Genes, environment and immunity in the development of rheumatoid arthritis

Concordant and discordant associations between rheumatoid arthritis, systemic lupus erythematosus and ankylosing spondylitis based on all hospitalizations in Sweden between 1973 and 2004

OBJECTIVES

To quantify the sibling risk of RA, SLE and AS. To analyse the concordant and discordant associations between RA, SLE and AS.

METHODS

Follow-up study of all individuals and their siblings born in or after 1932 and hospitalized for RA, SLE or AS between 1973 and 2004 (32 yrs). Data were retrieved from a comprehensive dataconstructed by using several national Swedish data registers, including the Total Population Register, the Swedish Hospital Discharge Register and the Multigeneration Register. Standardized incidence ratios (SIRs) were used to estimate sibling risks.

RESULTS

For males, the overall significant SIRs were 4.72, 4.35 and 4.14 for RA, SLE and AS, respectively, if a sibling was affected by any inflammatory disease. The corresponding significant SIRs for females were 4.12, 3.73 and 4.73. The concordant significant SIRs in siblings were 5.12, 17.02 and 17.14 for RA, SLE and AS, respectively. There were also discordant associations between RA and SLE, whereas AS was only associated with AS.

CONCLUSIONS

This study was able objectively to quantify the sibling risk of RA, SLE and AS, which represents useful knowledge for clinicians and geneticists. The analysis of concordant and discordant associations may be useful in future studies aimed at finding specific genes associated with these diseases.

Recent developments in the immunobiology of rheumatoid arthritis

Progress into the understanding of immunopathology in rheumatoid arthritis is reviewed in the present article with regard to pro-inflammatory cytokine production, cell activation and recruitment, and osteoclastogenesis. Studies highlight the potential importance of T helper 17 cells and regulatory T cells in driving and suppressing inflammation in rheumatoid arthritis, respectively, and highlight other potential T-cell therapeutic targets. The genetic associations of the HLA shared epitope alleles with antibodies to citrullinated peptides in rheumatoid arthritis patients indicate that T cells are providing help to B cells to produce autoantibodies, and there is increasing evidence that these autoantibodies are pathogenic in rheumatoid arthritis.

Association of STAT4 with rheumatoid arthritis in the Korean population

A recent study in the North American White population has documented the association of a common STAT4 haplotype (tagged by rs7574865) with risk for rheumatoid arthritis (RA) and systemic lupus erythematosus. To replicate this finding in the Korean population, we performed a case-control association study. We genotyped 67 single nucleotide polymorphisms (SNPs) within the STAT1 and STAT4 regions in 1123 Korean patients with RA and 1008 ethnicity-matched controls. The most significant four risk SNPs (rs11889341, rs7574865, rs8179673, and rs10181656 located within the third intron of STAT4) among 67 SNPs are identical with those in the North American study. All four SNPs have modest risk for RA susceptibility (odds ratio 1.21-1.27). A common haplotype defined by these markers (TTCG) carries significant risk for RA in Koreans [34 percent versus 28 percent, P=0.0027, OR (95 percent CI)=1.33 (1.10-1.60)]. By logistic regression analysis, this haplotype is an independent risk factor in addition to the classical shared epitope alleles at the HLA-DRB1 locus. There were no significant associations with age of disease onset, radiographic progression, or serologic status using either allelic or haplotypic analysis. Unlike several other risk genes for RA such as PTPN22, PADI4, and FCRL3, a haplotype of the STAT4 gene shows consistent association with RA susceptibility across Whites and Asians, suggesting that this risk haplotype predates the divergence of the major racial groups.

The course of established rheumatoid arthritis

Rheumatoid arthritis (RA) varies over time in individual patients and there are marked differences between patients in its impact and progression. The course of RA is therefore unique to each individual patient and is affected by the overall pattern of disease; many patients have classical polyarticular disease but there is also a range of subtypes, such as fibromyalgic and polymyalgic disease. Some patients with RA enter a period of sustained remission; this varies between 10% and 36% of cases; its frequency is mainly influenced by the different approaches to studying RA patients over time, and does not represent a true difference in disease outcome. Most patients have persisting synovial inflammation and disease activity scores average between 3 and 4; there is some evidence that inflammation is less marked in late RA. Persisting synovitis results in increasing disability - this worsens by an average of 0.6% each year - and in joint damage, which increases by an average of 2% each year. Comorbidities and extra-articular features are commonplace: about one-third of patients, respectively, have associated cardiovascular disease, lung disease or extra-articular features, although severe extra-articular problems like vasculitis affect only about 10% of patients. Some aspects of the course of RA are influenced by genetic risks; currently these are only weak predictors but it is anticipated their value will increase with time.

