily conserved, dictating cell fate decisions and influencing the survival and growth of progenitor cells that give rise to the cells of the immune system. The roles of Notch signaling in hematopoietic stem cell maintenance and in specification of T lineage cells have been well-described. Notch signaling also plays important roles in B cells. In particular, it is required for specification of marginal zone type B cells, but Notch signaling is also important in other stages of B cell development and activation. This review will focus on established and new roles of Notch signaling during B lymphocyte lineage commitment and describe the function of Notch within mature B cells involved in immune responses.

The Shaping of a B Cell Pool Maximally Responsive to Infections

B cell subsets differ in development, tissue distribution, and mechanisms of activation. In response to infections, however, all can differentiate into extrafollicular plasmablasts that rapidly provide highly protective antibodies, indicating that these plasmablasts are the main humoral immune response effectors. Yet, the effectiveness of this response type depends on the presence of antigen-specific precursors in the circulating mature B cell pool, a pool that is generated initially through the stochastic processes of B cell receptor assembly. Importantly, germinal centers then mold the repertoire of this B cell pool to be increasingly responsive to pathogens by generating a broad array of antimicrobial memory B cells that act as highly effective precursors of extrafollicular plasmablasts. Such B cell repertoire molding occurs in two ways: continuously via the chronic germinal centers of mucosal lymphoid tissues, driven by the presence of the microbiome, and via de novo generated germinal centers following acute infections. For effectively evaluating humoral immunity as a correlate of immune protection, it might be critical to measure memory B cell pools in addition to antibody titers.

Invariant natural killer T cells balance B cell immunity

Invariant natural killer T (iNKT) cells mediate rapid immune responses which bridge the gap between innate and adaptive responses to pathogens while also providing key regulation to maintain immune homeostasis. Both types of important iNKT immune responses are mediated through interactions with innate and adaptive B cells. As such, iNKT cells sit at the decision-making fulcrum between regulating inflammatory or autoreactive B cells and supporting protective or regulatory B cell populations. iNKT cells interpret the signals in their environment to set the tone for subsequent adaptive responses, with outcomes ranging from getting licensed to maintain homeostasis as an iNKT regulatory cell (iNKT_reg ) or being activated to become an iNKT follicular helper (iNKT_FH ) cell supporting pathogen-specific effector B cells. Here we review iNKT and B cell cooperation across the spectrum of immune outcomes, including during allergy and autoimmune disease, tumor surveillance and immunotherapy, or pathogen defense and vaccine responses. Because of their key role as influencers, iNKT cells provide a valuable target for therapeutic interventions. Understanding the nature of the interactions between iNKT and B cells will enable the development of clinical interventions to strategically target regulatory iNKT and B cell populations or inflammatory ones, depending on the circumstance.

Dysregulated H3K27 Acetylation Is Implicated in Fatty Liver Hemorrhagic Syndrome in Chickens

Epigenetic regulation of gene expression has been reported in the pathogenesis of metabolic disorders such as diabetes and liver steatosis in humans. However, the molecular mechanisms of fatty liver hemorrhagic syndrome (FLHS) in chickens have been rarely studied. H3K27ac chromatin immunoprecipitation coupled with high-throughput sequencing and high-throughput RNA sequencing was performed to compare genome-wide H3K27ac profiles and transcriptomes of liver tissue between healthy and FLHS chickens. In total, 1,321 differential H3K27ac regions and 443 differentially expressed genes were identified (| log2Fold change| ≥ 1 and P-value ≤ 0.05) between the two groups. Binding motifs for transcription factors involved in immune processes and metabolic homeostasis were enriched among those differential H3K27ac regions. Differential H3K27ac peaks were associated with multiple known FLHS risk genes, involved in lipid and energy metabolism (PCK1, APOA1, ANGPTL4, and FABP1) and the immune system (FGF7, PDGFRA, and KIT). Previous studies and our current results suggested that the high-energy, low-protein (HELP) diet might have an impact on histone modification and chromatin structure, leading to the dysregulation of candidate genes and the peroxisome proliferator-activated receptor (PPAR) signaling pathway, which causes excessive accumulation of fat in the liver tissue and induces the development of FLHS. These findings highlight that epigenetic modifications contribute to the regulation of gene expression and play a central regulatory role in FLHS. The PPAR signaling pathway and other genes implicated in FLHS are of great importance for the development of novel and specific therapies for FLHS-susceptible commercial laying hens.

