CD86 regulates IgG1 production via a CD19-dependent mechanism

PDZ Proteins SCRIB and DLG1 Regulate Myeloma Cell Surface CD86 Expression, Growth, and Survival

Despite advances in the treatment of multiple myeloma in the past decades, the disease remains incurable, and understanding signals and molecules that can control myeloma growth and survival are important for the development of novel therapeutic strategies. One such molecule, CD86, regulates multiple myeloma cell survival via its interaction with CD28 and signaling through its cytoplasmic tail. Although the CD86 cytoplasmic tail has been shown to be involved in drug resistance and can induce molecular changes in multiple myeloma cells, its function has been largely unexplored. Here, we show that CD86 cytoplasmic tail has a role in trafficking CD86 to the cell surface. This is due in part to a PDZ-binding motif at its C-terminus which is important for proper trafficking from the Golgi apparatus. BioID analysis revealed 10 PDZ domain-containing proteins proximal to CD86 cytoplasmic tail in myeloma cells. Among them, we found the planar cell polarity proteins, SCRIB and DLG1, are important for proper CD86 surface expression and the growth and survival of myeloma cells. These findings indicate a mechanism by which myeloma cells confer cellular survival and drug resistance and indicate a possible motif to target for therapeutic gain.

IMPLICATIONS

These findings demonstrate the importance of proper trafficking of CD86 to the cell surface in myeloma cell survival and may provide a new therapeutic target in this disease.

Integrated Analysis of Cancer Tissue and Vitreous Humor from Retinoblastoma Eyes Reveals Unique Tumor-Specific Metabolic and Cellular Pathways in Advanced and Non-Advanced Tumors

Retinoblastoma (Rb) is a pediatric intraocular malignancy that is proposed to originate from maturing cone cell precursors in the developing retina. The molecular mechanisms underlying the biological and clinical behaviors are important to understand in order to improve the management of advanced-stage tumors. While the genetic causes of Rb are known, an integrated understanding of the gene expression and metabolic processes in tumors of human eyes is deficient. By integrating transcriptomic profiling from tumor tissues and metabolomics from tumorous eye vitreous humor samples (with healthy, age-matched pediatric retinae and vitreous samples as controls), we uncover unique functional associations between genes and metabolites. We found distinct gene expression patterns between clinically advanced and non-advanced Rb. Global metabolomic analysis of the vitreous humor of the same Rb eyes revealed distinctly altered metabolites, indicating how tumor metabolism has diverged from healthy pediatric retina. Several key enzymes that are related to cellular energy production, such as hexokinase 1, were found to be reduced in a manner corresponding to altered metabolites; notably, a reduction in pyruvate levels. Similarly, E2F2 was the most significantly elevated E2F family member in our cohort that is part of the cell cycle regulatory circuit. Ectopic expression of the wild-type RB1 gene in the Rb-null Y79 and WERI-Rb1 cells rescued hexokinase 1 expression, while E2F2 levels were repressed. In an additional set of Rb tumor samples and pediatric healthy controls, we further validated differences in the expression of HK1 and E2F2. Through an integrated omics analysis of the transcriptomics and metabolomics of Rb, we uncovered a significantly altered tumor-specific metabolic circuit that reduces its dependence on glycolytic pathways and is governed by Rb1 and HK1.

The role of B7 family members in the generation of Immunoglobulin

Ig is a Y-shaped protein produced by plasma cells and exerts multiple functions in humoral immunity. There are five groups of Igs including IgA, IgD, IgE, IgG, and IgM, which differ in their heavy chain class. The primary function of Igs includes the neutralization of extrinsic pathogens, agglutination of foreign cells for phagocytosis, precipitation of soluble antigens in serum, and complement fixation. The B cells activated by antigen(s) can differentiate into antibody-producing cells that are called plasma cells and usually matured in the germinal center (GC). Follicular T helper (Tfh) cells crosstalk with antigen-presenting cells and play a crucial role in the development of the GC. Moreover, Tfh cells regulate trafficking through the GC to allow formative interaction with GC B cells that ultimately results in affinity maturation, B-cell memory, and Ig class switching. The B7 family is a series of number of structurally related membrane proteins that bind with a specific receptor to deliver costimulatory or co-inhibitory signals that regulate the activation of T cells in GC. Here, we review and summarize the recent advance of the effects of B7 family members on Ig production and relative diseases.

