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Anti-citrullinated protein antibodies (ACPAs) are involved in the pathogenesis of rheumatoid arthritis. N-glycosylation pattern of ACPA-IgG and healthy IgG Fc differs. The aim of this study is to determine the relative sialylation and galactosylation level of ACPAs and control IgG to assess their capability of inducing TNFα production, and furthermore, to analyze the correlations between the composition of Fc glycans and inflammatory markers in RA. We isolated IgG from sera of healthy volunteers and RA patients, and purified ACPAs on a citrulline-peptide column. Immunocomplexes (IC) were formed by adding an F(ab)2 fragment of anti-human IgG. U937 cells were used to monitor the binding of IC to FcγR and to trigger TNFα release determined by ELISA. To analyze glycan profiles, control IgG and ACPA-IgG were digested with trypsin and the glycosylation patterns of glycopeptides were analyzed by determining site-specific N-glycosylation using nano-UHPLC-MS/MS. We found that both sialylation and galactosylation levels of ACPA-IgG negatively correlate with inflammation-related parameters such as CRP, ESR, and RF. Functional assays show that dimerized ACPA-IgG significantly enhances TNFα release in an FcγRI-dependent manner, whereas healthy IgG does not. TNFα production inversely correlates with the relative intensities of the G0 glycoform, which lacks galactose and terminal sialic acid moieties.

Autoimmune diseases are caused by breaking the central and/or peripheral tolerance against self, leading to uncontrolled immune response to autoantigens. The incidences of autoimmune diseases have increased significantly worldwide over the last decades; nearly 5% of the world's population is affected. The current treatments aim to reduce pain and inflammation to prevent organ damage and have a general immunosuppressive effect, but they cannot cure the disease. There is a huge unmet need for autoantigen-specific therapy, without affecting the immune response against pathogens. This goal can be achieved by targeting autoantigen-specific T or B cells and by restoring self-tolerance by inducing tolerogenic antigen-presenting cells (APC) and the development of regulatory T (Treg) cells, for example, by using autoantigenic peptides bound to nanoparticles. Transferring in vitro manipulated autologous tolerogenic APC or autologous autoantigen-specific Treg cells to patients is the promising approach to develop cellular therapeutics. Most recently, chimeric autoantibody receptor T cells have been designed to specifically deplete autoreactive B cells. Limitations of these novel autoantigen-specific therapies will also be discussed.

The main goal of antigen-specific immunotherapy (ASI) in autoimmune and rheumatic diseases is to reprogramme or remove autoreactive cells and/or induce immune tolerance to self-antigens. Current therapies in these diseases either treat symptoms or slow down disease progression but are not yet curative or preventative - disease-specific treatments are urgently needed. In contrast to the nonspecific treatments in current use that induce generalized immune suppression, which is associated with several adverse effects including increased risk of infections, ASIs target a restricted subset of B cells or T cells, and thus do not compromise systemic immunity and host defence. This Review provides a summary of novel approaches for identifying autoepitopes and detecting and targeting autoreactive cells that might help in the development of ASIs. Promising approaches include the use of tolerizing peptides coupled to MHC constructs and/or nanocompounds, tolerizing dendritic cells and antigen-specific vaccines. Following studies in animal models of rheumatoid arthritis and systemic lupus erythematosus, several of these strategies have now entered clinical trials. However, to use these approaches in humans, several important limitations must first be addressed, such as; selecting the proper immunodominant autoantigen; identifying the optimal timing, dosing and route of administration; finding biomarkers for monitoring the therapy; and optimizing methodology.

