HLA-DR antigens in rheumatoid arthritis in North India

Reshaping the shared epitope hypothesis: HLA-associated risk for rheumatoid arthritis is encoded by amino acid substitutions at positions 67-74 of the HLA-DRB1 molecule

OBJECTIVE

To further analyze the association of HLA-DRB1 alleles with disease susceptibility in recent-onset rheumatoid arthritis (RA).

METHODS

One hundred sixty-seven Caucasian RA patients and 166 healthy controls were typed for HLA-DRB1.

RESULTS

The association of susceptibility to RA with the group of alleles encoding the shared epitope susceptibility sequences (SESSs) was confirmed in recent-onset RA. Among non-SESS alleles, DRB1*07, *1201, *1301, and *1501 showed significant protective effects. Even after correction for the influence of SESS alleles, significant independent protective effects of DRB1 alleles were observed. Protective alleles shared a third hypervariable region motif. Independent homozygosity effects were observed both for susceptibility and for protective alleles.

CONCLUSION

Nonsusceptibility alleles differ significantly with regard to RA risk. Protective alleles show clear homology at positions 67-74, often encoding isoleucine at position 67 or aspartic acid at position 70. Susceptibility and protective alleles both show homozygosity effects. Based on these results and on data reported in the literature, in order to incorporate the finding of differential risks among nonsusceptibility alleles, we propose to reshape the shared epitope hypothesis as follows: HLA-associated risk for RA is encoded by amino acid substitutions at positions 67-74 of the HLA-DRB1 molecule.

HLA antigens in Tlingit Indians with rheumatoid arthritis

HLA-DR4 has been described in association with rheumatoid arthritis (RA) in multiple populations. We have studied HLA antigens in Alaskan Tlingit Indians. HLA-DR4 was decreased in the RA group (n = 32) compared with controls (n = 62) (6% vs 21% p = 0.07). The predominant DR4 allele observed was DRB1*0403 (Dw13.1). The most striking observation in these studies was a marked predominance of the DRB1*1402 allele encoding Dw16 (DRw14). This allele was present in 91% of RA cases, but was also highly prevalent in controls (80%, OR = 2.4 p = 0.20). DRB1*1402 only was observed in 47% of cases and 31% of controls. The DRB3*0101 (DRw52), and the DQA*0501 and DQB*0301 alleles encoding a subset of DQw3 were associated with DRB1*1402 in cases and in controls. HLA-Bw62 was increased in RA cases (28%) compared with controls (8%) (OR = 4.5, p = 0.01, corrected p = ns).

HLA-DR4-DQw8, but not DR4-DQw7 haplotypes occur in Indian patients with rheumatoid arthritis

The distribution of HLA class II antigens in the Asian Indian patients with rheumatoid arthritis (RA) was studied in the present investigation. The results demonstrated that DR4 was significantly increased in both northern (chi 2 = 36.9, P less than 0.00001) as well as southern Indian (chi 2 = 17.3, P less than 0.0001) patients. HLA haplotype analysis revealed the presence of B17-DR4 among southern Indians. Amongst northern Indians, four DR4 haplotypes occurred significantly: A1,B17,DR4; A19,B7, DR4; A30,B13,DR4; and A33,B44,DR4. An analysis of TA10 and DQ'Wa' specificities revealed that all the DR4-DQw3 positive northern Indian RA patients were DQw8 as compared to its frequency of 33.3% in controls. A positive association observed between DR4-DQw7 and RA in some western Caucasian populations was not present in this series. A group of three DR4 positive RA patients were found to be DQw3 negative and DQ'Wa' or DQw4 positive. These results indicated that susceptibility to RA may be controlled by genes in the DR locus independent of any DQ associations.

Dw14(DRB1*0404) is a Dw4-dependent risk factor for rheumatoid arthritis. Rethinking the "shared epitope" hypothesis

HLA-DR4 has been shown to be associated with risk for developing rheumatoid arthritis (RA) in multiple populations and racial groups. The allelic variants of DR4 share the DR4 serologic specificity but differ by 1 to 3 amino acids in the third hypervariable region (positions 67 to 74) and at positions 57 and 86 of the DR beta 1 chain. We have examined DR4 variants in 61 DR4+ RA cases and 55 DR4+ healthy controls. Dw14 was not associated with RA risk in DR4 heterozygous (DR4,X) cases. Only 15% of DR4,X cases had the Dw14 allele compared with 28% of DR4,X controls. In homozygous (DR4,4) individuals who also expressed Dw4, however, Dw14 was associated with increased RA risk. Moreover, the relative risk for Dw4,Dw14 (16.1, p = 0.001) actually exceeded that of Dw4,Dw4 (2.2, p = ns). Thus Dw14 is not an independent risk factor for RA but is a synergistic risk factor for individuals who also have the Dw4 allele.

