IL-21 and IL-10 have redundant roles but differential capacities at different stages of Plasma Cell generation from human Germinal Center B cells

Distinct transcriptomes and autocrine cytokines underpin maturation and survival of antibody-secreting cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by multiple autoantibody types, some of which are produced by long-lived plasma cells (LLPC). Active SLE generates increased circulating antibody-secreting cells (ASC). Here, we examine the phenotypic, molecular, structural, and functional features of ASC in SLE. Relative to post-vaccination ASC in healthy controls, circulating blood ASC from patients with active SLE are enriched with newly generated mature CD19-CD138+ ASC, similar to bone marrow LLPC. ASC from patients with SLE displayed morphological features of premature maturation and a transcriptome epigenetically initiated in SLE B cells. ASC from patients with SLE exhibited elevated protein levels of CXCR4, CXCR3 and CD138, along with molecular programs that promote survival. Furthermore, they demonstrate autocrine production of APRIL and IL-10, which contributed to their prolonged in vitro survival. Our work provides insight into the mechanisms of generation, expansion, maturation and survival of SLE ASC.

Serum 3-phenyllactic acid level is reduced in benign multiple sclerosis and is associated with effector B cell ratios

BACKGROUND

3-phenyllactic acid (PLA) is produced by both intestinal bacteria and the human host. PLA exists in its D- and L- chiral forms. It modulates human immune functions, thereby acting as a mediator of bacterial-host interactions. We aim to determine the amount and potential influence of PLA on clinical and immunological features of MS.

METHODS

We measured D- and L-PLA levels in bacterial supernatants and in sera of 60 MS patients and 25 healthy controls. We investigated potential associations between PLA levels, clinical features of MS, serum cytokine levels and ratios of peripheral blood lymphocyte subsets.

RESULTS

Multiple gut commensal bacteria possessed the capacity to generate D- and L-PLA. MS patients with benign phenotype showed markedly lower PLA levels than healthy controls or other MS patients. Fingolimod resistant patients had higher PLA levels at baseline. Furthermore, MS patients with higher PLA levels tended to display increased memory B and plasma cell ratios, elevated IL-4 levels and increased ratios of IL-4 and IL-10 producing T cell subsets.

CONCLUSION

Collectively, our work indicates that reduced serum levels of PLA could be associated with a favorable clinical course in MS and possibly be used as a biomarker.

Development and function of tissue-resident memory B cells

Barrier tissues are the primary site of infection for pathogens likely to cause future pandemics. Tissue-resident lymphocytes can rapidly detect pathogens upon infection of barrier tissues and are critical in preventing viral spread. However, most vaccines fail to induce tissue-resident lymphocytes and are instead reliant on circulating antibodies to mediate protective immunity. Circulating antibody titers wane over time following vaccination leaving individuals susceptible to breakthrough infections by variant viral strains that evade antibody neutralization. Memory B cells were recently found to establish tissue residence following infection of barrier tissues. Here, we summarize emerging evidence for the importance of tissue-resident memory B cells in the establishment of protective immunity against viral and bacterial challenge. We also discuss the role of tissue-resident memory B cells in regulating the progression of non-infectious diseases. Finally, we examine new approaches to develop vaccines capable of eliciting barrier immunity.

IL-10 as a Th2 Cytokine: Differences Between Mice and Humans

The discovery of IL-10 more than 30 years ago marked the beginning of our understanding of how cytokines regulate immune responses, based on cross-regulation between Th1 and Th2 cytokines. Although multiple cell types were shown to produce IL-10, its identity as a Th2 cytokine remained strong because it was rigidly associated with Th2 clones in mice, whereas both Th1 and Th2 clones could secrete IL-10 in humans. However, as new Th1/Th2 cell functionalities emerged, anti-inflammatory action of IL-10 gained more attention than its inhibitory effect on Th1 cells, which may occur as an indirect consequence of suppression of APCs. This notion is also supported by the discovery of regulatory T cells, whose suppressor functions involve the mediation of IL-10, among other molecules. From this perspective, we discuss the functionalities of IL-10 by highlighting important differences between mice and humans with an emphasis on the Th1 and Th2 paradigm.