Research Advances in the Molecular Functions and Relevant Diseases of TAOKs, Novel STE20 Kinase Family Members

As serine/threonine-protein kinases, Thousand and One Kinases(TAOKs) are members of the GCKlike superfamily, one of two well-known branches of the Ste20 kinase family. Within the last two decades, three functionally similar kinases, namely TAOK1-3, were identified. TAOKs are involved in many molecular and cellular events. Scholars widely believe that TAOKs act as kinases upstream of the MAPK cascade and as factors that interact with MST family kinases, the cytoskeleton, and apoptosis-associated proteins. Therefore, TAOKs are thought to function in tumorigenesis. Additionally, TAOKs participate in signal transduction induced by Notch, TCR, and IL-17. Recent studies found that TAOKs play roles in a series of diseases and conditions, such as the central nervous system dysfunction, herpes viral infection, immune system imbalance, urogenital system malformation during development, cardiovascular events, and childhood obesity. Therefore, inhibitory chemicals targeting TAOKs may be of great significance as potential drugs for these diseases.

Modulation of TCR Signaling by Tyrosine Phosphatases: From Autoimmunity to Immunotherapy

Early TCR signaling is dependent on rapid phosphorylation and dephosphorylation of multiple signaling and adaptor proteins, leading to T cell activation. This process is tightly regulated by an intricate web of interactions between kinases and phosphatases. A number of tyrosine phosphatases have been shown to modulate T cell responses and thus alter T cell fate by negatively regulating early TCR signaling. Mutations in some of these enzymes are associated with enhanced predisposition to autoimmunity in humans, and mouse models deficient in orthologous genes often show T cell hyper-activation. Therefore, phosphatases are emerging as potential targets in situations where it is desirable to enhance T cell responses, such as immune responses to tumors. In this review, we summarize the current knowledge about tyrosine phosphatases that regulate early TCR signaling and discuss their involvement in autoimmunity and their potential as targets for tumor immunotherapy.

TAO-kinase 3 governs the terminal differentiation of NOTCH2-dependent splenic conventional dendritic cells

Antigen-presenting conventional dendritic cells (cDCs) are broadly divided into type 1 and type 2 subsets that further adapt their phenotype and function to perform specialized tasks in the immune system. The precise signals controlling tissue-specific adaptation and differentiation of cDCs are currently poorly understood. We found that mice deficient in the Ste20 kinase Thousand and One Kinase 3 (TAOK3) lacked terminally differentiated ESAM⁺ CD4⁺ cDC2s in the spleen and failed to prime CD4⁺ T cells in response to allogeneic red-blood-cell transfusion. These NOTCH2- and ADAM10-dependent cDC2s were absent selectively in the spleen, but not in the intestine of Taok3 ^-/- and CD11c-cre Taok3 ^fl/fl mice. The loss of splenic ESAM⁺ cDC2s was cell-intrinsic and could be rescued by conditional overexpression of the constitutively active NOTCH intracellular domain in CD11c-expressing cells. Therefore, TAOK3 controls the terminal differentiation of NOTCH2-dependent splenic cDC2s.

Notch signaling induces a transcriptionally permissive state at the Complement C3d Receptor 2 (CR2) promoter in a pre-B cell model

During mammalian lymphoid development, Notch signaling is necessary at multiple stages of T lymphopoiesis, including lineage commitment, and later stages of T cell effector differentiation. In contrast, outside of a defined role in the development of splenic marginal zone B cells, there is conflicting evidence regarding whether Notch signaling plays functional roles in other B cell sub-populations. Complement receptor 2 (CR2) modulates BCR-signaling and is tightly regulated throughout differentiation. During B lymphopoiesis, CR2 is detected on immature and mature B cells with high surface expression on marginal zone B cells. Here, we have explored the possibility that Notch regulates human CR2 transcriptional activity using in vitro models including a co-culture system, co-transfection gene reporters and chromatin accessibility assays. We provide evidence that Notch signaling regulates CR2 promoter activity in a mature B cell line, as well as the induction of endogenous CR2 mRNA in a non-expressing pre-B cell line. The dynamics of endogenous gene activation suggests additional unidentified factors are required to mediate surface CR2 expression on immature and mature B lineage cells.

