Reevaluation of the interaction between HLA-DRB1 shared epitope alleles, PTPN22, and smoking in determining susceptibility to autoantibody-positive and autoantibody-negative rheumatoid arthritis in a large UK Caucasian population

The balance of expression of PTPN22 splice forms is significantly different in rheumatoid arthritis patients compared with controls

Background

The R620W variant in protein tyrosine phosphatase non-receptor 22 (PTPN22) is associated with rheumatoid arthritis (RA). The PTPN22 gene has alternatively spliced transcripts and at least two of the splice forms have been confirmed to encode different PTPN22 (LYP) proteins, but detailed information regarding expression of these is lacking, especially with regard to autoimmune diseases.

Methods

We have investigated the mRNA expression of known PTPN22 splice forms with TaqMan real-time PCR in relation to ZNF592 as an endogenous reference in peripheral blood cells from three independent cohorts with RA patients (n = 139) and controls (n = 111) of Caucasian origin. Polymorphisms in the PTPN22 locus (25 SNPs) and phenotypic data (gender, disease activity, ACPA and RF status) were used for analysis. Additionally, we addressed possible effects of methotrexate treatment on PTPN22 expression.

Results

We found consistent differences in the expression of the PTPN22 splice forms in unstimulated peripheral blood mononuclear cells between RA patients and normal controls. This difference was more pronounced when comparing the ratio of splice forms and was not affected by methotrexate treatment.

Conclusions

Our data show that RA patients and healthy controls have a shift in balance of expression of splice forms derived from the PTPN22 gene. This balance seems not to be caused by treatment and may be of importance during immune response due to great structural differences in the encoded PTPN22 proteins.

Each type of cause that initiates rheumatoid arthritis or RA flares differentially affects the response to therapy

The autoimmune disease rheumatoid arthritis (RA) presents difficulty in diagnosis, commonly observed flare ups, polycyclical nature of RA progression, and variable response to therapies. Congruent with multiple causes, literature has documented various infectious agents, environmental factors, physical trauma, silica and food sensitivities as potential causes of RA or RA flares in different populations. We propose that these>36 events can initiate RA or RA flares which complicates treatment decisions. Each pharmaceutical medicine benefits 15-82% of RA patients. Predictive factors are needed. Because the initiating cause of RA or RA flare affects the type of joint damage, initial inflammatory response, adaptive immune response, and potential molecular mimicry, we propose the "RA cause affects response to therapy" (RACART) theory. The potential cause combined with confounding factors such as genetic risk factors, nutritional status, epigenetic status, inflammatory levels, and detoxification ability may help predict responses to various therapies.

Smoking is associated with an increased risk of developing ACPA-positive but not ACPA-negative rheumatoid arthritis in Asian populations: evidence from the Malaysian MyEIRA case-control study

We investigated the association between cigarette smoking and the risk of developing rheumatoid arthritis (RA) in the Malaysian population. A total of 1,056 RA patients and 1,416 matched controls aged 18-70 years within a defined area of Peninsular Malaysia were evaluated in a case-control study between August 2005 and December 2009. A case was defined as a person with early diagnosed RA using the 1987 American College of Rheumatology criteria for RA. Controls were randomly selected matched for sex, age, and residential area. Cases and controls answered a questionnaire on a broad range of issues, including lifestyle factors and smoking habits wherein current and former smoking was classified as ever-smoking. The presence of anti-citrullinated peptide antibodies (ACPA) was determined for cases and controls. We found that ever-smokers had an increased risk of developing ACPA-positive RA [odds ratio (OR) = 4.1, 95% confidence interval (CI) 1.9-9.2] but not ACPA-negative RA (OR = 0.7, 95% CI 0.3-2.0), compared with never-smokers. A significant dose-response relationship between cumulative dose of smoking and risk of ACPA-positive RA was observed (<20 pack-years OR = 3.3, 95% CI 1.1-9.8; at least 20 pack-years OR = 5.2, 95% CI 1.6-17.6). Hence, smoking is associated with an increased risk of ACPA-positive RA in the Malaysian population, in which the genetic context is similar to several other Asian countries.