Immune activation of Bio-Germanium in a randomized, double-blind, placebo-controlled clinical trial with 130 human subjects: Therapeutic opportunities from new insights

Germanium has long been considered a therapeutic agent with anticancer, antitumor, antiaging, antiviral and anti-inflammatory effects. Numerous clinical studies have explored the promising therapeutic effects of organic germanium on cancer, arthritis and senile osteoporosis. The immune activation property of organic germanium is considered the foundation of its various therapeutic effects. However, previous human clinical studies investigating immune activation with organic germanium compounds have certain limitations, as some studies did not strictly follow a randomized, double-blind, placebo-controlled design. To build a more clinically substantiated foundation for the mechanism underlying its immunostimulation, we structured by far the most rigorous clinical study to-date with a group of 130 human subjects to examine changes in immune profiles following germanium supplementation. We used Bio-Germanium, an organic germanium compound naturally synthesized via a yeast fermentation process. An 8-week randomized, double-blind, placebo-controlled study was conducted with 130 subjects with leukocyte counts of 4–8 (×10³/μL) divided into the Bio-Germanium group and the placebo group. Anthropometric measurements; blood collection; biochemical analysis; urinalysis; and natural killer cell activity, cytokine and immunoglobulin assays were conducted. Results showed the Bio-Germanium group exhibited NK cell activity increases at effector cell:target cell (E:T) ratios of 50:1, 10:1, 5:1 and 2.5:1 (12.60±32.91%, 10.19±23.88%, 9.28±16.49% and 7.27±15.28%, respectively), but the placebo group showed decreases (P<0.01). The difference in the IgG1 change from baseline to follow-up between the Bio-Germanium and placebo groups was significant (P = 0.044). Our results and earlier clinical study of Bio-Germanium confirm that Bio-Germanium acts as an effective immunostimulant by increasing the cytotoxicity of NK cells and activating immunoglobulin, B cells and tumor necrosis factor (TNF)-α (P<0.05). As we have added newly discovered clinical findings for germanium’s immunostimulation mechanism, we believe Bio-Germanium is a highly promising therapeutic agent and should certainly be further explored for potential development opportunities in immunotherapy.

Cytotoxic T lymphocyte-associated antigen-4-Ig (CTLA-4-Ig) suppresses Staphylococcus aureus-induced CD80, CD86, and pro-inflammatory cytokine expression in human B cells

Background

Cytotoxic T lymphocyte-associated antigen-4-Ig (CTLA-4-Ig) competes with CD28 for binding CD80/CD86 on antigen-presenting cells (APCs) to limit T cell activation. B cells are believed to be important APCs in the pathogenesis of autoimmune diseases and express CD80/CD86 after activation; however, relatively little is known about the effect of CTLA-4-Ig on B cells. This study tested the impact of CTLA-4-Ig on human B cell responses.

Methods

Human blood B cells were purified from healthy donors and activated in the presence of CTLA-4-Ig or the L6-Ig control protein in vitro. RT-q-PCR and immunofluorescence staining were performed to detect activation marker expression. ELISA was conducted to measure cytokine secretion. The CD80/CD86 levels on the surface of the memory B cells in the blood of 18 patients with rheumatoid arthritis (RA) were detected using immunofluorescence staining.

Results

CTLA-4-Ig suppressed the expression of Staphylococcus aureus (SAC)-induced CD80, CD86, TNFA, and IL6 in human B cells at the transcriptional level. Furthermore, CTLA-4-Ig concomitantly decreased SAC-induced CD80/CD86 surface expression on and TNF-α and IL-6 secretion from B cells. On the other hand, T cell-dependent (TD) stimulation-induced B cell activation, proliferation, plasma cell differentiation, and antibody secretion were not affected by CTLA-4-Ig. As expected, TD stimulation-induced surface CD80 was hindered by CTLA-4-Ig. Notably, a blockade of CD80/CD86 on the surface of the memory B cells was observed in the patients with RA after abatacept (CTLA-4-Ig) treatment. In a portion of the RA patients, restoration of CD80/CD86 staining on the surface of the memory B was detected starting in the 3rd month of abatacept treatment. Interestingly, the surface levels of CD80/CD86 on the patients’ memory B cells positively correlated with disease activity.

Conclusions

We found that CTLA-4-Ig directly suppressed SAC-induced B cell activation in vitro. Obstruction of CD80 and CD86 on the surface of the memory B cells was detected in the RA patients after abatacept treatment. Blocking CD80/CD86 on B cells by CTLA-4-Ig may hinder T cell activation and associated with the disease activity of RA in vivo. Our findings indicate that CTLA-4-Ig may regulate humoral responses by modulating B cell activation and interfering T cell-B cell interaction.