Influenza NG-34 T cell conserved epitope adjuvanted with CAF01 as a possible influenza vaccine candidate

Conserved epitopes are targets commonly researched to be part of universal vaccine candidates against influenza viruses (IV). These conserved epitopes need to be cross-protecting against distinct IV subtypes and to have a strong immunogenic potential. Nevertheless, subunit vaccines generally require a strong adjuvant to enhance their immunological effects. Herewith, we compare four different adjuvants differing in their immunological signatures that may enhance efficacy of a conserved hemagglutinin (HA)-epitope from IV, the NG-34, to define the most efficient combination of antigen/adjuvant to combat IV infections. Soluble NG-34 was mixed with adjuvants like aluminium hydroxide (AH) and AddaVax, known to induce Th2 and humoral responses; CAF01 which displays a biased Th1/Th17 profile and Diluvac Forte which augments the humoral response. Combinations were tested in different groups of mice which were subjected to immunological analyses. CAF01 + NG-34 induced a complete immune response with the highest IgG1, IgG2c titers and percentages of activated CD4 T cell promoting IFN-γ, IL-2 and TNF-α producing cells. Furthermore, in NG-34 stimulated mice splenocytes, cytokine levels of IFN-γ, IL-1β, IL-6, IL-10, IL-17 and TNF-α were also the highest in the CAF01 + NG-34 mouse group. This complete induced immune response covering the humoral and the cellular arms of the adaptive immunity promoted by CAF01 + NG-34 group suggests that CAF01 could be a good candidate as an adjuvant to combine with NG-34 for an efficacious vaccine against IV. However, more studies performed in IV hosts as well as studies with a challenge model are further required.

IL-10 producing regulatory and helper T-cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a highly heterogeneous autoimmune disease characterised by the production of pathogenic autoantibodies against nuclear self-antigens. The anti-inflammatory and tolerogenic cytokine Interleukin-10 appears to play a paradoxical pathogenic role in SLE and is therefore currently therapeutically targeted in clinical trials. It is generally assumed that the pathogenic effect of IL-10 in SLE is due to its growth and differentiation factor activity on autoreactive B-cells, but effects on other cells might also play a role. To date, a unique cellular source of pathogenic IL-10 in SLE has not been identified. In this review, we focus on the contribution of different CD4⁺T-cell subsets to IL-10 and autoantibody production in SLE. In particular, we discuss that IL-10 produced by different subsets of adaptive regulatory T-cells, follicular helper T-cells and extra-follicular B-helper T-cells is likely to have different effects on autoreactive B-cell responses. A better understanding of the role of IL-10 in B-cell responses and lupus would allow to identify the most promising therapies for individual SLE patients in the future.

Molecular regulation of peripheral B cells and their progeny in immunity

In this review, Boothby et al. summarize some salient advances toward elucidation of the molecular programming of the fate choices and function of B cells in the periphery. They also note unanswered questions that pertain to differences among subsets of B lymphocytes and plasma cells.

Mature B lymphocytes are crucial components of adaptive immunity, a system essential for the evolutionary fitness of mammals. Adaptive lymphocyte function requires an initially naïve cell to proliferate extensively and its progeny to have the capacity to assume a variety of fates. These include either terminal differentiation (the long-lived plasma cell) or metastable transcriptional reprogramming (germinal center and memory B cells). In this review, we focus principally on the regulation of differentiation and functional diversification of the “B2” subset. An overview is combined with an account of more recent advances, including initial work on mechanisms that eliminate DNA methylation and potential links between intracellular metabolites and chromatin editing.

Human Extrafollicular CD4+ Th Cells Help Memory B Cells Produce Igs

Follicular helper T (Tfh) cells are necessary for germinal center B cell maturation during primary immune responses; however, the T cells that promote humoral recall responses via memory B cells are less well defined. In this article, we characterize a human tonsillar CD4⁺ T cell subset with this function. These cells are similar to Tfh cells in terms of expression of the chemokine receptor CXCR5 and the inhibitory receptor PD-1, IL-21 secretion, and expression of the transcription factor BCL6; however, unlike Tfh cells that are located within the B cell follicle and germinal center, they reside at the border of the T cell zone and the B cell follicle in proximity to memory B cells, a position dictated by their unique chemokine receptor expression. They promote memory B cells to produce Abs via CD40L, IL-10, and IL-21. Our results reveal a unique extrafollicular CD4⁺ T cell subset in human tonsils, which specialize in promoting T cell-dependent humoral recall responses.