PTPN22 1858C>T polymorphism distribution in Europe and association with rheumatoid arthritis: case-control study and meta-analysis

Objective

The PTPN22 rs2476601 polymorphism is associated with rheumatoid arthritis (RA); nonetheless, the association is weaker or absent in some southern European populations. The aim of the study was to evaluate the association between the PTPN22 rs2476601 polymorphism and RA in Italian subjects and to compare our results with those of other European countries, carrying out a meta-analysis of European data.

Methods

A total of 396 RA cases and 477 controls, all of Italic ancestry, were genotyped for PTPN22 rs2476601 polymorphism. Patients were tested for autoantibodies positivity. The meta-analysis was performed on 23 selected studies.

Results

The PTPN22 T1858 allele was significantly more frequent in RA patients compared to controls (5.7% vs. 3.7%, p = 0.045). No clear relationship arose with the autoantibodies tested. The 1858T allele frequency in Italian RA patients was lower than the one described in northern European populations and similar to the frequency found in Spain, Turkey, Greece, Tunisia. A clear-cut North-South gradient arose from the analysis.

Conclusions

The PTPN22 T1858 allele is associated with RA in the Italian population. A North-South gradient of the allele frequency seems to exist in Europe, with a lower prevalence of the mutation in the Mediterranean area.

A systematic review of serum biomarkers anti-cyclic citrullinated Peptide and rheumatoid factor as tests for rheumatoid arthritis

This systematic review assesses the current status of anti-cyclic citrullinated peptide (anti-CCP) and rheumatoid factor (RF) tests in the diagnosis and prognosis of rheumatoid arthritis (RA). We reviewed publications on tests and biomarkers for early diagnosis of RA from English-language MEDLINE-indexed journals and non-MEDLINE-indexed sources. 85 publications were identified and reviewed, including 68 studies from MEDLINE and 17 non-MEDLINE sources. Anti-CCP2 assays provide improved sensitivity over anti-CCP assays and RF, but anti-CCP2 and RF assays in combination demonstrate a positive predictive value (PPV) nearing 100%, greater than the PPV of either of the tests alone. The combination also appears to be able to distinguish between patients whose disease course is expected to be more severe and both tests are incorporated in the 2010 ACR Rheumatoid Arthritis Classification Criteria. While the clinical value of anti-CCP tests has been established, differences in cut-off values, sensitivities and specificities exist between first-, second- and third-generation tests and harmonization efforts are under way. Anti-CCP and RF are clinically valuable biomarkers for the diagnosis and prognosis of RA patients. The combination of the two biomarkers in conjunction with other clinical measures is an important tool for the diagnosis and management of RA patients.

A spectrum of susceptibility to rheumatoid arthritis within HLA-DRB1: stratification by autoantibody status in a large UK population

Previously-proposed rheumatoid arthritis (RA) HLA-DRB1 susceptibility and protective models were compared, based on amino acids at positions 67-74 and autoantibody combinations. 3 657 RA patients and 1 357 controls were studied using logistic regression, with secondary stratification by anti-citrullinated peptide antibodies(ACPA) and rheumatoid factor(RF). Susceptibility models were based on previously defined HLA-DRB1 shared epitope(SE) subgroups. (70)DERAA(74), D(70) and I(67) protective models were compared, adjusting for HLA-DRB1 SE. A hierarchy of risk was observed within the HLA-DRB1 SE, particularly for ACPA-positive and RF-positive RA: HLA-DRB1(*)0401∼(*)0404>(*)0101∼(*)1001 ((*)0404>(*)0101: P=0.0003). HLA-DRB1(*)0401/(*)0404 compound heterozygosity conferred a risk similar to (*)0401 homozygosity (P=0.70). Protective effects of D(70) and I(67) were similar. Predictions of the D(70) model fitted the data better than those of the I(67) model. The protective effect of D(70) showed a gene-dose effect (OR 0.82, 95% CI 0.73-0.92, P=5.8 × 10(-4)), but was only seen in RA patients positive for RF or ACPA. HLA-DRB1 SE alleles were also associated with ACPA-negative, RF-positive RA (OR 1.42 (1.15-1.76), P=0.0012). In conclusion, HLA-DRB1 SE alleles show heterogeneity in RA susceptibility; their major effect appears to be mediated by ACPA positivity, but a significant association of HLA-DRB1 SE with RF-positive, ACPA-negative RA was also observed. D(70) specifically protected against antibody-positive RA.