TAOK3 is a MAP3K contributing to osteoblast differentiation and skeletal mineralization

Current anabolic drugs to treat osteoporosis and other disorders of low bone mass all have important limitations in terms of toxicity, contraindications, or poor efficacy in certain contexts. Addressing these limitations will require a better understanding of the molecular pathways, such as the mitogen activated protein kinase (MAPK) pathways, that govern osteoblast differentiation and, thereby, skeletal mineralization. Whereas MAP3Ks functioning in the extracellular signal-regulated kinases (ERK) and p38 pathways have been identified in osteoblasts, MAP3Ks mediating proximal activation of the c-Jun N-terminal kinase (JNK) pathway have yet to be identified. Here, we demonstrate that thousand-and-one kinase 3 (TAOK3, MAP3K18) functions as an upstream activator of the JNK pathway in osteoblasts both in vitro and in vivo. Taok3-deficient osteoblasts displayed defective JNK pathway activation and a marked decrease in osteoblast differentiation markers and defective mineralization, which was also confirmed using TAOK3 deficient osteoblasts derived from human MSCs. Additionally, reduced expression of Taok3 in a murine model resulted in osteopenia that phenocopies aspects of the Jnk1-associated skeletal phenotype such as occipital hypomineralization. Thus, in vitro and in vivo evidence supports TAOK3 as a proximal activator of the JNK pathway in osteoblasts that plays a critical role in skeletal mineralization.

The Diverse Roles of TAO Kinases in Health and Diseases

Thousand and one kinases (TAOKs) are members of the MAP kinase kinase kinase (MAP3K) family. Three members of this subfamily, TAOK1, 2, and 3, have been identified in mammals. It has been shown that TAOK1, 2 and 3 regulate the p38 MAPK and Hippo signaling pathways, while TAOK 1 and 2 modulate the SAPK/JNK cascade. Furthermore, TAOKs are involved in additional interactions with other cellular proteins and all of these pathways modulate vital physiological and pathophysiological responses in cells and tissues. Dysregulation of TAOK-related pathways is implicated in the development of diseases including inflammatory and immune disorders, cancer and drug resistance, and autism and Alzheimer’s diseases. This review collates current knowledge concerning the roles of TAOKs in protein–protein interaction, signal transduction, physiological regulation, and pathogenesis and summarizes the recent development of TAOK-specific inhibitors that have the potential to ameliorate TAOKs’ effects in pathological situations.

Innate B Cells: the Archetype of Protective Immune Cells

The innate B cell (IBC) population is heterogeneous and involved in the primary immune response. IBC functions include a high ability to produce natural antibodies with IgM isotype, the elimination of apoptotic cells, and a capacity to be cognate help to T cells. Among IBC subsets, B-1 cells and marginal zone B cells are the main producers of IgM, act as rapid immune responders that may relocate to follicular lymphoid and differentiate to cytokine and antibody-secreting cells shortly after infection. IBCs functions are highly dependent on their localization site and the nature of their B cell receptor repertoire, suggesting a high plasticity range of different immune responses. In this review, we will describe the nature and functions of the different innate-like B cell subsets, first in mice and then in humans. Besides this, we will emphasize the strong ability of these cells to undertake different protective functions from the first line of defense against pathogens to the regulatory role of the broader immune response.

ADAM28: Another ambivalent protease in cancer

Emergence of novel therapeutic options in a perspective of personalized therapy of cancer relies on the discovery of precise molecular mechanisms involved in the switch from a localized tumor to invasive metastasis spread. Pro-tumor functions have been mostly ascribed to proteolytic enzymes from the metalloproteinase family including A Disintegrin And Metalloproteinases (ADAMs). Particularly, when expressed by cancer cells, ADAM28 protease supports cancer cell proliferation, survival and migration as well as metastatic progression. In sharp contrast, ADAM28 derived from the tumor microenvironment has shown to exert strong protective effects against deleterious metastasis dissemination. Indeed, depletion of host-derived ADAM28 (ADAM28 KO mice) accelerates colonization lung tissues, increases tumor foci implantation, and impairs T cell immune response. In this review, we outline specific ADAM28 functions when specifically expressed by carcinoma cells or by tumor microenvironment. Finally, we discuss about future research strategies that could be pursued to highlight new functions of this protease in cancer.

