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Background: Allergic diseases begin early in life and are often chronic, thus creating an inflammatory environment that may precede or exacerbate other pathologies. In this regard, allergy has been associated to metabolic disorders and with a higher risk of cardiovascular disease, but the underlying mechanisms remain incompletely understood. Methods: We used a murine model of allergy and atherosclerosis, different diets and sensitization methods, and cell‐depleting strategies to ascertain the contribution of acute and late phase inflammation to dyslipidemia. Untargeted lipidomic analyses were applied to define the lipid fingerprint of allergic inflammation at different phases of allergic pathology. Expression of genes related to lipid metabolism was assessed in liver and adipose tissue at different times post‐allergen challenge. Also, changes in serum triglycerides (TGs) were evaluated in a group of 59 patients ≥14 days after the onset of an allergic reaction. Results: We found that allergic inflammation induces a unique lipid signature that is characterized by increased serum TGs and changes in the expression of genes related to lipid metabolism in liver and adipose tissue. Alterations in blood TGs following an allergic reaction are independent of T‐cell‐driven late phase inflammation. On the contrary, the IgG‐mediated alternative pathway of anaphylaxis is sufficient to induce a TG increase and a unique lipid profile. Lastly, we demonstrated an increase in serum TGs in 59 patients after undergoing an allergic reaction. Conclusion: Overall, this study reveals that IgG‐mediated allergic inflammation regulates lipid metabolism. [ABSTRACT FROM AUTHOR]

In addition to triggering humoral responses, conventional B cells have been described in vitro to cross‐present exogenous antigens activating naïve CD8+ T cells. Nevertheless, the way B cells capture these exogenous antigens and the physiological roles of B cell‐mediated cross‐presentation remain poorly explored. Here, we show that B cells capture bacteria by trans‐phagocytosis from previously infected dendritic cells (DC) when they are in close contact. Bacterial encounter "instructs" the B cells to acquire antigen cross‐presentation abilities, in a process that involves autophagy. Bacteria‐instructed B cells, henceforth referred to as BacB cells, rapidly degrade phagocytosed bacteria, process bacterial antigens and cross‐prime naïve CD8+ T cells which differentiate into specific cytotoxic cells that efficiently control bacterial infections. Moreover, a proof‐of‐concept experiment shows that BacB cells that have captured bacteria expressing tumor antigens could be useful as novel cellular immunotherapies against cancer. Synopsis: B cells capturing Listeria monocytogenes acquire antigen cross‐presentation abilities in a process that involves autophagy. These bacteria‐instructed B cells (BacB) effectively cross‐prime naïve CD8+ T cells which differentiate into specific cytotoxic cells that efficiently control bacterial infections. Conventional B cells capture bacteria by transphagocytosis.The capture of L. monocytogenes instructs B cells (BacB) to became antigen cross‐presenting cells.BacB capturing bacteria expressing tumor antigens could be useful as novel cellular immunotherapy against cancer. [ABSTRACT FROM AUTHOR]

ICAP‐1 regulates β1‐integrin activation and cell adhesion. Here, we used ICAP‐1‐null mice to study ICAP‐1 potential involvement during immune cell development and function. Integrin α4β1‐dependent adhesion was comparable between ICAP‐1‐null and control thymocytes, but lack of ICAP‐1 caused a defective single‐positive (SP) CD8+ cell generation, thus, unveiling an ICAP‐1 involvement in SP thymocyte development. ICAP‐1 bears a nuclear localization signal and we found it displayed a strong nuclear distribution in thymocytes. Interestingly, there was a direct correlation between the lack of ICAP‐1 and reduced levels in SP CD8+ thymocytes of Runx3, a transcription factor required for CD8+ thymocyte generation. In the spleen, ICAP‐1 was found evenly distributed between cytoplasm and nuclear fractions, and ICAP‐1–/– spleen T and B cells displayed upregulation of α4β1‐mediated adhesion, indicating that ICAP‐1 negatively controls their attachment. Furthermore, CD3+‐ and CD19+‐selected spleen cells from ICAP‐1‐null mice showed reduced proliferation in response to T‐ and B‐cell stimuli, respectively. Finally, loss of ICAP‐1 caused a remarkable decrease in marginal zone B‐ cell frequencies and a moderate increase in follicular B cells. Together, these data unravel an ICAP‐1 involvement in the generation of SP CD8+ thymocytes and in the control of marginal zone B‐cell numbers. [ABSTRACT FROM AUTHOR]

