Naturally processed peptides from rheumatoid arthritis associated and non-associated HLA-DR alleles.

Naturally processed peptides from immunoaffinity-purified HLA-DRB1*0401, -DRB1*0404 (rheumatoid arthritis (RA)-associated), and -DRB1*0402 (non-RA-associated) molecules were analyzed by capillary liquid chromatography and mass spectrometry. The molecular weights observed for more than 60 eluted peptides from each HLA-DR protein ranged from 788 to 3535 atomic mass units, corresponding to peptides 7 to 32 amino acids in length. Sequencing of more than 60 of the abundant peptides revealed nested sets of peptides that were derived from only 12 different proteins. The majority of these proteins were membrane-associated (HLA class I, class II, and Ig molecules). Synthetic peptides, corresponding to endogenous peptide sequences, bound with high affinity (5 to 80 nM) to the HLA-DR molecules from which they were eluted. In addition, most were promiscuous binding peptides in that they also bound to other HLA-DR molecules. Truncations of eluted peptide sequences and alanine scanning mutational analysis of a Mycobacterium leprae peptide were used to identify the peptide residues involved in binding to DRB1*0404 and DRB1*0402 molecules. Furthermore, an invariant chain peptide was eluted from the DRB1*0402 molecules but not from the RA-associated molecules. The lack of invariant chain peptides from DRB1*0401 and DRB1*0404 molecules may contribute to the loading of autoantigen peptides into these molecules and to their association with disease.

HLA-DR and tuberculin tests in rheumatoid arthritis and tuberculosis.

Responses to four new tuberculins were found to be significantly reduced in 46 patients with rheumatoid arthritis in comparison with a control group of 79. Except for tuberculin itself, the same was found in 111 patients with tuberculosis. In common with patients with tuberculosis and leprosy, those with rheumatoid arthritis did not respond to common mycobacterial (group i) antigen. Three DR haplotypes were found to have significant effects on skin test responsiveness of the rheumatoid patients but had little or no effect on that of the patients with tuberculosis and none on that of the healthy control group. Rheumatoid patients with the HLA-DR4 haplotype had significantly greater responses to all four reagents than did non-DR4 patients, but their responses to leprosin A and scrofulin remained significantly lower than those of the control group. Possession of HLA-DR3 haplotype was associated with skin test positivity approaching normal, but the sizes of responses were reduced. Possession of DR7 was associated with an unexpected reduction in skin test positivity, especially in the case of tuberculin. These results support the hypothesis that mycobacteria, or autoantigens cross reactive with mycobacteria, may be involved in the aetiology of rheumatoid arthritis. The results also show that the regulation and specificity of responsiveness to mycobacterial antigens are different in patients with rheumatoid arthritis with different HLA-DR haplotypes.

Evidence for an HLA-DR4-associated immune-response gene for Mycobacterium tuberculosis. A clue to the pathogenesis of rheumatoid arthritis?

Antigens of Mycobacterium tuberculosis, M leprae, M scrofulaceum, and M vaccae were injected intradermally in 86 caucasoid leprosy patients, and skin responses (measured in mm of induration at 72 h) were analysed in relation to HLA class II phenotypes. HLA-DR4 was associated with high responsiveness to antigens specific to M tuberculosis but not to antigens shared with other mycobacteria (p = 0.0005). Because DR4 is associated with rheumatoid arthritis (RA) and because a role for M tuberculosis antigens has been suggested both in experimentally induced autoimmune arthritis in rats and in RA, the DR4 associated regulation of the immune response to M tuberculosis may be relevant to the pathogenesis of RA.

Genetic heterogeneity of rheumatoid arthritis.

In a population survey in The Netherlands we investigated 6584 individuals for the presence of rheumatoid diseases and their determinants. We observed no overall association of rheumatoid arthritis (RA) with HLA-DR4 or GM. This result is in contrast to the marked association of HLA-DR4 with RA found in studies based mainly on hospital rheumatology clinics. The findings thus suggest a genetic basis for the disease heterogeneity. A study of 16 multicase RA families showed a co-segregation of RA with the DR4 carrying haplotype from the unaffected parent, whereas the non-DR4 haplotype was preferentially segregating to the healthy siblings (p = 0.001). These data suggest that HLA-DR4 is associated with disease susceptibility rather than with a disease modifying factor. In a further attempt to define a genetic basis for disease heterogeneity we compared five well-defined clinical groups of patients with RA. Although the frequency of HLA-DR4 was significantly elevated in all patient groups as compared to healthy controls, we observed a preferential association of HLA-DR4 with severe extra-articular manifestations as compared to patients without extra-articular manifestations (p = 0.002). These results provide an immunogenetical basis for the disease heterogeneity observed in RA and further extend the immunological analogy between RA and leprosy.

On the significance of C2, C4, and factor B polymorphisms in disease.

In this review article, recent evidence is presented that some diseases like insulin-dependent diabetes mellitus, multiple sclerosis, and idiopathic membranous nephropathy, which are primarily associated with HLA-D,DR, are also related to the rare C2, C4, and Factor B alleles. Circumstantial evidence is available that at least some of these rare variants may be functionally deficient. Based on the concept of functionally interacting gene clusters, mutant complement genes may lead to impaired effector mechanisms in virus neutralization or lysis of virus-infected cells. Other mechanisms such as alteration of vascular permeability may be involved in the development of proliferative retinopathy and familial hypertension. In lepromatous lepra, an impaired cell-mediated lysis of M. leprae may be related to the hemolytically inactive C4F1 allelic product.