In mice, marginal zone (MZ) B cells are found principally in the MZ of the spleen and characterized as CD23-negative cells, primarily express polyreactive BCRs, high levels of complement receptor-2 and TLRs. Collagen-induced arthritis (CIA) is a commonly used animal model of human rheumatoid arthritis, considered as a Th1-mediated disease. Although the importance of MZ B cells in the initiation of CIA is well established, their role in remission is unexplored. Besides, playing a central role in Th1 cell development, T-box transcription factor (T-bet) has important functions in B cells. T-bet is regulated by IFN-γ and through the BCR and TLR9, the signals that have an impact on regulatory IL-10 production. In this work, we aimed to analyze the contribution of T-bet to the function of IL-10-positive MZ B cells. We demonstrate that during the remission phase of CIA, MZ B cells express an elevated level of T-bet and confirm the existence of IL-10/T-bet coexpressing cells. Moreover, we show that T-bet-expressing MZ B cells migrate toward CXCR3 ligand and secrete IL-10 by inflammatory stimuli. Our data suggest that T-bet might contribute to the remission of CIA by facilitating the regulatory potential of IL-10-positive MZ B cells.

IL-10 is a suppressive cytokine that has been implicated in the pathophysiology of autoimmune disorders and can be produced by different cell types such as regulatory B-cells. Our previous work showed that under inflammatory condition MZ B-cells differentiated into IL-10 producing cells and contributed to the downregulation of collagen-induced arthritis, while follicular B-cells failed to do so. Based on these observations, we aimed to investigate how inflammatory signals mediated through the BCR, TLR9 and IFN-γ receptors trigger IL-10 production in MZ B-cells but leave FO B-cells unresponsive. We particularly focused on the CREB transcription factor as it is involved in all three signalling cascades and analysed its contribution to IL-10 production. Our results demonstrate that the IL-10 production of MZ B-cells induced by the BCR, TLR9 and IFN-γ receptors is mediated by CREB. We showed that the activation of CREB is prolonged in MZ B-cells while the transcription factor only transiently phosphorylated in FO B-cells. The sustained phosphorylation of CREB is clearly associated with its prolonged binding to molecular partner CBP, whereas inhibition of their association decreased IL-10 production. We assume that sustained activation of CREB is required for IL-10 production by B-cells under inflammatory conditions.

Background: In rheumatoid arthritis (RA), anti-citrullinated protein/peptide antibodies (ACPAs) are responsible for disease onset and progression, however, our knowledge is limited on ligand binding affinities of autoantibodies with different citrulline-peptide specificity. Methods: Citrulline-peptide specific ACPA IgGs were affinity purified and tested by ELISA. Binding affinities of ACPA IgGs and serum antibodies were compared by surface plasmon resonance (SPR) analysis. Bifunctional nanoparticles harboring a multi-epitope citrulline-peptide and a complement activating peptide were used to induce selective depletion of ACPA producing B cells. Results: KD values of affinity purified ACPA IgGs varies between 10-6-10-8 M and inversely correlate with disease activity. Based on their cross-reaction with citrulline-peptides we designed a novel multi-epitope peptide, containing Cit-Gly and Ala-Cit motifs in two-two copies, separated with a short, neutral spacer. This peptide detects antibodies in RA sera with 66 % sensitivity and 98 % specificity in ELISA and is recognized by 90% of RA sera, while none of the healthy samples in SPR. When coupled to nanoparticles, the multi-epitope peptide specifically targets and depletes ACPA producing B cells ex vivo. Conclusions: The unique multi-epitope peptide designed on the basis of ACPA cross-reactivity might be suitable to develop better diagnostics and novel therapies for RA.

