Compound heterozygosity for the shared epitope and the risk and severity of rheumatoid arthritis in extended pedigrees

Microchimeric cells promote production of rheumatoid arthritis-specific autoantibodies

BACKGROUND

Women are more likely to develop autoimmune diseases than men. Contribution from microchimerism (Mc) has been proposed, as women naturally acquire Mc from more sources than men because of pregnancy. Women with Rheumatoid Arthritis (RA) who lack RA-associated HLA alleles have been found to harbor Mc with RA-associated HLA alleles in higher amounts than healthy women in prior work. However, an immunological impact of Mc remains to be elucidated.

OBJECTIVES

To test the hypothesis that Mc with RA-risk associated HLA alleles can result in the production of RA-associated autoantibodies, when host genetic risk is absent.

METHODS

DBA/2 mice are unable to produce RA-specific anti-citrullinated autoantibodies (ACPAs) after immunization with the enzyme peptidyl arginine deiminase (PAD) in a previously developed model. DBA/2 females were mated with C57BL/6 males humanized to express HLA-DR4, which is associated with RA-risk and production of ACPAs, to evaluate DR4+ fetal Mc contribution. Next, DBA/2 females born of heterozygous DR4+/- mothers were evaluated for DR4+ Mc of maternal or littermate origin. Finally, DBA/2 females from DR4+/- mothers were crossed with DR4+ males, to evaluate the contribution of any Mc source to ACPA production.

RESULTS

After PAD immunization, between 20 % and 43 % of DBA/2 females (otherwise unable to produce ACPAs) had detectable ACPAs (CCP2 kit) after exposure to sources of Mc with RA-associated HLA alleles, compared to 0 % of unmated/unexposed DBA/2 females. Further the microchimeric origin of the autoantibodies was confirmed by detecting a C57BL/6-specific immunoglobulin isotype in the DBA/2 response.

CONCLUSION

Our study demonstrates that Mc cells can produce "autoantibodies" and points to a role of Mc in the biology of autoimmune diseases, including RA.

HLA-G and the MHC Cusp Theory

Human leukocyte antigens (HLA) are significant genetic risk factors in a long list of diseases. However, the mechanisms underlying these associations remain elusive in many cases. The best-characterized function of classical major histocompatibility complex (MHC) antigens is to allow safe presentation of antigenic peptides via a self/non-self-discrimination process. Therefore, most hypotheses to date have posited that the observed associations between certain HLA molecules and human diseases involve antigen presentation (AP). However, these hypotheses often represent inconsistencies with current knowledge. To offer answers to the inconsistencies, a decade ago we have invoked the MHC Cusp theory, postulating that in addition to its main role in AP, the MHC codes for allele-specific molecules that act as ligands in a conformationally-conserved cusp-like fold, which upon interaction with cognate receptors can trigger MHC-associated diseases. In the ensuing years, we have provided empirical evidence that substantiates the theory in several HLA-Class II-associated autoimmune diseases. Notably, in a recent study we have demonstrated that HLA-DRB1 alleles known to protect against several autoimmune diseases encode a protective epitope at the cusp region, which activates anti-inflammatory signaling leading to transcriptional and functional modulatory effects. Relevant to the topic of this session, cusp ligands demonstrate several similarities to the functional effects of HLA-G. The overall goal of this opinion article is to delineate the parallels and distinctive features of the MHC Cusp theory with structural and functional aspects of HLA-G molecules.