Is rheumatoid arthritis in Indians associated with HLA antigens sharing a DR beta 1 epitope?

HLA class II antigens were identified in a group of 44 patients with rheumatoid arthritis (RA) originating largely from the north or northeast of the Indian subcontinent and resident now in east London. Compared with 67 locally typed east London Asian controls, the prevalence of three HLA-DR antigens was raised in the patients: DR1 18.2% v 6.0% chi 2 = 3.99, DR4 20.5% v 11.9% chi 2 = 1.48, and DRw10 27.3% v 8.9% chi 2 = 6.56. These differences were also found when the patients with RA were compared with a larger control group of 110 northern Indians: DR1 18.2% v 7.2% chi 2 = 4.02, DR4 20.5% v 7.2% chi 2 = 5.56, and DRw10 27.3% v 8.1% chi 2 = 9.7. Twenty five (57%) of the patients expressed at least one of these antigens. All patients were also characterised for HLA-Dw types by mixed lymphocyte culture typing. The prevalence of the HLA-DR4 associated Dw types in the patients was: Dw4 2.3%, Dw10 0%, Dw14 11.4%, and Dw15 6.8%. The DR beta 1 chains of DR1 and DRw10 together with the Dw types of DR4 other than Dw10 share amino acid residues in a region of the third hypervariable region considered to be critical in antigen presentation. It is concluded that RA in Indians is associated with these HLA antigens, and data from this study support the hypothesis of a cross reactive epitope common to HLA specificities associated with RA.

Susceptibility epitope on HLA-DR beta chain for rheumatoid arthritis and the effect of the positivity on the clinical features

A highly significant association of an amino acid sequence, '70Q71R72R73A74A' located on the DR beta-1 chain, with rheumatoid arthritis (RA) was confirmed in Japanese patients using polymerase chain reaction. The '70QRRA74A' is the most plausible candidate of susceptibility epitope in Japanese RA patients. The patients carrying the sequence showed slightly higher but not significant familial incidence. The positivity of the 'QRRAA' showed no effect on the positivity of the rheumatoid factor, rheumatoid nodules, and extra-articular signs. Also no significant differences in other clinical parameters (ESR, CRP, Hb, A/G) and age at onset were observed regarding the positivity. The risk that the 'QRRAA' positive subjects would suffer from RA was estimated to be about 1.3% which meant 7.2 times easier to get RA than those without 'QRRAA'.

Putative amino acid sequence of HLA-DRB chain contributing to rheumatoid arthritis susceptibility

The association between HLA-DR4 and rheumatoid arthritis (RA) has been established in many ethnic groups. To clarify the determinant of susceptibility to RA, a polymorphic segment of the HLA-DRB gene was amplified in vitro by polymerase chain reaction and analyzed with oligonucleotide probes specific for the HLA-DR4 DNA sequences. A particular sequence encoding amino acids Gln70-Arg71-Arg72-Ala73-Ala74 showed a strong association with RA (p less than 0.005, relative risk 6.0). This amino acid sequence occurs in the DRB molecules with three RA-associated specificities, DR4/Dw14, DR4/Dw15, and DR1. DR4/Dw4, which is common in Caucasian RA patients, has a strikingly similar amino acid sequence Gln70-Lys71-Arg72-Ala73-Ala74 in terms of polarity and charge profiles. Other RA nonassociated sequences differ from this sequence by at least one amino acid substitution that causes the change of the net charge. The composition of amino acid residues at the positions 70-74 may play a crucial role in the pathogenesis of RA.

Rheumatoid arthritis

The results of family and twin studies suggest that RA may result from an interaction between an oligogenic susceptibility and unknown environmental factors. Part of this genetic predisposition is accounted for by genes within the MHC where there is a well-documented association with HLA-DR4. Studies of DR and other MHC variants have shown different associations with particular subgroups. One subgroup is Felty's syndrome where there is a strong association with DR4, as well as associations with DQ-beta and C4B null variants when DR4-matched Felty's and RA subjects are analysed. These DQ-beta and C4B null variants may characterize a single haplotype which is associated with extra-articular disease. A further rheumatoid subgroup characterized by circulating antibodies to native type II collagen, shows an association with HLA-DR3 and 7. Genes on chromosome 14 may also influence susceptibility to RA, probably by interaction with MHC genes and there are different Gm associations for DR4-positive and collagen-antibody-positive rheumatoid subgroups. HLA and Gm markers so far identified only account for a small part of the total genetic predisposition to RA and a third or further loci may also be involved. Possible candidates include T-cell alpha- and beta-chain genes and immunoglobulin light chain genes. One present concept of the genetic predisposition to RA is of several independent immunogenetic pathways each including interactions at two or more loci.

