Objective Gut-residing bacteria, such as Escherichia coli, can acetylate their proteome under conditions of amine starvation. It is postulated that the (gut) microbiome is involved in the breach of immune tolerance to modified self-proteins leading to the anti-modified protein antibodies (AMPAs), hallmarking seropositive rheumatoid arthritis (RA). Our aim was to determine whether acetylated bacterial proteins can induce AMPA responses cross-reactive to modified self-proteins and be recognised by human AMPA (hAMPA).Methods E. coli bacteria were grown under amine starvation to generate endogenously acetylated bacterial proteins. Furthermore, E. coli proteins were acetylated chemically. Recognition of these proteins by hAMPA was analysed by western blotting and ELISA; recognition by B cells carrying a modified protein-reactive B cell receptor (BCR) was analysed by pSyk (Syk phosphorylation) activation assay. C57BL/6 mice were immunised with (modified) bacterial protein fractions, and sera were analysed by ELISA.Results Chemically modified bacterial protein fractions contained high levels of acetylated proteins and were readily recognised by hAMPA and able to activate B cells carrying modified protein-reactive BCRs. Likely due to substantially lower levels of acetylation, endogenously acetylated protein fractions were not recognised by hAMPA or hAMPA-expressing B cells. Immunising mice with chemically modified protein fractions induced a strong cross-reactive AMPA response, targeting various modified antigens including citrullinated proteins.Conclusions Acetylated bacterial proteins are recognisable by hAMPA and are capable of inducing cross-reactive AMPA in mice. These observations provide the first conceptual evidence for a novel mechanism involving the (endogenous) acetylation of the bacterial proteome, allowing a breach of tolerance to modified proteins and the formation of cross-reactive AMPA.

Abs can be glycosylated in both their Fc and Fab regions with marked effects on Ab function and binding. High levels of IgG Fab glycosylation are associated with malignant and autoimmune conditions, exemplified by rheumatoid arthritis and highly Fab-glycosylated (∼90%) anti-citrullinated protein Abs (ACPAs). Important properties of IgG, such as long half-life and placental transport, are facilitated by the human neonatal Fc receptor (hFcRn). Although it is known that glycosylation of Abs can affect binding to Fc receptors, little is known on the impact of IgG Fab glycosylation on hFcRn binding and transplacental transport. Therefore, we analyzed the interaction between hFcRn and IgG with and without Fab glycans in vitro with various methods as well as in vivo by studying placental transfer of Fab-glycosylated Abs from mothers to newborns. No effect of Fab glycosylation on IgG binding to hFcRn was found by surface plasmon resonance and hFcRn affinity chromatography. In contrast, studies in a cell membrane context revealed that Fab glycans negatively impacted IgG-hFcRn interaction. In line with this, we found that Fab-glycosylated IgGs were transported ∼20% less efficiently across the placenta. This appeared to be a general phenomenon, observed for ACPAs, non-ACPAs, as well as total IgG in rheumatoid arthritis patients and healthy controls. Our results suggest that, in a cellular context, Fab glycans inhibit IgG-hFcRn interaction and thus negatively affect the transplacental transfer of IgG. As Fab-glycosylated Abs are frequently associated with autoimmune and malignant disorders and may be potentially harmful, this might encompass a regulatory mechanism, limiting the half-life and transport of such Abs.

The presence of autoreactive antibodies is a hallmark of many autoimmune diseases. The effector functions of (auto)antibodies are determined by their constant domain, which defines the antibody isotype and subclass. The most prevalent isotype in serum is IgG, which is often the only isotype used in diagnostic testing. Nevertheless, autoantibody responses can have their own unique isotype/subclass profile. Because comparing autoantibody isotype profiles may yield new insights into disease pathophysiology, here we summarize the isotype/subclass profiles of the most prominent autoantibodies. Despite substantial variation between (and within) autoantibody responses, this unprecedented comparison shows that autoantibodies share distinctive isotype patterns across different diseases. Although most autoantibody responses are dominated by IgG (and mainly IgG1), several specific diseases are characterized by a predominance of IgG4. In other diseases, IgE plays a key role. Importantly, shared features of autoantibody isotype/subclass profiles are seen in clinically unrelated diseases, suggesting potentially common trajectories in response evolution, disease pathogenesis, and treatment response. Isotypes beyond IgG are scarcely investigated in many autoantibody responses, leaving substantial gaps in our understanding of the pathophysiology of autoimmune diseases. Future research should address isotype/subclass profiling in more detail and incorporate autoantibody measurements beyond total IgG in disease models and clinical studies.

