Influence of FcγRIIA H131R polymorphism on TF gene expression and procoagulant activity induced by HIT antibodies in whole blood. (A) Relative increase in TF levels measured by quantitative PCR (see “Patients and methods” section) after addition of HIT plasma and heparin (0.5 IU/mL) to the whole blood from 24 donors (HH: n = 12; RR: n = 12), as compared to the condition without heparin. Plasma samples from 5 HIT patients, all positive in PF4-specific enzyme-linked immunosorbent assay (A_405nm values between 1.6 and 3) and serotonin release assay, were tested. P values were calculated using the Mann-Whitney U test. Relative increase in TF mRNA levels (B) and relative shortening of plasma clotting time (C) were measured after addition to the whole blood of 20 donors (HH: n = 8; HR: n = 6; RR: n = 6) of 5B9 (10 μg/mL) with heparin (0.5 IU/mL), as compared to the condition without heparin. P values were calculated using the Mann-Whitney U test.