Abatacept modulates CD80 and CD86 expression and memory formation in human B-cells

BACKGROUND

Cytotoxic T lymphocyte antigen-4 (CTLA-4) limits T-cell activation and is expressed on T-regulatory cells. Human CTLA-4 deficiency results in severe immune dysregulation. Abatacept (CTLA-4 Ig) is approved for the treatment of rheumatoid arthritis (RA) and its mechanism of action is attributed to effects on T-cells. It is known that CTLA-4 modulates the expression of its ligands CD80 and CD86 on antigen presenting cells (APC) by transendocytosis. As B-cells express CD80/CD86 and function as APC, we hypothesize that B-cells are a direct target of abatacept.

OBJECTIVES

To investigate direct effects of abatacept on human B-lymphocytes in vitro and in RA patients.

METHODS

The effect of abatacept on healthy donor B-cells' phenotype, activation and CD80/CD86 expression was studied in vitro. Nine abatacept-treated RA patients were studied. Seven of these were followed up to 24 months, and two up to 12 months only and treatment response, immunoglobulins, ACPA, RF concentrations, B-cell phenotype and ACPA-specific switched memory B-cell frequency were assessed.

RESULTS

B-cell development was unaffected by abatacept. Abatacept treatment resulted in a dose-dependent decrease of CD80/CD86 expression on B-cells in vitro, which was due to dynamin-dependent internalization. RA patients treated with abatacept showed a progressive decrease in plasmablasts and serum IgG. While ACPA-titers only moderately declined, the frequency of ACPA-specific switched memory B-cells significantly decreased.

CONCLUSIONS

Abatacept directly targets B-cells by reducing CD80/CD86 expression. Impairment of antigen presentation and T-cell activation may result in altered B-cell selection, providing a new therapeutic mechanism and a base for abatacept use in B-cell mediated autoimmunity.

Enhanced B-cell differentiation driven by advanced cirrhosis resulting in hyperglobulinemia

BACKGROUND AND AIM

The mechanism underlying hyperglobulinemia in cirrhosis, a long appreciated phenomenon, has never been clearly understood. The aim of this study is to investigate the basis for changes in humoral immunity observed in cirrhosis.

METHODS

We retrospectively reviewed our medical record to analyze serum immunoglobulin (Ig) levels in patients with liver disease. We also prospectively analyzed peripheral blood mononuclear cells and sera from liver disease patients. Peripheral blood mononuclear cell surface marker expressions were measured by flow cytometry and serum B-cell-activating factor was measured by enzyme-linked immunosorbent assay. Expression of specific gene expression in magnetically separated B cells was also analyzed by real-time polymerase chain reaction.

RESULTS

In retrospective analysis, we found that advancing cirrhosis, irrespective of underlying etiology or hepatocellular carcinoma, resulted in progressively increasing levels of serum IgG and IgA. In prospective analysis using clinical samples, we demonstrated that advancing cirrhosis stage was associated with increased toll-like-receptor (TLR)9 expression in CD27+ B cell and serum B-cell-activating factor levels but decreased CD27+ memory B-cell frequency. The remaining CD27+ B cells in peripheral blood exhibited increased activation-induced cytidine deaminase mRNA expression. Finally, we also demonstrated isolated B cells from advanced cirrhosis were more reactive to TLR9 stimulation that drove antibody secreting cells differentiation leading to hyperimmunoglobulinemia in vitro.

CONCLUSIONS

Enhanced TLR9-induced differentiation into antibody secreting cell may explain peripheral reductions of circulating CD27+ memory B cells as well as increased serum Ig levels in cirrhosis.

Control of Humoral Response in Renal Transplantation by Belatacept Depends on a Direct Effect on B Cells and Impaired T Follicular Helper-B Cell Crosstalk

Generation of de novo donor-specific antibodies (dnDSAs) after renal transplant is recognized as the leading cause of late transplant failure. Hence, the optimal immunosuppressive strategies to limit dnDSA development need to be defined. Recent clinical trials using the novel costimulatory blockade agent CTLA4-Ig (Belatacept) have shown that kidney transplant recipients (KTRs) treated with Belatacept have better graft survival and function and a lower proportion of dnDSAs than control-treated KTRs. Mechanisms involved in the control of humoral responses by Belatacept remain to be investigated. Here, we analyzed the effect of Belatacept on different steps of the B cell-mediated response in humans. In vitro, Belatacept reduced plasmablast differentiation, Ig production, and the expression of the major transcription factor involved in plasma cell function, Blimp-1, in a T cell-independent manner. Moreover, Belatacept induced activation of the STAT3 transcription factor in stimulated B cells and reduced the expression of CD86. Additionally, Belatacept blocked CD28-mediated activation of T follicular helper cells (Tfhs) in an autologous Tfh-memory B cells model. We then validated these observations in KTRs treated with Belatacept, who had a reduced proportion of blood effector B cells and activated Tfh (PD1⁺ICOS⁺) compared with control-treated KTRs. Our in vitro and in vivo results suggest that Belatacept modulates B cell function directly and at the level of B cell-Tfh interaction. These mechanisms likely account for the optimal control of humoral responses observed in KTRs treated with Belatacept.

