The Association Between Cytokine Gene Polymorphisms And Patients With Tubercusis

BackgroundHuman genes, to a large extent, determine the phenotypes of an individual, including outward appearance, body weight and other characteristics of the body. In terms of diseases, genes may affect the susceptibility of an individual to certain diseases. This is very obvious in genetic diseases, such as familial high blood pressure, daltonism and hemophilia and so on. Since 1970s, convincing evidences from linkage analysis based on family and case-control studies show that the variance of susceptibility of individuals is caused by the genes of host. As study goes in greater depth, it has been found that natural resistance associated macrophage protein-1 gene (NRAMP1), vitamin D receptor gene (VDR), mannose- binding lectin gene (MBL) may be associated with TB susceptibility. This study explores the relationship between Th1/Th2 cytokine gene polymorphisms, which play important roles in the tuberculosis immunity, and Mycobacterium tuberculosis infections.ObjectiveTo investigate the association between Th1/Th2 cytokines IL-4, IL -10, IL -18, IFN-γ, TNF-αgene polymorphisms and susceptibility to pulmonary tuberculosis by a case-control study.Methods(1) To detect the polymorphisms of cytokines IL-4, IL -10, IL -18, IFN-γand tumor necrosis factor-αgenes with polymerase chain reaction with sequence specific primer(PCR-SSP) and sequencing. The genotype or allele distribution in both case and control groups were analyzed.(2) The level of IL-10 in serum samples were measured by the enzyme- linked immunosorbent assay (ELISA). The relationship between cytokine genotypes and serum concentration was analyzed.Results1.The genotype frequencies of A/A homozygotes,A/G heterozygous and G/G homozygous at -1082 site of IL-10 gene in patients with pulmonary tuberculosis were 85.4%, 13.1%, 1.5% respectively; A, G allele frequencies were 91.5%, 8.5% respecti- vely. In normal healthy subjects the genotype frequencies of A/A homozygotes,A/G heterozygous and G/G homozygous were 77.5%, 22.0%, 0.5% respectively; A, G al- lele frequencies were 88.8%, 11.2% respectively. Genotype distribution between two groups was significantly different (P <0.05). The genotype frequencies of A/A of IL-10 in the patient group were higher than that of control group. In contrast, the genotype frequencies of G/A in the control group were higher than that in the patient group (P <0.05). A and G allele distribution showed no statistical difference between the two groups (P<0.05). For IL-4 (-590),IL-18(-607, -137) , IFN-γ(+874) and TNF-α(-308, -238), no significant difference was found on the distribution of genotypes or alleles between the two groups.2. The haplotype/diplotype polymorphisms of the promoter of TNF-αand IL-18 were analyzed in the two groups. Frequencies of haplotype/diplotype of TNF-αpromoter were not different between the two groups (P> 0.05). But frequencies of CC haplotype at -607(C/A) and -137(G/C) in promoter region of IL-18 gene were significantly lower in Tuberculosis group than the control one (P <0.05).3. The IL-10 levels were very low in both groups. Among 168 samples, only 12 samples were found to have concentrations over detection limit. Seven were cases and five were controls. The average values were 30.04pg/ml and 5.51pg/ml respectively.Conclusion:1. The single nucleotide polymorphisms of cytokines IFN-γ(+874), TNF-α(-308, -238), IL-18 (-607, -137) and IL-4 (-590) may not be associated with the susceptibility to tuberculosis in china han populations.2. The IL-10 (-1082) gene single nucleotide polymorphism may be associated with tuberculosis susceptibility. A/A genotype may be a risk factor for tuberculosis susceptibility in china han populations.3. The IL-18 (-607, -137) allele and genotype polymorphism may not be associated with the susceptibility to tuberculosis, but the CC haplotype may be a resistant gene of tuberculosis in china han populations.