Interleukin-10 from CD4+ follicular regulatory T cells promotes the germinal center response

CD4⁺ follicular regulatory T (T_fr) cells suppress B cell responses through modulation of follicular helper T (T_fh) cells and germinal center (GC) development. We found that T_fr cells can also promote the GC response through provision of interleukin-10 (IL-10) after acute infection with lymphocytic choriomeningitis virus (LCMV). Sensing of IL-10 by B cells was necessary for optimal development of the GC response. GC B cells formed in the absence of T_reg cell-derived IL-10 displayed an altered dark zone state and decreased expression of the transcription factor Forkhead box protein 1 (FOXO1). IL-10 promoted nuclear translocation of FOXO1 in activated B cells. These data indicate that T_fr cells play a multifaceted role in the fine-tuning of the GC response and identify IL-10 as an important mediator by which T_fr cells support the GC reaction.

A Unique Subset of γδ T Cells Expands and Produces IL-10 in Patients with Naturally Acquired Immunity against Falciparum Malaria

Although expansions in γδ T cell populations are known to occur in the peripheral blood of patients infected with Plasmodium falciparum, the role of these cells in people with naturally acquired immunity against P. falciparum who live in malaria-endemic areas is poorly understood. We used a cross-sectional survey to investigate the role of peripheral blood γδ T cells in people living in Lao People's Democratic Republic, a malaria-endemic area. We found that the proportion of non-Vγ9 γδ T cells was higher in non-hospitalized uncomplicated falciparum malaria patients (UMPs) from this region. Notably, we found that the non-Vγ9 γδ T cells in the peripheral blood of UMPs and negative controls from this region had the potential to expand and produce IL-10 and interferon-γ when cultured in the presence of IL-2 and/or crude P. falciparum antigens for 10 days. Furthermore, these cells were associated with plasma interleukin 10 (IL-10), which was elevated in UMPs. This is the first report demonstrating that, in UMPs living in a malaria-endemic area, a γδ T cell subset, the non-Vγ9 γδT cells, expands and produces IL-10. These results contribute to understanding of the mechanisms of naturally acquired immunity against P. falciparum.

Influence of Plasma Cell Niche Factors on the Recruitment and Maintenance of IRF4hi Plasma Cells and Plasmablasts in Vaccinated, Simian Immunodeficiency Virus-Infected Rhesus Macaques with Low and High Viremia

In a recent study, we found that protection following simian immunodeficiency virus (SIV) exposure correlated with rectal plasma cell frequency in vaccinated female rhesus macaques. We sought to determine if the same macaques maintained high mucosal plasma cell frequencies postinfection and if this translated to reduced viremia. Although delayed SIV acquisition did not predict subsequent viral control, alterations existed in the distribution of plasma cells and plasmablasts between macaques that exhibited high or low viremia. Flow cytometric analysis of cells from rectal biopsy specimens, bone marrow, and mesenteric lymph nodes of vaccinated infected, unvaccinated infected, and uninfected macaques identified two main IRF4^hi subsets of interest: CD138⁺ plasma cells, and CD138^- plasmablasts. In rectal tissue, plasma cell frequency positively correlated with plasma viremia and unvaccinated macaques had increased plasma cells and plasmablasts compared to vaccinated animals. Likewise, plasmablast frequency in the mesenteric lymph node correlated with viremia. However, in bone marrow, plasmablast frequency negatively correlated with viremia. Accordingly, low-viremic macaques had a higher frequency of both bone marrow IRF4^hi subsets than did animals with high viremia. Significant reciprocal relationships between rectal and bone marrow plasmablasts suggested that efficient trafficking to the bone marrow as opposed to the rectal mucosa was linked to viral control. mRNA expression analysis of proteins involved in establishment of plasma cell niches in sorted bone marrow and rectal cell populations further supported this model and revealed differential mRNA expression patterns in these tissues.

