Analysis of the influence of PTPN22 gene polymorphisms in systemic sclerosis

OBJECTIVE

Two functional single nucleotide polymorphisms (SNP) in the PTPN22 gene (rs24746601 and rs33996649) have been associated with autoimmunity. The aim of this study was to investigate the role of the R263Q SNP for the first time and to re-evaluate the role of the R620W SNP in the genetic predisposition to systemic sclerosis (SSc) susceptibility and clinical phenotypes.

METHODS

3422 SSc patients (2020 with limited cutaneous SSc and 1208 with diffuse cutaneous SSc) and 3638 healthy controls of Caucasian ancestry from an initial case--control set of Spain and seven additional independent replication cohorts were included in our study. Both rs33996649 and rs2476601 PTPN22 polymorphisms were genotyped by TaqMan allelic discrimination assay. A meta-analysis was performed to test the overall effect of these PTPN22 polymorphisms in SSc.

RESULTS

The meta-analysis revealed evidence of association of the rs2476601 T allele with SSc susceptibility (p(FDRcorrected)=0.03 pooled, OR 1.15, 95% CI 1.03 to 1.28). In addition, the rs2476601 T allele was significantly associated with anticentromere-positive status (p(FDRcorrected)=0.02 pooled, OR 1.22, 95% CI 1.05 to 1.42). Although the rs33996649 A allele was significantly associated with SSc in the Spanish population (p(FDRcorrected)=0.04, OR 0.58, 95% CI 0.36 to 0.92), this association was not confirmed in the meta-analysis (p=0.36 pooled, OR 0.89, 95% CI 0.72 to 1.1).

CONCLUSION

The study suggests that the PTPN22 R620W polymorphism influences SSc genetic susceptibility but the novel R263Q genetic variant does not. These data strengthen evidence that the R620W mutation is a common risk factor in autoimmune diseases.

New treatment options in spondyloarthropathies: increasing evidence for significant efficacy of anti-tumor necrosis factor therapy

Tumor necrosis factor-alpha is a major effector and regulatory cytokine, which seems to have an outstanding position in rheumatic and other inflammatory states. Because TNF-alpha has been detected in the inflamed gut and sacroiliac joints of patients with chronic inflammatory bowel diseases and spondyloarthritides, like ankylosing spondylitis, there was need for studies of the efficacy of the modern biologic anti-TNF agents infliximab and etanercept in these diseases. Infliximab is approved for the treatment of Crohn disease. In addition, there are now also positive data for infliximab in the treatment of ankylosing spondylitis and for etanercept and infliximab in the treatment of psoriatic arthritis.

Current use of biologicals for the treatment of spondyloarthropathies

Spondyloarthropathies (SpA) are a group of related disorders. The hallmark symptoms include spondylitis, pauci-articular synovitis and enthesiopathy. In an important number of cases, subclinical gut inflammation with pathological findings resembling Crohn's disease can be found. Some of these patients may eventually develop overt Crohn's disease. Conventional medical therapy in patients with SpA consists of non-steroidal anti-inflammatory drugs (NSAIDs). Sulphasalazin can be co-administered, especially in cases of chronic synovitis or enthesiopathy. Recently, experience with anti-TNF-alpha monoclonal antibodies (infliximab), a new class of biological compounds, has opened new avenues for treating patients with SpA. In particular, infliximab used in two open studies gave significant benefit on the locomotor manifestations in patients with Crohn's disease, in patients with ankylosing spondylitis, undifferentiated SpA and psoriatic arthritis. Etanercept, another TNF-alpha antagonist (soluble receptor), was shown to induce benefit in a placebo-controlled study in patients with psoriatic arthritis. The relationship between SpA and inflammatory bowel disease lead to the hypothesis that interfering with gut inflammation in patients with SpA would yield a potential target for modulating the synovitis in these patients. Thus, besides TNF-alpha blockade, other strategies with potential efficacy can be envisioned, such as IL-10, ICAM-1 antisense or anti-(4)beta(7) antibodies.

The C-terminal RG dipeptide repeats of the spliceosomal Sm proteins D1 and D3 contain symmetrical dimethylarginines, which form a major B-cell epitope for anti-Sm autoantibodies

The Sm proteins B/B', D1, D2, D3, E, F, and G are components of the small nuclear ribonucleoproteins U1, U2, U4/U6, and U5 that are essential for the splicing of pre-mRNAs in eukaryotes. D1 and D3 are among the most common antigens recognized by anti-Sm autoantibodies, an autoantibody population found exclusively in patients afflicted with systemic lupus erythematosus. Here we demonstrate by protein sequencing and mass spectrometry that all arginines in the C-terminal arginine-glycine (RG) dipeptide repeats of the human Sm proteins D1 and D3, isolated from HeLa small nuclear ribonucleoproteins, contain symmetrical dimethylarginines (sDMAs), a posttranslational modification thus far only identified in the myelin basic protein. The further finding that human D1 individually overexpressed in baculovirus-infected insect cells contains asymmetrical dimethylarginines suggests that the symmetrical dimethylation of the RG repeats in D1 and D3 is dependent on the assembly status of D1 and D3. In antibody binding studies, 10 of 11 anti-Sm patient sera tested, as well as the monoclonal antibody Y12, reacted with a chemically synthesized C-terminal peptide of D1 containing sDMA, but not with peptides containing asymmetrically modified or nonmodified arginines. These results thus demonstrate that the sDMA-modified C terminus of D1 forms a major linear epitope for anti-Sm autoantibodies and Y12 and further suggest that posttranslational modifications of Sm proteins play a role in the etiology of systemic lupus erythematosus.

