Recognition of new citrulline-containing peptide epitopes by autoantibodies produced in vivo and in vitro by B cells of rheumatoid arthritis patients.

Anti-citrullinated peptide/protein antibodies (ACPAs) are highly sensitive and specific markers of rheumatoid arthritis (RA). Identification of peptide epitopes that may detect different subgroups of RA patients might have diagnostic and prognostic significance. We have investigated citrulline- and arginine-containing peptide pairs derived from filaggrin, collagen or vimentin, and compared this citrulline-peptide panel with the serological assays conventionally used to detect ACPAs. Furthermore, we studied if the same citrulline-peptides identify antibody-secreting cells in in vitro cultures of RA B cells. Recognition of citrulline- and arginine-containing filaggrin, vimentin and collagen peptide epitopes were tested by Multipin ELISA system, by indirect ELISA and by a peptide-specific microarray. B cells were purified from blood by negative selection; antibody-producing cells were enumerated by ELISPOT assay. The panel composed of citrulline-peptide epitopes of filaggrin, collagen and vimentin was recognized by RA sera with a sensitivity and specificity comparable with the currently used tests. Moreover, the combined citrulline-peptide panel including the new short epitope peptide of filaggrin, fil311-315, also identified nearly one-third of RA cases that were negative for antibodies against cyclic citrullinated peptides, mutated citrullinated vimentin or for rheumatoid factor. The results with the peptide-specific microarray have shown that although most ACPAs recognizing the four citrulline peptides are IgG, some of them specifically recognizing citrulline-containing filaggrin peptides (fil311-315 and fil306-326) are IgM, and so may be produced either by newly formed activated B cells or by unswitched B memory cells. Furthermore, the citrulline-peptides of filaggrin and vimentin detect ACPA-producing cells, and so could also be applied to study the B cells of RA patients.

Basic calcium phosphate crystals induce monocyte/macrophage IL-1ß secretion through the NLRP3 inflammasome in vitro.

Basic calcium phosphate (BCP) crystals are associated with severe osteoarthritis and acute periarticular inflammation. Three main forms of BCP crystals have been identified from pathological tissues: octacalcium phosphate, carbonate-substituted apatite, and hydroxyapatite. We investigated the proinflammatory effects of these BCP crystals in vitro with special regard to the involvement of the NLRP3-inflammasome in THP-1 cells, primary human monocytes and macrophages, and mouse bone marrow-derived macrophages (BMDM). THP-1 cells stimulated with BCP crystals produced IL-1ß in a dose-dependent manner. Similarly, primary human cells and BMDM from wild-type mice also produced high concentrations of IL-1ß after crystal stimulation. THP-1 cells transfected with short hairpin RNA against the components of the NLRP3 inflammasome and mouse BMDM from mice deficient for NLRP3, apoptosis-associated speck-like protein, or caspase-1 did not produce IL-1ß after BCP crystal stimulation. BCP crystals induced macrophage apoptosis/necrosis as demonstrated by MTT and flow cytometric analysis. Collectively, these results demonstrate that BCP crystals induce IL-1ß secretion through activating the NLRP3 inflammasome. Furthermore, we speculate that IL-1 blockade could be a novel strategy to inhibit BCP-induced inflammation in human disease.

Marked diversity of IL23R gene haplotype variants in rheumatoid arthritis comparing with Crohn's disease and ankylosing spondylitis.

Haplotype tagging SNPs of interleukin-23 receptor gene rs1004819, rs7517847, rs7530511, rs2201841, rs1343151 and rs10889677 were determined in 396 patients with rheumatoid arthritis, 190 patients with Crohn's disease, 206 patients with ankylosing spondylitis and 182 controls. Using regression analysis models the rs1004819, rs2201841, and rs10889677 SNPs were found to confer risk for Crohn's disease and ankylosing spondylitis, while rs1343151 had a protective effect in both of these diseases, and the rs2201841 and rs10889677 SNPs showed susceptibility nature for rheumatoid arthritis. Using these SNPs we could study the susceptibility haplotype profiles in these diseases with special attention to the rheumatoid arthritis, first in the literature. Seven different haplotypes could be differentiated. We found that the SNPs exert their susceptibility character in specific haplotype blocks: thus, for rheumatoid arthritis the rs1343151 SNP was risk factor only in a specific haplotype surrounding; this can explain the controversial results published so far about this variant. More importantly, we observed, that while a specific haplotype can confer risk for rheumatoid arthritis, the same haplotype tended to protect against the development of the other two diseases. The data presented here serve evidence for the need of haplotype analysis instead of just single standing SNP analysis when susceptibility to or protection against a certain disease are interpreted.

Octacalcium phosphate crystals induce inflammation in vivo through interleukin-1 but independent of the NLRP3 inflammasome in mice.

