A role for RAD51 in the generation of immunoglobulin gene diversity in rabbits.

Ig VDJ genes in rabbit somatically diversify by both hyperpointmutation and gene conversion. To elucidate the mechanism of gene conversion of IgH genes, we cloned a rabbit homologue of RAD51, a gene involved in gene conversion in Saccharomyces cerevisiae (yeast), and tested whether it could complement a yeast rad51 mutant deficient in recombination repair. We found that rabbit RAD51 partially complemented the defect in switching mating types by gene conversion as well as in DNA double-strand break repair after gamma-irradiation. Further, by Western blot analysis, we found that levels of Rad51 were higher in appendix-derived B lymphocytes of 6-wk-old rabbits, a time at which IgH genes diversify by somatic gene conversion. We suggest that Rad51 is involved in somatic gene conversion of rabbit Ig genes.

Somatic diversification of IgH genes in rabbit.

Rabbits have helped elucidate one of the major immunologic puzzles, namely the genetic control of antibody diversity. The primary IgH antibody repertoire in rabbits is dominated by B cells that use the same germline VH-gene segment in VDJ gene rearrangements. The VDJ genes of essentially all B lymphocytes undergo somatic diversification within the first few weeks of the rabbit's life. Such diversification occurs both by a somatic gene conversion-like mechanism as well as by somatic hyperpointmutation. The diversification that occurs early in ontogeny takes place in gut-associated lymphoid tissues and potentially depends on external factors such as microbial antigens. Few, if any, new B lymphocytes develop in adult rabbits and we discuss how the antibody repertoire is maintained throughout life. Finally, we discuss the molecular mechanism of somatic gene conversion of Ig genes, including the possibility that this involves the use of RAD51, an enzyme required for gene conversion-mediated mating type switch in yeast.

Rheumatoid arthritis in Tlingit Indians: clinical characterization and HLA associations.

OBJECTIVE: To characterize the features of rheumatoid arthritis (RA) in Tlingit Indians, to identify the HLA-DR alleles associated with RA in the Tlingit, and to determine whether disease severity or specific clinical manifestations correlate with the presence of specific HLA antigens. METHOD: Thirty-seven Tlingit patients with RA and 75 controls were evaluated clinically; comparative HLA studies were carried out in 33 patients and 62 controls. RESULTS: The results of this clinical study of RA in the Tlingit confirms that the disease found in them is classical RA, characterized by an early age of onset, a high frequency of nodules, serum rheumatoid factor (RF) and antinuclear antibodies (ANA); an often severe clinical course, with a high frequency of erosive disease and frequent need for surgical joint repair, and an often positive family history. In Tlingit volunteers who did not have RA we also found an increased prevalence of RF and ANA. Neither HLA-DR1 nor DR4 was found to be associated with RA in the Tlingit. The commonest DR antigen in patients with RA was DR14. The most frequent DRB1 allele was DRB1*1402 (Dw16). CONCLUSION: The Tlingit population had a very high frequency of the DRB1*1402 allele, which shares key sequence homology with DRB1*0401 (Dw4) and DRB1*0101 (Dw1), associated with RA in other racial groups. No correlations were found between specific HLA-DRB1 alleles or combinations of alleles and specific disease features or severity.

Rheumatoid factor, HLA-DR4, and allelic variants of DRB1 in women with recent-onset rheumatoid arthritis.

OBJECTIVE: To examine the relationship of rheumatoid factor (RF) to HLA-DR4 and alleles of DRB1 in women with recent-onset rheumatoid arthritis (RA). METHODS: Incident cases of RA were identified as part of a prospective, population-based case-control study. HLA typing was completed for 246 cases meeting criteria for definite or classic RA. RESULTS: One hundred thirty-six patients (55%) were positive for DR4, and 130 (53%) were RF positive. DR4 was found to be strongly associated with seropositivity (odds ratio 4.1, P < 0.0001). Patients with a shorter interval from RA onset to RF testing had a higher frequency of seropositivity than those with a longer interval (< or = 18 months 60%, > 18 months 33%). Further analysis of patients who had RF testing within 18 months of RA onset showed that the frequency of seropositivity was significantly greater among DR4-positive patients who had the shared sequence stretch of DR beta 1 associated with RA susceptibility (76% RF positive) than among DR1-positive patients who had this sequence (45% RF positive) (odds ratio 3.8, P = 0.01). Moreover, the frequency of seropositivity among DR1-positive patients with the sequence did not differ from that among all patients without the shared sequence (47%) (odds ratio 0.9, P = 0.8). CONCLUSION: HLA-DR4 is strongly associated with seropositivity in women with recent-onset RA. The amino acid sequence of DR beta 1 that is associated with susceptibility to RA and is shared between DR4 and DR1 appears not to be the primary determinant of seropositivity in these women.

T-cell receptor polymorphisms in Tlingit Indians with rheumatoid arthritis.

Rheumatoid arthritis (RA) develops as a result of the interaction of both genetic and environmental factors. Among the genes in humans that have been suggested as candidate susceptibility genes in RA are those encoding the T cell receptor for antigen (TCR). A high prevalence and early age of onset of RA has previously been reported in Alaskan Tlingit Indians. In this study, the frequency of seven different restriction fragment length polymorphisms (RFLPs) in the TCR alpha and beta gene complexes were measured in a population of Alaskan Tlingit Indians. No statistically significant differences were noted when the frequencies of these RFLPs were compared between Tlingits with RA and healthy controls (p > 0.05). These results do not support the hypothesis of an RA-susceptibility allele in the vicinity of these TCR alpha or beta genes. Since TCR RFLPs have not been extensively studied in native American populations, TCR polymorphism frequencies in the Tlingits were also compared to the frequencies observed in a second control group of healthy Caucasians. Statistically significant differences were observed in these comparisons implying a different distribution of individuals in these populations with different TCR repertoires.