Immune challenge alters neural functioning via cytokine production. Inflammation has profound impact on the central regulation of fertility, but the mechanisms involved are not clearly defined. The anti-inflammatory cytokine interleukin (IL)-10 is responsible for balancing the immune response in the brain. To examine whether IL-10 has an effect on the function of the gonadotropin-releasing hormone (GnRH) neurons, we first examined the effect of immune responses with distinct cytokine profiles, such as the T cell-dependent (TD) and T cell-independent (TI) B-cell response. We investigated the effect of the TD and TI immune responses on ERK1/2 phosphorylation in GnRH neurons by administering fluorescein isothiocyanate/keyhole limpet hemocyanin (KLH-FITC) or dextran-FITC to female mice. Although dextran-FITC had no effect, KLH-FITC induced ERK1/2 phosphorylation in GnRH neurons after 6 d. KLH-FITC treatment increased the levels of IL-10 in the hypothalamus (HYP), but this treatment did not cause lymphocyte infiltration or an increase in the levels of proinflammatory cytokines. In IL-10 knock-out (KO) mice, KLH-FITC-induced ERK1/2 phosphorylation in the GnRH neurons was absent. We also showed that in IL-10 KO mice, the estrous cycle was disrupted. Perforated patch-clamp recordings from GnRH-GFP neurons, IL-10 immunohistochemistry, and in vitro experiments on acute brain slices revealed that IL-10 can directly alter GnRH neuron firing and induce ERK1/2 phosphorylation. These observations demonstrate that IL-10 plays a role in influencing signaling of GnRH neurons in the TD immune response. These results also provide the first evidence that IL-10 can directly alter the function of GnRH neurons and may help the maintenance of the integrity of the estrous cycle.

Background: In rheumatoid arthritis (RA), anti-citrullinated protein/peptide antibodies (ACPAs) are responsible for disease onset and progression, however, our knowledge is limited on ligand binding affinities of autoantibodies with different citrulline-peptide specificity. Methods: Citrulline-peptide-specific ACPA IgGs were affinity purified and tested by ELISA. Binding affinities of ACPA IgGs and serum antibodies were compared by surface plasmon resonance (SPR) analysis. Bifunctional nanoparticles harboring a multi-epitope citrulline-peptide and a complement-activating peptide were used to induce selective depletion of ACPA-producing B cells. Results: KD values of affinity-purified ACPA IgGs varied between 10−6 and 10−8 M and inversely correlated with disease activity. Based on their cross-reaction with citrulline-peptides, we designed a novel multi-epitope peptide, containing Cit-Gly and Ala-Cit motifs in two–two copies, separated with a short, neutral spacer. This peptide detected antibodies in RA sera with 66% sensitivity and 98% specificity in ELISA and was recognized by 90% of RA sera, while none of the healthy samples in SPR. When coupled to nanoparticles, the multi-epitope peptide specifically targeted and depleted ACPA-producing B cells ex vivo. Conclusions: The unique multi-epitope peptide designed based on ACPA cross-reactivity might be suitable to develop better diagnostics and novel therapies for RA.

Cytokines, including tumor necrosis factor alpha (TNFα) are involved in Rheumatoid arthritis (RA) pathogenesis by augmenting autoimmunity, sustaining long term inflammation in the synovium, and promoting joint damage. Anti-TNF therapy is one of the most efficient and widely used therapies for RA, although its mechanism is not clarified yet. Earlier we demonstrated that RA patients have a reduced number of IL-10 producing regulatory B cells (B10 cells) as compared to healthy individuals and they are functionally impaired. Our aim was to study the influence of anti-TNF therapy on B10 cells in RA, to follow the alteration of B cell activation markers (CD25, CD69) and to monitor the level of citrullinated peptid-specific antibodies and the secreted IL-10 in patients' sera during the therapy. We have observed that at six month after starting the therapy the frequency of B10 cells remarkably increased, while the expression of the activation marker, CD69 decreased on B cells. In contrast, serum levels of IL-10 and anti-citrullinated peptide antibodies did not change post-treatment. Conclusion The reduced activation state of B cells and the increasing number of regulatory B10. cells might contribute to the therapeutic efficacy of anti-TNF agents in RA.