IMPORTANCE

As key antibody producers, plasma cells and plasmablasts are critical components of vaccine-induced immunity to human immunodeficiency virus type 1 (HIV-1) in humans and SIV in the macaque model; however, few have attempted to examine the role of these cells in viral suppression postinfection. Our results suggest that plasmablast trafficking to and retention in the bone marrow play a previously unappreciated role in viral control and contrast the potential contribution of mucosal plasma cells to mediate protection at sites of infection with that of bone marrow plasmablasts and plasma cells to control viremia during chronic infection. Manipulation of niche factors influencing the distribution and maintenance of these critical antibody-secreting cells may serve as potential therapeutic targets to enhance antiviral responses postvaccination and postinfection.

Synergy of interleukin 10 and toll-like receptor 9 signalling in B cell proliferation: Implications for lymphoma pathogenesis

A network of autocrine and paracrine signals defines B cell homeostasis and is thought to be involved in transformation processes. Investigating interactions of these microenvironmental factors and their relation to proto-oncogenes as c-Myc (MYC) is fundamental to understand the biology of B cell lymphoma. Therefore, B cells with conditional MYC expression were stimulated with CD40L, insulin-like growth factor 1, α-IgM, Interleukin-10 (IL10) and CpG alone or in combination. The impact of forty different interventions on cell proliferation was investigated in MYC deprived cells and calculated by linear regression. Combination of CpG and IL10 led to a strong synergistic activation of cell proliferation (S-phase/doubling of total cell number) comparable to cells with high MYC expression. A synergistic up-regulation of CDK4, CDK6 and CCND3 expression by IL10 and CpG treatment was causal for this proliferative effect as shown by qRT-PCR analysis and inhibition of the CDK4/6 complex by PD0332991. Furthermore, treatment of stimulated MYC deprived cells with MLN120b, ACHP, Pyridone 6 or Ruxolitinib showed that IL10/CpG induced proliferation and CDK4 expression were JAK/STAT3 and IKK/NF-κB dependent. This was further supported by STAT3 and p65/RELA knockdown experiments, showing strongest effects on cell proliferation and CDK4 expression after double knockdown. Additionally, chromatin immunoprecipitation revealed a dual binding of STAT3 and p65 to the proximal promotor of CDK4 after IL10/CpG treatment. Therefore, the observed synergism of IL10R and TLR9 signalling was able to induce proliferation in a comparable way as aberrant MYC and might play a role in B cell homeostasis or transformation.

A Recombinant G Protein Plus Cyclosporine A-Based Respiratory Syncytial Virus Vaccine Elicits Humoral and Regulatory T Cell Responses against Infection without Vaccine-Enhanced Disease

Respiratory syncytial virus (RSV) infection can cause severe disease in the lower respiratory tract of infants and older people. Vaccination with a formalin-inactivated RSV vaccine (FI-RSV) and subsequent RSV infection has led to mild to severe pneumonia with two deaths among vaccinees. The vaccine-enhanced disease (VED) was recently demonstrated to be due to an elevated level of Th2 cell responses following loss of regulatory T (Treg) cells from the lungs. To induce high levels of neutralizing Abs and minimize pathogenic T cell responses, we developed a novel strategy of immunizing animals with a recombinant RSV G protein together with cyclosporine A. This novel vaccine induced not only a higher level of neutralizing Abs against RSV infection, but, most importantly, also significantly higher levels of Treg cells that suppressed VED in the lung after RSV infection. The induced responses provided protection against RSV challenge with no sign of pneumonia or bronchitis. Treg cell production of IL-10 was one of the key factors to suppress VED. These finding indicate that G protein plus cyclosporine A could be a promising vaccine against RSV infection in children and older people.

CD99 regulates CXCL12-induced chemotaxis of human plasma cells

Migration of plasma cells (PCs) is crucial for the control of PC survival and antibody production and is controlled by chemokines, most importantly by CXCL12. This study investigated the role of CD99 in CXCL12-induced PC migration. Among B cell subsets in the tonsils, CD99 expression was highest in PCs. CD99 expression increased during in vitro differentiation of germinal center B cells and was highest in PCs. CD99 engagement reduced chemotactic migration of PCs toward CXCL12 and reduced extracellular signal-regulated kinase (ERK) activation by CXCL12. An ERK inhibitor reduced CXCL12-mediated chemotactic migration, which suggests that ERK has a critical role in migration. CD99 engagement did not influence apoptosis, differentiation, or antibody secretion of PCs. We propose a novel role of CD99 in PCs that suppresses ERK activation and chemotactic migration of these cells.