How microchimerism can impart HLA susceptibility in patients with rheumatoid arthritis

Rheumatoid arthritis, a chronic inflammatory joint disease, is strongly associated with HLA-DRB1*01 and *04 alleles that have in common similar 5-amino acid motifs in the third hypervariable region of DRB1 (QKRAA, QRRAA, RRRAA), the so called shared epitope (SE). Most patients with RA carry 1 or 2 doses of the SE, with particular genetic combinations at higher risk. In recent work we provided evidence that patients who lack HLA-DRB1*01 and/or *04 alleles can acquire RA susceptibility through fetal, maternal or iatrogenic microchimerism. We also discuss how Mc carrying HLA-DRB1*04 alleles is more likely to be present in the peripheral blood of RA patients compared to Mc carrying HLA-DRB1*01 alleles. We further analyze our results in light of the hierarchy for RA risk with different combinations of the SE. How Mc could contribute to RA susceptibility and whether it also contributes to the hierarchy of risk observed with particular combinations of SE-containing alleles is certainly the beginning of an intriguing story and may offer hope for future therapeutic and/or preventative interventions.

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.

Transfer of the shared epitope through microchimerism in women with rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is an autoimmune disease that affects mostly women and is associated with HLA-DRB1 genes having in common a shared epitope sequence. In parallel, cells and/or DNA originating from pregnancy (microchimerism) persist for decades and could contribute to autoimmunity. The aim of this study was to examine whether microchimerism may be a source of the shared epitope among women with RA.

METHODS

Women with RA and healthy women who lacked RA-associated genes such as HLA-DRB1*01 (n=33 and n=46, respectively) and/or HLA-DRB1*04 (n=48 and n=64, respectively), were tested for DRB1*01 or DRB1*04 microchimerism by HLA-specific quantitative polymerase chain reaction assays. As controls, alleles not associated with RA (DQB1*02 and DRB1*15/16) were also analyzed.

RESULTS

Compared with healthy women, women (42% with RA had a higher frequency and higher levels of DRB1*04 microchimerism versus 8%; P=0.00002) as well as DRB1*01 microchimerism (30% versus 4%; P=0.0015). Moreover, no difference in microchimerism was observed for alleles not associated with RA.

CONCLUSION

Women with RA had microchimerism with RA-associated HLA alleles, but not with non-RA-associated HLA alleles, more often and at higher levels compared with healthy women. These observations are the first to indicate that microchimerism can contribute to the risk of an autoimmune disease by providing HLA susceptibility alleles.

Mapping of a novel susceptibility gene for rheumatoid arthritis in the telomeric MHC region

Rheumatoid arthritis (RA) is a complex heterogeneous disease with an estimated genetic contribution to of 30-50%. Approximately one third arises from the major histocompatibility complex (MHC) at 6p21.3. The contribution of specific DRB1 alleles encoding the shared epitope has been well described, however, several recent studies have suggested that additional telomeric genetic influences may exist. This region is difficult to study as a result of the presence of strong linkage disequilibrium (LD) within the MHC and high gene density particularly in the central class III region. In this article we review the current data supporting the existence of a non-DRB1 susceptibility gene for rheumatoid arthritis, in particular within the class III region.

Particular HLA-DRB1 shared epitope genotypes are strongly associated with rheumatoid vasculitis

OBJECTIVE

To examine the relationship of the HLA-DRB1 shared epitope (SE) to rheumatoid vasculitis, using individual patient data (IPD) meta-analytic methods.

METHODS

Published studies that enrolled adult patients with rheumatoid arthritis (RA) were identified by searches of Medline and Embase, and by manual searches of medical journals. All authors were contacted for IPD. Meta-analyses were performed to assess the association of SE presence, dose, and genotype with rheumatoid vasculitis.

RESULTS

A total of 14 studies and 1,568 patients (129 with vasculitis) were included in the analysis. RA patients with vasculitis were significantly more likely to have rheumatoid nodules (odds ratio [OR] 2.5, 95% confidence interval [95% CI] 1.5-3.9], but there was no significant association with male sex, rheumatoid factor positivity, or erosive disease. No significant association was observed between the presence of the SE (i.e., 1 or 2 alleles versus 0 alleles) and rheumatoid vasculitis (summary OR 1.4, 95% CI 0.7-2.7). Analysis by SE genotype, however, demonstrated a striking relationship of vasculitis to 3 genotypes containing a double dose of the SE, specifically HLA-DRB1*0401/*0401 (OR 6.2, 95% CI 1.01-37.9), *0401/*0404 (OR 4.1, 95% CI 1.1-16.2), and *0101/*0401 (OR 4.0, 95% CI 1.4-11.6).

