Enhanced costimulation by CD70+ B cells aggravates experimental autoimmune encephalomyelitis in autoimmune mice.

OBJECTIVE: Assess whether CD70+ B cells contribute to EAE. MATERIALS AND METHODS: MOG-specific TCR transgenic mice (2D2) were crossed with mice with constitutive CD70 expression on B cells. The development of EAE and the phenotype of B-T lymphocytes were studied in 2D2xCD70 animals. RESULTS: Spontaneous EAE developed in 20% of 2D2xCD70 and 3% of 2D2 mice. EAE was also more severe in 2D2xCD70 versus 2D2 animals upon MOG immunization. The susceptibility of 2D2xCD70 to EAE was associated with fewer FoxP3+ T cells. CONCLUSIONS: Expression of CD70 by B cells aggravates EAE possibly by reducing the number of regulatory T cells.

Inflamed target tissue provides a specific niche for highly expanded T-cell clones in early human autoimmune disease.

OBJECTIVE: To profile quantitatively the T-cell repertoire in multiple joints and peripheral blood of patients with recent onset (early) or established rheumatoid arthritis (RA) using a novel next-generation sequencing protocol to identify potential autoreactive clones. METHODS: Synovium of patients with recent onset (early) RA (<6 months) (n=6) or established RA (>18 months) (n=6) was screened for T-cell clones by sequencing over 10 000 T-cell receptors (TCR) per sample. T cells from paired blood samples were analysed for comparison. From two patients synovial T cells were obtained from multiple inflamed joints. The degree of expansion of each individual clone was based on its unique CDR3 sequence frequency within a sample. Clones with a frequency of over 0.5% were considered to be highly expanded clones (HEC). RESULTS: In early RA synovium, the T-cell repertoire was dominated by 35 HEC (median, range 2-70) accounting for 56% of the TCR sequenced. The clonal dominance in the synovium was patient specific and significantly greater than in established RA (median of 11 HEC (range 5-24) in established RA synovium accounting for 9.8% of T cells; p<0.01). 34% (range 28-40%) of the most expanded T-cell clones were shared between different joints in the same patients, compared with only 4% (range 0-8%) between synovium and blood (p=0.01). CONCLUSIONS: In RA, a systemic autoimmune disease, the inflamed synovium forms a niche for specific expanded T-cell clones, especially in early disease. This suggests that, at least in RA, autoreactive T cells should be addressed specifically in the inflamed tissue, preferably in the early phase of the disease.

Exposure to nuclear antigens contributes to the induction of humoral autoimmunity during tumour necrosis factor alpha blockade.

OBJECTIVE: Type I interferons and apoptotic particles contribute to antinuclear autoimmunity in experimental models. This study assessed whether similar mechanisms contribute to break peripheral B-cell tolerance in humans by studying the induction of antinuclear antibodies by tumour necrosis factor blockade in spondyloarthritis. METHODS: 40 spondyloarthritis patients treated with infliximab or etanercept and 20 renal cell carcinoma patients treated with sorafenib were studied. Serum antinucleosome IgM and nucleosomes were measured by ELISA. Type I interferon serum activity was measured using a functional reporter cell assay. Synovial apoptosis was assessed by terminal transferase nick end-labelling (TUNEL) assay and anti-active caspase-3 immunostaining. Complement was measured by nephelometry. RESULTS: Despite a similar clinical improvement and reduction of synovial inflammation, antinucleosome IgM were induced by infliximab but not etanercept. This induction did not correlate with type I interferon activity, which was transiently downmodulated by infliximab but persistently upregulated by etanercept. In contrast, antinucleosome IgM levels did correlate with serum nucleosome levels, which were significantly upregulated by infliximab but not by etanercept treatment. This increase in serum nucleosome levels was not directly related to massive cell death, but rather to a decrease of complement 3 and 4 serum levels during infliximab treatment. CONCLUSION: Infliximab and etanercept have a differential effect on both type I interferon activity and nucleosome levels. Only elevated serum nucleosomes relate to the induction of antinucleosome antibodies after infliximab treatment.

Melanoma inhibitory activity, a biomarker related to chondrocyte anabolism, is reversibly suppressed by proinflammatory cytokines in rheumatoid arthritis.