CD86 regulates myeloma cell survival

Although prognosis for patients with multiple myeloma has improved over the past decade, research toward discovery of new therapeutic avenues is important and could lead to a cure for this plasma cell malignancy. Here we show that blocking the CD28-CD86 pathway via silencing of either CD28 or CD86 leads to myeloma cell death. Inhibiting this pathway leads to downregulation of integrins and IRF4, a known myeloma survival factor. Our data also indicate that CD86, the canonical ligand in this pathway, has prosurvival activity that is dependent on its cytosolic domain. These findings indicate that targeting of this pathway is a promising therapeutic avenue for myeloma, because it leads to modulation of different processes important in cell viability.

Comparative In Vitro Immune Stimulation Analysis of Primary Human B Cells and B Cell Lines

B cell specific immunomodulatory drugs still remain an unmet medical need. Utilisation of validated simplified in vitro models would allow readily obtaining new insights in the complexity of B cell regulation. For this purpose we investigated which human B lymphocyte stimulation assays may be ideally suited to investigate new B lymphocyte immunosuppressants. Primary polyclonal human B cells underwent in vitro stimulation and their proliferation, production of immunoglobulins (Igs) and of cytokines, and expression of cell surface molecules were analysed using various stimuli. ODN2006, a toll-like receptor 9 (TLR9) agonist, was the most potent general B cell stimulus. Subsequently, we investigated on which human B cell lines ODN2006 evoked the broadest immunostimulatory effects. The Namalwa cell line proved to be the most responsive upon TLR9 stimulation and hence may serve as a relevant, homogeneous, and stable B cell model in an in vitro phenotypic assay for the discovery of new targets and inhibitors of the B cell activation processes. As for the read-out for such screening assay, it is proposed that the expression of activation and costimulatory surface markers reliably reflects B lymphocyte activation.

Effect of Immunosuppressive Drugs on Humoral Allosensitization after Kidney Transplant

The negative effect of donor-specific antibodies on the success of solid transplant is now clearly established. However, the lack of effective treatment to prevent the development of antibody-mediated lesions deepens the need for clinicians to focus on primary prevention of de novo humoral allosensitization. Among the factors associated with the risk of developing de novo donor-specific antibodies, therapeutic immunosuppression is the most obvious parameter in which improvement is possible. Beyond compliance and the overall depth of immunosuppression, it is likely that the nature of the drugs is also crucial. Here, we provide an overview of the molecular effect of the various immunosuppressive drugs on B cell biology. Clinical data related to the effect of these drugs on de novo humoral allosensitization are also examined, providing a platform from which clinicians can optimize immunosuppression for prevention of de novo donor-specific antibody generation at the individual level.

Anti-CD83 promotes IgG1 isotype switch in marginal zone B cells in response to TI-2 antigen

CD83 is a transmembrane glycoprotein that is rapidly up-regulated on activated B cells. Although CD83 itself is incapable to transduce intracellular signaling, it acts as a negative regulator of B cell function. We have recently described that a single application of anti-CD83 antibody results in dramatically enhanced production of antigen-specific IgG1 but not other isotypes upon immunization of mice with the TI-2 model antigen (Ag) NIP-Ficoll. This effect was mediated by the binding of anti-CD83 to CD83 on the surface of B cells themselves. In the current study we show that administration of anti-CD83 enhances IgG1-production independent of IL-4. Application of anti-CD83 does not alter the proliferation and general expansion of NIP-specific B cells. In the presence of anti-CD83, immunized mice develop normal frequencies of plasmablasts in response to NIP-Ficoll of which an increased number produces IgG1. These cells localize in extrafollicular foci in the spleen of immunized mice and originate from the marginal zone B cell pool. Taken together, our results indicate that CD83 engagement in vivo does not generally enhance B cell activation but selectively promotes IgG1 class switch in marginal zone B cells in response to TI-2 Ag.

The role of microRNA-1246 in the regulation of B cell activation and the pathogenesis of systemic lupus erythematosus

Background

The pathogenesis of systemic lupus erythematosus (SLE) has not yet been completely elucidated. One of the hallmarks of SLE is the production of autoantibodies by uncontrolled over-activated B cells. Early B cell factor 1 (EBF1) contributes to the development, activation, and proliferation of B cells through activation of the AKT signaling pathway. Accumulating evidence has demonstrated that several microRNAs (miRNAs) contribute to the pathogenesis of autoimmune diseases through the regulation of B cells in SLE. We aim to investigate the expression patterns of miR-1246 in B cells and its contribution to pathogenesis of SLE.