CONCLUSION

The HLA-DRB1 SE genotypes *0401/*0401, *0401/*0404, and *0101/*0401 may be of particular importance to rheumatoid vasculitis. It is hoped that additional investigation of these and other SE genotypes will lead to improved insight into the mechanisms influencing the clinical expression of RA.

Impact of shared epitope genotype and ethnicity on erosive disease: a meta-analysis of 3,240 rheumatoid arthritis patients

OBJECTIVE

The strongest known genetic association in rheumatoid arthritis (RA) is with HLA-DRB1 alleles that share a similar amino acid sequence, termed the shared epitope (SE). Although many studies have examined the association of the SE with disease severity, the results have been inconsistent, which may reflect the relatively small sample sizes or ethnic differences. The aim of this study was to assess the association of HLA-DRB1 SE alleles and genotype with the development of bony erosions in RA by meta-analysis.

METHODS

We identified English-language articles published between January 1, 1987 and June 1, 1999 through Medline, EMBase, and manual searches of 6 relevant journals. Included were studies in which molecular typing of HLA-DRB1 alleles was performed and in which the presence or absence of bony erosions was reported. Data were extracted from the studies, and erosions were coded as present or absent. Authors were contacted for missing information and data on individual patients.

RESULTS

A total of 29 studies and 3,240 patients were available for analysis. The summary odds ratios (ORs), when all patients were evaluated as a single group, demonstrated a significant association of the presence of the SE (2 or 1 versus 0 SE alleles) with erosions (OR 2.0; 95% confidence interval [95% CI] 1.8-2.2), although significant heterogeneity was present (P = 0.002). Subgroup analyses demonstrated the important influence of ethnic background. For example, no association of the SE with erosions was demonstrated in Greeks (OR 0.8 [95% CI 0.2-1.5]). In contrast, there was a striking dose-dependent relationship in southern European Caucasians and Asians, with ORs as high as 6.2 and 5.4, respectively, in patients with 2 SE alleles. Although our ability to assess the relationship between SE genotype and erosions was limited, particular importance of the DRB1*0401 SE allele was suggested in an analysis restricted to northern European Caucasians.

CONCLUSION

The SE is associated with the development of erosive disease in many ethnic groups; however, striking exceptions exist. These variations may be due to allele differences between populations, such as the frequency of DRB1*0401 among different ethnic groups. Further study to better understand the genetic and environmental differences between these populations may provide insight into mechanisms that influence the clinical expression of RA.

Lack of association of the HLA-DRB1 shared epitope with rheumatoid nodules: An individual patient data meta-analysis of 3,272 Caucasian patients with rheumatoid arthritis

OBJECTIVE

The objective of this individual patient data (IPD) meta-analysis was to examine the relationship of rheumatoid nodules to the HLA-DRB1 shared epitope (SE) and to individual SE genotypes.

METHODS

English-language studies that enrolled adult non-Hispanic Caucasian patients with rheumatoid arthritis (RA) were identified by searches of Medline and Embase, and by manual searches of medical journals. All authors were contacted for IPD. Meta-analysis was performed to assess the association of SE presence, dose, and genotype with rheumatoid nodules. Meta-analyses adjusted for disease duration and cumulative meta-analyses were also performed to assess the influence of RA duration and year of study publication on the results.

RESULTS

A total of 24 studies and 3,272 patients were available for analysis. IPD were obtained for 22 of the studies. There was a nonsignificant association between the presence of the SE (i.e., 1 or 2 alleles versus 0 alleles) and rheumatoid nodules (summary odds ratio [OR] 1.3, 95% confidence interval [95% CI] 0.97-1.6). Analysis by SE genotype, however, demonstrated a weak relationship with inheritance of a single DRB1*0401 SE allele (OR 1.4, 95% CI 1.1-1.8). No other genotypes achieved statistical significance in the adjusted or unadjusted analyses.