OBJECTIVE: In mice, melanoma inhibitory activity (MIA) is a chondrocyte-specific molecule with similar regulation to collagen type II. As MIA is a small secreted protein, its value as cartilage biomarker in human inflammatory arthritis was assessed. METHODS: MIA tissue distribution was studied by quantitative PCR and immunohistochemistry. The regulation of MIA production was studied in vivo in rheumatoid arthritis (RA) (n = 37) and spondyloarthritis (SpA) (n = 30) synovial fluid (SF), and in vitro in alginate embedded human chondrocytes. Therapeutic modulation of serum MIA was evaluated during tumour necrosis factor (TNF)alpha and interleukin (IL)1 blockade in RA. RESULTS: MIA was primarily expressed by chondrocytes in the human joint. SF MIA levels were lower in RA than in SpA despite similar levels of overall synovial inflammation. Further analysis indicated that these levels were inversely correlated with the degree of joint inflammation in RA, but not in SpA, and that the levels of TNFalpha and IL1beta were significantly increased in RA versus SpA. Accordingly, these proinflammatory cytokines suppressed MIA mRNA and protein in cultured chondrocytes. This suppression was paralleled by suppression of cartilage anabolism as assessed by collagen type 2 and aggrecan mRNA. Treatment of patients with RA with TNF blockade or IL1 blockade induced an increase of serum MIA levels. CONCLUSION: The decreased levels of MIA in the inflamed RA joint and the coregulation of MIA and cartilage matrix molecules by proinflammatory cytokines indicate that joint inflammation in RA not only drives accelerated cartilage degradation but also suppresses cartilage anabolism. This inflammation-driven suppression is reversible in vivo.

Synovial detection and autoantibody reactivity of processed citrullinated isoforms of vimentin in inflammatory arthritides.

OBJECTIVES: To investigate the presence and characteristics of citrullinated vimentin in protein extracts of inflamed synovial tissue. METHODS: Cytosolic protein extracts obtained from RA (n = 14) and SpA patients (n = 14) were analysed by gel electrophoresis and western blotting. Citrullinated vimentin isoforms were visualized by a combination of anti-modified citrulline (AMC) staining and anti-vimentin detections (V9, H-84). This was subsequently confirmed by immunoprecipitation. Autoantibody detection was verified using sera obtained form RA (n = 6) and SpA (n = 6) patients. RESULTS: A specific cluster of spots displayed on the 2D gel images of cytosolic synovial tissue extracts, was identified by mass spectrometry as vimentin. Interestingly, our results suggested that these isoforms could be the result of caspase cleavage. In addition, these cleaved forms of vimentin were found to be citrullinated in synovial cytosolic protein extracts of inflammatory arthritides, mainly in RA patients. Caspase-3 is able to cleave vimentin at amino acid 85. Western blot analysis with a specific antibody against amino acids 1-84 of vimentin (H-84) confirmed that the citrullinated isoforms of vimentin were lacking this part of the protein. These results were also confirmed by immunoprecipitation of vimentin derived from cytosolic protein extracts of RA and SpA patients. Furthermore, the presence of autoantibodies against these citrullinated processed forms of vimentin was found to be predominantly associated with RA patients. CONCLUSIONS: These findings show the presence of processed citrullinated vimentin in inflammatory arthritides, mainly in RA and suggest a possible origin of the ACPA immune response in RA.

A functional polymorphism of TIR-domain-containing adaptor protein is not associated with axial spondyloarthritis.

OBJECTIVE: A genetic variant of the toll-like receptor (TLR)2/4 adaptor protein TIRAP (single nucleotide polymorphism (SNP) C539T) was identified in a UK and in several African populations. The heterozygous genotype of this SNP has been associated with protection from severe infections. This allele results in an attenuated response to bacterial pathogens. As an exaggerated innate immune response to pathogens has been implicated in spondyloarthritis (SpA) pathogenesis, we analysed if the heterozygous C/T genotype was underrepresented in axial SpA compared with healthy controls. METHODS: 204 patients with axial SpA and 175 population-matched controls were included. SNP C539T was determined with a sequence-specific polymerase chain reaction and direct sequencing. RESULTS: The frequency of the haplotypes was similar in cases and controls (87% for C and 13% for T in both groups). The C/T genotype, which attenuates TLR signalling, was not underrepresented in cases versus controls (19% in controls vs 24% in cases, p = 0.44). The T/T genotype, was slightly lower in cases than in controls, although this was not significant (3.4% in controls vs 1% in cases, p = 0.15). Within the cases, there were no differences in disease phenotype or activity between patients with the C/C or C/T genotype. CONCLUSIONS: This study did not show significant associations of SNP S180L of the TLR2/4 adaptor protein TIRAP with axial SpA.