Results

Our results showed that the expression of miR-1246 was significantly decreased in B cells from SLE patients. We verified that miR-1246 specifically targeted the EBF1 messenger RNA (mRNA) by interacting with its 3′-untranslated region (3′-UTR) and regulated the expression of EBF1. Transfection of miR-1246 inhibitors into healthy B cells upregulated the expression of EBF1, enhanced B cell function, and increased the production of B cell surface co-stimulatory molecules CD40, CD80, and CD86. We also observed that abnormal activation of the AKT signaling pathway was associated with decreased P53 expression, leading to the downregulation of the miR-1246 expression; and upregulation of the miR-1246 expression reversed the responsiveness of B cells by inhibiting EBF1 expression.

Conclusions

Activated B cells in lupus could decrease the expression of miR-1246 through the AKT-P53 signaling pathway, which in turn enhances the expression of EBF1, thereby promoting further activation of B cells. Conversely, upregulation of miR-1246 could interrupt this amplification pathway. Our findings thus provide a theoretical framework towards the research of novel biological targets in SLE treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-015-0063-7) contains supplementary material, which is available to authorized users.

Critical role of NKT cells in posttransplant alloantibody production

We previously reported that posttransplant alloantibody production in CD8-deficient hosts is IL-4+ CD4+ T cell-dependent and IgG1 isotype-dominant. The current studies investigated the hypothesis that IL-4-producing natural killer T cells (NKT cells) contribute to maximal alloantibody production. To investigate this, alloantibody levels were examined in CD8-deficient WT, CD1d KO and Jα18 KO transplant recipients. We found that the magnitude of IgG1 alloantibody production was critically dependent on the presence of type I NKT cells, which are activated by day 1 posttransplant. Unexpectedly, type I NKT cell contribution to enhanced IgG1 alloantibody levels was interferon-γ-dependent and IL-4-independent. Cognate interactions between type I NKT and B cells alone do not stimulate alloantibody production. Instead, NKT cells appear to enhance maturation of IL-4+ CD4+ T cells. To our knowledge, this is the first report to substantiate a critical role for type I NKT cells in enhancing in vivo antibody production in response to endogenous antigenic stimuli.

Neuroendocrine regulation of inflammation

The interaction between the sympathetic nervous system and the immune system has been documented over the last several decades. In this review, the neuroanatomical, cellular, and molecular evidence for neuroimmune regulation in the maintenance of immune homeostasis will be discussed, as well as the potential impact of neuroimmune dysregulation in health and disease.

CD19 as a therapeutic target in a spontaneous autoimmune polyneuropathy

Spontaneous autoimmune polyneuropathy (SAP) in B7-2 knock-out non-obese diabetic (NOD) mice is mediated by myelin protein zero (P0)-reactive T helper type 1 (Th1) cells. In this study, we investigated the role of B cells in SAP, focusing on CD19 as a potential therapeutic target. We found that P0-specific plasmablasts and B cells were increased in spleens of SAP mice compared to wild-type NOD mice. Depletion of B cells and plasmablasts with anti-CD19 monoclonal antibody (mAb) led to attenuation of disease severity when administered at 5 months of age. This was accompanied by decreased serum immunoglobulin (Ig)G and IgM levels, depletion of P0-specific plasmablasts and B cells, down-regulation/internalization of surface CD19 and increased frequency of CD4(+) regulatory T cells in spleens. We conclude that B cells are crucial to the pathogenesis of SAP, and that CD19 is a promising B cell target for the development of disease-modifying agents in autoimmune neuropathies.

Alloprimed CD8(+) T cells regulate alloantibody and eliminate alloprimed B cells through perforin- and FasL-dependent mechanisms

While it is well known that CD4(+) T cells and B cells collaborate for antibody production, our group previously reported that CD8(+) T cells down-regulate alloantibody responses following transplantation. However, the exact mechanism involved in CD8(+) T cell-mediated down-regulation of alloantibody remains unclear. We also reported that alloantibody production is enhanced when either perforin or FasL is deficient in transplant recipients. Here, we report that CD8(+) T cell-deficient transplant recipient mice (high alloantibody producers) exhibit an increased number of primed B cells compared to WT transplant recipients. Furthermore, CD8(+) T cells require FasL, perforin and allospecificity to down-regulate posttransplant alloantibody production. In vivo CD8-mediated clearance of alloprimed B cells was also FasL- and perforin-dependent. In vitro data demonstrated that recipient CD8(+) T cells directly induce apoptosis of alloprimed IgG1(+) B cells in co-culture in an allospecific and MHC class I-dependent fashion. Altogether these data are consistent with the interpretation that CD8(+) T cells down-regulate posttransplant alloantibody production by FasL- and perforin-dependent direct elimination of alloprimed IgG1(+) B cells.

