Antibodies against citrullinated peptides are associated with clinical and radiological outcomes in patients with early rheumatoid arthritis: a prospective longitudinal inception cohort study.

Introduction: Anticitrullinated peptide antibody (ACPA) responses for 22 citrullinated peptides in patients with early rheumatoid arthritis (RA) were analysed and related to radiological and clinical outcome during the first 2 years in a prospective inception cohort. Methods: The ACPA reactivities were assessed in 1022 patients with early RA (symptoms <12 months) using the custom-made microarray chip (Thermo Fisher Scientific, Uppsala, Sweden) in a prospective longitudinal study of observational assessments of Disease Activity Score (DAS28 and its components) and radiology during the first 24 months, accounting for the treatment. Results: Frequency of ACPA reactivities varied between 13.3% and 63.1%. Of the anticyclic citrullinated peptide-2 (anti-CCP2) antibody-negative patients, ACPA reactivities were positive in 32.6%. Smoking, human leucocyte antigen-shared epitope (HLA-SE), anti-CCP2/rheumatoid factor, protein tyrosine phosphatase non-receptor type 22 (1858C/T) and DAS28 were significantly associated with number of ACPA reactivities. The ACPA reactivities modified differently the development of DAS28 over 24 months (identified using trajectories). Anti-Filaggrin307-324, anti-hnRNP (Peptide)-Z1 and anti-F4-CIT-R antibodies anticipated lower DAS28 values (p<0.01-0.05), while positivity for anti-Fibrinogen(Fib)ß62-78(74), and anti-Fibα563-583 predicted higher DAS28 (p<0.01 both). Interaction between anti-Fibß36-52, anti-Pept-5 and anti-Bla-26 antibodies, respectively, and DAS28 during 24 months decreased significantly the DAS28 values (p<0.01-0.05). Corticosteroids and biologicals were related to DAS28-area under the curve and Larsen score 24 months. Anti-vimentin2-17 antibodies remained significantly associated with Larsen score at baseline and 24 months, respectively, and radiological progression, besides biologicals at 24 months adjusted for sex and age. Conclusions: Several ACPA reactivities modified significantly the DAS28 development during the first 24 months and were significantly associated with Larsen score at baseline, 24 months and radiological progression.

Protein tyrosine phosphatase non-receptor 22 and C-Src tyrosine kinase genes are down-regulated in patients with rheumatoid arthritis.

Several protein tyrosine phosphatase non-receptor 22 (PTPN22) single-nucleotide polymorphisms (SNPs) have been significantly related with rheumatoid arthritis (RA) susceptibility. Nevertheless, its potential influence on PTPN22 expression in RA has not been completely elucidated. Furthermore, PTPN22 binds to C-Src tyrosine kinase (CSK) forming a key complex in autoimmunity. However, the information of CSK gene in RA is scarce. In this study, we analyzed the relative PTPN22 and CSK expression in peripheral blood from 89 RA patients and 43 controls to determine if the most relevant PTPN22 (rs2488457, rs2476601 and rs33996649) and CSK (rs34933034 and rs1378942) polymorphisms may influence on PTPN22 and CSK expression in RA. The association between PTPN22 and CSK expression in RA patients and their clinical characteristics was also evaluated. Our study shows for the first time a marked down-regulation of PTPN22 expression in RA patients carrying the risk alleles of PTPN22 rs2488457 and rs2476601 compared to controls (p = 0.004 and p = 0.007, respectively). Furthermore, CSK expression was significantly lower in RA patients than in controls (p < 0.0001). Interestingly, a reduced PTPN22 expression was disclosed in RA patients with ischemic heart disease (p = 0.009). The transcriptional suppression of this PTPN22/CSK complex may have a noteworthy clinical relevance in RA patients.

Measuring the specific activity of the protein tyrosine phosphatase Lyp.

Altered function of the protein tyrosine phosphatase (PTP) Lyp (PTPN22) has been implicated in the pathogenesis of a number of human diseases, and so accurate assessment of its functional activity is needed to further our understanding of its biology. We have developed an in vitro method to measure the specific catalytic activity of the Lyp phosphatase. Lyp is captured from cell lysates using an anti-Lyp monoclonal antibody coated 96-well plate, and activity measured by dephosphorylation of a fluorescent substrate, 6,8-difluoro-4-methylumbelliferyl phosphate (DiFMUP). The amount of protein is measured using an anti-Lyp HRP conjugate, with reference to a standard curve generated with purified Lyp. These two measurements are then used to calculate the specific phosphatase activity. We used this assay to show that the specific activity of the Lyp phosphatase is decreased by H(2)O(2) in Jurkat T cells and primary CD4+ T cells. We also modified this assay to measure the specific activity of CD45, the other main PTP regulating T cell receptor (TCR) signalling, in order to compare the relative susceptibility of CD45 and Lyp to oxidation by H(2)O(2). By measuring specific activity in Jurkat T cells and primary CD4+ T cells, we demonstrated that CD45 is more susceptible to oxidation by H(2)O(2) when compared to Lyp. Reduced function of CD45 and Lyp has been associated with human immune mediated inflammatory diseases, and a differential susceptibility to oxidation could be an important regulatory mechanism associated with both physiological and pathological changes in signalling through the TCR.