Background:Rheumatoid arthritis (RA) is characterized by autoantibodies against post-translationally modified proteins (AMPA) such as citrullinated, carbamylated and acetylated proteins. Importantly, these antibodies are highly multireactive, as they often recognize more than one of these post-translational modifications. Despite extensive research, the antigens inducing the breach of tolerance remain unknown, although microbial antigens are often suspected. Various bacteria are known to be capable of acetylation, therefore, it is intriguing to know what mechanisms can underlie the breach of tolerance towards acetylated proteins and development of anti-acetylated protein antibodies (AAPA).Objectives:To investigate whether acetylated proteins of bacterial origin (1) are recognized by human derived AMPA and AMPA expressing B cells; and (2) can induce AMPA development when used to immunize mice.Methods:Acetylated E. coli proteins were acquired with two separate methods (Figure 1A): by culturing E. coli in a condition promoting auto-acetylation (intrinsically acetylated bacterial proteins, IABP), or by directly acetylating lysate-derived proteins via a chemical reaction (extrinsically acetylated BP, EABP). Acetylated ovalbumin (AcOVA) served as positive control for AAPA induction in mice, non-acetylated BP (NABP) and phosphate buffer saline (PBS) served as negative control. Mice were immunized with these proteins and the resulting antibody response was studied by ELISA. Furthermore, EABP/IABP/NABP were investigated for recognition by human-derived AAPA with ELISA and AAPA-expressing B cells with spleen tyrosine kinase (Syk) phosphorylation assay; acetylated human fibrinogen and native fibrinogen served as positive and negative control.Results:Repetitive immunization of mice with EABP resulted in an AMPA response recognizing acetylated, carbamylated and citrullinated proteins. AMPA titers in these mice exceeded the titers in the positive control mice immunized with AcOVA and were substantially higher than in the NABP-immunized mice (Figure 1B). Human-derived monoclonal AAPA recognized EABP and IABP (not shown). B cell activation (measured by Syk phosphorylation) assay indicated that AAPA expressing B cells recognized EABP and (to a lesser extent) IABP, but not NABP (Figure 1C).Conclusion:Acetylated bacterial proteins are potent antigens that can induce cross-reactive AMPA responses in mice and they are recognized by human AAPA. This suggests that acetylated bacterial proteins could possibly be involved in the breach of tolerance in RA.Acknowledgements:We thank Dr. Can Araman and Prof. Chunaram Choudhary for their advice regarding optimization of bacterial auto-acetylation.Disclosure of Interests:None declared

Rheumatoid arthritis (RA) is an autoimmune disease characterized by joint inflammation. In the last few decades, new insights into RA‐specific autoantibodies and B cells have greatly expanded our understanding of the disease. The best‐known autoantibodies in RA—rheumatoid factor (RF) and anti‐citrullinated protein antibodies (ACPA)—are present long before disease onset, and both responses show signs of maturation around the time of the first manifestation of arthritis. A very intriguing characteristic of ACPA is their remarkably high abundance of variable domain glycans. Since these glycans may convey an important selection advantage of citrulline‐reactive B cells, they may be the key to understanding the evolution of the autoimmune response. Recently discovered autoantibodies targeting other posttranslational modifications, such as anti‐carbamylated and anti‐acetylated protein antibodies, appear to be closely related to ACPA, which makes it possible to unite them under the term of anti‐modified protein antibodies (AMPA). Despite the many insights gained about these autoantibodies, it is unclear whether they are pathogenic or play a causal role in disease development. Autoreactive B cells from which the autoantibodies originate have also received attention as perhaps more likely disease culprits. The development of autoreactive B cells in RA largely depends on the interaction with T cells in which HLA “shared epitope” and HLA DERAA may play an important role. Recent technological advances made it possible to identify and characterize citrulline‐reactive B cells and acquire ACPA monoclonal antibodies, which are providing valuable insights and help to understand the nature of the autoimmune response underlying RA. In this review, we summarize what is currently known about the role of autoantibodies and autoreactive B cells in RA and we discuss the most prominent hypotheses aiming to explain the origins and the evolution of autoimmunity in RA.