Immunoregulatory profile of monocytes from cutaneous leishmaniasis patients and association with lesion size

Leishmaniasis is an important tropical disease composed of several clinical forms that adversely affect millions of people globally. Critical cells involved in the host-Leishmania interaction are monocytes and macrophages, which act to protect against infections due to their ability to both control intracellular infections and regulate the subsequent adaptive immune response. Both soluble factors and cell surface receptors are keys in directing the immune response following interaction with pathogens such as Leishmania. Toll-like receptors (TLRs) have an essential role in immune responses against infections, but little is known about their role in human infection with Leishmania braziliensis. In this work, we evaluated peripheral blood CD14+ monocytes for the expression of immunoregulatory cytokines, co-stimulatory molecules and TLR9 from cutaneous leishmaniasis patients infected with L. braziliensis and noninfected individuals. Our results showed that patients present decreased expression of co-stimulatory molecules such as CD80 and CD86 following culture with media alone or after stimulus with soluble Leishmania antigen. Interestingly, TLR9 expression was higher after culture with soluble Leishmania antigen (SLA), suggesting a role of this molecule in immunoregulation of active disease. Lastly, higher frequencies of TLR9+ monocytes were correlated with greater lesion size. These findings demonstrate a peripheral monocytes profile compatible with important immunoregulatory potential.

Combinatorial signaling through TLR-2 and CD86 augments activation and differentiation of resting B cells

B cells are an integral component in mounting humoral immune responses and they are also crucial in programming T cell mediated immunity. Usually, B cell activation is initiated by recognition of antigen through B cell receptor (BCR), followed by its processing and presentation to T cells. But very little is known about BCR independent activation of B cells. Now, there is an increasing body of evidence indicating the combinatorial effect of innate and adaptive immune components in modulating the functions of B cells. In this study, we demonstrate the activation of resting B cells (RB) by simultaneous involvement of Toll like Receptor-2 (TLR-2) and costimulatory molecule, CD86. Interestingly, these B cells exhibited significant level of activation and proliferation. Furthermore, this process of activation leads to the differentiation of RB cells, preferably into marginal zone precursors (CD19(+)IgD(hi)IgM(hi)CD21/35(hi)CD23(hi)) in a shorter time window and showed increased secretion of IgG isotype. These RB cells also showed enhanced antigen uptake capacity. These observations were also substantiated by microarray gene expression results, which strengthen the notion that combinatorial signaling through innate and adaptive immune components enhances B cell mediated immune response. Thus, the present study elucidates a novel BCR independent B cell activation mechanism that links TLR-2 and CD86. Hence signaling of TLRs in conjunction with costimulatory molecules will substantially help in bolstering humoral immune response, which can be extrapolated to formulate vaccination strategies for diseases involving B cell-mediated immunity.

Prohibitins and the cytoplasmic domain of CD86 cooperate to mediate CD86 signaling in B lymphocytes

CD86 engagement on a CD40L/IL-4-primed murine B cell activates signaling intermediates that promote NF-κB activation to increase Oct-2 and mature IgG1 mRNA and protein expression, as well as the rate of IgG1 transcription, without affecting class switch recombination. One of the most proximal signaling intermediates identified is phospholipase Cγ2, a protein reported to bind tyrosine residues, which are absent in the cytoplasmic domain of CD86. Using a proteomics-based identification approach, we show that the tyrosine-containing transmembrane adaptor proteins prohibitin (Phb)1 and Phb2 bind to CD86. The basal expression of Phb1/2 and association with CD86 was low in resting B cells, whereas the level of expression and association increased primarily after priming with CD40. The CD86-induced increase in Oct-2 and IgG1 was less when either Phb1/2 expression was reduced by short hairpin RNA or the cytoplasmic domain of CD86 was truncated or mutated at serine/threonine protein kinase C phosphorylation sites, which did not affect Phb1/2 binding to CD86. Using this approach, we also show that Phb1/2 and the CD86 cytoplasmic domain are required for the CD86-induced phosphorylation of IκBα, which we previously reported leads to NF-κB p50/p65 activation, whereas only Phb1/2 was required for the CD86-induced phosphorylation of phospholipase Cγ2 and protein kinase Cα/β(II), which we have previously reported leads to NF-κB (p65) phosphorylation and subsequent nuclear translocation. Taken together, these findings suggest that Phb1/2 and the CD86 cytoplasmic domain cooperate to mediate CD86 signaling in a B cell through differential phosphorylation of distal signaling intermediates required to increase IgG1.

