Effects of a polymorphism in the human tumor necrosis factor α promoter on transcriptional activation

Tumor necrosis factor α (TNFα) is a potent immunomodulator and proinflammatory cytokine that has been implicated in the pathogenesis of autoimmune and infectious diseases. For example, plasma levels of TNFα are positively correlated with severity and mortality in malaria and leishmaniasis. We have previously described a polymorphism at −308 in the TNFα promoter and shown that the rare allele, TNF2, lies on the extended haplotype HLA-A1-B8-DR3-DQ2, which is associated with autoimmunity and high TNFα production. Homozygosity for TNF2 carries a sevenfold increased risk of death from cerebral malaria. Here we demonstrate, with reporter genes under the control of the two allelic TNF promoters, that TNF2 is a much stronger transcriptional activator than the common allele (TNF1) in a human B cell line. Footprint analysis using DNase I and B cell nuclear extract showed the generation of a hypersensitive site at −308 and an adjacent area of protection. There was no difference in affinity of the DNA-binding protein(s) between the two alleles. These results show that this polymorphism has direct effects on TNFα gene regulation and may be responsible for the association of TNF2 with high TNFα phenotype and more severe disease in infections such as malaria and leishmaniasis.