IgG-repleted normal plasma inhibits platelet activation induced by HIT-1 more effectively than IgG-depleted plasma. (A-B) The abscissa indicates dilution ratio of HIT-1 with IgG-depleted and -repleted samples obtained from 3 different normal plasmas (normal plasma #1-#3), and the ordinate depicts the PEA as a percentage of the value obtained with undiluted HIT-1. FcγRIIa genotype is indicated on the abscissa. Red and blue bars represent HIT-1 diluted with IgG-depleted and -repleted normal plasma, respectively. (C) IgG status of the diluent has little to no effect on results obtained with HIT-1 dilution in the PF4 enzyme-linked immunosorbent assay (ELISA). The abscissa indicates dilution ratio used, and the ordinate depicts the optical density (OD) of IgG-specific PF4-polyvinylsulfonate ELISA (PF4 ELISA). All PF4 ELISA reactions (ODs) were inhibited ≥50% with high-dose (100 U/mL) heparin (data not shown). Means +1 SD of triplicate determinations are presented and were compared by using the Student t test. P < .05 was considered significant. *P < .05; **P < .01; ***P < .001; ****P < .0001.