TNF-alpha gene 1031 T/C polymorphism in Turkish patients with Behçet's disease

Genetic factors that predispose individuals to Behçet's disease (BD) are considered to play an important role in development of the disease. The tumour necrosis factor (TNF)-alpha gene, which is closely linked to the HLA-B51 gene, is involved in susceptibility for BD. Recently, a polymorphism at position -1031 within the TNF-alpha promoter region was demonstrated to be responsible for susceptibility to BD in a British population. However, the functional effects of this polymorphism have not yet been determined.

To investigate the possible relation of the TNF-alpha-1031 T/C polymorphism with susceptibility to BD in a Turkish population and to determine the functional importance of this polymorphism.

Ninety-nine unrelated patients (47 women, 52 men; mean +/- SD age, 34.10 +/- 10.53 years) with BD and 103 ethnically matched healthy controls (52 males, 51 females; mean +/- SD age, 40.25 +/- 14.15) were enrolled in the study. For genotyping, polymerase chain reaction - restriction fragment length polymorphism (PCR-RFLP) analysis was employed. The functional importance of TNF-alpha-1031 T/C polymorphism was determined with an enzyme-linked immunospot (ELISPOT) assay. For this purpose, mononuclear cells obtained from BD patients and controls were analysed for TNF-alpha and interferon (IFN)-gamma production.

A significant difference was observed between BD patients and controls with respect to the allele frequency of TNF-alpha-1031C [P = 0.018, OR = 1.83, 95% confidence interval (CI) = 1.07-3.13]. When the allele frequencies were analysed according to the clinical features, the T allele in patients with positive skin pathergy test (SPT) was significantly increased when compared with those of patients without these findings (P = 0.004, OR = 2.75, 95% CI = 1.3-5.86). To demonstrate the frequency of TNF-alpha and IFN-gamma producing cells, mononuclear cells from four representative individuals of each genotype were used and the spontaneous and stimulated TNF-alpha and IFN-gamma values (spot numbers) were analysed. Compared with the control groups, a significant increase was observed in the number of cells producing TNF-alpha obtained from BD patients (P < 0.001). Moreover, the stimulation index for TNF-alpha [bacterial lipopolysaccharide (LPS) stimulated/unstimulated] was higher for the CC genotype (9 +/- 9.5) with respect to the other genotypes (TT; 1.3 +/- 0.3 and TC; 1.2 +/- 0.2). While the difference in the spontaneous IFN-gamma values between groups were not statistically significant, the stimulated IFN-gamma values were found to be significantly increased in the BD group when compared with the healthy control group (P = 0.004).

Our results showed that, in the Turkish population the TNF-alpha-1031C allele is associated with susceptibility to BD. On the other hand, carrying the T allele may render patients more prone to developing a positive skin pathergy test. In addition, ELISPOT assays revealed that BD patients exhibited a significantly higher number of mononuclear cells producing TNF-alpha, and cells obtained from patients with a CC genotype had a stronger response to LPS stimulation. The strong IFN-gamma response upon LPS stimulation in BD patients supports the previous findings that BD is a Th1 driven disease. These findings suggest that the TNF-alpha-1031 polymorphism may have a functional effect and could explain the reason for high levels of TNF-alpha production observed in BD patients.