HLA-linked susceptibility to rheumatoid arthritis in north India

Nine multiplex RA families of North Indian origin were tissue typed to determine the segregation of parental haplotypes among sibs. The assortment of haplotypes in 18 affected sibs was not random, with seven sib pairs being HLA identical and two haploidentical with the proband (P = 0.0007). HLA-DR4 occurred in eight out of nine probands (88.8%) and in 11 out of 13 familial RA subjects (84.6%).

HLA haplotype sharing by siblings with rheumatoid arthritis: evidence for genetic heterogeneity

HLA haplotype sharing was studied in 35 sibships in which there were two or more members with rheumatoid arthritis (RA). Haplotype sharing RA siblings was random in 15 sibships which included members with clinical or immunological features of autoimmune thyroid disease. In the remaining 20 'non-thyroid' sibships the frequencies of RA siblings sharing 0, 1, or 2 haplotypes were 0.04, 0.48, and 0.48 respectively (p = 0.006). 67% of RA probands in the 'thyroid' families and 90% in the other families were HLA-DR4 positive. It is suggested that there is genetic heterogeneity in the pathogenesis of RA with at least two independent genes within the major histocompatibility complex (MHC) predisposing to RA. One gene is in linkage disequilibrium with HLA-DR4, while results of comparison of DR antigen frequencies in DR4 negative RA and control groups suggest that the other is in linkage disequilibrium with HLA-DR1 and 3. In the thyroid disease families both genes are frequently present and as either may predispose to arthritis, HLA haplotype sharing is random. The frequencies of HLA haplotype sharing in the 'non-thyroid' families suggest that there is a dominant susceptibility gene in linkage disequilibrium with HLA-DR4, whose frequency is 5% and penetrance about 20%.

Paradoxical inheritance of HLA-linked susceptibility to rheumatoid arthritis

In order to clarify the discrepancy between population studies showing association of rheumatoid arthritis (RA) with HLA-DR4/Dw4 and family studies failing to show linkage with HLA, we analysed 16 multicase families in which RA and DR4 status of both parents was known. 120 HLA-haplotypes of affected and unaffected children could be analysed for co-segregation with RA. In a combined analysis of both affected and unaffected children co-segregation of RA with the DR4 carrying haplotype was observed when both parents were unaffected (p = 0.001). Co-Segregation of RA with one of the two haplotypes of affected parents was observed (p = 0.01), but in this case there was no preference for the DR4 carrying haplotype. In both cases preferential inheritance of the other (not associated with RA) haplotype was observed in unaffected siblings. These data indicate that susceptibility to RA is controlled by an HLA-linked gene. This gene is often but not always identical to the gene coding for a product carrying the DR4 epitope or in strong linkage disequilibrium with it. Combined with previous population data, the present data provide evidence for genetic heterogeneity of RA. Finally, they contain a paradox, based on which a new hypothesis for HLA-linked susceptibility to RA is formulated.

HLA genotypes in two three-generation families with rheumatoid arthritis

Two three-generation families from Northern Sweden with rheumatoid arthritis (RA) were clinically examined. Tissue typing was performed for HLA-A, -B, -C, and -DR antigens. No disease-associated haplotype could be defined within these families. Six of nine members with RA were HLA-DR4 positive. Both families had a HLA-DR4 containing haplotype in the first generation and second-generation members married DR4 positive individuals, which probably increased the risk to develop RA in the third-generation members.

HLA and disease

This review describes the greater portion of a large number of new studies on HLA and disease association which has appeared in the literature since 1979. The majority of these are concerned with the association of certain diseases with class II major histocompatibility complex antigens. The possible biologic significance of these associations in terms of their probable etiology appears to be the prevailing theme. Current thinking regarding certain heritable diseases is described. It seems that although much has been done to resolve the genetics of insulin-dependent diabetes mellitus, other diseases such a multiple sclerosis still remain a mystery. Doubtlessly, much will be gained from DNA cloning and sequencing studies proposed for the future. A great deal of new information has been obtained relative to HLA itself. New loci have been postulated in the HLA-D/DR region through the use of powerful immunochemical procedures made possibly by the advent of modern technological advances. The impact of these developments on our understanding of the function of the MHC in man and its possible relationship to disease are discussed.