The most important feature of B cells is the production of Abs upon activation; additionally, B cells produce pro- and anti-inflammatory cytokines in response to certain stimuli. IL-10–producing B cells represent a major subset of regulatory B cells (Bregs) that suppress autoimmune and inflammatory responses. B cells play a crucial role in the development and maintenance of the chronic inflammatory autoimmune disease rheumatoid arthritis (RA); however, controversial data are available on IL-10– producing Bregs in RA. Our aim was to identify the optimal conditions that induce IL-10+ Bregs and, furthermore, to shed light on the signaling pathways that are responsible for their expansion. The results show that dual stimulation by CpG and CD40L for 48 h is optimal for IL-10 induction, and this can be synergistically boosted by IL-21. We identified the CD19+CD27+ memory B cell population as the major source of IL-10+ Bregs. We detected significantly fewer CD19+CD27+IL-10+ cells in RA patients compared with healthy controls, and these were functionally defective in suppressing IFN-γ production by CD4+ T cells in coculture. IL-21 drastically increased the number of IL-10+ Bregs within the CD19+CD27+ and CD19+CD27− populations; furthermore, it induced the appearance of IL-10+Blimp-1+ plasmablasts. Monitoring the phosphorylation of key signaling molecules revealed that activation of ERK, p38, and CREB is indispensable for the induction of IL-10 production, whereas phosphorylation of STAT3 further enhances IL-10 expression in human Bregs. We conclude that CREB and STAT3 are the key transcription factors responsible for the expansion and differentiation of human IL-10–producing Bregs.

Background: Autoreactive B cells are crucial players in the pathogenesis of rheumatoid arthritis (RA). Autoantibodies specific for citrullinated proteins (ACPA), present in the serum of approximately 60-70 % of patients, have a pathogenic role in the disease. B cell depleting therapies may result in a transient immunosuppression, increasing the risk of infections. Our aim was to develop a new therapeutic approach to selectively deplete the ACPA producing autoreactive B cells. Methods: To target B cells synthetic citrullinated peptide derived from the beta chain of fibrin, beta 60-74Cit(60,72,74) (beta 60-74Cit), the predominant epitope recognized by ACPA was used. Complement dependent cytotoxicity (CDC) was induced by a modified peptide derived from gp120 of HIV-1. To trigger CDC both the targeting peptide and the complement activating peptide were covalently coupled in multiple copies to the surface of poly (DL-lactic-co-glycolic acid) nanoparticles (NPs). Ex vivo antibody synthesis was examined by ELISA and ELISpot. CDC was tested after dead cell staining by flow cytometry. Results: The beta 60-74Cit peptide was selectively recognized by a small subset of B cells from RA patients having high level of peptide specific serum antibody, suggesting that the peptide can target diseased B cells. The modified gp120 peptide covalently coupled to NPs induced the formation of the complement membrane attack complex, C5b-9 in human serum. We show here for the first time that bifunctional NPs coupled to multiple copies of both the targeting peptide and the complement activating effector peptide on their surface significantly reduce beta 60-74Cit peptide specific ex vivo ACPA production, by inducing complement dependent lysis of the citrullinated peptide specific B cells of seropositive RA patients. Conclusions: Bifunctional NPs covalently coupled to autoantigen epitope peptide and to a lytic peptide activating complement may specifically target and deplete the peptide specific autoreactive B-cells.

Enzyme-linked immunosorbent assay (ELISA) is an invaluable diagnostic tool to detect serum autoantibody binding to target antigen. To map the autoantigenic epitope(s), overlapping synthetic peptides covering the total sequence of a protein antigen are used. A large set of peptides synthesized on the crown of pins can be tested by Multipin ELISA for fast screening. Next, to validate the results, the candidate epitope peptides are resynthesized by solid-phase synthesis, coupled to ELISA plate directly, or in a biotinylated form, bound to neutravidin-coated surface and the binding of autoantibodies from patients' sera is tested by indirect ELISA. Further, selected epitope peptides can be applied in enzyme-linked immunospot assay to distinguish individual, citrullinated peptide-specific autoreactive B cells in a pre-stimulated culture of patients' lymphocytes.