Recent advances in pharmacology have greatly expanded the drug repertoire for treatment of anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis. Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare multisystemic disorder, a type of the ANCA-associated vasculitis. Important features of this disease are eosinophilia and anti-myeloperoxidase ANCA presence in around 30–70% of patients. Primary therapy of EGPA includes steroids and cytotoxic drugs, e.g., cyclophosphamide, azathioprine, or methotrexate. Nevertheless, some patients are refractory to this therapy. Alternative approaches include rituximab, mepolizumab, and intravenous immunoglobulin. Accumulating evidence highlight a new promising drug in EGPA therapy—imatinib mesylate (IM), tyrosine kinase inhibitor. This drug is a key pharmacological agent in treating various types of hematological malignancies and FIP1L1/PDGF-RA-positive hypereosinophilia. In this article, we present a case demonstrating successful treatment of EGPA with IM; we also discuss possible mechanisms of IM efficacy in EGPA treatment and future perspectives of this therapeutic approach.

Systemic vasculitis (SV) associated with antineutrophil cytoplasmic antibodies (ANCA) is characterized by severe multiple organ lesions with a poor prognosis. The successful introduction of standard therapy with cyclophosphamide (CP) and innovative anti-B-cell therapy with rituximab (RTM) for the treatment of ANCA SV gives no grounds to stop further searching for effective and safe therapy since about 10–15% of patients with ANCA SV are refractory to standard therapy with CP; after the latter, approximately 40% of patients develop recurrences, and granulomatous inflammation in the respiratory organs in granulomatosis with polyangiitis (GPA) can be resistant to RTM treatment, especially following its single cycle. There is increasing evidence that the efficiency of anti-B-cell therapy can be enhanced by adding belimumab (BLM). The paper describes a clinical case of effective sequential combined anti-B-cell therapy with BLM and RTM for remission induction in a female patient who has GPA with severe granulomatous lung injury refractory to previous therapy with CP (a total dose of 6.2 g) and a single cycle of therapy with RTM (a total dose of 2.6 g). BLM was used 12 months after RTM administration because there were no positive changes in lung injury. At 12 months after initiations of treatment with BLM (800 mg twice at a weekly interval, then 800 mg monthly), there was a substantial reduction in the lung parenchymal foci, as evidenced by multislice spiral computed tomography (MSCT); and the treatment was continued for another 6 months, thereafter discontinued due to the occurrence of ulcerative stomatitis. After its relief, RTM was again given at reduced dose cycles of 500 mg every 6 months; lung MSCT showed further improvement and remission achieved. BLM may be effective in treating the GPA patients who are refractory to CP and have an insufficient response to RMT treatment. Combined anti-B-cell therapy aimed at depleting SD20+ B-cells and at blocking BAFF may be a promising area for the treatment of patients with ANCA SV.

In 2015, guidelines for the diagnosis and treatment of eosinophilic granulomatosis with polyangiitis, formerly known as Churg-Strauss syndrome, were prepared with the participation of experts from 5 countries of Europe, the USA, and Canada, who accumulated scientific achievements and currently gained clinical experience. The proposed guidelines should not be regarded as final standards, but must become a guide for the selection of a personification strategy for managing patients with eosinophilic granulomatosis with polyangiitis and serve as a starting point for further investigations. The purposes of the publication are general characterization of the key points of the guidelines and discussion of some debate problems.

The 2015 international guidelines for the diagnosis and treatment of eosinophilic granulomatosis with polyangiitis, formerly known as the Churg-Strauss syndrome, are detailed and an attempt is made to expand an evidence base, by attracting more recent available publications. The new guidelines should not be regarded as final standards; these are primarily to extend the possibilities of choosing a personified management strategy for patients with eosinophilic granulomatosis with polyangiitis and to serve as the starting point for further in-depth investigations.