Antibodies generated against conserved antigens expressed by bacteria and allergen-bearing fungi suppress airway disease

There has been a sharp rise in allergic asthma and asthma-related deaths in the developed world, in contrast to many childhood illnesses that have been reduced or eliminated. The hygiene hypothesis proposes that excessively sanitary conditions early in life result in autoimmune and allergic phenomena because of a failure of the immune system to receive proper microbial stimulation during development. We demonstrate that Abs generated against conserved bacterial polysaccharides are reactive with and dampen the immune response against chitin and Aspergillus fumigatus. A reduction in Ag uptake, cell influx, cell activation, and cytokine production occurred in the presence of anti-polysaccharide Abs, resulting in a striking decrease in the severity of allergic airway disease in mice. Overall, our results suggest that Ag exposure--derived from environmental sources, self-antigens, or vaccination--during the neonatal period has dramatic effects on the adult Ab response and modifies the development of allergic airway disease.

The beta2-adrenergic receptor on T and B lymphocytes: do we understand it yet?

The role played by the beta2-adrenergic receptor (β(2)AR) in regulating the level of T and B lymphocyte function has been studied for over half a century. During this time, we have learned that T and B lymphocytes express almost exclusively the β(2)AR, and that the level of expression on a specific lymphocyte subset differs due to epigenetic regulation by histone and DNA methylation. We have also learned that engagement of the β(2)AR on lymphocytes, by either norepinephrine or a selective pharmacologic ligand, regulates the level of lymphocyte activity differentially, depending on the time of receptor engagement in relation to the activation and differentiation state of the cell, the molecular signaling pathway activated, and the cytokine microenvironment. The challenge now is to determine if we understand enough about how this receptor functions on lymphocytes to predict the relevance of such regulation to overall immune homeostasis and the development/progression of human disease.

Cathelin-related antimicrobial peptide differentially regulates T- and B-cell function

Mammalian antimicrobial peptides (AMPs) play an important role in host defense via direct antimicrobial activity as well as immune regulation. The mouse cathelin-related antimicrobial peptide (mCRAMP), produced from the mouse gene Camp, is the only mouse cathelicidin identified and the ortholog of the human gene encoding the peptide LL-37. This study tested the hypothesis that mouse B and T cells produce and respond to mCRAMP. We show that all mature mouse B-cell subsets, including follicular (FO), marginal zone (MZ), B1a, and B1b cells, as well as CD4(+) and CD8(+) T cells produce Camp mRNA and mCRAMP protein. Camp(-/-) B cells produced equivalent levels of IgM, IgG3, and IgG2c but less IgG1 and IgE, while Camp(-/-) CD4(+) T cells cultured in Th2-inducing conditions produced more IL-4-expressing cells when compared with WT cells, effects that were reversed upon addition of mCRAMP. In vivo, Camp(-/-) mice immunized with TNP-OVA absorbed in alum produced an enhanced TNP-specific IgG1 response when compared with WT mice. ELISpot analysis revealed increased numbers of TNP-specific IgG1-secreting splenic B cells and FACS analysis revealed increased CD4(+) T-cell IL-4 expression. Our results suggest that mCRAMP differentially regulates B- and T-cell function and implicate mCRAMP in the regulation of adaptive immune responses.

CD40 signaling synergizes with TLR-2 in the BCR independent activation of resting B cells

Conventionally, signaling through BCR initiates sequence of events necessary for activation and differentiation of B cells. We report an alternative approach, independent of BCR, for stimulating resting B (RB) cells, by involving TLR-2 and CD40 - molecules crucial for innate and adaptive immunity. CD40 triggering of TLR-2 stimulated RB cells significantly augments their activation, proliferation and differentiation. It also substantially ameliorates the calcium flux, antigen uptake capacity and ability of B cells to activate T cells. The survival of RB cells was improved and it increases the number of cells expressing activation induced deaminase (AID), signifying class switch recombination (CSR). Further, we also observed increased activation rate and decreased threshold period required for optimum stimulation of RB cells. These results corroborate well with microarray gene expression data. This study provides novel insights into coordination between the molecules of innate and adaptive immunity in activating B cells, in a BCR independent manner. This strategy can be exploited to design vaccines to bolster B cell activation and antigen presenting efficiency, leading to faster and better immune response.