CONCLUSION

The presence of the HLA-DRB1 SE does not appear to significantly increase the risk of rheumatoid nodules among Caucasian patients with RA. Analysis by DRB1 SE genotype was uninformative, suggesting only a potential (and at most modest) role of the DRB1*0401 SE allele. Results from this IPD meta-analysis implicate other genetic, stochastic, and/or environmental factors in the susceptibility to rheumatoid nodules.

Effect of human leukocyte antigen heterozygosity on infectious disease outcome: the need for allele-specific measures

BACKGROUND

Doherty and Zinkernagel, who discovered that antigen presentation is restricted by the major histocompatibility complex (MHC, called HLA in humans), hypothesized that individuals heterozygous at particular MHC loci might be more resistant to particular infectious diseases than the corresponding homozygotes because heterozygotes could present a wider repertoire of antigens. The superiority of heterozygotes over either corresponding homozygote, which we term allele-specific overdominance, is of direct biological interest for understanding the mechanisms of immune response; it is also a leading explanation for the observation that MHC loci are extremely polymorphic and that these polymorphisms have been maintained through extremely long evolutionary periods. Recent studies have shown that in particular viral infections, heterozygosity at HLA loci was associated with a favorable disease outcome, and such findings have been interpreted as supporting the allele-specific overdominance hypothesis in humans.

METHODS

An algebraic model is used to define the expected population-wide findings of an epidemiologic study of HLA heterozygosity and disease outcome as a function of allele-specific effects and population genetic parameters of the study population.

RESULTS

We show that overrepresentation of HLA heterozygotes among individuals with favorable disease outcomes (which we term population heterozygote advantage) need not indicate allele-specific overdominance. On the contrary, partly due to a form of confounding by allele frequencies, population heterozygote advantage can occur under a very wide range of assumptions about the relationship between homozygote risk and heterozygote risk. In certain extreme cases, population heterozygote advantage can occur even when every heterozygote is at greater risk of being a case than either corresponding homozygote.

CONCLUSION

To demonstrate allele-specific overdominance for specific infections in human populations, improved analytic tools and/or larger studies (or studies in populations with limited HLA diversity) are necessary.

The shared epitope and severity of rheumatoid arthritis

After two decades of research involving thousands of RA patients, it is still not possible to precisely define the relation of HLA-DRB1 SE alleles to RA severity. Improvements in our understanding require more careful consideration of several factors such as ethnicity, gender, and the specific SE allele and genotype inherited. Large studies of heterogeneous groups of patients are required and indicate the need for collaborative efforts among researchers. In the interim, meta-analysis of the existing literature may provide some insight, because it allows utilization of the tremendous amount of research already completed. A preliminary meta-analysis highlighted the significant heterogeneity among the existing literature, and a more ambitious meta-analysis that uses individual patient-level data is currently ongoing. Profound implications exist for determination of the precise relationship between the SE and RA severity. This information could be valuable in identifying patients at greater risk of severe complications or as a stratification variable for clinical trials. Moreover, patients genetically predisposed to severe disease may benefit from early initiation of more aggressive therapy. Ultimately, clarification of the role of the SE may be valuable for the development of specific therapies directed toward DRB1 and related targets.

Early rheumatoid arthritis: can we predict its outcome?

The continuing trend towards more aggressive treatment of rheumatoid arthritis (RA) has seen an increasing interest in the early phase of this chronic inflammatory disease. Optimal benefit from present and emerging therapies is limited by our prognostic abilities during this period. The present review attempts to outline first the many methodological issues encountered in studies of early RA, and second the extent to which each major outcome measure can be explained, both by readily available clinical variables and by HLA-DR genotyping. The evidence supporting the clinical usefulness of genotyping is discussed separately. Based on this information, a clinically appropriate approach to the management of early RA and the identification of patients suitable for experimental therapies is suggested.