Background and objectives The most important feature of B-cells is the production antibodies upon activation; additionally, B-cells produce both pro-inflammatory and anti-inflammatory cytokines in response to certain stimuli. IL-10 producing B10 cells represent a major subset of regulatory B-cells (Bregs). Bregs suppress autoimmune and inflammatory responses by multiple mechanisms. B-cells play crucial role in the development and maintenance of the chronic inflammatory autoimmune disease, Rheumatoid arthritis (RA); however, controversial data are available on B10 population in RA. Our aim was to identify the optimal conditions inducing B10 cells in samples from healthy controls and RA patients; furthermore, to shed light on signalling pathways resulting in the expansion of the B10 subset. Materials and methods Peripheral blood mononuclear cells (PBMC) were isolated from heparinized blood of healthy donors and RA patients. B cells were purified by magnetic separation, using negative selection. We assessed IL-10 and TNF expressing B-cells after intracellular staining by flow cytometry, and measured the secreted cytokines with multiplex bead array. Phosphorylation of key signalling molecules was monitored by phospho-flow method. Results The results show that dual stimulation by CpG and CD40L for 48h was optimal for IL-10 induction, which was synergistically boosted by IL-21. We identified CD19 + CD27 + memory B-cells as the major source of B10 cells. IL-21 increased the ratio of BLIMP1 and IL-10 double positive plasmablasts. In RA patients we detected significantly less CD27 + B10 cells as compared to the controls, while addition of IL-21 to the dual stimuli significantly elevated the number of B10 cells both in the CD19 + CD27 + and in the CD19 + CD27 - population. Different combinations of stimuli induced preferentially the secretion of pro-inflammatory cytokines (TNF, IFNγ, IL-17) and the suppressor cytokine, IL-10. We assumed that activation of ERK, p38 and CREB are indispensable to induce IL-10, while STAT3 appears to be a co-activator for IL-10 transcription in human Bregs. Conclusions CD19 + CD27 + memory B-cells are the major source of human B10 cells, which may expand and differentiate to IL-10 producing plasmablasts in the presence of IL-21. CREB and the co-activator STAT3 are the key transcription factors responsible for the expansion of the B10 population. Support: National Research, Development and Innovation Office (OTKA104846), and ELTE TAMOP 4.2.1./B-09/1/KMR-2010–0003

Background and objectives Anti-citrullinated peptide/protein antibodies (ACPA) have diagnostic significance and a pathological role in rheumatoid arthritis (RA). Multiple specificities of ACPA have been described, targeting various proteins such as filaggrin, fibrin, vimentin, collagen, enolase and some citrullinated peptides of Epstein-Barr virus nuclear antigen (EBNA) as well. Specificities as well as affinities of ACPA may influence its ability to trigger inflammatory cytokine production, modifying local and systemic inflammation in patients. Therefore we compared binding affinities of serum samples from 60 RA patients to citrullinated 19mer filaggrin peptide. Materials and methods The peptide specific IgG was affinity purified from sera of RA patients on insolubilized citrullinated peptides derived from filaggrin, fibrin, collagen, and vimentin. Peptide specific IgG concentrations in sera were calculated by ELISA, using a calibration curve prepared from the affinity purified IgG. Binding affinities of IgG and serum samples were tested on citrullinated peptide covalently coupled to the surface of ProteOn XPR36 GLH sensor chip. The 1:1 binding model was employed to calculate the apparent affinity constant, K D . Results 26 of the 60 serum samples have shown measurable binding affinity to citrullinated filaggrin peptide with K D values between 10 –5 –10 –7 M. In general, individual sera showing multiple specificities to citrullinated peptides in ELISA possess a higher K D to filaggrin peptide. An inverse correlation was observed between disease severity (DAS28 index) and binding affinities. Surprisingly, high degree of cross-reactivity was detected between affinity purified IgGs specific for citrullinated filaggrin, fibrin, vimentin and collagen. Conclusions Biosensor analysis has shown that ACPA are very heterogeneous regarding both specificities and affinities, furthermore, the affinity purified IgGs from individual ACPA are highly cross-reactive. Support: National Research, Development and Innovation Office (OTKA104846) and ELTE KMOP-4.2.1/B-10–2011–0002

