Single nucleotide polymorphisms of the inflammatory cytokine genes in adults with chronic immune thrombocytopenic purpura

Single nucleotide polymorphisms (SNPs) of inflammatory cytokine genes were examined in 84 adult Japanese patients with chronic immune thrombocytopenic purpura (ITP) and 56 race-matched healthy controls. The SNPs examined were within the genes encoding tumour necrosis factor (TNF)-α (-238 G/A and -308 G/A), TNF-β (+252 G/A), and interleukin (IL)-1β (-511 C/T and +3953 T/C). Of these SNPs, the frequency of the TNF-β (+252) G/G phenotype was significantly higher in ITP patients than in healthy controls (21% vs. 7%, P = 0.04, odds ratio = 3.6, 95% confidence interval 1.1-11.1), while no significant association was detected for the other SNPs. The distribution of the TNF-β (+252) phenotype was not associated with human leucocyte antigen class II alleles or the therapeutic response in ITP patients. The frequency of circulating anti-glycoprotein IIb/IIIa antibody-producing B cells was significantly higher in ITP patients with the TNF-β (+252) G/G phenotype than in those with the G/A or A/A phenotype (11.9 ± 4.9 vs. 6.8 ± 4.9 and 3.7 ± 2.8 per 10⁵ peripheral blood mononuclear cells; P = 0.02 and P < 0.001, respectively). These findings suggest that the SNP located at TNF-β (+252) contributes to susceptibility to chronic ITP by controlling the autoreactive B-cell responses to platelet membrane glycoproteins.