Receptors and signaling mechanisms for B-lymphocyte activation, proliferation and differentiation--insights from both in vivo and in vitro approaches

Characterization of IgD and IgT with their expressional analysis following subtype II megalocytivirus vaccination and infection in rock bream (Oplegnathus fasciatus)

In this study, heavy chain genes of IgD and IgT were sequenced and characterized their gene expression in rock bream (Oplegnathus fasciatus). Rock bream (RB)-IgD cDNA is 3319 bp in length and encodes a leader region, variable domains, a μ1 domain, and seven constant domains (CH1-CH7). A membrane-bound (mIgT) and secretory form (sIgT) of RB-IgT cDNAs are 1902 bp and 1689 bp in length, respectively, and encode a leader region, variable domains, four constant domains (CH1-CH4) and C-terminus. Their predicted 3D-structure and phylogenetic relation were similar to those of other teleost. In healthy fish, RB-IgD and mIgT gene expressions were higher in major lymphoid organs and blood, while RB-sIgT gene was more highly expressed in midgut. IgT expressing cells were detected in melano-macrophage centers (MMC) of head kidney in immunohistochemistry analysis. Under immune stimulation in vitro, RB-IgD and IgT gene expressions were upregulated in head kidney and spleen cells by bovine serum albumin or a rock bream iridovirus (RBIV) vaccine. In vivo, their expressions were significantly upregulated in head kidney, blood, and gill upon vaccination. Especially, RB-mIgT gene expression in head kidney and blood was upregulated at day 3 after vaccination while upregulated at earlier time point of day 1 by challenge with RBIV. This may suggest that memory cells might be produced during the primary response by vaccination and rapidly proliferated by secondary immune response by viral infection. RB-sIgT gene expression was highly upregulated in peripheral blood in vaccinated fish after viral infection, indicating that IgT plays an important role in systemic immune response as well as mucosal immune system. Our findings provide information on the role of RB-IgT in adaptive immunity during vaccination and viral infection in the vaccinated fish.

Intruders or protectors - the multifaceted role of B cells in CNS disorders

B lymphocytes are immune cells studied predominantly in the context of peripheral humoral immune responses against pathogens. Evidence has been accumulating in recent years on the diversity of immunomodulatory functions that B cells undertake, with particular relevance for pathologies of the central nervous system (CNS). This review summarizes current knowledge on B cell populations, localization, infiltration mechanisms, and function in the CNS and associated tissues. Acute and chronic neurodegenerative pathologies are examined in order to explore the complex, and sometimes conflicting, effects that B cells can have in each context, with implications for disease progression and treatment outcomes. Additional factors such as aging modulate the proportions and function of B cell subpopulations over time and are also discussed in the context of neuroinflammatory response and disease susceptibility. A better understanding of the multifactorial role of B cell populations in the CNS may ultimately lead to innovative therapeutic strategies for a variety of neurological conditions.

Barcoding of live peripheral blood mononuclear cells to assess immune cell phenotypes using full spectrum flow cytometry

Barcoded flow cytometry is a multiplexing technique allowing for the simultaneous acquisition of cells from different donors or experimental conditions in a high-throughput manner. This approach allows to synchronize acquisition of samples and reduce variance introduced through the operator or technical platform. However, to date, only very few flow cytometry barcoding protocols have been developed, which often suffer from technical limitations. Here, we developed a novel barcoding protocol for a full-spectrum flow cytometry platform. We developed a 21-color immunophenotyping assay for up to 20 different samples analyzed simultaneously with comparable variance between repeated single-tube acquisition and postde-multiplexing. Barcoding offers great potential in parallelizing the analysis of complex cell populations such as peripheral blood mononuclear cells (PBMCs). Consequently, we assessed the performance of our method in situations where PBMCs were challenged with phytohaemagglutinin (PHA), a strong mitogen and broad activator of B cells and T cells, and superantigen Staphylococcus enterotoxin B (SEB) that has been reported to induce polyclonal T cell activation. PBMCs were either barcoded before pooled challenge or challenged individually pre-barcoding. Our final workflow included pooled immunophenotyping followed by machine learning aided single-cell data analysis and enabled us to identify robust PHA and SEB mode of action related phenotypic changes in PBMC immune cell lineages. Conclusively, we present a novel technique allowing the barcoded acquisition and analysis of PBMCs from up to 20 different donors and present a valid basis for the future development of complex immunophenotyping protocols.