Anti-perinuclear factor compared with the so called "antikeratin" antibodies and antibodies to human epidermis filaggrin, in the diagnosis of arthritides

OBJECTIVE

Antiperinuclear factor (APF), "antikeratin antibodies" ("AKA"), and antibodies to human epidermis filaggrin (AFA), are highly specific serological markers of rheumatoid arthritis (RA), which recognise epitopes on various isoforms of (pro)filaggrin. It was proposed that these antibodies are globally named antifilaggrin autoantibodies. Here the diagnostic value of the detection of each one is compared and the overlap between the three tests evaluated.

METHODS

492 serum samples were tested, including 279 RA serum samples, taken from patients in France and Belgium. APF and "AKA" titres were estimated by indirect immunofluorescence, and AFA titres by immunoblotting on filaggrin enriched human epidermis extracts.

RESULTS

By a convenient choice of the positivity thresholds, the diagnostic sensitivity and specificity of the tests were shown to be similar (0.52 and 0.97, respectively). Although the antibody titres were strongly correlated, the associations APF-AFA or AFA-"AKA" permitted more than 52% or 55% of RA to be diagnosed, with a specificity of 0.99.

CONCLUSION

APF, "AKA", and AFA detection have a similar diagnostic value. However, because the three tests do not totally overlap, associating APF with "AKA" or AFA with "AKA" can improve diagnostic sensitivity. None of the three antigens used bear all the epitopes recognised by antifilaggrin autoantibodies.

Selection of self-reactive peptides within human aggrecan by use of a HLA-DRB1*0401 peptide binding motif

The pathogenesis of joint destruction in rheumatoid arthritis remains ill-defined. Joint destruction is thought to be the result of tissue damage mediated by T cells. The mere presence of articular cartilage appears responsible for sustaining chronic synovitis and thereby forwards a role for cartilage-responsive T cells in RA. Taking advantage of the positive DRB1*0401 association with RA susceptibility, we reasoned that T-cell recognition of autoantigens in RA would be restricted by DRB1*0401-encoded molecules. A DR4 (B1*0401) peptide binding motif was used for the identification of putative T-cell epitopes within human aggrecan, a candidate autoantigen. Thirteen peptides were synthesized and tested for binding DRB1*0401 or 0404-encoded molecules. Selected binders were tested for induction of proliferative responses in peripheral blood mononuclear cells from donors carrying the DR4 or DR1 specificity. Both healthy and RA donors responded to human aggrecan-derived peptides, thereby identifying these sequences as T-cell epitopes. Interestingly, responses to aggrecan-derived epitopes were significantly decreased in RA patients compared to controls. This was not due to an overall hyporesponsiveness of RA patients since responses to a recall antigen or mitogen did not differ from controls. The data suggest that in RA, aggrecan-specific T cells may exist in a different stage of activation or may have left the periphery to home to the joint.

Human cartilage glycoprotein-39 as a candidate autoantigen in rheumatoid arthritis

OBJECTIVE

To identify a cartilage-derived autoantigen that is relevant to the rheumatoid arthritis (RA) disease process.

METHODS

A DR4 (DRB1*0401) peptide binding motif was used for the selection of potential self reactive peptides within human cartilage glycoprotein-39 (HC gp-39), a protein that is differentially expressed at the site of chronic inflammation. Synthetic peptides accommodating the motif were tested for binding the RA-associated DR4 (DRB1*0401) molecules. High-affinity binders were then tested for their capacity to stimulate peripheral blood mononuclear cell responses in RA patients or healthy donors. To assess the arthritogenic nature of native HC gp-39, the protein was injected into BALB/c mice.

RESULTS

HC gp-39-derived motif-based peptides were selectively recognized by peripheral blood T cells from RA patients. Injection of the intact protein into BALB/c mice resulted in immunity to HC gp-39, which was found to be associated with the development of a chronic, relapsing arthritis. Moreover, inhalation of the protein led to tolerization of antigen-specific T cells and to suppression of HC gp-39-induced arthritis.

CONCLUSION

These data indicate that HC gp-39 is a target of the immune response in RA. Consequently, HC gp-39 is a candidate for antigen-specific immunotherapy.

Association of multiple intracranial aneurysms and collagen type III deficiency

The results of a collagen assay performed on cultured skin fibroblasts from a 55-year-old man with multiple cerebral aneurysms are presented. Estimation of the collagen type III production by gel electrophoresis and scanning densitometry shows a reduction of collagen type III levels to 5% of normal. These findings point to the presence of a constitutional connective tissue disorder related to Ehlers-Danlos Syndrome type IV. It is suggested that biochemical collagen studies may be a useful alternative to angiography for detecting relatives at risk in families affected by intracranial aneurysms.