Histocompatibility antigens in Omanis: Comparison with other Gulf populations and implications for disease association.

BACKGROUND: This is the first comprehensive report of HLA antigens in Omanis, and the first application of HLA sequence-specific primer (SSP) DNA typing in a Gulf population. The objective was to compare the findings with other Gulf populations and assess their implications for disease association. PATIENTS AND METHODS: HLA typing was carried out on 321 healthy Omanis. One hundred and twenty-six of these were typed for Class II antigens by low-resolution SSP DNA typing. The results were compared with other HLA antigen frequencies recorded from Kuwait and Saudi Arabia. RESULTS: The Omani population was characterized by a very high incidence of HLA-DR2 (66%), with associated HLA-DQ1 (76%) and a reduced incidence of DR4, DR7 and DR53. The incidence of DR2 is the highest recorded worldwide. HLA-A11, A32, B17, B35 and B40 were significantly higher than in Kuwait and Saudi Arabia, and A9, B21(B50) significantly lower (Pc<0.05). HLA-B27 is very low in the Omani population (0.3%). The high incidence of HLA-DR2 in Oman and disparities in the frequency of other antigens would indicate that there has not been any significant migration from northern Arabia. Class II DNA typing revealed that DR16 was the predominant split of DR2 (63%), with DR15 being 18% and both DR15 and 16 being found in 6%, giving a total of 87% for A centAADR2A centAA-associated antigens (serology of the same individuals gave a DR2 incidence of 74%). The major disparity between serology and DNA typing was in the definition of DR4 (serology 8%, DNA 14%) and DR51 (53% vs. 70%). CONCLUSION: The frequency of many HLA antigens in Omanis differs significantly from frequencies found in the populations of Kuwait and Saudi Arabia, possibly reflecting different migration patterns. The high incidence of HLA-DR2 in Oman may have important implications for disease association.

HLA antigens in Omanis with blinding trachoma: markers for disease susceptibility and resistance.

AIM: To determine the presence of HLA antigens in people with blinding trachoma. METHODS: Fifty Omanis with blinding trachoma were serologically typed for HLA A, B, C, DR, and DQ antigens and DNA typed for class II DR beta and DQ beta alleles and compared with a population of 100 healthy controls. RESULTS: chi 2 analysis of serological reactions did not reveal any significant differences in HLA antigen frequencies after correction of probability, although DR4, DR7, and DR53 were completely absent in the patients and all of the patients were HLA DQ1 positive. In the case of DQ1 the relative risk was 22.6 (95% confidence interval of 20.7-24.7). Class II DNA low resolution DR beta typing showed a significant increase in HLA DR16 (pc = 0.036, relative risk = 3.8) and a significant decrease in HLA DR53 (pc = 0.018, relative risk = 0.05). CONCLUSION: The finding that HLA DR16 (a DR2 subtype) is associated with susceptibility to blinding trachoma, a disease that is caused by an intracellular micro-organism, is consistent with reports of an HLA DR2 association with leprosy and tuberculosis, diseases also caused by an intracellular micro-organism. Similarly, resistance to leprosy is associated with HLA DR53 as is the case with blinding trachoma described here. It is postulated that HLA DR2 or subtypes in association with HLA DQ 1 may enable an intracellular micro-organism to enter the cell or are involved in presentation of peptides derived from intracellular micro-organisms to T lymphocytes initiating a delayed hypersensitivity or autoimmune reaction. These findings are the first report that genetic factors are of major importance in the development and protection against blinding trachoma.

Immunoglobulins, immunoglobulin G subclasses and complement in adult Omanis.

Immunoglobulins and complement were quantitated in 100 healthy adult Omanis in order to establish a reference range based on local data. Mean values were IgA 2.38 g/L, IgM 1.14 g/L, IgE 241 kiu/L, C3 7.44 micro mol/L and C4 1.57 micro mol/L, values similar to those found in the West. However, the mean level of IgG was almost 50% higher than that found in North America and Europe, that is, 14.63 g/L compared with 10-11 g/L. The values for IgG, IgA, IgM and IgE are similar to those reported for Iraq, but IgG levels were much lower than those found in Iran (25.52 g/L), although IgA, IgM and IgE were comparable. Comparison of Omani data with that for Saudi Arabia showed significantly more IgG in Oman (14.63 versus 11.68 g/L) and significantly less IgM (1.14 versus 1.66 g/L). IgA and IgE levels were similar. As reported elsewhere, females had significantly more IgM than males (1.32 versus 0.97 g/L). The levels of IgG subclasses in Oman are 9.44, 4.01, 1.06 and 0.62 g/L for IgG1-4 respectively. The percentage of the various subclasses are very similar to those reported elsewhere, that is, 62%, 27%, 7% and 4% for IgG1-4. However, in Iraq, a higher percentage (and level) of IgG3 (16%) and the lower IgG2 (18%) compared to Oman may reflect differing immune responses resulting from exposure to different microorganisms. It is essential to use local reference data when evaluating patients.