Differential immunological effects of silica nanoparticles on peripheral blood mononuclear cells of silicosis patients and controls

Silicosis is a fibrotic disease caused by the inhalation of respirable silica particles, which are typically engulfed by alveolar macrophages and subsequently induce the release of inflammatory cytokines. Various animal experimental and human studies have focused on modeling silicosis, to assess the interactions of macrophages and other cell types with silica particles. There is still, however, limited knowledge on the differential response upon silica-exposure between silicosis patients and controls. We focused on studying the responsiveness of peripheral blood mononuclear cells (PBMCs) to silica nanoparticles (SiNPs) - Ludox and NM-200 - of silicosis patients and controls. The proliferative capacity of T- CD3⁺ and B- CD19⁺ cells, were evaluated via Carboxyfluorescein succinimidyl ester (CFSE) assay. The activation status of lymphocyte subsets and response to silica were also evaluated by comparing the extent of micro-granuloma or aggregate formation with the cytokine secretion profiles between both groups of individuals. The proliferative capacity of CD19⁺ cells was elevated in silicotic patients as opposed to controls. Subsets of regulatory T cells (CD4⁺ CD25⁺ and CD8⁺ CD25⁺) and immunoglobulins IgM and IgG were also significantly increased in patients. The number and the size of aggregates formed were higher with SiNPs stimulation in patients compared to controls. Multivariable analysis also elucidated the role of key cytokines like interleukin-1β (IL-1β), IL-6 and interferon-gamma (IFN-γ), which were upregulated in SiNP-stimulated PBMCs of patients compared to controls. Our ex vivo model thus has potential to provide insights into the immunological effects of silica particles in lymphocytes of silicosis patients and controls.

Inhibitory effects of superoxide dismutase 3 on IgE production in B cells

Immunoglobulin E (IgE) functions as a first-line defense against parasitic infections. However, aberrant production of IgE is known to be associated with various life-threatening allergic diseases. Superoxide dismutase 3 (SOD3) has been found to suppress IgE in various allergic diseases such as allergic conjunctivitis, ovalbumin-induced allergic asthma, and dust mite-induced atopic dermatitis-like skin inflammation. However, the role of SOD3 in the regulation of IgE production in B cells remains elusive. In this study, we investigated the effect of SOD3 on LPS/IL-4 and anti-CD40/IL-4-mediated secretion of IgE in murine B cells. Our data showed that SOD3 can suppress both LPS/IL-4 and antiCD40/IL-7-induced IgE secretion in B cells isolated from both wild-type (SOD3^+/+) and SOD3 knock-out (SOD3^−/−) mice. Interestingly, B cells isolated from SOD3^−/− mice showed higher secretion of IgE, whereas, the use of DETCA, a known inhibitor of SOD3 activity, reversed the inhibitory effect of SOD3 on IgE production. Similarly, SOD3 was found to reduce the proliferation, IgE isotype switch, ROS level, and CCL17 and CCL22 productions in B cells. Furthermore, SOD3 was found to suppress both LPS/IL-4 and anti-CD40/IL-4-mediated activation of downstream signaling such as JAK1/JAK3, STAT6, NF-κB, p38, and JNK in B cells. Taken together, our data showed that SOD3 can be used as an alternative therapy to restrict IgE-mediated allergic diseases.

