HLA class I/class II interaction in early onset pauciarticular juvenile chronic arthritis

HLA-DRB1, TAP2/TAP1, and HLA-DPB1 haplotypes in Finnish juvenile idiopathic arthritis: more complexity within the MHC

This study further defines genetic susceptibility to JIA in the region centromeric to HLA-DRB1. DNA from 234 Finnish JIA nuclear families and 639 elderly Finnish control individuals was genotyped for five functional SNPs within the TAP2 and TAP1 loci ( approximately 200 kb centromeric of HLA-DRB1). Subsets of the controls (186) and patients (145) that had been previously typed for HLA-DRB1 were also genotyped by sequence for the HLA-DPB1 locus. Case/control and transmission disequilibrium test (TDT) methods revealed an association with the DPB1(*)030101 allele for JIA (OR 2.3, 95% CI 1.5-3.5). Notably, a detailed haplotypic analysis of the TAP2/TAP1 loci and their interaction with the HLA-DPB1(*)030101 and DRB1(*)08 and (*)11 alleles showed a variety of over-represented and under-represented TAP2/TAP1 haplotypes not evident in the single marker analysis. The strongest effect was observed in the polyarticular RF negative JIA subgroup for the 2-2-1-2-1 TAP2/TAP1 haplotype (TAP2B and TAP1A alleles) which showed an independent effect from both DRB1(*)08 and (*)11 (P<0.000003) and DPB1(*)030101 (P=0.02). We have provided evidence that the extended haplotypes (including HLA-DRB1, TAP2/TAP1, and HLA-DPB1) of pauciarticular and polyarticular RF negative disease are distinct. This observation may have implications for functional etiological differences between the pauciarticular and polyarticular JIA patients.

Identification of a genetic risk factor for systemic juvenile rheumatoid arthritis in the 5'-flanking region of the TNFalpha gene and HLA genes

OBJECTIVE

To study polymorphisms in the 5'-flanking promoter/enhancer region of the tumor necrosis factor alpha (TNFalpha) gene and in the coding regions of HLA class I and class II genes, in order to better understand the genetic background of juvenile rheumatoid arthritis (JRA).

METHODS

One hundred eleven Japanese JRA patients (50 with systemic disease, 29 with pauciarticular disease, and 32 with polyarticular disease) and 575 healthy Japanese subjects were examined for the allele frequencies of the TNFalpha, HLA-A, and HLA class II (DRB1, DRB3, DRB4, DRB5, DQA1, DQB1, DPA1, and DPB1) genes, by DNA typing using the polymerase chain reaction-sequence-specific oligonucleotide probe method.

RESULTS

The frequencies of the polymorphic allele at positions -1,031 (T to C substitution, termed -1,031C), -863 (C to A, termed -863A), and -857 (C to T, termed -857T) of the TNFalpha gene in patients with systemic JRA, but not in those with polyarticular or pauciarticular JRA, were significantly higher than in the healthy controls. The allele frequencies of DRB1*0405 and DQB1*0401 in systemic JRA, but not in the other JRA types, were significantly higher than in controls. Linkage analysis showed that the presence of both the TNFalpha -857T allele and DRB1*0405 yielded a significantly increased odds ratio (3.84), while the presence of only 1 of them did not yield a high odds ratio (0.87 and 1.58).

CONCLUSION

The -1,031C/-863A allele and the -857T allele of the TNFalpha gene, both of which are related to high production of tumor necrosis factor alpha, are associated with systemic JRA. The -857T allele may enhance the effect of the DRB1*0405/DQB1*0401 haplotype in predisposing to development of systemic JRA.

HLA region microsatellite polymorphisms in juvenile arthritis

A number of microsatellite polymorphisms located in the MHC region of the human chromosome 6 have been analysed in a large group of patients with juvenile arthritis (JA) (n = 177) and in 157 controls. There have been no significant associations for the alleles of the microsatellite polymorphisms D6S-105, D6S-510, TNFA, TNFC, TNFD, TNFE, HSP. Allele frequencies and HLA associations were listed for the non-associated microsatellite loci. The microsatellite locus DQ CAR, which is localized between DQA1 and DQB1, shows a significant positive association with JA for the allele DQ CAR 121 and a negative association for the allele DQ CAR 111. The allele DQ CAR 121 is strongly associated with DQA1*0501 and with DQB1*0301 both in the normal controls and in the patient population. This pair of DQA/DQB alleles corresponds to the DQ molecule DQ7 on the cell surface, which has been described to be strongly associated with JA. Investigations of the two and three-point haplotypes of DQ CAR with alleles of its neighboring loci have shown that the association with DQ CAR 121 is secondary to the association with DQ7 previously observed. Thus, using eight HLA linked microsatellite polymorphisms in the region from HLA-A to HLA-DQ, we have not found any evidence for further loci which might be involved in the coding for susceptibility for JA.