Rheumatoid arthritis in southern Spain: toward elucidation of a unifying role of the HLA class II region in disease predisposition

OBJECTIVE

To evaluate the contributions of HLA-DQ and -DR polymorphisms to susceptibility to rheumatoid arthritis (RA) in a population in southern Spain, and to compare the value of the shared epitope (SE) and RA protection (RAP) models in accounting for the HLA class II region's contribution to RA predisposition.

METHODS

One hundred sixty RA patients and 153 healthy controls were typed for HLA-DRB1 and -DQB1 using high-resolution DNA techniques. Distributions of predisposing DRB1 alleles in patients and control subjects according to the SE model were compared with distributions of predisposing DQ and protective DERAA-positive DRBI alleles according to the RAP model.

RESULTS

DQ3 (DQBI*03 and *04 combined with DQA1*03) and DQ5 (DQB1*0501/DQA1*0101) alleles predisposed individuals to RA independently of SE-positive DRB1 alleles. DQ3/3-homozygous individuals had the strongest risk of developing RA. DQ3 molecules predisposed to RA more than did DQ5 molecules. The weaker predisposition mediated by DQ5 included the DRB1*1001-carrying haplotype; no DRB1*1001-homozygous patients were observed. DRBI*0401 played a unique role in the contribution of DQ3-DR4 haplotypes to RA, in spite of its low frequency in southern Spain.

CONCLUSION

The low prevalences of RA and of mild disease observed in Spain, and in southern Europe in general, can be explained in great part by the low frequency of DQ3-DR4 haplotypes, especially those carrying DRB1*0401. However, the overall distribution of HLA-DQ and -DR alleles in RA patients compared with control subjects is similar to that in other European and North American populations. A model involving both DQ and DR can best account for the contribution of HLA to RA.

HLA class II association with rheumatoid arthritis: facts and interpretations

We have reviewed the literature on the association of HLA class II with rheumatoid arthritis (RA). Strong linkage disequilibrium among DQB1, DQA1 and DRB1 alleles makes it difficult to evaluate the individual contribution of each locus. Nonetheless, there is a strong case for the role of DQB1*03 and *04 combined with DQA1*03 in susceptibility to severe RA while DQB1*0501 combined with DQA1*0101 and *0104 weakly predisposes to a mild form of RA. However, it is also clear that DRB1*0401 has a particular role in predisposition to the most severe form of the disease while other DRB1 alleles might provide protection. We would like to propose that in RA, as in type I diabetes, both DQ and DR loci contribute to predisposition to the disease.

Racial origin and its effect on disease expression and HLA-DRB1 types in patients with rheumatoid arthritis: a matched cross-sectional study

OBJECTIVE

There are a significant number of patients with rheumatoid arthritis (RA) of North Indian or Pakistani origin (Asian) now living in the UK. RA has been poorly studied in this racial group. The aim of this study was to compare RA in this Asian group with RA in the indigenous northern European (European) population. It was hypothesized that these two racial groups would have different disease expressions and immunogenetics that could be relevant to pathogenesis, prognosis and therapy.

METHODS

One hundred and seven Asian RA patients, who fulfilled the 1987 American College of Rheumatology criteria, were stringently matched for age, sex and disease duration with 107 European RA patients, and were fully assessed.

RESULTS

The Asian RA patients had significantly fewer bony erosions [median Larsen score 58.5 (interquartile range 45.5-77.8) vs 68 (52-93) for European patients; P: = 0.0066, Mann-Whitney U:-test] and rarely had nodules (5.7 vs 20%, P: = 0. 0019, Fisher's exact test). The two groups had the same prevalence of rheumatoid factor positivity, number of swollen joints and level of inflammation (C-reactive protein). The Asian RA patients had a reduced prevalence of the conserved third allelic hypervariable region (3AHVR) (45 vs 82%, P: < 0.0001, Fisher's exact test), particularly DRB1*0401 (4.5 vs 55%). However, the prevalence of the conserved 3AHVR was significantly increased in the Asian RA patients compared with Asian controls. By contrast, the Asian patients had more tender joints [13.5 (7-22) vs 5.5 (2-11.8); P: < 0.0001 Mann-Whitney U:-test]. The Health Assessment Questionnaire score was also significantly worse in the Asians compared with the Europeans [median 2.0 (1.13-2.63) vs 1.25 (0.5-2.13), P: = 0.0001).