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SOD3 suppresses LPS/IL-4 and anti-CD40/IL-4-induced secretion of IgE in B cells

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SOD3 reduces the expression of IgE isotype class switch recombination genes.

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SOD3 suppresses the LPS/IL-4 and anti-CD40/IL-4-induced superoxide production.

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SOD3 suppresses the LPS/IL-4 and anti-CD40/IL-4-induced chemokines secretions.

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SOD3 modulate JAK-STAT, p38, JNK, and NF-κB signaling pathways in B cells.

Differential capability of Bacillus thuringiensis Cry1Ac protoxin and toxin to induce in vivo activation of dendritic cells and B lymphocytes

The insecticidal Bacillus thuringiensis protein Cry1Ac is produced as a protoxin and becomes activated to a toxin when ingested by larvae. Both proteins are immunogenic and able to activate macrophages. The proposed mechanism of immunostimulation by Cry1Ac protoxin has been related to its capacity to activate antigen-presenting cells (APC), but its ability to activate dendritic cells (DC) has not been explored. Here we evaluated, in the popliteal lymph nodes (PLN), spleen and peritoneum, the activation of DC CD11c⁺ MHC-II⁺ following injection with single doses (50 μg) of Cry1Ac toxin or protoxin via the intradermal (i.d.) and intraperitoneal (i.p.) routes in C57BL/6 mice. In vivo stimulation with both Cry1Ac proteins induced activation of DC via upregulation of CD86, primarily in PLN 24 h after i. d. injection. Moreover, this activation was detected in DC, displaying CD103+, a typical marker of migratory DC, while upregulation of CD80 was uniquely induced by toxin. Tracking experiments showed that Cy5-labeled Cry1Ac proteins could rapidly reach the PLN and localize near DC, but some label remained in the footpad. When the capacity of Cry1Ac-activated DC to induce antigen presentation was examined, significant proliferation of naïve T lymphocytes was induced exclusively by the protoxin. The protoxin elicited a Th17-biased cytokine profile. Moreover, only the Cry1Ac toxin induced a pronounced proliferation of B cells from both untreated and Cry1Ac-injected mice, suggesting that it acts as a polyclonal activator. In conclusion, Cry1Ac protoxin and toxin show a distinctive capacity to activate APCs.

Isolation of primary human B lymphocytes from tonsils compared to blood as alternative source for ex vivo application

B lymphocytes ('B cells') are components of the human immune system with obvious potential for medical and biotechnological applications. Here, we discuss the isolation of primary human B cells from both juvenile and adult tonsillar material using a two-step procedure based on gradient centrifugation followed by separation on a nylon wool column as alternative to the current gold standard, i.e., negative immunosorting from buffy coats by antibody-coated magnetic beads. We show that the nylon wool separation is a low-cost method well suited to the isolation of large amounts of primary B cells reaching purities ≥ 80%. More importantly, this method allows the preservation of all B cell subsets, while MACS sorting seems to be biased against a certain B cell subtype, namely the CD27⁺ B cells. Importantly, compared to blood, the excellent recovery yield during purification of tonsillar B cells provides high number of cells, hence increases the number of subsequent experiments feasible with identical cell material, consequently improving comparability of results. The cultivability of the isolated B cells was demonstrated using pokeweed mitogen (PWM) as a stimulatory substance. Our results showed for the first time that the proliferative response of tonsillar B cells to mitogens declines with the age of the donor. Furthermore, we observed that PWM treatment stimulates the proliferation of a dedicated subpopulation and induces some terminal differentiation with ASCs signatures. Taken together this indicates that the proposed isolation procedure preserves the proliferative capability as well as the differentiation capacity of the B cells.