Prednisone treatment inhibits the differentiation of B lymphocytes into plasma cells in MRL/MpSlac-lpr mice

AIM

A number of evidence shows that the differentiation of B lymphocytes into plasma cells plays an important role in lupus pathogenesis. In this study we investigated how prednisone, a classical therapeutic drug for autoimmune diseases, regulated plasma cell differentiation in MRL/MpSlac-lpr mice.

METHODS

MRL/lpr mice were treated with prednisone (2.5 or 5 mg·kg(-1)·d(-1), ig) for 13 weeks, and the proteinuria levels and survival times were monitored. After the mice were euthanized, blood sample, spleen and thymus were collected. The serum levels of anti-dsDNA antibody, anti-nuclear antibody, IL-21, and IL-10 were detected using ELISA kits. Subsets of splenic B and T lymphocytes were quantified with flow cytometry. Transcription factor Blimp-1 and Bcl-6 expression was determined using qPCR and Western blot.

RESULTS

Prednisone treatment dose-dependently attenuated the lupus symptoms in MRL/lpr mice with decreased proteinuria levels, prolonged survival times, decreased serum anti-nuclear antibody levels, and reduced spleen and thymus indices. Prednisone treatment also significantly decreased the elevated percentages of plasma cells and plasma cell precursors, decreased the percentages of activated T cells, and increased the frequency of CD4(+)CD62L(+) cells, demonstrated that decreased anti-nuclear antibodies and improvements in lupus symptoms were associated with decreased plasma cells. Furthermore, prednisone treatment decreased serum IL-21 and IL-10 levels and reduced the expression of splenic Blimp-1 and Bcl-6 (two key regulatory factors for plasma cell differentiation) in MRL/lpr mice.

CONCLUSION

Prednisone treatment restricts B lymphocyte differentiation into plasma cells in MRL/lpr mice, which may be correlated with the inhibition of IL-21 production and the restoration of the balance between Blimp-1 and Bcl-6.

Regulator of G protein signaling 1 suppresses CXCL12-mediated migration and AKT activation in RPMI 8226 human plasmacytoma cells and plasmablasts

Migration of plasma cells to the bone marrow is critical factor to humoral immunity and controlled by chemokines. Regulator of G protein signaling 1 (RGS1) is a GTPase-activating protein that controls various crucial functions such as migration. Here, we show that RGS1 controls the chemotactic migration of RPMI 8226 human plasmacytoma cells and human plasmablasts. LPS strongly increased RGS1 expression and retarded the migration of RPMI 8226 cells by suppressing CXCL12-mediated AKT activation. RGS1 knockdown by siRNA abolished the retardation of migration and AKT suppression by LPS. RGS1-dependent regulation of migration via AKT is also observed in cultured plasmablasts. We propose novel functions of RGS1 that suppress AKT activation and the migration of RPMI 8226 cells and plasmablasts in CXCL12-mediated chemotaxis.

Circulating CXCR5+CD4+helper T cells in systemic lupus erythematosus patients share phenotypic properties with germinal center follicular helper T cells and promote antibody production

OBJECTIVE

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies. Recently, a specific highly activated T helper cell subset, follicular helper T (Tfh) cell, has emerged as a key immunoregulator of germinal center (GC) formation and high-affinity antibody production. To identify the pathophysiological role of Tfh cells in SLE patients, we compared the phenotypic and functional properties of circulating Tfh-like cells in lupus patients to GC-Tfh cells, and correlated the percentage of Tfh-like cells with autoantibody production and SLE disease activity.

METHODS

Peripheral blood was collected from 29 lupus patients and 25 healthy controls. Tonsils were obtained surgically from non-SLE controls and used as a source of GC-Tfh cells. Tfh cells were defined by their signature surface markers (CXCR5, ICOS, CD57, PD-1 and BTLA) via flow cytometry. IL-21 expression levels from Tfh cells were measured by real-time PCR and intracellular staining. The function of Tfh cells was carried out by co-culture of Tfh cells and autologous B cells in vitro. IgG in the culture supernatant was detected by ELISA.