[Antibodies to citrullinated peptides in rheumathoid arthritis]

Rheumatoid arthritis is a systemic autoimmune disease characterized by chronic inflammation of the synovial joints leading to progressive joint destruction. The serum of these patients contains a large repertoire of autoantibodies, mainly rheumatoid factor, which is part of the ACR classification criteria in spite of having only moderate specificity. Antibodies directed to citrullinated proteins provide clinicians with a valuable tool for early diagnosis. It has been shown that these antibodies can be detected years before presentation of the first symptom and are very useful for diagnosis and prognosis, due to good sensitivity and specificity and prediction of development of erosive disease. The immune response against citrullinated antigens is characteristic of an immuno-genetic subtype of disease, in which the combined role of genes, environmental factors and autoimmunity has become the prime suspected for disease pathogenesis. A model is proposed of how these antibodies are produced and lead to chronic synovial inflammation.

Gendefekt im Promoter der endothelialen NO-Synthase als Risikofaktor für Rheumatoide Arthritis

The risk to develop rheumatoid arthritis (RA) includes environmental as well as genetic factors. Moreover, RA, being an inflammatory disease, is itself considered to be a risk factor for coronary artery disease, as it - or its treatment - may lead to endothelial dysfunction. Likewise, a single nucleotide polymorphism in the promoter of the endothelial NO synthase ((-786)C/T) leads to endothelial dysfunction in (-786)CC homozygous individuals. This genetic defect occurs in significantly higher frequencies in patients with RA, and therefore must be regarded as a genetic risk factor for RA.

In vivo expression pattern of MICA and MICB and its relevance to auto-immunity and cancer

Non-conventional MHC class I MIC molecules interact not with the TCR, but with NKG2D, a C-type lectin activatory receptor present on most NK, gammadelta and CD8(+) alphabeta T cells. While this interaction is critical in triggering/calibrating the cytotoxic activity of these cells, the actual extent of its in vivo involvement, in man, in infection, cancer or autoimmunity, needs further assessment. The latter has gained momentum along with the reported expansion of peripheral CD4(+)CD28(-)NKG2D(+) T cells in rheumatoid arthritis (RA). We first initiated to extend this report to a larger cohort of not only RA patients, but also those affected by systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS). In RA and SS, this initial observation was further tested in target tissues: the joint and the salivary glands, respectively. In conclusion and despite occasional and indiscriminate expansion of the previously incriminated T cell subpopulation, no correlation could be observed between the CD4(+)CD28(-)NKG2D(+) and auto-immunity. Moreover, in situ, the presence of NKG2D matched that of CD8(+), but not that of CD4(+) T cells. In parallel, a total body tissue scan of both MICA and MICB transcription clearly shows that despite original presumptions, and with the exception of the central nervous system, both genes are widely transcribed and therefore possibly translated and membrane-bound. Extending this analysis to a number of human tumors did not reveal a coherent pattern of expression vs. normal tissues. Collectively these data question previous assumptions, correlating a tissue-specific expression/induction of MIC in relevance to auto-immune or tumor processes.

The remission of rheumatoid arthritis during pregnancy

Rheumatoid arthritis (RA) is an autoimmune disease that is favorably influenced by pregnancy but relapses after delivery. A variety of circulating factors has been considered as candidates for inducing gestational improvement of RA; however, the factors/pathways responsible remain still elusive. This review discusses recent research on the effect of pregnancy on RA with a focus on immunregulation, cytokine secretion, HLA antigens, microchimerism, and innate immunity. The complex hormonal and immunological alterations of pregnancy may temporarily correct the disturbed immunregulation of RA.

The target tissue in autoimmunity – an influential niche

Central and peripheral tolerance mechanisms were for a long time the only regulatory circuits known in autoimmunity. It is now becoming clear that the target tissue itself may have the capacity to control its own destiny. Here we review mechanisms by which the target tissue regulates local inflammation, and the way this could influence progression to overt autoimmunity. Moreover, we discuss recent data showing that physiological properties of the target tissue can determine the organ specificity of autoimmune disease. These recent discoveries and ideas concerning the regulatory potential of the target tissue may, in the future, add a new dimension to our concept of regulatory circuits in autoimmunity.

Rheumatoid arthritis and the complement system

Complement activation contributes to a pathological process in a number of autoimmune and inflammatory diseases, including rheumatoid arthritis (RA). In this review we summarize current knowledge of complement contribution to RA, based on clinical observations in patients and in vivo animal models, as well as on experiments in vitro aiming at elucidation of underlying molecular mechanisms. There is strong evidence that both the classical and the alternative pathways of complement are pathologically activated during RA as well as in animal models for RA. The classical pathway can be initiated by several triggers present in the inflamed joint such as deposited autoantibodies, dying cells, and exposed cartilage proteins such as fibromodulin. B cells producing autoantibodies, which in turn form immune complexes, contribute to RA pathogenesis partly via activation of complement. It appears that anaphylatoxin C5a is the main product of complement activation responsible for tissue damage in RA although deposition of membrane attack complex as well as opsonization with fragments of C3b are also important. Success of complement inhibition in the experimental models described so far encourages novel therapeutic approaches to the treatment of human RA.