Linkage between TNF regulatory region SNPs and correlation of TNF haplotypes with plasma TNF levels. A, r2 LD plot of four TNF SNPs (-1031, -863, -308, -238). Value in each cell is the percent D' between SNP pairs. B, Correlation of TNF promoter haplotype (-1031C, -863A, -857C, -308G, -238G) with elevated TNF levels compared to the major haplotype TCCGG. Mean plasma TNF levels were compared using Mann-Whitney test (z = -3.73, P = 0.0002). C, Plasma TNF level in patients and controls. Pairwise comparison of means by non-parametric Mann-Whitney test: severe versus control, z = 4.41, P < 0.0001; non-severe versus control, z = 0.67, P = 0.25; severe versus non-severe, z = 3.13, P = 0.0009.