Abstract
Mycobacterium tuberculosis, the causative agent of pulmonary tuberculosis (TB), remains a major public health risk worldwide. It is still not clear why a small percentage of the infected progress to active disease during their lifetime. It seems likely that TB develops by complex environmental factors and genetic susceptibility. Genetic factors, such as Human Leukocyte Antigens (HLA) in particular, are important determinants of susceptibility to TB. The HLA system is a T cell restriction element closely related to immuneresponsive and immune-suppressive genes. The expression of particular HLA class I and II antigens in an individual determines the ability of that individual to respond to particular mycobacterial antigens and epitopes. The most frequently reported immunogenetic associations have been found with HLA-B5,-B8,-B15,- B27,-B35,-Cw5 antigens and DRB1*1501, DRB1*1506, DRB1*1601, DRB1*1602, DQB1*0501, DQB1*0502, DQB1*0503, DQB1*0601 alleles, but these associations varied in reported studies of TB patients from different races and ethnic populations from Asia, North and Latin America and Europe. Although variations were apparent in the antigens/alleles associated with susceptibility, the increase in the frequency of DR2 antigen and DQB*05 allele was remarkably consistent in the analysed populations. A negative correlation of M. tuberculosis with HLA-DR4,-DR6,-DR8 antigens, DRB1*07, DRB1*13 and DQB1*0201, DQB1*0301, DQB1*0402 alleles was noted, but reductions in the frequency of alleles associated with protection were inconsistent in TB patients from different ethnic groups.
Keywords: hla class I and II, different ethnic groups, pulmonary tuberculosis
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