Smoking, citrullination and genetic variability in the immunopathogenesis of rheumatoid arthritis

This review describes how studies on interactions between genetic variants, and environmental factors, mainly smoking, contribute to the understanding of how autoimmunity to post-translationally (citrullinated) proteins/peptides may occur and potentially contribute to certain subsets of rheumatoid arthritis. A main message is that studies on specific immune mechanisms in a complex and heterogeneous disease like RA should be undertaken with the help of results from genetic epidemiology. By those means, it may be possible to identify subsets of RA in a way that in the end allows development and testing of precise and subset-specific interventions against environment as well as genetically defined molecular pathways, in particular those that regulate specific immune responses.

The swollen joint, the thickened artery, and the smoking gun: tobacco exposure, citrullination and rheumatoid arthritis

Autoimmune diseases result from an interplay between susceptibility genes and environmental factors. These interacting etiopathogenetic components converge in a critical step preceding disease, the loss of tolerance to self. In this review, we examine the evidences linking tobacco smoking with the initiation and perpetuation of inflammation affecting both the synovial membrane and the endothelial lining in patients with rheumatoid arthritis. This disease is a compelling argument for the decisive role of environment in the triggering of a human autoimmune disease in genetically prone individuals.

The influence of early life factors on the risk of developing rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease that develops as a result of the interaction between genetic and environmental risk factors. Although increasing evidence shows the importance of genes in determining the risk of RA, it is clear that environmental factors also have a vital role. Studies to date have tended to concentrate on environmental influences around the time of disease onset. However, a number of pieces of evidence, including the fact that autoantibodies, such as rheumatoid factor (RF), can develop several years before the onset of clinical disease, suggest that environmental factors may influence disease susceptibility during early life. Several recent studies lend weight to this possibility, with an increased risk of RA in the offspring of mothers who smoked during pregnancy and in those with higher birth weight. There has also been a suggestion that the risk of RA is reduced in breast-fed infants. We describe the evidence surrounding the effect of early life factors on the risk of developing RA and possible mechanisms by which they may act.

Rheumatoid arthritis

Rheumatoid arthritis is characterised by persistent synovitis, systemic inflammation, and autoantibodies (particularly to rheumatoid factor and citrullinated peptide). 50% of the risk for development of rheumatoid arthritis is attributable to genetic factors. Smoking is the main environmental risk. In industrialised countries, rheumatoid arthritis affects 0·5-1·0% of adults, with 5-50 per 100 000 new cases annually. The disorder is most typical in women and elderly people. Uncontrolled active rheumatoid arthritis causes joint damage, disability, decreased quality of life, and cardiovascular and other comorbidities. Disease-modifying antirheumatic drugs (DMARDs), the key therapeutic agents, reduce synovitis and systemic inflammation and improve function. The leading DMARD is methotrexate, which can be combined with other drugs of this type. Biological agents are used when arthritis is uncontrolled or toxic effects arise with DMARDs. Tumour necrosis factor inhibitors were the first biological agents, followed by abatacept, rituximab, and tocilizumab. Infections and high costs restrict prescription of biological agents. Long-term remission induced by intensive, short-term treatment selected by biomarker profiles is the ultimate goal.

The rheumatoid arthritis HLA-DRB1 shared epitope

PURPOSE OF REVIEW

To update progress made between December 2008 and November 2009 on the role of the rheumatoid arthritis (RA)-shared epitope in the cause and pathogenesis of RA.

