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.