Dynamical properties of feedback signalling in B lymphopoiesis: A mathematical modelling approach

Haematopoiesis is the process of generation of blood cells. Lymphopoiesis generates lymphocytes, the cells in charge of the adaptive immune response. Disruptions of this process are associated with diseases like leukaemia, which is especially incident in children. The characteristics of self-regulation of this process make them suitable for a mathematical study. In this paper we develop mathematical models of lymphopoiesis using currently available data. We do this by drawing inspiration from existing structured models of cell lineage development and integrating them with paediatric bone marrow data, with special focus on regulatory mechanisms. A formal analysis of the models is carried out, giving steady states and their stability conditions. We use this analysis to obtain biologically relevant regions of the parameter space and to understand the dynamical behaviour of B-cell renovation. Finally, we use numerical simulations to obtain further insight into the influence of proliferation and maturation rates on the reconstitution of the cells in the B line. We conclude that a model including feedback regulation of cell proliferation represents a biologically plausible depiction for B-cell reconstitution in bone marrow. Research into haematological disorders could benefit from a precise dynamical description of B lymphopoiesis.

Down-regulation of LncRNA 2900052N01Rik inhibits LPS-induced B cell function in vitro

B cells play a crucial role in immune responses. The main functions include B cell protective antibody production, inflammation reduction, activation and proliferation. Long non-coding RNAs (lncRNAs) have been reported to act as important regulators of many pathological processes. However, few lncRNAs have been reported to affect B cell function. In this study, we explored the expression and role of lncRNA 2900052N01Rik (lnc-290) in lipopolysaccharide (LPS)-induced B cells purified from mouse spleens in vitro. Here, we confirmed that lnc-290 was highly expressed in B cells stimulated by LPS. Knockdown of lnc-290 inhibited the expression of CD69/CD86 and the growth of B cells. Moreover, down-regulated lnc-290 reduced B cell differentiation and immunoglobulin production in vitro. In addition, we found that lnc-290 regulated LPS-induced B cell activation via the NF-κB/ERK pathways. Interestingly, abnormal lnc-290 expression did not alter the B cell activation or proliferation induced by IL-4 or CD40/CD40L. Accordingly, these results indicated, for the first time, that lnc-290 down-regulation inhibits LPS-induced B cell proliferation, activation and differentiation by blocking the LPS/TLR4 signaling pathway. Together, the in vitro data demonstrate that lnc-290 participated in the inflammation and tissue damage mediated by LPS-activated B cells.

Allergy-A New Role for T Cell Superantigens of Staphylococcus aureus?

Staphylococcus aureus superantigens (SAgs) are among the most potent T cell mitogens known. They stimulate large fractions of T cells by cross-linking their T cell receptor with major histocompatibility complex class-II molecules on antigen presenting cells, resulting in T cell proliferation and massive cytokine release. To date, 26 different SAgs have been described in the species S. aureus; they comprise the toxic shock syndrome toxin (TSST-1), as well as 25 staphylococcal enterotoxins (SEs) or enterotoxin-like proteins (SEls). SAgs can cause staphylococcal food poisoning and toxic shock syndrome and contribute to the clinical symptoms of staphylococcal infection. In addition, there is growing evidence that SAgs are involved in allergic diseases. This review provides an overview on recent epidemiological data on the involvement of S. aureus SAgs and anti-SAg-IgE in allergy, demonstrating that being sensitized to SEs—in contrast to inhalant allergens—is associated with a severe disease course in patients with chronic airway inflammation. The mechanisms by which SAgs trigger or amplify allergic immune responses, however, are not yet fully understood. Here, we discuss known and hypothetical pathways by which SAgs can drive an atopic disease.

Developments in Carbohydrate-Based Cancer Therapeutics

Cancer cells of diverse origins express extracellular tumor-specific carbohydrate antigens (TACAs) because of aberrant glycosylation. Overexpressed TACAs on the surface of tumor cells are considered biomarkers for cancer detection and have always been prioritized for the development of novel carbohydrate-based anti-cancer vaccines. In recent years, progress has been made in developing synthetic, carbohydrate-based antitumor vaccines to improve immune responses associated with targeting these specific antigens. Tumor cells also exhaust more energy for proliferation than normal cells, by consuming excessive amounts of glucose via overexpressed sugar binding or transporting receptors located in the cellular membrane. Furthermore, inspired by the Warburg effect, glycoconjugation strategies of anticancer drugs have gained considerable attention from the scientific community. This review highlights a small cohort of recent efforts which have been made in carbohydrate-based cancer treatments, including vaccine design and the development of glycoconjugate prodrugs, glycosidase inhibiting iminosugars, and early cancer diagnosis.

