TNF-α promoter polymorphism: a factor contributing to the different immunological and clinical phenotypes in Japanese encephalitis

BACKGROUND More than three billion populations are living under the threat of Japanese encephalitis in South East Asian (SEA) countries including India. The pathogenesis of this disease is not clearly understood and is probably attributed to genomic variations in viral strains as well as the host genetic makeup. The present study is to determine the role of polymorphism of TNF-alpha promoter regions at positions -238G/A, -308G/A, -857C/T and -863C/A in the severity of Japanese encephalitis patients. METHODS Total of 142 patients including 66 encephalitis case (IgM/RT-PCR positive), 16 fever cases (IgM positive) without encephalitis and 60 apparently healthy individuals (IgG positive) were included in the study. Polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) using site specific restriction enzymes were implemented for polymorphism study of TNF alpha promoter. RESULTS Following the analysis of the digestion patterns of four polymorphic sites of the TNF-alpha promoter region, a significant association was observed between the allele -308A and -863C with the patients of Japanese encephalitis. CONCLUSIONS TNF-alpha 308 G/A has been shown to be associated with elevated TNF-alpha transcriptional activity. On the other hand, polymorphism at position -863C/A in the promoter region has been reported to be associated with reduced TNF-alpha promoter activity and lower plasma TNF levels. As per the literature search, this is the first study to identify the role of TNF-alpha promoter in JE infection. Our results show that subjects with -308A and -863C alleles are more vulnerable to the severe form of JE infection.