CONCLUSIONS

The Asian patients had similar levels of inflammation and less damage but more pain and disability than the matched European RA patients. Of the known prognostic factors for erosions (rheumatoid factor, conserved 3AHVR, swollen joints and C-reactive protein), only the conserved 3AHVR was reduced in the Asian RA patients, and this was consistent with their less erosive disease. These data also indicate the importance of pain as well as erosive damage in determining disability in Asian patients and stress the importance of adequate pain relief, in addition to disease suppression, when treating Asian RA patients.

Immunogenetic differences between patients with familial and non-familial rheumatoid arthritis

OBJECTIVE

To search for possible immunogenetic differencies between the patients with familial and non-familial rheumatoid arthritis (RA).

METHODS

The study compared 129 familial RA patients with 217 non-familial patients for the frequencies of HLA-DR antigens including DR4 subtypes, DR4-DQB1*0301 and DR4-DQB1*0302 haplotypes and HLA-B27 antigen as well as the age of disease onset and existence of rheumatoid factor or joint erosions.

RESULTS

Two major differences between familial and non-familial groups were found: firstly, familial RA patients had increased frequency of HLA-DR4 as compared with the non-familial RA group (68.2 v. 54.8%; p = 0.019). Secondly, the mean age at onset of RA was significantly lower in the familial than in the sporadic RA patients (42.0 v. 46.5 years; p = 0.0020) and the difference still remained when the DR4 positive and negative subgroups were compared separately.

CONCLUSION

These results confirm the more prominent association with HLA-DR4 in familial than in the non-familial cases and suggest that accumulation of HLA risk genes may, at least partly, explain the familial occurrence of the disease. Other susceptibility genes may also be concentrated in multiplex case families as suggested by an earlier age at the onset of RA in both HLA-DR4 positive and negative familial patients.

The influence of HLA-DRB1 alleles encoding the DERAA amino acid motif on radiological outcome in rheumatoid arthritis

OBJECTIVES

To investigate the influence of HLA-DRB1 alleles encoding the QK/RRAA shared epitope (SE) on radiological outcome in rheumatoid arthritis (RA), and to determine whether it is modulated by alleles carrying the putative rheumatoid arthritis-protective (RAP) sequence DERAA. Patients and methods. The association between erosive damage and HLA-DRB1 status was examined in 315 RA patients with a disease duration of 5-30 yr. Radiological outcome was measured by scoring X-rays of the hands and feet using the standard radiographs of Larsen (Larsen score). HLA-DRB1 typing was carried out using polymerase chain reaction methodology.

RESULTS

Patients with two alleles encoding the QK/RRAA SE had significantly higher Larsen scores than SE-negative patients (96.9 vs 83.3; P=0.04, after correction for multiple testing), with DRB1*0401/*0401 homozygotes demonstrating the greatest radiological damage (99.9). The lowest Larsen score (65.6) was observed in patients carrying the DERAA motif without an accompanying SE allele (RAP+/SE-). This was significantly lower than in patients with RAP+/SE+ (105.6; P=0.04), RAP-/SE- (88.2; P=0.05) and RAP-/SE+ (95.8; P=0.009), after correction for multiple testing. There was no evidence that the RAP sequence was modulating the effect of the SE since radiological outcome in RAP+/SE+ patients was not significantly different to that in RAP-/SE+ individuals.

CONCLUSIONS

Our data support a possible role for DRB1 alleles encoding the DERAA motif in protection against severe erosive damage in patients lacking the QK/RRAA SE, but not in patients heterozygous for the SE. This suggests that DRB1 alleles encoding the SE have a dominant influence over 'protective alleles' and are not merely 'non-protective'.