Helicobacter pylori Deregulates T and B Cell Signaling to Trigger Immune Evasion

Helicobacter pylori is a prevalent human pathogen that successfully establishes chronic infection, which leads to clinically significant gastric diseases including chronic gastritis, peptic ulcer disease (PUD), and gastric cancer (GC). H. pylori is able to produce a persistent infection due in large part to its ability to hijack the host immune response. The host adaptive immune response is activated to strategically and specifically attack pathogens and normally clears them from the infected host. Since B and T lymphocytes are central mediators of adaptive immunity, in this chapter we review their development and the fundamental mechanisms regulating their activation in order to understand how some of the normal processes are subverted by H. pylori. In this review, we place particular emphasis on the CD4⁺ T cell responses, their subtypes, and regulatory mechanisms because of the expanding literature in this area related to H. pylori. T lymphocyte differentiation and function are finely orchestrated through a series of cell-cell interactions, which include immune checkpoint receptors. Among the immune checkpoint receptor family, there are some with inhibitory properties that are exploited by tumor cells to facilitate their immune evasion. Gastric epithelial cells (GECs), which act as antigen-presenting cells (APCs) in the gastric mucosa, are induced by H. pylori to express immune checkpoint receptors known to sway T lymphocyte function and thus circumvent effective T effector lymphocyte responses. This chapter reviews these and other mechanisms used by H. pylori to interfere with host immunity in order to persist.

Expression kinetics of ISG15, IRF3, IFNγ, IL10, IL2 and IL4 genes vis-a-vis virus shedding, tissue tropism and antibody dynamics in PPRV vaccinated, challenged, infected sheep and goats

Here, we studied the in vivo expression of Th1 (IL2 and IFN gamma) and Th2 (IL4 and IL10) - cytokines and antiviral molecules - IRF3 and ISG15 in peripheral blood mononuclear cells in relation to antigen and antibody dynamics under Peste des petits ruminants virus (PPRV) vaccination, infection and challenge in both sheep and goats. Vaccinated goats were seropositive by 9 days post vaccination (dpv) while in sheep idiosyncratic response was observed between 9 and 14 dpv for different animals. Expression of PPRV N gene was not detected in PBMCs of vaccinated and vaccinated challenged groups of both species, but was detected in unvaccinated infected PBMCs at 9 and 14 days post infection. The higher viral load at 9 dpi coincided with the peak clinical signs of the disease. The peak in viral replication at 9 dpi correlated with significant expression of antiviral molecules IRF3, ISG15 and IFN gamma in both the species. With the progression of disease, the decrease in N gene expression also correlated with the decrease in expression of IRF3, ISG15 and IFN gamma. In the unvaccinated infected animals ISG15, IRF3, IFN gamma and IL10 expression was higher than vaccinated animals. The IFN gamma expression predominated over IL4 in both vaccinated and infected animals with the infected exhibiting a stronger Th1 response. The persistent upregulation of this antiviral molecular signature - ISG15 and IRF3 even after 2 weeks post vaccination, presumably reflects the ongoing stimulation of innate immune cells.