The ability of a cell to migrate, adhere, and change its morphology is determinant in developing its functions; these capacities reach their maximum relevance in immune cells. For an efficient immune response, immune cells must localize in the right place at the right time; that implies crossing tissue barriers and migrating in the interstitial space of the tissues at high velocities. The dependency on trafficking abilities is even higher for B cells, one of the arms of the adaptive immune system, considering that they must encounter specific antigens for their clonal receptor in the enormous tissue volume of the secondary lymphoid organs (spleen, lymph nodes, Peyer patches). The regulated interplay between cell motility and cell adhesion allows B cells to reach distinct lymphoid tissues and, within them, to explore the stromal cell networks where antigen might be exposed. In this meeting‐invited review, I summarize the current knowledge on the molecular cues and mechanisms that shapes B cell dynamics at the initial phase of the humoral immune response, including homeostatic chemoattractants and innate/inflammatory stimuli. I also revised the B cell behavior alterations caused by BCR recognition of antigen and the molecular mechanisms involved. [ABSTRACT FROM AUTHOR]

Efficient generation of antibodies by B cells is one of the prerequisites of protective immunity. B cell activation by cognate antigens via B cell receptors (BCRs), or pathogen-associated molecules through pattern-recognition receptors, such as Toll-like receptors (TLRs), leads to transcriptional and metabolic changes that ultimately transform B cells into antibody-producing plasma cells or memory cells. BCR signaling and a number of steps downstream of it rely on coordinated action of cellular membranes and the actin cytoskeleton, tightly controlled by concerted action of multiple regulatory proteins, some of them exclusive to B cells. Here, we dissect the role of Missing-In-Metastasis (MIM), or Metastasis suppressor 1 (MTSS1), a cancer-associated membrane and actin cytoskeleton regulating protein, in B cell-mediated immunity by taking advantage of MIM knockout mouse strain. We show undisturbed B cell development and largely normal composition of B cell compartments in the periphery. Interestingly, we found that MIM−/− B cells are defected in BCR signaling in response to surface-bound antigens but, on the other hand, show increased metabolic activity after stimulation with LPS or CpG. In vivo , MIM knockout animals exhibit impaired IgM antibody responses to immunization with T cell-independent antigen. This study provides the first comprehensive characterization of MIM in B cells, demonstrates its regulatory role for B cell-mediated immunity, as well as proposes new functions for MIM in tuning receptor signaling and cellular metabolism, processes, which may also contribute to the poorly understood functions of MIM in cancer. [ABSTRACT FROM AUTHOR]

Balancing B cell signals: Diacylglycerol kinases (DGKs) catalyze the conversion of the lipid signaling molecule DAG into phosphatidic acid (PA), both of which have distinct effects. Merino-Cortés et al. found that the DGKζ isoform was critical in promoting signaling required for the optimal function of B cells. Compared with wild-type B cells, DGKζ-deficient B cells exhibited decreased mechanical forces at the plasma membrane, impairing the ability of these cells to form stable contacts with antigen-presenting cells, extract antigen, and present it to T cells. As a result, mice with DGKζ-deficient B cells showed diminished antibody responses in germinal centers. These data suggest that DGKζ regulates the balance in signaling between DAG and PA that is required for optimal B cell function. Diacylglycerol kinases (DGKs) limit antigen receptor signaling in immune cells by consuming the second messenger diacylglycerol (DAG) to generate phosphatidic acid (PA). Here, we showed that DGKζ promotes lymphocyte function–associated antigen 1 (LFA-1)–mediated adhesion and F-actin generation at the immune synapse of B cells with antigen-presenting cells (APCs), mostly in a PA-dependent manner. Measurement of single-cell mechanical force generation indicated that DGKζ-deficient B cells exerted lower forces at the immune synapse than did wild-type B cells. Nonmuscle myosin activation and translocation of the microtubule-organizing center (MTOC) to the immune synapse were also impaired in DGKζ-deficient B cells. These functional defects correlated with the decreased ability of B cells to present antigen and activate T cells in vitro. The in vivo germinal center response of DGKζ-deficient B cells was also reduced compared with that of wild-type B cells, indicating that loss of DGKζ in B cells impaired T cell help. Together, our data suggest that DGKζ shapes B cell responses by regulating actin remodeling, force generation, and antigen uptake–related events at the immune synapse. Hence, an appropriate balance in the amounts of DAG and PA is required for optimal B cell function. [ABSTRACT FROM AUTHOR]

The CD95 SP + sp memory B-cell subset showed a high response after stimulation, indicating that these cells are effector memory B cells.2 Of the four tissues studied, they found that only CD39 SP + sp B cells were tissue-specific. Keywords: B cells; cell atlas; mass cytometry; multi-omic; single cell EN B cells cell atlas mass cytometry multi-omic single cell 2644 2646 3 07/19/21 20210801 NES 210801 Abbreviations Ig immunoglobulin SHM somatic hypermutation Since their discovery in the 60s, B cells have been extensively studied because of their unique and critical role in immunoglobulin (Ig) production. For example, CD27 was long considered a classical marker of memory B cells and associated with somatic hypermutation (SHM); however, some memory B cells lack CD27 expression.1 In this context, B-cell biologists were demanding to update the criteria used to classify B cells and the inclusion of novel functionality markers, which has been possible with the advent of single cell multi-omics. [Extracted from the article]