RESULTS

The frequency of circulating Tfh-like cells was significantly increased in SLE patients compared to healthy controls (p < 0.05). The Tfh-like cells not only display similar phenotypes and signature cytokines with GC-Tfh cells, but also are capable of driving B cells to differentiate into IgG-secreting plasma cells in vitro. In addition, the frequency of Tfh-like cells correlated positively with the percentage of circulating plasmablasts, levels of serum anti-dsDNA antibodies and ANA.

CONCLUSION

The accumulated circulating Tfh-like cells in lupus patients share phenotypic and functional properties with GC-Tfh cells. Tfh-like cells may serve as perpetuators in the pathogenesis of SLE by enhancing the self-reactive B cell clones to further differentiate into auto antibody-producing plasmablasts, and ultimately cause autoimmunity.

Factors regulating immunoglobulin production by normal and disease-associated plasma cells

Immunoglobulins are molecules produced by activated B cells and plasma cells in response to exposure to antigens. Upon antigen exposure, these molecules are secreted allowing the immune system to recognize and effectively respond to a myriad of pathogens. Immunoglobulin or antibody secreting cells are the mature form of B lymphocytes, which during their development undergo gene rearrangements and selection in the bone marrow ultimately leading to the generation of B cells, each expressing a single antigen-specific receptor/immunoglobulin molecule. Each individual immunoglobulin molecule has an affinity for a unique motif, or epitope, found on a given antigen. When presented with an antigen, activated B cells differentiate into either plasma cells (which secrete large amounts of antibody that is specific for the inducing antigen), or memory B cells (which are long-lived and elicit a stronger and faster response if the host is re-exposed to the same antigen). The secreted form of immunoglobulin, when bound to an antigen, serves as an effector molecule that directs other cells of the immune system to facilitate the neutralization of soluble antigen or the eradication of the antigen-expressing pathogen. This review will focus on the regulation of secreted immunoglobulin by long-lived normal or disease-associated plasma cells. Specifically, the focus will be on signaling and transcriptional events that regulate the development and homeostasis of long-lived immunoglobulin secreting plasma cells.

IL-21 acts as a promising therapeutic target in systemic lupus erythematosus by regulating plasma cell differentiation

Plasma cells, which secrete auto-antibodies, are considered to be the arch-criminal of autoimmune diseases such as systemic lupus erythematosus, but there are many cytokines involved in inducing the differentiation of B-cell subsets into plasma cells. Here, we emphasize IL-21, which has emerged as the most potent inducer of plasma cell differentiation. In this review, we focused on the promoting effects of IL-21 on plasma cell differentiation and discuss how these effects contribute to B cell-mediated autoimmune disease.

IL-21 promotes CD4 T cell responses by phosphatidylinositol 3-kinase-dependent upregulation of CD86 on B cells

The cytokine IL-21 is a potent immune modulator with diverse mechanisms of action on multiple cell types. IL-21 is in clinical use to promote tumor rejection and is an emerging target for neutralization in the setting of autoimmunity. Despite its clinical potential, the biological actions of IL-21 are not yet fully understood and the full range of effects of this pleiotropic cytokine are still being uncovered. In this study, we identify a novel role for IL-21 as an inducer of the costimulatory ligand CD86 on B lymphocytes. CD86 provides critical signals through T cell-expressed CD28 that promote T cell activation in response to Ag engagement. Expression levels of CD86 are tightly regulated in vivo, being actively decreased by regulatory T cells and increased in response to pathogen-derived signals. In this study, we demonstrate that IL-21 can trigger potent and sustained CD86 upregulation through a STAT3 and PI3K-dependent mechanism. We show that elevated CD86 expression has functional consequences for the magnitude of CD4 T cell responses both in vitro and in vivo. These data pinpoint CD86 upregulation as an additional mechanism by which IL-21 can elicit immunomodulatory effects.