Exploration of genetic basis of differential immune response to CSF vaccination in desi (indigenous) piglets using RNA-Seq approach

In the present study, the transcriptome profiling of peripheral blood mononuclear cells (PBMCs) of indigenous piglets against classical swine fever (CSF) vaccination was performed for elucidating the genetic basis of their differential humoral immunity. Piglets were vaccinated with lapinised strain of CSF virus (CSFV) followed by measurement of humoral immune response using c-ELISA at 28th day post vaccination (28dpv). The RNA sequencing data was analysed using established pipeline to determine set of differentially expressed genes (DEGs) in high responder as compared to low responder piglet. The differentially expressed important immune molecules were involved in regulating important pathways including antigen processing and presentation, T cell receptor signalling, B cell development, activation and signaling genes. The genes with differential expression also included TLR 3, 6, 7, 8, 9, and antiviral molecules such as MX, and ISG (Interferon stimulated genes) family members. The proteinprotein interaction of the immune genes was extracted for network representation. Most of the immune genes involved showed upregulation except the genes for antigen processing and presentation and T cell receptor signaling that were downregulated in the high responder. The immunologically important genes namely IFIT1, IFIT5, TAPBP, and TLR7 were validated using qRT-PCT and were observed to be in concordance with the RNA Seq results.

Are the innate and adaptive immune systems setting hypertension on fire?

Hypertension is the most common chronic cardiovascular disease and is associated with several pathological states, being an important cause of morbidity and mortality around the world. Low-grade inflammation plays a key role in hypertension and the innate and adaptive immune systems seem to contribute to hypertension development and maintenance. Hypertension is associated with vascular inflammation, increased vascular cytokines levels and infiltration of immune cells in the vasculature, kidneys and heart. However, the mechanisms that trigger inflammation and immune system activation in hypertension are completely unknown. Cells from the innate immune system express pattern recognition receptors (PRR), which detect conserved pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) that induce innate effector mechanisms to produce endogenous signals, such as inflammatory cytokines and chemokines, to alert the host about danger. Additionally, antigen-presenting cells (APC) act as sentinels that are activated by PAMPs and DAMPs to sense the presence of the antigen/neoantigen, which ensues the adaptive immune system activation. In this context, different lymphocyte types are activated and contribute to inflammation and end-organ damage in hypertension. This review will focus on experimental and clinical evidence demonstrating the contribution of the innate and adaptive immune systems to the development of hypertension.

Naïve Human Antibody Libraries for Infectious Diseases

Many countries are facing an uphill battle in combating the spread of infectious diseases. The constant evolution of microorganisms magnifies the problem as it facilitates the re-emergence of old infectious diseases as well as promote the introduction of new and more deadly variants. Evidently, infectious diseases have contributed to an alarming rate of mortality worldwide making it a growing concern. Historically, antibodies have been used successfully to prevent and treat infectious diseases since the nineteenth century using antisera collected from immunized animals. The inherent ability of antibodies to trigger effector mechanisms aids the immune system to fight off pathogens that invades the host. Immune libraries have always been an important source of antibodies for infectious diseases due to the skewed repertoire generated post infection. Even so, the role and ability of naïve antibody libraries should not be underestimated. The naïve repertoire has its own unique advantages in generating antibodies against target antigens. This chapter will highlight the concept, advantages and application of human naïve libraries as a source to isolate antibodies against infectious disease target antigens.

Friend or foe? The tumour microenvironment dilemma in colorectal cancer

The network of bidirectional homotypic and heterotypic interactions established among parenchymal tumour cells and surrounding mesenchymal stromal cells generates the tumour microenvironment (TME). These intricate crosstalks elicit both beneficial and adverse effects on tumour initiation and progression unbalancing the signals and responses from the neighbouring cells. Here, we highlight the structure, activities and evolution of TME cells considering a novel colorectal cancer (CRC) classification based on differential stromal composition and gene expression profiles. In this scenario, we scrutinise the molecular pathways that either change or become corrupted during CRC development and their relative prognostic value. Finally, we survey the therapeutic molecules directed against TME components currently available in clinical trials as well as those with stronger potential in preclinical studies. Elucidation of dynamic variations in the CRC TME cell composition and their relative contribution could provide novel diagnostic or prognostic biomarkers and allow more personalised therapeutic strategies.