PTPN22.6, a dominant negative isoform of PTPN22 and potential biomarker of rheumatoid arthritis.

PTPN22 is a tyrosine phosphatase and functions as a damper of TCR signals. A C-to-T single nucleotide polymorphism (SNP) located at position 1858 of human PTPN22 cDNA and converting an arginine (R620) to tryptophan (W620) confers the highest risk of rheumatoid arthritis among non-HLA genetic variations that are known to be associated with this disease. The effect of the R-to-W conversion on the phosphatase activity of PTPN22 protein and the impact of the minor T allele of the C1858T SNP on the activation of T cells has remained controversial. In addition, how the overall activity of PTPN22 is regulated and how the R-to-W conversion contributes to rheumatoid arthritis is still poorly understood. Here we report the identification of an alternative splice form of human PTPN22, namely PTPN22.6. It lacks the nearly entire phosphatase domain and can function as a dominant negative isoform of the full length PTPN22. Although conversion of R620 to W620 in the context of PTPN22.1 attenuated T cell activation, expression of the tryptophan variant of PTPN22.6 reciprocally led to hyperactivation of human T cells. More importantly, the level of PTPN22.6 in peripheral blood correlates with disease activity of rheumatoid arthritis. Our data depict a model that can reconcile the conflicting observations on the functional impact of the C1858T SNP and also suggest that PTPN22.6 is a novel biomarker of rheumatoid arthritis.

The role of PTPN22 gene polymorphism in childhood immune thrombocytopenic purpura.

Immune thrombocytopenia is an autoimmune disorder characterized by antibody-mediated platelet destruction. A protein tyrosine phosphatase (PTPN22) present in lymphocytes is an important negative regulator of signal transduction for the T-cell receptor-MHC complex and has been associated with autoimmune disorders that produce autoantibodies. The present study investigated the frequency of the 1858C>T single-nucleotide polymorphism (SNP) in the PTPN22 gene in idiopathic thrombocytopenic purpura (ITP) patients. This case series study included 50 children with ITP, 24 acute and 26 chronic cases, and 50 normal children as a control group. All were subjected to clinical history and laboratory investigations including complete blood count, genotyping of PTPN22 1858C/T SNP by polymerase chain reaction-restriction fragment length polymorphism and platelet antibodies using platelets suspension immunofluorescence test for the cases. Thirteen patients (26%) were positive for the PTPN22 1858C>T SNP. Three patients were homozygous for the mutation and 10 were heterozygous. Comparison of the 26% of the ITP patients who were positive for the PTPN22 1858C>T mutation with the 6% positive in the control group yielded a P value of 0.006. Antiplatelet antibodies were detected in five patients (20.8%) with acute ITP and in three patients (11.5%) with chronic ITP; no significant association between the presence of PTPN22 1858C>T mutation and the presence of antiplatelet antibodies was detected. The prevalence of PTPN22 gene mutation was higher in ITP patients, thus it may be considered as a genetic risk factor in the development of ITP in Egyptian children.

Association of the PTPN22 gene polymorphism with autoantibody positivity in Turkish rheumatoid arthritis patients.

The PTPN22 C1858T gene polymorphism has been recently reported to be associated with rheumatoid arthritis (RA) in European and North American ancestry. In contrast, the frequency of PTPN22 C1858T polymorphism is extremely rare in Asian and African populations. As the genetic heterogeneity between populations is clearly present in RA, we wanted to investigate whether the PTPN22 C1858T polymorphism is associated with RA in Turkey and with autoantibody positivity. A total of 323 RA patients and 426 healthy controls were genotyped by polymerase chain reaction restriction fragment length polymorphism for the PTPN22 C1858T polymorphism (rs2476601). The frequencies of heterozygote genotype (CT) were 8.4% in RA patients and 5.4% in the healthy controls, respectively [odds ratio (OR): 1.6, P = 0.14]. The homozygote genotype (T/T) was absent in both RA patients and the healthy controls. When compared with the healthy controls, we found the significant associations between the frequency of PTPN22 heterozygote (CT) polymorphism and RA patients with RF positivity and anti-CCP positivity, respectively (OR: 2.05, P = 0.04 and OR: 2.1, P = 0.03, respectively). Our study suggests that the PTPN22 C1858T polymorphism acts as a susceptibility gene for autoantibody-positive RA in Turkey.

Sex-specific association of the human PTPN22 1858T-allele with type 1 diabetes.

Type 1 diabetes (T1D) is a common organ-specific autoimmune disease of complex aetiology, involving the interaction of a large number of disease-associated genes. By comparison of a Danish population sample of 253 Caucasian children and adolescents with T1D and a control group consisted of 354 unrelated healthy blood donors, the present study provides evidence of an isolated association of the disease-associated PTPN22 1858T-allele with T1D to the female sex. Furthermore, the present data suggest that PTPN22 genotypes affect the age of onset in a sex-specific manner. The increased frequency of the risk allele and its association with age at onset in female T1D children and adolescents indicates that the genetic contribution to disease pathogenesis is more prominent in females in this population of Danish patients.