B-cell targeted therapeutics in clinical development

B lymphocytes are the source of humoral immunity and are thus a critical component of the adaptive immune system. However, B cells can also be pathogenic and the origin of disease. Deregulated B-cell function has been implicated in several autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis. B cells contribute to pathological immune responses through the secretion of cytokines, costimulation of T cells, antigen presentation, and the production of autoantibodies. DNA-and RNA-containing immune complexes can also induce the production of type I interferons, which further promotes the inflammatory response. B-cell depletion with the CD20 antibody rituximab has provided clinical proof of concept that targeting B cells and the humoral response can result in significant benefit to patients. Consequently, the interest in B-cell targeted therapies has greatly increased in recent years and a number of new biologics exploiting various mechanisms are now in clinical development. This review provides an overview on current developments in the area of B-cell targeted therapies by describing molecules and subpopulations that currently offer themselves as therapeutic targets, the different strategies to target B cells currently under investigation as well as an update on the status of novel therapeutics in clinical development. Emerging data from clinical trials are providing critical insight regarding the role of B cells and autoantibodies in various autoimmune conditions and will guide the development of more efficacious therapeutics and better patient selection.

CD9 is a novel marker for plasma cell precursors in human germinal centers

The germinal center (GC) is the dynamic microenvironment where Ag-activated B cells rapidly expand and differentiate, generating plasma cells (PC) that produce high affinity antibodies. B cells within the GC have great heterogeneity, containing B cells at different stages of activation and differentiation. However, there are few surface markers that allow subsets of GC-B cells to be distinguished. In the present study, we show that GC-B cells in human tonsils contain two distinct populations regarding CD9 expression; CD9- and CD9+ cells. CD9+ GC-B cells are functionally more differentiated towards PC based upon the following evidence; (1) CD9+ cells express higher levels of PC transcription factor, Blimp-1 while lower levels of B cell transcription factors, Bcl-6 and Pax-5, compared to CD9- cells, (2) CD9+ cells differentiate into plasmablasts faster than CD9- cells in the presence of cytokines that generate PC, and (3) CD9 expression was induced in CD9- GC-B cells under PC generating condition and gradually increased in the course of PC differentiation. Taken together, our data suggest that CD9 is a novel marker for a human GC-B cell subset that is committed to PC lineage.

Long-lived memory B-cell responses following BCG vaccination

The role of T-cells in immunity against Mycobacterium tuberculosis (M. tuberculosis) infection has been extensively studied, however, that of B-cells still remains comparatively unexplored. In this study, we determined the presence and frequencies of mycobacteria-specific memory B-cells (MBCs) in peripheral blood from clinically healthy, Bacillus Calmette Guerin (BCG) vaccinated (n = 79) and unvaccinated (n = 14) donors. Purified protein derivative (PPD)-specific MBCs were present in most donors (both vaccinated and unvaccinated) but their frequencies were significantly higher in vaccinated than in unvaccinated donors. MBCs specific for other mycobacterial antigens [antigen-85A (Ag85A), antigen-85B (Ag85B), 6 kDalton early secretory antigenic target (ESAT-6) and the 10 kDalton-culture filtrate protein (CFP-10)] were less prevalent than those recognising PPD. Furthermore, PPD-specific MBCs were detected in BCG vaccinated donors without ESAT-6 and CFP-10 specific responses. Together, these results indicate that BCG vaccination induces long-lived MBC responses. Similar patterns of response were seen when we examined mycobacteria-specific antibody and T-cell responses in these donors. Our data show for the first time that BCG vaccination elicits long-lived mycobacteria-specific MBC responses in healthy individuals, suggesting a more substantial role of B-cells in the response to BCG and other mycobacterial infections than previously thought.

High efficiency human memory B cell assay and its application to studying Plasmodium falciparum-specific memory B cells in natural infections

Memory B cells (MBCs) are a key component of long term humoral immunity to many human infectious diseases. Despite their importance, we know little about the generation or maintenance of antigen-(Ag)-specific MBCs in humans in response to infection. A frequently employed method for quantifying Ag-specific MBCs in human peripheral blood (Crotty et al., 2004) relies on the ability of MBCs but not naïve B cells to differentiate into antibody secreting cells (ASCs) in response to polyclonal activators and Toll-like receptor agonists in vitro and the measurement of Ag-specific ASCs by ELISPOT assays. Here we report on studies to optimize the efficiency of this ELISPOT-based assay and to apply this assay to the detection of Plasmodium falciparum (Pf)-specific MBCs in adults living in a malaria endemic area where immunity to Pf is acquired through natural infection. We show that the addition of IL-10 to in vitro cultures of human peripheral blood mononuclear cells increased the efficiency of the assay from 10% to over 90% without increasing the ASC burst size and without any substantial increase in background from naïve B cells or plasma cells (PCs). Using this assay we were able to quantify the frequency of Pf-specific MBCs in peripheral blood of adults living in a malaria endemic area. Thus, this highly efficient assay appears to be well suited to field studies of the generation and maintenance of MBCs where the volumes of blood obtainable are often limiting.

