We examined the association of TNFα promoter single nucleotide polymorphisms and haplotypes with gene expression in terms of mRNA levels and with outcome in a cohort of patients with severe sepsis.
Sixty-two Irish Caucasian patients presenting with severe sepsis were enrolled. Blood sampling was carried out on day 1 and on day 7. Mononuclear cells were isolated and TNFα mRNA quantified using the technique of quantitative real-time polymerase chain reaction (QRT-PCR). DNA was extracted and assayed for four TNFα promoter polymorphisms. Haplotypes were inferred using PHASE software.
Twenty-seven patients died. Patients carrying an A allele at position -863 produced more TNFα mRNA on day 1 than C homozygotes (P = 0.037). There was a trend for patients homozygous for the G allele at position -308 to produce more TNFα mRNA on day 1 than those carrying an A allele (P = 0.059). Carrier status for haplotype 1 (with A at position -863 and G at position -308) was associated with greater TNFα mRNA levels on day 1 (P = 0.0374). Carrier status for haplotype 4 (with C at position -863 and A at position -308) was associated with a nonsignificant decrease in TNFα mRNA levels on day 1 (P = 0.059). When directly compared, haplotype 1 was associated with significantly greater levels of TNFα mRNA than with haplotype 4 on day 1 (P = 0.02). Patients homozygous for the A allele at position -308 were more likely to succumb to severe sepsis than those carrying the G allele (P = 0.01).
These results contradict previous in vitro functional studies on the TNF2 allele. This may be secondary to the method of quantification of in vivo gene expression with QRT-PCR providing more accurate and sensitive data when compared with prior ELISA-based assays. Indeed, the extrapolation of functionality from in vitro functional genetic tests after lipopolysaccharide stimulation may be of questionable value. We conclude that genotypic analysis does have a place in risk stratification in sepsis and that genetic variants at positions -863 and -308, or sites in linkage disequilibrium with these variants, may influence TNFα production.