Abstract: The Myc family of oncogenic transcription factors regulates myriad cellular functions. Myc proteins contain a basic region/helix‐loop‐helix/leucine zipper domain that mediates DNA binding and heterodimerization with its partner Max. Among the Myc proteins, c‐Myc is the most widely expressed and relevant in primary B lymphocytes. There is evidence suggesting that c‐Myc can perform some of its functions in the absence of Max in different cellular contexts. However, the functional in vivo interplay between c‐Myc and Max during B lymphocyte differentiation is not well understood. Using in vivo and ex vivo models, we show that while c‐Myc requires Max in primary B lymphocytes, several key biological processes, such as cell differentiation and DNA replication, can initially progress without the formation of c‐Myc/Max heterodimers. We also describe that B lymphocytes lacking Myc, Max, or both show upregulation of signaling pathways associated with the B‐cell receptor. These data suggest that c‐Myc/Max heterodimers are not essential for the initiation of a subset of important biological processes in B lymphocytes, but are required for fine‐tuning the initial response after activation. [ABSTRACT FROM AUTHOR]

Bruton's tyrosine kinase (Btk) has a key role in the signaling pathways of receptors essential for the B lymphocyte response. Given its implication in B cell-related immunodeficiencies, leukemias/lymphomas and autoimmunity, Btk is studied intensely and is a target for therapy. Here, using primary B cells from distinct mouse models and the pharmacological inhibitors ibrutinib and acalabrutinib, we report distinct roles for Btk in antigen-triggered immune synapse (IS) formation. Btk recruitment to the plasma membrane regulates the B cell ability to trigger IS formation as well as its appropriate molecular assembly; Btk shuttling/scaffold activities seem more relevant than the kinase function on that. Btk-kinase activity controls antigen accumulation at the IS through the PLCγ2/Ca2+ axis. Impaired Btk membrane-recruitment or kinase function likewise alters antigen-triggered microtubule-organizing center (MTOC) polarization to the IS, B cell activation and proliferation. Data also show that, for B cell function, IS architecture is as important as the quantity of antigen that accumulates at the synapse. [ABSTRACT FROM AUTHOR]

The spatial distribution of signals downstream from receptor tyrosine kinases (RTKs) or G-protein coupled receptors (GPCR) regulates fundamental cellular processes that control cell migration and growth. Both pathways rely significantly on actin cytoskeleton reorganization mediated by nucleation-promoting factors such as the WASP-(Wiskott-Aldrich Syndrome Protein) family. WIP (WASP Interacting Protein) is essential for the formation of a class of polarised actin microdomain, namely dorsal ruffles, downstream of the RTK for PDGF (platelet-derived growth factor) but the underlying mechanism is poorly understood. Using lentivirally-reconstituted WIP-deficient murine fibroblasts we define the requirement for WIP interaction with N-WASP (neural WASP) and Nck for efficient dorsal ruffle formation and of WIP-Nck binding for fibroblast chemotaxis towards PDGF-AA. The formation of both circular dorsal ruffles in PDGF-AA-stimulated primary fibroblasts and lamellipodia in CXCL13-treated B lymphocytes are also compromised by WIP-deficiency. We provide data to show that a WIP-Nck signalling complex interacts with RTK to promote polarised actin remodelling in fibroblasts and provide the first evidence for WIP involvement in the control of migratory persistence in both mesenchymal (fibroblast) and amoeboid (B lymphocytes) motility. [ABSTRACT FROM AUTHOR]

Janus kinases (JAKs) are central signaling molecules in cytokine receptor cascades. Although they have also been implicated in chemokine receptor signaling, this function continues to be debated. To address this issue, we established a nucleofection model in primary, nonactivated mouse T lymphocytes to silence JAK expression and to evaluate the ability of these cells to home to lymph nodes. Reduced JAK1 and JAK2 expression impaired naïve T-cell migration in response to gradients of the chemokines CXCL12 and CCL21. In vivo homing of JAK1/JAK2-deficient cells to lymph nodes decreased, whereas intranodal localization and motility were unaffected. JAK1 and JAK2 defects altered CXCL12- and CCL21-triggered ezrin/radixin/moesin (ERM) dephosphorylation and F-actin polymerization, as well as activation of lymphocyte function-associated Ag-1 and very late Ag-4 integrins. As a result, the cells did not adhere firmly to integrin substrates in response to these chemokines. The results demonstrate that JAK1/JAK2 participate in chemokine-induced integrin activation and might be considered a target for modulation of immune cell extravasation and therefore, control of inflammatory reactions. [ABSTRACT FROM AUTHOR]