Tolerance in Kidney Transplantation: What Is on the B Side?

Regulatory B cells (Breg) are in the spotlight for their role in immune homeostasis maintenance and tolerance achievement as in the last years the correlation with functional and increased Breg numbers in autoimmune diseases and transplantation has been extensively proven. Their study is, however, in its infancy with still little knowledge and consensus on their origin, phenotype, and mechanism of action. All this hampers the pursuit of an effective Breg induction method for therapeutic purposes. In this review we aim to summarize the studies on human Breg and their implication in kidney transplantation and to further discuss the issues surrounding therapeutic applications of this cell subset.

TAK1 and IKK2, novel mediators of SCF-induced signaling and potential targets for c-Kit-driven diseases

NF-κB activation depends on the IKK complex consisting of the catalytically active IKK1 and 2 subunits and the scaffold protein NEMO. Hitherto, IKK2 activation has always been associated with IκBα degradation, NF-κB activation, and cytokine production. In contrast, we found that in SCF-stimulated primary bone marrow-derived mast cells (BMMCs), IKK2 is alternatively activated. Mechanistically, activated TAK1 mediates the association between c-Kit and IKK2 and therefore facilitates the Lyn-dependent IKK2 activation which suffices to mediate mitogenic signaling but, surprisingly, does not result in NF-κB activation. Moreover, the c-Kit-mediated and Lyn-dependent IKK2 activation is targeted by MyD88-dependent pathways leading to enhanced IKK2 activation and therefore to potentiated effector functions. In neoplastic cells, expressing constitutively active c-Kit mutants, activated TAK1 and IKKs do also not induce NF-κB activation but mediate uncontrolled proliferation, resistance to apoptosis and enables IL-33 to mediate c-Kit-dependent signaling. Together, we identified the formation of the c-Kit-Lyn-TAK1 signalosome which mediates IKK2 activation. Unexpectedly, this IKK activation is uncoupled from the NF-κB-machinery but is critical to modulate functional cell responses in primary-, and mediates uncontrolled proliferation and survival of tumor-mast cells. Therefore, targeting TAK1 and IKKs might be a novel approach to treat c-Kit-driven diseases.

Dengue Virus Directly Stimulates Polyclonal B Cell Activation

Dengue infection is associated to vigorous inflammatory response, to a high frequency of activated B cells, and to increased levels of circulating cross-reactive antibodies. We investigated whether direct infection of B cells would promote activation by culturing primary human B lymphocytes from healthy donors with DENV in vitro. B cells were susceptible, but poorly permissive to infection. Even though, primary B cells cultured with DENV induced substantial IgM secretion, which is a hallmark of polyclonal B cell activation. Notably, DENV induced the activation of B cells obtained from either DENV immune or DENV naïve donors, suggesting that it was not dependent on DENV-specific secondary/memory response. B cell stimulation was dependent on activation of MAPK and CD81. B cells cultured with DENV also secreted IL-6 and presented increased expression of CD86 and HLA-DR, which might contribute to B lymphocyte co-stimulatory function. Indeed, PBMCs, but not isolated B cells, secreted high amounts of IgG upon DENV culture, suggesting that interaction with other cell types in vivo might promote Ig isotype switching and IgG secretion from different B cell clones. These findings suggest that activation signaling pathways triggered by DENV interaction with non-specific receptors on B cells might contribute to the exacerbated response observed in dengue patients.

HIV-1 induces B-cell activation and class switch recombination via spleen tyrosine kinase and c-Jun N-terminal kinase pathways

OBJECTIVE

Patients infected by the HIV type 1 (HIV-1) frequently show a general deregulation of immune system. A direct influence of HIV-1 particles on B-cell activation, proliferation and B-cell phenotype alterations has been recently described. Moreover, expression of activation-induced cytidinedeaminase (AID) mRNA, which is responsible for class switch recombination (CSR) and somatic hypermutation (SHM), was reported to be overexpressed in B cells exposed to HIV-1.