OBJECTIVE: To determine the mechanisms involved in inflammatory responses to octacalcium phosphate (OCP) crystals in vivo. METHODS: OCP crystal-induced inflammation was monitored using a peritoneal model of inflammation in mice with different deficiencies affecting interleukin-1 (IL-1) secretion (IL-1α(-/-) , IL-1ß(-/-) , ASC(-/-) , and NLRP3(-/-) mice) or in mice pretreated with IL-1 inhibitors (anakinra [recombinant IL-1 receptor antagonist] and anti-IL-1ß). The production of IL-1α, IL-1ß, and myeloid-related protein 8 (MRP-8)-MRP-14 complex was determined by enzyme-linked immunosorbent assay. Peritoneal neutrophil recruitment and cell viability were determined by flow cytometry. Depletion of mast cells or resident macrophages was performed by pretreatment with compound 48/80 or clodronate liposomes, respectively. RESULTS: OCP crystals induced peritoneal inflammation, as demonstrated by neutrophil recruitment and up-modulation of IL-1α, IL-1ß, and MRP-8-MRP-14 complex, to levels comparable with those induced by monosodium urate monohydrate crystals. This OCP crystal-induced inflammation was both IL-1α- and IL-1ß-dependent, as shown by the inhibitory effects of anakinra and anti-IL-1ß antibody treatment. Accordingly, OCP crystal stimulation resulted in milder inflammation in IL-1α(-/-) and IL-1ß(-/-) mice. Interestingly, ASC(-/-) and NLRP3(-/-) mice did not show any alteration in their inflammation status in response to OCP crystals. Depletion of the resident macrophage population resulted in a significant decrease in crystal-induced neutrophil infiltration and proinflammatory cytokine production in vivo, whereas mast cell depletion had no effect. Finally, OCP crystals induced apoptosis/necrosis of peritoneal cells in vivo. CONCLUSION: These data indicate that macrophages, rather than mast cells, are important for initiating and driving OCP crystal-induced inflammation. Additionally, OCP crystals induce IL-1-dependent peritoneal inflammation without requiring the NLRP3 inflammasome.

Association of ARTS1 gene polymorphisms with ankylosing spondylitis in the Hungarian population: the rs27044 variant is associated with HLA-B*2705 subtype in Hungarian patients with ankylosing spondylitis.

OBJECTIVE: Associations have been found between ankylosing spondylitis (AS) and polymorphisms in the aminopeptidase regulator of TNFR1 shedding (ARTS1) gene. We studied the association of 5 polymorphisms within the ARTS1 gene with AS in Hungarian patients. We also investigated the prevalence of HLA-B27 subtypes in the Hungarian population. METHODS: A case-control study including 297 patients with AS and 200 sex and ethnically matched healthy controls was performed. Patients and controls were genotyped for rs27044, rs17482078, rs10050860, rs30187, and rs2287987 single-nucleotide polymorphisms using real-time polymerase chain reaction (PCR) allelic discrimination. HLA-B27 subtypes were determined with PCR sequence-specific primer (PCR-SSP) technique. RESULTS: We observed a significant increase in the minor allele frequency of rs27044 (p = 0.001) in the AS group compared to controls. The minor allele frequencies of rs10050860 (p = 0.006) and rs2287987 (p = 0.002) showed a significant decrease in AS patients compared to controls. Haplotype analysis revealed association of 2 ARTS1 haplotypes with AS in the Hungarian population. We found that HLA-B*2705 was the predominant subtype in Hungarians with AS. Carriage of the G allele of rs27044 was significantly associated with the HLA-B*2705 subtype (p = 0.009) in AS patients. CONCLUSION: We confirmed reported associations of ARTS1 gene polymorphisms with AS in a Hungarian cohort study. We found HLA-B*2705 as the predominant subtype in Hungarian AS patients in accord with other studies on Caucasian populations. Our results suggest that the ARTS1 gene variants together with HLA-B27 strongly contribute to disease susceptibility in patients with AS.

Structural polymorphisms in the mannose-binding lectin gene are associated with juvenile idiopathic arthritis.

OBJECTIVE: To investigate the possible association between polymorphisms of the mannose-binding lectin gene (MBL2) and susceptibility to juvenile idiopathic arthritis (JIA). METHODS: We performed a case-control association study including 118 Hungarian patients with JIA and 118 sex-matched healthy controls. MBL genotyping for the 3 mutant structural alleles at codons 54 (B), 57 (C), and 52 (D) in exon 1 and the promoter polymorphisms at position -550 (HL) and -221 (YX) were carried out by real-time PCR allelic discrimination. Serum level of MBL was determined by ELISA. RESULTS: Variant allele frequencies of both codon 52 and 57 polymorphisms in the MBL2 gene were significantly overrepresented in JIA (p=0.001 and p=0.004, respectively). The frequency of low MBL genotypes (XA/XA, YA/YO, XA/YO, and YO/YO) in JIA was higher than that in healthy controls (p=0.001). Serum MBL concentrations were found to be significantly lower in JIA patients versus control subjects (p=0.001). The 2 promoter polymorphisms and codon 54 SNP of the MBL2 gene were not associated with JIA. CONCLUSION: Our findings suggest that genetically determined low MBL levels may predispose children to JIA in a Hungarian population. These data warrant further research to investigate the role of the lectin-dependent complement system in the pathogenesis of JIA.