RECENT FINDINGS

New evidence has been recently presented to suggest that noninherited human leukocyte antigens (HLAs) originating through pregnancy or exposure to maternal antigens in utero could contribute to RA development in shared epitope-negative women. An interaction between smoking and shared epitope-coding non-*04 HLA-DRB1 alleles (particularly HLA-DRB1*01 and HLA-DRB1*10) was formally established for the first time. Progress has been made in determining the relative contributions and the interaction of the shared epitope, PTPN22 and smoking in conferring the risk of anticitrullinated protein antibodies-positive and negative RA. The autoantigen that anticitrullinated protein antibodies recognize in a significant number of RA patients has been identified as citrullinated alpha-enolase and the importance of genetic factors in anticitrullinated protein antibodies-negative RA has been highlighted. Additionally, associations of RA risk with several new genetic markers have been reported. Among them: two new major histocompatibility complex, non-DRB1 loci, a polymorphism marker in major histocompatibility complex class I polypeptide-related sequence A, an allele of the Fcgamma receptor, a polymorphism marker in the beta2-adrenergic receptor and a low-inducible allele of the cytochrome P450 subtype 1A2.

SUMMARY

Although the mechanistic basis of shared epitope-RA association remains an enigma, observations made during the last year shed new light on the conditions in which the shared epitope - alone or in combination with other genes or environmental factors - affects the risk of RA and the phenotype of the disease.

Epidemiology: Interpreting studies of interactions between RA risk factors

Interactions between HLA and PTPN22 genotypes and smoking have been implicated in overall susceptibility to rheumatoid arthritis as well as the incidence of particular disease phenotypes in case-control and case-only studies. As recent epidemiological evidence shows, deciphering these interactions demands consideration of the analytical approach used.

Evaluation of the rheumatoid arthritis susceptibility loci HLA-DRB1, PTPN22, OLIG3/TNFAIP3, STAT4 and TRAF1/C5 in an inception cohort

INTRODUCTION

This study investigated five confirmed rheumatoid arthritis (RA) susceptibility genes/loci (HLA-DRB1, PTPN22, STAT4, OLIG3/TNFAIP3 and TRAF1/C5) for association with susceptibility and severity in an inception cohort.

METHODS

The magnitude of association for each genotype was assessed in 1,046 RA subjects from the Yorkshire Early RA cohort and in 5,968 healthy UK controls. Additional exploratory subanalyses were undertaken in subgroups defined by autoantibody status (rheumatoid factor and anti-cyclic citrullinated peptide) or disease severity (baseline articular erosions, Health Assessment Questionnaire (HAQ) score and swollen joint count (SJC)).

RESULTS

In the total RA inception cohort, the HLA-DRB1 shared epitope (per-allele odds ratio (OR) = 2.1, trend P < 0.0001), PTPN22 (per-allele OR = 1.5, trend P < 0.0001), OLIG3/TNFAIP3 locus (per-allele OR = 1.2, trend P = 0.009) and TRAF1/C5 locus (per-allele OR = 1.1, trend P = 0.04) were associated with RA. The magnitude of association for these loci was increased in those patients who were autoantibody-positive. PTPN22 was associated with autoantibody-negative RA (per-allele OR = 1.3, trend P = 0.04). There was no evidence of association between these five genetic loci and baseline erosions or SJC in the total RA cohort, after adjustment for symptom duration. TRAF1/C5 was significantly associated with baseline HAQ, however, following adjustment for symptom duration (P trend = 0.03).

CONCLUSIONS

These findings support the mounting evidence that different genetic loci are associated with autoantibody-positive and autoantibody-negative RA, possibly suggesting that many of the genes identified to date are associated with autoantibody production. Additional studies with a specific focus on autoantibody-negative RA will be needed to identify the genes predisposing to this RA subgroup. The TRAF1/C5 locus in particular warrants further investigation in RA as a potential disease severity locus.

Lymphoid tyrosine phosphatase and autoimmunity: human genetics rediscovers tyrosine phosphatases

A relatively large number of protein tyrosine phosphatases (PTPs) are known to regulate signaling through the T cell receptor (TCR). Recent human genetics studies have shown that several of these PTPs are encoded by major autoimmunity genes. Here, we will focus on the lymphoid tyrosine phosphatase (LYP), a critical negative modulator of TCR signaling encoded by the PTPN22 gene. The functional analysis of autoimmune-associated PTPN22 genetic variants suggests that genetic variability of TCR signal transduction contributes to the pathogenesis of autoimmunity in humans.