During antigen-specific T-cell activation, mitochondria mobilize towards the vicinity of the immune synapse. We show here that the mitochondrial fission factor dynamin-related protein 1 (Drp1) docks at mitochondria, regulating their positioning and activity near the actin-rich ring of the peripheral supramolecular activation cluster (pSMAC) of the immune synapse. Mitochondrial redistribution in response to T-cell receptor engagement was abolished by Drp1 silencing, expression of the phosphomimetic mutant Drp1S637D and the Drp1-specific inhibitor mdivi-1. Moreover, Drp1 knockdown enhanced mitochondrial depolarization and T-cell receptor signal strength, but decreased myosin phosphorylation, ATP production and T-cell receptor assembly at the central supramolecular activation cluster (cSMAC). Our results indicate that Drp1-dependent mitochondrial positioning and activity controls T-cell activation by fuelling central supramolecular activation cluster assembly at the immune synapse. [ABSTRACT FROM AUTHOR]

Despite compelling evidence that a large proportion of antigens encountered in vivo by B cells are membrane bound, the general view is that B cells are mainly activated by soluble antigens. This notion may have been biased somewhat over the years because the high affinity of the B-cell receptor (BCR) for soluble intact ligands allows efficient B-cell stimulation in vitro. In vivo, however, even soluble antigens are likely to be deposited on the surface of antigen-presenting cells, either by complement or Fc receptors in the form of immune complexes, thus becoming more potent stimulators of B-cell activation. In this framework, the BCR works in a complex environment of integrins and coreceptors, as well as the B-cell cytoskeleton. Over the last few years, we have focused on B-cell membrane-bound antigen recognition. Here, we discuss some of our findings in the context of what is currently known in this exciting new field. [ABSTRACT FROM AUTHOR]

VCAM-1 is one of the main ligands of VLA-4, an integrin that is highly expressed on the surface of mature B cells. Here we find that coexpression of VCAM-1 on an antigen-bearing membrane facilitates B-cell activation. Firstly, this is achieved by mediating B-cell tethering, which in turn increases the likelihood of a B cell to be activated. Secondly, VLA-4 synergizes with the B-cell receptor (BCR), providing B cells with tight adhesion and enhanced signalling. This dual role of VCAM-1 in promoting B-cell activation is predominantly effective when the affinity of the BCR for the antigen is low. In addition, we show that the VCAM-1 ectodomain alone is sufficient to carry out this function. However, it requires the transmembrane domain to segregate properly into a docking structure characteristic of the B-cell immunological synapse (IS). These results show that the VLA-4/VCAM-1 interaction during membrane antigen recognition enhances B-cell activation and this function appears to be independent of its final peripheral localization at the IS. [ABSTRACT FROM AUTHOR]

The article focuses on the role for immune complex (IC) relay by subcapsular sinus (SCS) macrophages and noncognate B cells in driving antibody affinity maturation at germinal centres. As reported, non-cognate B cells deliver IC from the SCS macrophages to surface of follicular dendritic cells (FDC) at germinal centre in receptor-dependent manner. As cited, this IC relay to the germinal centre drives the affinity maturation process.

Sorting nexin 27 (SNX27) belongs to the sorting nexin family of proteins, which participate in vesicular and protein trafficking. Similarly to all sorting nexin proteins, SNX27 has a functional PX domain that is important for endosome binding, but it is the only sorting nexin with a PDZ domain. We identified SNX27 as a partner of diacylglycerol kinase ζ(DGKζ), a negative regulator of T cell function that metabolises diacylglycerol to yield phosphatidic acid. SNX27 interacts with the DGKζ PDZ-binding motif in early/recycling endosomes in resting T cells; however, the dynamics and mechanisms underlying SNX27 subcellular localisation during T cell activation are unknown. We demonstrate that in T cells that encounter pulsed antigen-presenting cells, SNX27 in transit on early/recycling endosomes polarise to the immunological synapse. A fraction of SNX27 accumulates at the mature immunological synapse in a process that is dependent on vesicular trafficking, binding of the PX domain to phosphatidylinositol 3-phosphate and the presence of the PDZ region. Downmodulation of expression of either SNX27 or DGKζ results in enhanced basal and antigen-triggered ERK phosphorylation. These results identify SNX27 as a PDZ-containing component of the T cell immunological synapse, and demonstrate a role for this protein in the regulation of the Ras-ERK pathway, suggesting a functional relationship between SNX27 and DGKζ. [ABSTRACT FROM AUTHOR]