Gene conversion. A mechanism to explain HLA-D region and disease association

Human leukocyte antigen-DQB1*03 alleles are associated with alopecia areata

Alopecia areata (AA) is characterized by hair loss in patches (patchy AA), over the entire scalp (AT, totalis), or universally (AU). An autoimmune mechanism has been hypothesized, because the inflammatory infiltrate targeted to the hair follicles includes activated T cells. To investigate whether or not genetic polymorphism of the human leukocyte antigen (HLA) region contributes to disease susceptibility, we used sequence-specific oligonucleotides and amplified genomic DNA to define HLA-DQA1, -DQB1, and -DPB1 alleles in a cohort of 85 white patients. The frequency of DQB1*0301 was significantly increased to 41% in all patients, and to 47% in AT/AU patients relative to controls (27%). Analyzed together, DQB1*03 alleles (DQB1*0301-*0303) were increased to 80% (all patients) and to 92% (AT/AU) (odds ratio = 12.14, p = 0.00003, corrected). This striking association implicates the DQB1*03 alleles in the pathogenesis of AA. DQB1*06 was decreased relative to controls (56%) in all patients (32%, odds ratio = 0.37, p = 0.0045, corrected). An increase was observed in the HLA-DRB1*11(DR5) allele DRB1*1104, which may result from linkage disequilibrium with DQB1 alleles. Sequence comparison among the allele products associated with AA indicates that the DQB1*03 alleles carry a unique proline at position 55 that is not present in alleles that are neutral or negatively associated with the disease. This highly significant association may exert considerable control over immune responsiveness and the initiation or persistence of a T-cell autoimmune response against the hair follicle.

Disease-associated human histocompatibility leukocyte antigen determinants in patients with seropositive rheumatoid arthritis. Functional role in antigen-specific and allogeneic T cell recognition

The susceptibility to develop seropositive rheumatoid arthritis (RA) has been linked to specific genomic polymorphisms within the HLA complex. Two different haplotypes have been associated with the disease, HLA-DR1 and HLA-DR4. To investigate the link between such phenotypic disease associations and potential immune mechanisms we used alloreactive and antigen-specific human T cell clones. Here we describe a panel of alloreactive T cell clones directed to polymorphic determinants encoded by the third hypervariable region (hvr) of the HLA-DR beta 1-chain. T cell determinants defined by these clones are shared among HLA-DR1, HLA-Dw4, HLA-Dw13, HLA-Dw14, and HLA-Dw15, and are frequent in a population of RA patients. To study the role of such disease-associated epitopes in antigen-restricted T cell recognition we generated T cell clones from RA patients specific for mycobacterial antigens, Epstein-Barr virus antigens, and tetanus toxoid. In all three antigenic systems T cell clones were restricted to either HLA-DR1 or HLA-DR4. These data suggest that the polymorphisms within the first and second hvr of the HLA-DR beta 1-chain that are distinct in HLA-DR1 and HLA-DR4 and not associated with the disease are crucially involved in the recognition of antigens. Polymorphic determinants encoded by the third hvr are shared among disease-associated haplotypes and may function to mediate the interaction of alloreactive T cell receptor molecules with the HLA complex.

A newly characterized HLA DQ beta allele associated with pemphigus vulgaris

The inheritance of particular alleles of major histocompatibility complex class II genes increases the risk for various human autoimmune diseases; however, only a small percentage of individuals having an allele associated with susceptibility develop disease. The identification of allelic variants more precisely correlated with disease susceptibility would greatly facilitate clinical screening and diagnosis. Oligonucleotide-primed gene amplification in vitro was used to determine the nucleotide sequence of a class II variant found almost exclusively in patients with the autoimmune skin disease pemphigus vulgaris. In addition to clinical implications, the disease-restricted distribution of this variant should provide insight into the molecular mechanisms underlying associations between diseases and HLA-class II genes.