Scientific background A functionally important subset of B cells, known as regulatory B cells (Breg), are specialised to control immune response and immunological diseases such as autoimmunity. Breg cells are best characterised by their inducible production of IL-10 and can appear in different phenotypic forms. Various activation signals, including Toll-like receptors (TLRs), B cell antigen receptor (BCR) or CD40 stimulation can trigger the regulatory transformation of B cells, although it is not clear which of these signals are the most effective and which B cells have the most susceptible phenotype. We have studied the effect of the BCR and TLR9 stimulation on three populations of B cells in mouse spleen (Transitional-2-Marginal Zone Precursors (T2-MZP), Marginal Zone (MZ) and Follicular (FO) B cells) to induce differentiation into Bregs. Materials and methods We set up in vitro cultures using sorted B cells from T2-MZP, MZ or FO pools from the spleen of adult mice and stimulated them via the BCR and/or TLR9. The transformation to Breg was monitored by following IL-10 production using gene expression analysis, IL-10-specific ELISA or intracellular IL-10 staining measured by FACS. Results Based on our experimental set up, we found that the BCR signal alone was not sufficient to induce IL-10 production, while TLR9 stimulation mediated the regulatory transformation of all B cell types with different extent. Comparing the three populations, we found that B cells from the marginal zone responded more efficiently for TLR9 stimulation. We detected the highest level of secreted IL-10 and the highest number of induced IL-10 positive cells among MZ B cells. The results at protein level were confirmed by gene expression analysis, additionally, at mRNA level a time-dependent synergistic crosstalk through the BCR and TLR9 was observed. Conclusion We concluded that MZ B cells were the most inducible B cell population and TLR9 signal alone was efficient to trigger IL-10 production. Using the most sensitive B cell population with the efficient stimulus will help us to study the signalling characteristics of Bregs and their important role in autoimmune diseases. This project was supported by OTKA NK 104846 and by the Janos Bolyai Research Scholarship of the Hungarian Academy of Sciences.

Background Regulatory B cells (Breg) are newly defined B cell subsets that downregulate the immune response. The pleiotrophic cytokine, IL-10 seemed to be responsible for this function. B cells play a crucial role in the development and maintenance of Rheumatoid arthritis (RA). Therefore this study was undertaken to identify the optimal stimuli (BCR, CpG, CD40L) that induce Breg cells, furthermore, our aim was to compare the number of Breg in RA patients and healthy controls. We also aimed to examine, which inflammatory cytokines are produced by B cells in response to the same stimuli. Materials and methods Blood samples were collected from healthy donors and RA patients. Intracellular IL-6, IL-10 and TNF were measured in purified B cells and in PBMC. Cytokines were detected in B cells prior or after stimulation by intracellular fluorescent staining using specific antibodies. IL-10, IL-6, TNF, IL-1b and INFg were measured in the supernatants of purified B cell with FlowCytomix multiplex bead array. Results At our experimental conditions, dual stimulation by CpG and CD40L for 48 h was found to be optimal for IL-10 induction in B cells. We identified CD19 + CD27 + memory B cells as the main source of IL-10. The dual stimuli induced significantly lower number of IL-10 producing B cells from RA patients as compared to healthy controls, while we didn’t find a difference in the inflammatory cytokine (IL-6 and TNF) production. However, in unstimulated samples the frequency of IL-6 producing B cells was lower in healthy controls, than in RA patients. Furthermore, we observed that in the supernatant of purified B cells, beside IL-10, other inflammatory cytokines (IL-6, TNF, IL-1b and INFg) were also present. Therefore we double stained B cells with anti-IL-10 and anti-TNF antibodies and found that these cytokines were produced by different subsets. Conclusion We detected a significant difference between the number of IL-10 producing CD27 + Breg cells of RA patients and healthy controls. The lower frequency of activation-induced IL-10 producing Bregs and on the other hand, the increased ratio of spontaneously IL-6 secreting B cells in RA patients may contribute to the exacerbation of the disease. Support: OTKA NK 104846