B cell-specific expression of B7-2 is required for follicular Th cell function in response to vaccinia virus

Follicular Th (T(FH)) cells are specialized in provision of help to B cells that is essential for promoting protective Ab responses. CD28/B7 (B7-1 and B7-2) interactions are required for germinal center (GC) formation, but it is not clear if they simply support activation of naive CD4 T cells during initiation of responses by dendritic cells or if they directly control T(FH) cells and/or directly influence follicular B cell differentiation. Using a model of vaccinia virus infection, we show that B7-2 but not B7-1 deficiency profoundly impaired T(FH) cell development but did not affect CD4 T cell priming and Th1 differentiation. Consistent with this, B7-2 but not B7-1 was required for acquisition of GC B cell phenotype, plasma cell generation, and virus-specific neutralizing Ab responses. Mixed adoptive transfer experiments indicated that bidirectional interactions between CD28 expressed on activated T cells and B7-2 expressed on follicular B cells were essential for maintenance of the T(FH) phenotype and GC B cell development. Our data provide new insight into the source and nature of molecules required for T(FH) cells to direct GC B cell responses.

B7-1/2 (CD80/CD86) direct signaling to B cells enhances IgG secretion

B cell responses are regulated by Ag recognition, costimulatory signals provided by interaction with helper T cells, and by innate signals. We recently provided evidence for a link between the effects of innate and costimulatory signals on B cells during influenza virus infection, by demonstrating that most B cells in the regional lymph nodes of the respiratory tract enhance surface expression of the costimulator B7-2 (CD86) within 24-48 h following infection via a type I IFNR-dependent mechanisms, a finding we are confirming here. While the role of B7-1/2 for helper T cell activation is well documented, its role in direct B cell regulation is poorly understood. Here, our in vivo studies with mixed bone marrow irradiation chimeric mice, lacking B7-1/2 only on B cells, demonstrated that B7-1/2 expression is crucial for induction of maximal local, but to a lesser extent systemic, IgG Ab responses following influenza virus infection. In contrast to mice that completely lack B7-1/2 expression, loss of B7-1/2 on B cells alone did not significantly affect germinal center formation or the extent of CD4(+) T cell activation and IFN-gamma secretion. Instead, our in vitro studies identify a dramatic effect of B7-2 engagement on IgG, but not IgM secretion by already class-switched B cells. Concomitantly, B7-2 engagement induced expression of X-box binding protein 1 (XBP-1) and spliced XBP1, evidence for increased protein synthesis by these cells. Taken together, these results identify direct signaling through B7-1/2 as a potent regulator of IgG secretion by previously activated B cells.

Engagement of CD83 on B cells modulates B cell function in vivo

The transmembrane glycoprotein CD83 is an important regulator of both thymic T cell maturation and peripheral T cell response. Recent studies suggested that CD83 is also involved in the regulation of B cell maturation, activation, and homeostasis. In this study, we show that in vivo overexpression of CD83 dose dependently interfered with the Ig response to thymus-dependent and thymus-independent model Ag immunization. CD83 deficiency, in contrast, which was restricted to B cells in mixed bone marrow chimeras, led to unchanged or even slightly increased Ig responses. Strikingly, the engagement of CD83 that is naturally up-regulated on wild-type B cells by injection of anti-CD83 mAb in vivo induced a 100-fold increase in the IgG1 response to immunization. Kinetic analysis revealed that CD83 had to be engaged simultaneously or shortly after the B cell activation through injection of Ag, to modulate the IgG1 secretion. Furthermore, using mixed bone marrow chimeras in which either selectively the B cells or the dendritic cells were CD83 deficient, we demonstrate that anti-CD83 mAb mediated its biologic effect by engaging CD83 on B cells and not on CD11c(+) dendritic cells. Taken together, we provide strong evidence that CD83 transduces regulatory signals into the very B cell on which it is expressed.

DNA microarray gene expression profile of marginal zone versus follicular B cells and idiotype positive marginal zone B cells before and after immunization with Streptococcus pneumoniae

Marginal zone (MZ) B cells play an important role in the clearance of blood-borne bacterial infections via rapid T-independent IgM responses. We have previously demonstrated that MZ B cells respond rapidly and robustly to bacterial particulates. To determine the MZ-specific genes that are expressed to allow for this response, MZ and follicular (FO) B cells were sort purified and analyzed via DNA microarray analysis. We identified 181 genes that were significantly different between the two B cell populations. Ninety-nine genes were more highly expressed in MZ B cells while 82 genes were more highly expressed in FO B cells. To further understand the molecular mechanisms by which MZ B cells respond so rapidly to bacterial challenge, Id-positive and -negative MZ B cells were sort purified before (0 h) or after (1 h) i.v. immunization with heat-killed Streptococcus pneumoniae, R36A, and analyzed via DNA microarray analysis. We identified genes specifically up-regulated or down-regulated at 1 h following immunization in the Id-positive MZ B cells. These results give insight into the gene expression pattern in resting MZ vs FO B cells and the specific regulation of gene expression in Ag-specific MZ B cells following interaction with Ag.