Citrullination in extra-articular manifestations of rheumatoid arthritis.

BACKGROUND: Anti-citrullinated protein antibodies have been detected with high specificity in serum of patients with rheumatoid arthritis (RA), and citrullination of proteins may play a key role in the pathogenesis of RA. We therefore investigated the presence of citrullination in two extra-articular manifestations of RA, interstitial pneumonia (IP) and rheumatoid nodules. METHODS: Open-lung biopsy specimens from patients with RA-associated IP (n = 18), idiopathic IP (n = 20) and controls (n = 10), as well as specimens of rheumatoid nodules from 26 patients, were examined. All sections were incubated with an anti-modified citrulline antibody. Masked scoring of stained sections and analysis of results by stratification according to demographic and clinical characteristics was performed. RESULTS: Presence of citrulline could be detected in eight lung specimens of patients with RA-associated IP (44%) and nine patients with idiopathic IP (46%). Conversely, lung tissue from control patients showed weak extracellular citrullination in only two cases (20%). Citrullination did not show any significant associations with demographic or clinical characteristics such as age, gender, smoking habits, disease severity, histological subtype, degree of inflammation or steroid use. Rheumatoid nodules were citrulline positive in a majority of cases (70%). CONCLUSION: Citrullination is present in extra-articular manifestations of RA such as IP and nodules. In contrast to the high specificity of anti-citrulline antibodies in RA, citrullination is not only restricted to RA but can also be observed in idiopathic IP. Whether citrullination significantly contributes to the initiation or perpetuation of autoimmunity or merely reflects ongoing inflammation remains to be clarified.

Anti-citrullinated protein/peptide antibodies (ACPA) in rheumatoid arthritis: specificity and relation with rheumatoid factor.

Anti-citrullinated protein/peptide antibodies (ACPA) are highly specific and sensitive markers for rheumatoid arthritis (RA). For instance, for the anti-CCP2 assay, sensitivities ranging from 55% to 80% and specificities ranging from 90% to 98% have been reported. Despite their high specificity, recent reports have suggested that ACPA may be found in some patients with other rheumatic autoimmune diseases, including psoriatic arthritis, systemic lupus erythematosus and Sjögren's syndrome. Also, the differences between the classical rheumatoid factor (RF) and ACPA, as well as the complementarity between both tests have recently been demonstrated more clearly. Indeed, both antibody systems have a different association with specific RA features like extra-articular manifestations, a different association with the HLA shared epitope and, behave differently following anti-TNF therapy.

Functional haplotypes of PADI4: relevance for rheumatoid arthritis specific synovial intracellular citrullinated proteins and anticitrullinated protein antibodies.

BACKGROUND: Haplotypes of PADI4, encoding for a citrullinating enzyme, were associated with rheumatoid arthritis in a Japanese population. It was suggested they were related to the presence of anticitrullinated protein antibodies (ACPA). OBJECTIVE: To explore the relation between PADI4 haplotypes, the presence of rheumatoid arthritis specific intracellular citrullinated proteins in synovial membrane, and serum ACPA titres. METHODS: Synovial biopsies and peripheral blood samples were obtained in 59 patients with rheumatoid arthritis. Synovial intracellular citrullinated proteins were detected by immunohistochemistry. Serum ACPA titres were measured by anti-CCP2 ELISA. PADI4 haplotypes were determined by direct sequencing of the four exonic PADI4 single nucleotide polymorphisms. RESULTS: PADI4 haplotype frequencies and the presence of synovial intracellular citrullinated proteins and ACPA were comparable with previous studies. There was no significant association between PADI4 haplotype 1 or 2 and the presence of synovial intracellular citrullinated proteins, although these proteins were associated with higher serum ACPA. There was no correlation between PADI4 haplotypes and serum ACPA, either by continuous analysis using the titres or by dichotomous analysis using the diagnostic cut off. Further analyses in homozygotes for haplotype 1 or 2 or in heterozygotes (1/2) also failed to show an association between PADI4 polymorphisms and ACPA. This contrasted with the clear association between ACPA levels and HLA-DR shared epitope. CONCLUSIONS: The link between synovial intracellular citrullinated proteins and ACPA emphasises the role of deimination of synovial proteins in rheumatoid arthritis, but the biological relevance of the PADI4 haplotypes for this autoimmune process is questionable, at least in a European population.