Genetic susceptibility to the connective tissue diseases

Genes important in the connective tissue diseases are being recognized in two basic ways: association studies and linkage analysis. Traditionally, association studies have confirmed a genetic influence in disease pathogenesis, especially in systemic lupus erythematosus, rheumatoid arthritis, juvenile rheumatoid arthritis, and the spondyloarthropathies. One of the strongest associations is with the HLA region. As techniques improve, genome scan studies suggest that multiple genes are involved in each of the connective tissue diseases, with some genes in common that confer an autoimmune susceptibility. Linkage analysis is identifying new candidate genes that will help to explain the etiology of connective tissue diseases.

Quantifying the exact role of HLA-DRB1 alleles in susceptibility to inflammatory polyarthritis: results from a large, population-based study

OBJECTIVE

To accurately determine the contributions of HLA-DRB1 alleles in explaining susceptibility to inflammatory polyarthritis in a large, true population-based cohort of new-onset cases.

METHODS

A cohort of 680 consecutive patients with inflammatory polyarthritis, of whom 404 satisfied the American College of Rheumatology (ACR) criteria for rheumatoid arthritis (RA), was recruited from the population-based Norfolk Arthritis Register. All cases were compared with 286 local population controls. A standardized clinical assessment was performed on all patients. HLA-DRB1 phenotypes, including DR4 subtypes, were determined using a semiautomated, reverse dot-blot method. Results were expressed as odds ratios (OR) and 95% confidence intervals (95% CI).

RESULTS

There was only a modest association (OR 1.8, 95% CI 1.4-2.4) between inflammatory polyarthritis and the presence of any shared epitope (SE) allele; the strongest individual risk was with DRB1*0404 (OR 3.5, 95% CI 1.8-6.8). Comparison of the genotypes demonstrated that the effect of being SE homozygous (OR 2.1, 95% CI 1.5-3.0) was only moderately greater than the effect of being SE heterozygous (OR 1.3, 95% CI 1.1-1.6). The exception to this was genotypic combinations that included HLA-DRB1*0404, which exhibited ORs ranging up to 18.0. There were no differences between either the phenotype or genotype data when the patients were stratified by RA status (defined by the ACR criteria). In contrast, the associations were substantially stronger in patients who were positive for rheumatoid factor.

CONCLUSION

Previous studies had not been able to clarify whether the influence of HLA-DRB1 on RA was related to disease susceptibility or to disease severity and progression. These data on a unique population-based incident cohort suggest only weak effects on susceptibility, with the exception of the clearly distinct influence of HLA-DRB1*0404.

HLA-DQ-associated predisposition to and dominant HLA-DR-associated protection against rheumatoid arthritis

We have recently proposed a new hypothesis to explain the association of Human Leukocyte Antigen (HLA) with rheumatoid arthritis (RA) predisposition. In this model, which challenges the Shared Epitope (SE) hypothesis, HLA-DQ predisposes while HLA-DR protects. In the present study, we have compared these two models in an Early Arthritis Clinic started in 1993 in the Department of Rheumatology at the Leiden University Medical Centre. Out of 524 patients who enrolled this programme in the period 1993-1998 and completed the one year follow-up, 155 have been classified as RA. These patients along with 306 consecutive cadaveric renal organ donors have been typed for HLA-DR and -DQ. The distributions of predisposing DR alleles according to SE, and predisposing DQ and protective DR according to our model were analysed. We found that two doses of predisposing DQ alleles strongly predisposed to RA, even in individuals with a single dose of SE while DRB1 alleles carrying the motif DERAA confered a dominant protection in DQ5-positive individuals. We conclude that the present findings are consistent with our previously described model of HLA and RA association. Using this new model, we have been able to characterise two novel groups of individuals on the basis of their HLA typing: one strongly predisposed to RA and one protected. Knowing the mechanism of HLA-related dominant natural protection may help in designing novel treatment modalities for RA.