Antibodies to PRT/H in patients undergoing CPB. (A) Plasma from healthy subjects (“Normal,” n = 45) and patients undergoing CPB (n = 15) were screened for antibodies to PRT/H by ELISA at baseline, D5, and D30. (B) Specificity of antibodies to PRT/H. Plasma from 4 patients with antibodies to PRT/H (solid symbols) and 3 seronegative CPB patients (open symbols) were incubated with wells coated with BSA, hPF4/H, Lys, Lys/H, PRT, or PRT/H. P values were calculated for panels A and B using a 1-way ANOVA. For panel B, a Bonferroni posttest was applied for calculating differences between conditions. **P < .001 for PRT/H vs BSA, Lys, Lys/H, and hPF4/H.