Functional significance of polymorphism among MHC class II gene promoters

The functional significance of polymorphism among MHC class II promoters in man and mouse is here reviewed, mainly in terms of the hypothesis of differential expression. The hypothesis proposes that differences between antigen-presenting cells in MHC class II expression exert a co-dominant effect on the Th1-Th2 cytokine balance, such that class II molecules of one type come to control to a greater extent the production of one group of cytokines, and those of another type the production of the alternative group. The survey deals with the influence of signal strength and antigen-presenting cell type on T-cell subset differentiation; functional differences between MHC class II molecules not obviously related to determinant selection; disease protection mediated by HLA alleles; mechanisms possibly responsible for allotypic and isotypic bias; overdominance (heterozygous advantage) in selection for expression of class II alleles; MHC class II promoter structure and function; inter-locus and inter-allele variability within human MHC class II gene upstream regulatory regions; a comparison of these polymorphisms in mouse and man; read-out of class II promoter function; and a comparison with expression of MHC class I. We conclude that the evidence that this variation is functionally active (i.e. controls expression) is increasing, but is not yet compelling. The crucial test still to come, we suggest, is whether or not the biological effects attributable to this polymorphism will line up with molecular studies on expression.

Clinical and genetic evidence that juvenile arthritis is not a single disease

Ample evidence shows that what was formerly called "juvenile rheumatoid arthritis" is not a single disease. At least six separate diseases were included as subgroups or subtypes of juvenile rheumatoid arthritis in other classifications. The clinical and laboratory features that differentiate these diseases are discussed. Genetic differences, primarily within the HLA system but also for T-cell receptor genes are described and correlated with the new clinical classification of arthritis.

Genetic background and environment contribute synergistically to the onset of autoimmune diseases

Autoimmune diseases result from the breakdown of "self" tolerance. Environmental factors appear to be responsible for triggering this errant immune response, directed against self-tissue determinants, only when a susceptible genetic background is present in an individual. Autoimmune diseases, normally characterized by their association with certain HLA alleles, also share other features: the presence of autoantibodies, autoreactive T lymphocytes, and an intermittent clinical course of exacerbations and remissions. In cases of organ-specific diseases, as well as in cases of multi-system autoimmune diseases, viruses are increasingly implicated as such environmental triggers. Current molecular biology techniques have permitted a fine dissection of the genetic background of susceptible individuals and have enabled a more complete characterization of the immunocompetent cells involved in this autoaggression. Molecular approaches will soon allow us to pinpoint the characteristics of the environmental stimuli, so that protective strategies could be formulated to spare susceptible individuals from their ill effects.

Early-onset pauciarticular juvenile chronic arthritis is associated with a mutation in the Y-box of the HLA-DQA1 promoter

Early-onset pauciarticular juvenile chronic arthritis (EOPA-JCA) has associations with different alleles of the MHC region (HLA-A2, DR5, 6, 8, DQA1*0401, *0501, *0601 and DPB1*0201). All susceptible DQA1 alleles carry an exclusive sequence motif. MHC-class II gene expression is controlled by 5' flanking upstream regulatory regions (URR). A hypervariable region in the promoter region of the HLA-DQA1 gene (-240 and -200 base pairs upstream) defines ten different QAP (DQA1-Promoter) alleles, which are associated with certain DQA1-alleles. The Y-Box in the DQA1 promoter (YC-Box -125 to -115 upstream from the ATG) differs from the consensus sequence (-123 A for G) of all other MHC class II Y-Boxes, resulting in a lower affinity to the NF-Y transcription factor and in a reduced expression of DQA1. A second substitution in the Y-Box of QAP 4.1 and 4.2 (-119 A for G) is found in the promoter alleles of the DQA1-alleles (DQA1*0401, *0501, *0601) and is strongly associated with susceptibility to EOPA-JCA.

Susceptible and protective major histocompatibility complex class II alleles in early-onset pauciarticular juvenile chronic arthritis

Oligonucleotide typing for alleles of the MHC loci DRB1, DQA1, and DQB1 was performed in 160 patients suffering from EOPA, JCA (or JRA = juvenile rheumatoid arthritis). Allele and haplotype frequencies of the patients were compared with the data of an unrelated healthy control group consisting of 200 individuals. Analysis of frequencies shows that HLA alleles are associated not only with susceptibility to EOPA-JCA but also with protection from the disease. The presence of protection connected with certain HLA alleles was assessed using a calculation which takes into account the condition that if one allele is increased, all other alleles of the same locus must be decreased in compensation. Protection can be assumed only in cases where a given allele has an observed frequency which is significantly beyond the expected compensatory decrease. Thus a hierarchy of associations was observed in EOPA-JCA patients. The alleles of the haplotypes DRB1*11 (12)-DQA1*0501-DQB1*0301 as well as DRB1*08-DQA1*0401-DQB1*0402 were found to be associated with susceptibility to disease, whereas the alleles DRB1*07 and DQA1*0201 converge with significant protection from the disease. Whereas the association with disease susceptibility seems to depend on a sequence motif encoded in certain DQA1 alleles, protection is associated either with alleles of DRB1 or DQA1.