Despite great advances in the study of the pathogenesis of rheumatoid arthritis (RA), which could design a radically new class of fundamentally sound therapeutic agents, many immunological aspects remain fully unstudied. The role of innate immunity mechanisms in the development of autoimmune inflammation is one of the important issues in the pathogenesis of not only RA, but also all rheumatic diseases. The discovery of pattern recognition receptors (PRRs) has allowed fundamental immunology to make a great stride toward understanding how these mechanisms are implemented. The study of membranous and endosomal Toll-like receptors (TLRs), the most extensive and well-studied group of PRRs, is a promising area of modern rheumatology. It is significant to note that some molecular agents, the presence of which in tissue is associated with its damage, are able to stimulate TLRs. They have received the name damage-associated molecular patterns (DAMPs). The paper provides a review of the literature on the mechanisms of TLR-mediated signaling pathways, on different aspects of a role of individual TLRs and DAMPs in the induction and maintenance of autoimmune inflammation in RA, and on prospects for targeted therapy aimed at inhibiting some TLRs and DAMPs.

One of the most common causes of rapidly progressive glomerulonephritis (GN) is the so-called pauci-immune crescentic GN that is characterized by no luminescence in kidney tissue samples during immunofluorescence microscopy and by the hyperproduction of antineutrophil cytoplasmic antibodies (ANCA). At the same time, serum ANCAs are absent in a number of cases of pauci-immune GN. Based on their own experience, the authors present the clinical and morphological characteristics of patients with ANCA-negative pauci-immune GN and analyze the data available in the literature.Subjects and methods. This retrospective study included 8 patients with ANCA-negative pauci-immune GN, who were followed up at two Russian centers (the Center of Nephrology and the Center of Rheumatology) in 2011 to 2015. Results and discussion. According to our data, ANCAs are not detectable in 6% of the patients with ANCA-associated systemic vasculitis (SV) with renal involvement and/or pauci-immune GN. The mean age at onset of the disease in the ANCA-negative patients was 50±18 years (range 19 to 74 years); the male/female ratio was 1:1. Four (50%) cases were diagnosed with microscopic polyangiitis; 2 cases had granulomatosis with polyangiitis; isolated renal injury was present in other 2 patients. The Birmingham SV activity index averaged 19.6±7.9. Hematuria was observed in all cases and it was massive in 4. The mean daily urinary protein level was 3.4±2.7 g; three (38%) patients were observed to have nephrotic syndrome. The blood creatinine level averaged 704±405 μmol/l; GN was characterized by a rapidly progressive course in 6 (75%) patients; hemodialysis was needed in 5. A morphological study of the kidney determined crescents (in on an average of 52 glomeruli) in the majority of cases and glomerulosclerosis in one patient. All the patients were observed to have varying degrees of interstitial fibrosis. Three (38%) treated patients achieved remission. The mortality rates were 38%. Interestingly, the data from our group as well those obtained by the study of European cohorts were slightly different from those of the studies conducted in Asia, according to which a renal biopsy more frequently revealed glomerular crescents; the levels of protein in the urine were higher and renal survival was worse.Thus, serum ANCAs are absent in 3–39% of cases of pauci-immune crescentic GN, but the clinical and morphological picture corresponds to ANCA-associated SV. A kidney biopsy helps establish the correct diagnosis, timely use induction treatment, and improve prognosis.

The link between rheumatoid arthritis and exposure to a bacterial toxin was not found in a population of rheumatoid arthritis patients from Netherlands.