T. brucei infections abrogate diverse plasma cell-mediated effector B cell responses, independently of their specificity, affinity and host genetic background

Antibody-mediated parasite killing is considered the most effective host immune response against extracellular trypanosome parasites. However, due to host-parasite co-evolution pressure, these parasites have "learned" how to hijack the host immune system via the development of immune evasion strategies. Hereby they prevent elimination and promote transmission. In the past, our group has shown that African trypanosome parasites are able to "shut down" the host B cell compartment, via the abolishment of the homeostatic B cell compartment. In line with this, we have reported that trypanosome infections result in detrimental outcomes on auto-reactive and cancer B cells. To unravel the immune mechanisms involved in these processes we adopted here a well-defined B cell vaccine model, i.e. the thymo-dependent hapten-carrier NP-CGG (4-Hydroxy-3-nitrophenylacetyl-Chicken Gamma Globulin) emulsified in Alum adjuvant. Results show that T. brucei infections abrogate the circulating titres of vaccine-induced CGG-specific as well as NP-specific IgG1+ antibodies, a hallmark of memory B cell responses in this model. This happens independently of their affinity and IFNɣ signalling. Next, we demonstrate that T. brucei infections also induce a decrease of anti-NP IgG3+ antibodies induced by the administration of NP coupled to Ficoll, a thymo-independent antigen. Confirming the non-specificity of the infection-associated immunopathology, this report also shows that trypanosome infections abolish vaccine-induced memory response against malaria parasite in BALB/c mice. Together, these data indicates that T. brucei infections impair every stages of B cell development, including effector plasma B cells, independently of their specificity and affinity as well as the host genetic background.

Regulation of immune system development and function by Cbl-mediated ubiquitination

Ubiquitination is a form of posttranslational protein modification that affects the activity of target proteins by regulating their intracellular degradation, trafficking, localization, and association with other regulators. Recent studies have placed protein ubiquitination as an important regulatory mode to control immune system development, function, and pathogenesis. In this review, we will mainly update the research progress from our laboratory on the roles of the Cbl family of E3 ubiquitin ligases in the development and function of lymphocytes and non-lymphoid cells. In addition, we will highlight our current understanding of the mechanisms used by this family of proteins, especially Cbl and Cbl-b, to co-ordinately regulate the function of various receptors and transcription factors in the context of immune regulation and diseases.

Myosin IIa Promotes Antibody Responses by Regulating B Cell Activation, Acquisition of Antigen, and Proliferation

B cell responses are regulated by antigen acquisition, processing, and presentation to helper T cells. These functions are thought to depend on contractile activity of non-muscle myosin IIa. Here, we show that B cell-specific deletion of the myosin IIa heavy chain reduced the numbers of bone marrow B cell precursors and splenic marginal zone, peritoneal B1b, and germinal center B cells. In addition, myosin IIa-deficient follicular B cells acquired an activated phenotype and were less efficient in chemokinesis and extraction of membrane-presented antigens. Moreover, myosin IIa was indispensable for cytokinesis. Consequently, mice with myosin IIa-deficient B cells harbored reduced serum immunoglobulin levels and did not mount robust antibody responses when immunized. Altogether, these data indicate that myosin IIa is a negative regulator of B cell activation but a positive regulator of antigen acquisition from antigen-presenting cells and that myosin IIa is essential for B cell development, proliferation, and antibody responses.

•

Myosin IIa is important for B cell antigen acquisition from antigen-presenting cells

•

Myosin IIa is a negative regulator of B cell activation

•

Myosin IIa is essential for B cell cytokinesis

•

Myosin IIa is required for efficient B cell responses

B cell ADAM17 controls T cell independent humoral immune responses through regulation of TACI and CD138

ADAM17 is known to contribute to the immune system through its shedding of tumor necrosis factor alpha (TNFα). However, the role of ADAM17 in B cell biology is not well characterized. To determine whether B cell ADAM17 contributes to T cell-independent humoral immune responses, we crossed CD19 Cre transgenic mice with mice bearing a floxed allele of ADAM17 (ADAM17^CD19). In this study, we show a B cell intrinsic role for ADAM17 in regulating marginal zone B cell (MZB) numbers in mice. Interestingly, we demonstrate that the loss of B cell ADAM17 results in reduced MZB numbers in the naïve state and after immunization with T-independent antigen, yet enhanced humoral immunity to T cell independent antigens. We additionally find elevated TACI and CD138 levels on plasma cells following immunization in ADAM17^CD19 mice. Overall, these findings suggest that B cell ADAM17 may orchestrate T independent immune responses through both MZB numbers and plasma cell antibody production.