DESIGN

Study of primary human B cells in an in-vitro model.

METHODS

In the current study, we evaluated which signalling pathways are activated in primary B cells after a direct contact with HIV-1 particles in vitro using different kinase inhibitors.

RESULTS

Here, we report that B-cell activation together with the increase of AID mRNA expression and the subsequent class switch recombination (CSR) in HIV-exposed B cells occurred through spleen tyrosine kinase (SYK) and c-Jun N-terminal kinase (JNK) pathways.

CONCLUSION

Therefore, we showed that HIV-1 could directly induce primary B-cell deregulation via SYK/B-cell receptor (BCR) engagement, and that activation was followed by the JNK pathway activation. To our knowledge, these data provide the first evidence that SYK/BCR activation was the first step for B-cell activation and CSR mechanism after HIV-1 stimulation in a T-cell-free context.

Glucose-dependent de novo lipogenesis in B lymphocytes: a requirement for atp-citrate lyase in lipopolysaccharide-induced differentiation

Bacterially derived lipopolysaccharide (LPS) stimulates naive B lymphocytes to differentiate into immunoglobulin (Ig)-secreting plasma cells. Differentiation of B lymphocytes is characterized by a proliferative phase followed by expansion of the intracellular membrane secretory network to support Ig production. A key question in lymphocyte biology is how naive B cells reprogram metabolism to support de novo lipogenesis necessary for proliferation and expansion of the endomembrane network in response to LPS. We report that extracellularly acquired glucose is metabolized, in part, to support de novo lipogenesis in response to LPS stimulation of splenic B lymphocytes. LPS stimulation leads to increased levels of endogenous ATP-citrate lyase (ACLY), and this is accompanied by increased ACLY enzymatic activity. ACLY produces cytosolic acetyl-CoA from mitochondrially derived citrate. Inhibition of ACLY activity in LPS-stimulated B cells with the selective inhibitor 2-hydroxy-N-arylbenzenesulfonamide (compound-9; C-9) blocks glucose incorporation into de novo lipid biosynthesis, including cholesterol, free fatty acids, and neutral and acidic phospholipids. Moreover, inhibition of ACLY activity in splenic B cells results in inhibition of proliferation and defective endomembrane expansion and reduced expression of CD138 and Blimp-1, markers for plasma-like B cell differentiation. ACLY activity is also required for LPS-induced IgM production in CH12 B lymphoma cells. These data demonstrate that ACLY mediates glucose-dependent de novo lipogenesis in response to LPS signaling and identify a role for ACLY in several phenotypic changes that define plasma cell differentiation.

Direct phenotypical and functional dysregulation of primary human B cells by human immunodeficiency virus (HIV) type 1 in vitro

Background

Human immunodeficiency virus type 1 (HIV-1) induces a general dysregulation of immune system. Dysregulation of B cell compartment is generally thought to be induced by HIV-related immune activation and lymphopenia. However, a direct influence of HIV-1 particles on B cells was recently proposed as the third pathway of B cells dysregulation.

Methods/Principal Findings

We evaluated the direct and specific consequences of HIV-1 contact on activation, survival, proliferation and phenotype of primary B cells in vitro. Moreover, we examined expression of activation-induced cytidine deaminase (AID) mRNA that is responsible for class switch recombination (CSR) and somatic hypermutation (SHM). Here, we report that changes observed in cellular proliferation, phenotypes and activation of B cells could be caused by direct contact between HIV-1 particles and primary B cells in vitro. Finally, direct HIV-1-derived B cells activation led to the increase of AID mRNA expression and its subsequent CSR function was detected in vitro.

Conclusion/Significance

We showed that HIV-1 could directly induce primary B cells dysregulation triggering phenotypical and functional abilities of B cells in vitro that could explain in some extent early B-cell abnormalities in HIV disease.