Background Anti-CD20 antibody rituximab (RTX) has proved beneficial in ANCA-associated vasculitis (AAV). However, granulomatous features typical for the granulomatosis with polyangiitis (GPA) can be resistant to RTX, primarily after a single course. Local production of B-cell activating factor (BAFF) in granulomatous lesions and elevated levels of serum BAFF in AAV provide a rationale for BAFF-targeted therapies. The anti-BAFF monoclonal antibody (belimumab) has shown efficacy in SLE, and its role as a relapse prevention agent in AAV is being assessed in a randomized trial (BREVAS), but whether BAFF-neutralization can be used to induce remission of AAV remains unsolved. There is some evidence for increasing of BAFF levels after RTX treatment (Holden et al., 2011) and high levels of BAFF are associated with a shorter duration of the RTX-induced B-cell depletion. Thus, addition of belimumab should potentially enhance B-cell suppression. Objectives Here we present the first clinical case report of effective belimumab use for remission induction in GPA with severe pulmonary granulomatous inflammation, which was refractory to cyclophosphamide (CYC) and one course of RTX. Results A 56-year-old woman with 6-month history of fever, rhinitis, otitis, cough, polyarthralgia and cranial nerve affection was admitted to hospital. A chest X-ray revealed bilateral nodules. Fiberoptic bronchoscopy revealed infiltration in the subglottic area and ulcerated lesions along the tracheobronchial tree. She also had elevated inflammatory markers (ESR 24 mm/h, CRP 48 mg/dL), thrombocytosis (PLT 781×103/mm3) and cytoplasmatic pattern positive ANCA by indirect immunofluorescence screening. GPA was diagnosed. Induction therapy included prednisolone (40 mg/day) and pulses of CYC and methylprednisolone. 6 mo later CYC total dose (TD) was 6.2 g, prednisolone 15 mg/day. A CT scan revealed new focuses of granulomatous inflammation in lungs. Birmingham Vasculitis Activity Score (BVAS)=8. ESR 45 mm/h, CRP 13 mg/dL, platelets 323×103/mm3, ANCA was negative. RTX (TD 2.6 g) was administered due to the refractory GPA and resulted in B-cell depletion. After 6 mo of RTX clinical improvement was achieved, however, a CT scan revealed persistence of pulmonary lesions (A). BVAS=6. CRP 2 mg/dL, CD19+ B-cells 0%. Mycophenolate mofetil 1 g/day was initiated but soon discontinued due to nausea and replaced by azathioprine 100 mg/day. As there was no significant improvement after 12 mo of RTX (B), treatment with belimumab was initiated (800 mg/wk N2, then 800 mg/mo). CT monitoring showed consistent improvement of pulmonary lesions after administration of belimumab (C), but at 12 mo the lesions failed to resolve completely, necessitating the prolongation of Belimumab to total 18 mo, then due to poor tolerability (emerging stomatitis) it had to be discontinued. Thus, RTX was restarted at 500 mg twice with 6 mo interval, providing further improvement in CT images. Conclusions Belimumab can be useful in treatment of patients with GPA, who are refractory to CYC and RTX. Combined approach to B-cell targeting with both anti-CD20 and anti-BAFF treatment can represent promising strategy for patients with severe refractory GPA. References Holden NJ, Williams JM, Morgan MD, et al. ANCA-stimulated neutrophils release BLyS and promote B-cell survival: a clinically relevant cellular process. Ann Rheum Dis. 2011; 70(12):2229–33. Disclosure of Interest None declared

Goodpasture’s syndrome (GS) is a severe autoimmune disease, which is characterized by kidney and lung affection. Antibodies to glomerular basal membrane (AGBM) are considered to be a specific marker. We present a literature review and a clinical case of GS with typical clinical presentation and low effectiveness of glucocorticosteroid treatment in 17-year-old patient. The disease was characterized by the AGBM disappearance from peripheral blood, positive test for cryoglobulins and improvement of patient condition during therapy with rituximab.

Despite great advances in the study of the pathogenesis of rheumatoid arthritis (RA), which could design a radically new class of fundamentally sound therapeutic agents, many immunological aspects remain fully unstudied. The role of innate immunity mechanisms in the development of autoimmune inflammation is one of the important issues in the pathogenesis of not only RA, but also all rheumatic diseases. The discovery of pattern recognition receptors (PRRs) has allowed fundamental immunology to make a great stride toward understanding how these mechanisms are implemented. The study of membranous and endosomal Toll-like receptors (TLRs), the most extensive and well-studied group of PRRs, is a promising area of modern rheumatology. It is significant to note that some molecular agents, the presence of which in tissue is associated with its damage, are able to stimulate TLRs. They have received the name damage-associated molecular patterns (DAMPs). The paper provides a review of the literature on the mechanisms of TLR-mediated signaling pathways, on different aspects of a role of individual TLRs and DAMPs in the induction and maintenance of autoimmune inflammation in RA, and on prospects for targeted therapy aimed at inhibiting some TLRs and DAMPs.