Macrophages, rather than T and B cells are principal immunostimulatory target cells of Lycium barbarum L. polysaccharide LBPF4-OL

AIM OF THE STUDY

Lycium barbarum L. is a renowned Yin strengthening agent in traditional Chinese medicine. Lycium barbarum L. polysaccharide-protein complex is well-known for its immunoregulatory and antitumor effects. LBPF4-OL is the glycan part of Lycium barbarum L. polysaccharide-protein complex fraction 4 (LBPF4). LBPF4-OL's active contribution in LBPF4 is still blank. In the study, we enrich the polysaccharide part of Lycium barbarum L. polysaccharide-protein complex, and investigate its immunostimulatory effects on mouse spleen cells, T cells, B cells and macrophages.

MATERIALS AND METHODS

Balb/C mice were used in vitro and in vivo studies. In in vitro study, lymphocyte proliferations were analyzed with (3)H-TdR incorporation method. Miltenyi MicroBeads were used in the purification of lymphocytes. Activation of T and B cells was analyzed by flow cytometry. In order to obtain the peritoneal macrophages, mice were injected i.p. with 1mL of sodium thioglycollate 3 days prior to killing. Spleen cells were stimulated with LBPF4-OL and cytokine concentrations in the supernatants were determined by multiplex bead analysis. In in vivo study, mice were injected i.p. with 1 mL of normal saline or 100 μg/mL LBPF4-OL daily for 6 days. Peritoneal macrophage functions were analyzed by enzyme-linked immunosorbent assay and flow cytometry assay.

RESULTS

Spleen cells and lymphocyte proliferation assay indicated that LBPF4-OL markedly induced the spleen cell proliferation, but could not induce proliferation of purified T and B lymphocytes. Further research revealed that B cell proliferation took place in the presence of activated macrophages or LPS. Multiplex bead analysis showed that LBPF4-OL can obviously induce IL-6, IL-8, IL-10 and TNF-α production of the spleen cells in a concentration-dependent manner. Flow cytometric analysis showed that LBPF4-OL (i.p.) prompts CD86 and MHC-II molecules expression on macrophages. ELISA assay showed that LBPF4-OL can greatly strengthen macrophage releasing of TNF-α and IL-1β.

CONCLUSION

These results suggested that glycan LBPF4-OL plays an important role in the immunopharmacological activity of Lycium barbarum L. polysaccharide-protein complex, and primary mouse macrophages, rather than T and B cells, are the principal target cells of it.

ZEB1 and CtBP form a repressive complex at a distal promoter element of the BCL6 locus

BCL6 is essential for normal antibody responses and is highly expressed in germinal centre B-cells. Constitutive expression due to chromosomal translocations or mutations of cis-acting regulatory elements contributes to diffuse large B-cell lymphoma. BCL6 expression is therefore tightly regulated in a lineage- and developmental-stage-specific manner, and disruption of normal controls can contribute to lymphomagenesis. In order to discover potential cis-acting control regions we carried out DNase I-hypersensitive site mapping. Gel-shift assays and chromatin immunoprecipitation of the core region of a hypersensitive site 4.4 kb upstream of BCL6 transcription initiation (HSS-4.4) showed an E-box element-binding ZEB1 (zinc finger E-boxbinding homeobox 1) and the co-repressor CtBP (C-terminal binding protein). As compared with peripheral blood B-cells, ZEB1, a two-handed zinc finger transcriptional repressor, is expressed at relatively low levels in germinal centre cells, whereas BCL6 has the opposite pattern of expression. Transfection of ZEB1 cDNA caused a reduction in BCL6 expression and a mutated ZEB1, incapable of binding CtBP, lacked this effect. siRNA (small interfering RNA)-mediated knockdown of ZEB1 or CtBP produced an increase in BCL6 mRNA. We propose that HSS-4.4 is a distal promoter element binding a repressive complex consisting of ZEB1 and CtBP. CtBP is ubiquitously expressed and the results of the present study suggest that regulation of ZEB1 is required for control of BCL6 expression.