Immunogenetic and cellular immune mechanisms in rheumatoid arthritis: relevance to new therapeutic strategies.
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Evidence suggests that polymyalgia rheumatica (PMR) may be an immune-mediated disease. Therefore, the role of HLA class II genes, the switch region of immunoglobin mu and alpha 1 heavy chain as the T-cell receptor (TcR) genes were investigated by Southern blot analysis. The frequency of DR4 specificity was increased in PMR (67.4% versus 30.3%; P = 0.00017). No association was found with the DQA and DQB genes, the switch region of immunoglobulin mu and alpha 1 heavy chain genes, and the TcR alpha, beta and gamma genes. This study suggests that HLA-DR4 is an important susceptibility factor for PMR. Further studies are needed to elucidate the role of Ig and TcR genes.
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The genetic contribution to the development of autoimmune disease is most likely complex. Along with loci controlling histocompatibility antigens and T-cell receptor proteins, genes that encode autoreactive immunoglobulins may have an important role in the pathogenesis of rheumatoid arthritis and related autoimmune diseases. Although much previous work in this area has concentrated on human monoclonal paraproteins and autoimmune mouse strains, the studies reviewed here examine immunoglobulin genes in the normal human population and normal mouse strains as well as in patients with autoimmune disease. Taken together, these studies suggest that genetic control of the expression of autoimmunity in rheumatoid arthritis and related autoimmune disorders is complex and most likely involves multiple gene loci.
The arthritogenic peptide hypothesis has inspired research aimed at defining the peptide-presenting properties of HLA-B27 subtypes and their relation to ankylosing spondylitis. Various studies have shed new light on the influence of HLA-B27 polymorphism in modulating peptide binding and T-cell antigen presentation. Moreover, multiple factors along the antigen processing-loading pathway, including tapasin, contribute to shaping the HLA-B27 repertoire. Other studies have revealed significant peptide-binding similarities between HLA-B27 and subtypes of HLA-B39, supporting a role of this antigen in spondyloarthropathy. A putative pathogenetic role of the HLA-B27 heavy chain, initially suggested from studies in transgenic mice, is claimed on the basis of novel, yet circumstantial, evidence concerning an apparently unusual capacity of the heavy chain to form stable homodimers or misfold after biosynthesis. Finally, it appears that arthritogenic infections might downregulate HLA-B27 expression, favoring bacterial survival. The specificity and mechanism of this phenomenon are yet to be defined.
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Familial SLE provides a unique opportunity to study the relationships of previously associated genetic factors (HLA and complement component deficiencies) to the occurrence of SLE, other immune disorders, and autoantibodies in families. Thus, eight families containing two or more affected members with SLE (n = 22) and their relatives (n = 40) were examined for HLA genotypes, complement components and autoantibodies. Among the 40 non-SLE relatives, 7 (18%) had other immune diseases, including thyroid disease in 2, rheumatoid arthritis in 2, ITP in 2, and Henoch-Schönlein purpura in one. This compared to 4 of the 22 SLE patients (also 18%) of whom 3 had thyroid disease and one PSS. Eleven non-SLE relatives (28%) had ANA, which was in high-titer in 5 (13%). Eleven (28%) had antibodies to ssDNA, and one had a BFP. Only the SLE patients had antidsDNA, Ro(SSA), Sm or nRNP. A heterozygous C2 deficiency (C2D) was found in only one of the seven kindreds studied, and followed an A25, B18 DR7 haplotype. Heterozygous C2D, however, was inherited by only one of three family members with SLE. HLA-DR2 occurred in 36% and DR3 in 36% of SLE patients, which was not significantly different from either non-SLE family members or unrelated local controls. Sib pair analysis of seven sets presented here and seven from two published reports, demonstrated only random distribution with SLE. Similarly, other immune disorders and autoantibodies followed no consistent HLA haplotypes or DR specificities. Interestingly, DR2 and/or DR3 were found in five of the six patients (83%) having anti-ro(SSA) antibodies (p = NS). These data strongly suggest that genetic factors (other than HLA and complement component deficiencies) and/or environmental factors are necessary for the expression of SLE and other immune abnormalities in lupus families.
