Cristina Tommasi

Antibodies from patients with rheumatoid arthritis target citrullinated histone 4 contained in neutrophils extracellular traps

Background Histone deimination regulates gene function and contributes to antimicrobial response, allowing the formation of neutrophil extracellular traps (NETs). Deiminated proteins are target of anti-citrullinated peptides antibodies (ACPA) in rheumatoid arthritis (RA). Objective The objective of this paper is to test the hypothesis that RA sera react with deiminated histones contained in NETs. Methods Neutrophils from peripheral blood were stimulated with A23187 and acid treated; NETosis was induced by phorbol myristate acetate, and NET proteins were isolated. Sera were tested by immunoblot on acid extracted proteins from neutrophils and from NETs, and by ELISA on deiminated histone H4 or H4-derived peptides. Bands reactive with RA sera were excised from gels, digested with trypsin and subjected to matrix-assisted laser desorption/ionisation time of flight (MALDI-TOF) analysis, before and after derivatisation to detect citrullinated peptides. Results RA sera reacted with a deiminated antigen of 11 KDa from activated neutrophils, recognised also by anti-H4 and antideiminated H4 antibodies. A similar reactivity was observed with NET proteins. The antigen from neutrophils or NETs was identified as citrullinated H4 by MALDI-TOF analysis. By ELISA, RA sera bound in vitro citrullinated H4. Citrullinated H4 14–34 and 31–50 peptides detected antibodies in 67% and 63% of RA sera and in less than 5% of controls; antibody titre was correlated with anti-CCP2. Conclusions Citrullinated H4 from activated neutrophils and NETs is a target of antibodies in RA, and synthetic citrullinated H4-derived peptides are a new substrate for ACPA detection. As NETosis can generate antigens for ACPA, these data suggest a novel connection between innate and adaptive immunity in RA.

Peptidylarginine deiminase 4 and citrullination in health and disease.

Deimination is catalyzed by a family of calcium binding enzymes, called peptidylarginine deiminases (PADs). Among these, the PAD4 isoform has been more extensively studied for its role in some autoimmune diseases. PAD4 is localized in the cytoplasm of monocytes, T and B cells, neutrophils, eosinophils and NK cells and can move to the nucleus upon cell activation. PAD4 plays a physiological role in gene regulation via citrullination of histones. In rheumatoid arthritis (RA), PAD4 contributes to the generation of ACPA specific substrates and is itself a target of autoantibodies; alleles of the PADI4 gene confer susceptibility to RA in Asians but not in Caucasians. In multiple sclerosis, extensive deimination of brain proteins is observed in active lesions, but no role for the PADI4 gene in susceptibility to MS has been so far described.

Antibodies to a new viral citrullinated peptide, VCP2: fine specificity and correlation with anti‐cyclic citrullinated peptide (CCP) and anti‐VCP1 antibodies

Anti‐citrullinated protein/peptide antibodies (ACPA) are a hallmark of rheumatoid arthritis (RA) and can be measured using different citrullinated substrates. In this paper we describe a new viral citrullinated peptide – VCP2 – derived from the Epstein–Barr virus‐encoded protein EBNA‐2 and analyse its potential as substrate for ACPA detection. Analysing sera from 100 RA patients and 306 controls, anti‐VCP2 immunoglobulin (Ig)G were found in 66% of RA sera, IgM in 46% and IgA in 39%, compared with less than 3% of control sera. Anti‐VCP2 IgG was associated with erosive arthritis, the presence of rheumatoid factor and anti‐VCP1 and anti‐cyclic citrullinated peptide (CCP) antibodies. Anti‐VCP2 antibodies were detected in 1% and anti‐VCP1 antibodies in 4% of CCP‐negative RA sera; conversely, 3% of the VCP‐negative sera were CCP‐positive. Taken together, these data suggest that VCP2 could offer a valuable tool for ACPA detection. Inhibition assays showed that two non‐overlapping epitopes – a citrulline–glycine stretch shared between VCP1 and VCP2 and the N‐terminal portion of the VCP2 sequence – were targeted by anti‐VCP2 antibodies. Moreover, in some RA sera that tested positive in CCP and VCP2 assays, preincubation with VCP2 inhibited binding to CCP, whereas in other sera the binding was unaffected. Thus, the reactivity with more than one ACPA substrate might be due in some RA patients to antibody populations with different specificities, and in others to cross‐reactive antibody populations. Finally, affinity‐purified anti‐VCP2 antibodies immunoprecipitated deiminated Epstein–Barr virus nuclear antigen (EBNA‐2) from an EBNA‐2‐transfected cell line, suggesting that viral sequences may be involved in the generation of the ACPA response.

Free circulating interleukin-18 is increased in Schnitzler syndrome: a new autoinflammatory disease?

Schnitzler syndrome is a rare disease characterised by chronic urticaria and arthralgia. The recent evidence that the IL-1 receptor antagonist IL-1Ra could induce rapid and complete remission of Schnitzler symptoms has pointed to IL-1 as a major pathological factor in this disease. To examine the possibility that Schnitzler syndrome may be considered to be an autoinflammatory disease, in this study we measured the serum levels of IL-18, another cytokine of the IL-1 family that is cleaved by caspase-1, in two recently diagnosed Schnitzler patients before and after treatment with IL-1Ra. In parallel, mRNA expression of IL-1 family cytokines and caspase-1 were assessed in isolated blood monocytes. Treatment with IL-1Ra significantly inhibited IL-1beta gene expression, indicating that IL-1beta activity in Schnitzler syndrome is central to IL-1beta gene upregulation in a type of auto-amplification loop. While no IL-1beta was detected in serum, free circulating IL-18 was increased in patients with Schnitzler syndrome, despite low IL-18 gene expression in monocytes. This suggests constitutive activation of the IL-1beta/IL-18-producing inflammasome, and supports the hypothesis that Schnitzlers syndrome is a new autoinflammatory disease.

A Deiminated Viral Peptide to Detect Antibodies in Rheumatoid Arthritis

Abstract: The data presented suggest that a deiminated viral peptide is specifically recognized by antibodies contained in rheumatoid arthritis (RA) sera. Antipeptide antibodies are not associated with the presence or severity of specific manifestations of RA, but are more frequent in subjects with erosive arthritis. Taking into account the association with rheumatoid factor and with erosive arthritis, we can conclude that antipeptide antibodies are markers of severe forms of RA. Our data also show familial aggregation of anticitrullinated peptide antibodies.