SDHA gain-of-function engages inflammatory mitochondrial retrograde signaling via KEAP1-Nrf2

Whether screening the metabolic activity of immune cells facilitates discovery of molecular pathology remains unknown. Here we prospectively screened the extracellular acidification rate as a measure of glycolysis and the oxygen consumption rate as a measure of mitochondrial respiration in B cells from patients with primary antibody deficiency. The highest oxygen consumption rate values were detected in three study participants with persistent polyclonal B cell lymphocytosis (PPBL). Exome sequencing identified germline mutations in SDHA, which encodes succinate dehydrogenase subunit A, in all three patients with PPBL. SDHA gain-of-function led to an accumulation of fumarate in PPBL B cells, which engaged the KEAP1-Nrf2 system to drive the transcription of genes encoding inflammatory cytokines. In a single patient trial, blocking the activity of the cytokine interleukin-6 in vivo prevented systemic inflammation and ameliorated clinical disease. Overall, our study has identified pathological mitochondrial retrograde signaling as a disease modifier in primary antibody deficiency.

Innate-like B cell subsets during immune responses: Beyond antibody production

B lymphocytes are recognized for their crucial role in the adaptive immunity since they represent the only leukocyte lineage capable of differentiating into Ab-secreting cells. However, it has been demonstrated that these lymphocytes can exert several Ab-independent functions, including engulfing and processing Ags for presentation to T cells, secreting soluble mediators, providing co-stimulatory signals, and even participating in lymphoid tissues development. Beyond that, several reports claiming the existence of multiple B cell subsets contributing directly to innate immune responses have appeared. These "innate-like" B lymphocytes, whose phenotype, development pathways, tissue distribution, and functions are in most cases notoriously different from those of conventional B cells, are crucial to early protective responses against pathogens by exerting "crossover" defensive strategies that blur the established boundaries of innate and adaptive branches of immunity. Examples of these mechanisms include the rapid secretion of the polyspecific natural Abs, increased susceptibility to innate receptors-mediated activation, cytokine secretion, downstream priming of other innate cells, usage of specific variable immunoglobulin gene-segments, and other features. As these new insights emerge, it is becoming preponderant to redefine the functionality of B cells beyond their classical adaptive-immune tasks.

TAOK3 Regulates Canonical TCR Signaling by Preventing Early SHP-1-Mediated Inactivation of LCK

Activation of LCK is required for canonical TCR signaling leading to T cell responses. LCK activation also initiates a negative feedback loop mediated by the phosphatase SHP-1 that turns off TCR signaling. In this article, we report that the thousand-and-one amino acid kinase 3 (TAOK3) is a key regulator of this feedback. TAOK3 is a serine/threonine kinase expressed in many different cell types including T cells. TAOK3-deficient human T cells had impaired LCK-dependent TCR signaling resulting in a defect in IL-2 response to canonical TCR signaling but not to bacterial superantigens, which use an LCK-independent pathway. This impairment was associated with enhanced interaction of LCK with SHP-1 after TCR engagement and rapid termination of TCR signals, a defect corrected by TAOK3 reconstitution. Thus, TAOK3 is a positive regulator of TCR signaling by preventing premature SHP-1-mediated inactivation of LCK. This mechanism may also regulate signaling by other Src family kinase-dependent receptors.

Expression and Function of Tetraspanins and Their Interacting Partners in B Cells

Tetraspanins are transmembrane proteins that modulate multiple diverse biological processes, including signal transduction, cell–cell communication, immunoregulation, tumorigenesis, cell adhesion, migration, and growth and differentiation. Here, we provide a systematic review of the involvement of tetraspanins and their partners in the regulation and function of B cells, including mechanisms associated with antigen presentation, antibody production, cytokine secretion, co-stimulator expression, and immunosuppression. Finally, we direct our focus to the signaling mechanisms, evolutionary conservation aspects, expression, and potential therapeutic strategies that could be based on tetraspanins and their interacting partners.