It has now become clear that certain HLA antigens are associated with disease susceptibility more than any other genetic markers. Insulin-dependent diabetes mellitus (IDDM or type I) is an HLA-associated condition. Moreover, there is evidence to show that IDDM is a genetically programmed autoimmune disease. Studies of the HLA-DR region have shown a strong association with IDDM, with over 90 per cent of IDDM patients possessing DR3 and/or DR4. Although the HLA-DR region is a major component in the inherited disease susceptibility, it is not the only gene region involved. Recent studies demonstrated that HLA-DQ may be more closely linked to the disease locus than HLA-DR. Sequence analysis of the HLA-DQ3 gene products suggest that a single amino acid (aspartic acid) at position 57 is uniquely important for determining susceptibility or resistance to IDDM. Although there is a strong association of certain HLA loci with IDDM, it may not explain nor account for all the genetic susceptibility to the disease. It seems that 60 per cent of the genetic basis of IDDM is related to the HLA gene (chromosome 6) and another 40 per cent is non-HLA-associated (i.e., chromosomes 2, 7, 11, and 14). Even though great progress has been made in the understanding of the genetics of IDDM, the mode of inheritance of the disease remains controversial. The present review discusses various aspects of the autoimmune process believed to be involved in pancreatic beta cell destruction in individuals genetically susceptible to IDDM. The possible modes of inheritance and new data regarding estimated risks of transmitting the disease are presented.
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Blood samples were collected from more than 100 animals in each of 2 Spanish cattle breeds (Retinto and De Lidia), 2 Portuguese breeds (Alentejana and Mertolenga), and American Longhorn cattle. All samples for the 4 Iberian breeds were tested for 20 polymorphic systems; American Longhorn were tested for 19 of the 20. For each breed an average inbreeding coefficient was estimated by a comparison of the observed and expected heterozygosity at 7 or 8 codominant systems tested. All breeds had positive values but only 3 breeds had estimates of inbreeding that were statistically significantly different from 0: De Lidia with f = 0.17, Retinto with f = 0.08 and Mertolenga with f = 0.05. The De Lidia breed especially may be suffering from inbreeding depression since this high value is greater than expected if all of the animals were progeny of half-sib matings. Genetic distances were calculated from the gene frequency data on these 5 breeds plus 9 other European breeds. Analyses of these distances show a closely related group of the 4 Iberian breeds and American Longhorn, confirming the close relationships among the Iberian breeds and the Iberian, probably Portuguese, origin of American Longhorn cattle.
OBJECTIVES: Autoimmune thyroid diseases (AITD) encompass a number of conditions that have in common cellular and humoral responses targeting the thyroid gland. Interactions between susceptibility genes and environmental triggers are thought to initiate an autoimmune response to thyroid antigens leading to disease manifestation. Commencement of the disease in childhood leads to the presumption that genetics may have an important role in the causation of the disease. DESIGN: The present study was aimed at evaluating the human leucocyte antigen (HLA) encoded susceptibility to develop juvenile autoimmune thyroiditis (JAT) in patients from North India. PATIENTS: We studied 48 consecutive patients of JAT along with 176 first-degree relatives for their thyroid function (FT4, TSH) and anti-thyroid peroxidase antibody status (AbTPO). MEASUREMENTS: HLA studies were carried out using serology for HLA-class I antigens and DNA analysis of HLA-class II alleles. The data were compared with a cohort of 308 ethnically matched healthy individuals. RESULTS: We observed overt hypothyroidism in 50% and AbTPO positivity in 70.8% of the index cases. Among the first-degree relatives, goitre was observed in 51.7%, thyroid dysfunction in 28.4% and AbTPO in 29.5% of individuals. Of the 37 relatives who underwent fine-needle aspiration cytology (FNAC), 60% had evidence of chronic lymphocytic thyroiditis (CLT). A strong positive association of HLA-DRB1*1404 was observed with the JAT (35.4%vs. 10.4%, chi2 = 19.8, Pc = 0.0001). We also observed a higher (72%, P = 0.03) paternal transmission of HLA-DRB1*1404 to affected offspring in comparison to unaffected offspring. HLA-DRB1*03 was also increased among JAT patients but did not reach statistical significance. CONCLUSION: These studies point towards an important role of immune modifying genes, such as HLA, in influencing susceptibility to juvenile-onset AITD.
The second example of an HLA-B*44 null allele (B*4423N) was identified by discrepancies between serological and polymerase chain reaction-sequence-specific primer (PCR-SSP) typing in two north-western European Caucasoid unrelated stem cell donor volunteers. HLA-B*4423N was identical to B*440201 except for a single nucleotide substitution at position 493 in exon 3, resulting in a premature stop codon at bases 493-495 (TAG rather than CAG at codon 141). As expected, comprehensive serological testing using 54 antisera, directed towards B44 or Bw4, failed to identify the HLA-B44 (Bw4) specificity. The B*4423N-bearing haplotype was identified as A*0201, Cw*0501, DRB1*0408, DRB4*01, DQA1*03, DQB1*0304 and the frequency of B*4423N estimated as 0.00006 (carriage frequency 0.0121%) in 16 533 subjects resident in Wales.
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