Platelet-associated IgG in childhood idiopathic thrombocytopenic purpura: measurements on intact and solubilized platelets and after gammaglobulin treatment.

An immunoradiometric assay was developed for determining platelet-associated IgG (PAIgG) both on intact and solubilized platelets. In 20 healthy subjects PAIgG was 0.28 +/- 0.20 ng/10(6) platelets and 2.2 +/- 1.1 ng/10(6) platelets on intact and on solubilized platelets, respectively. 13 children with acute ITP all had increased concentrations of PAIgG, but no correlation was found between the severity of thrombocytopenia and PAIgG concentrations, either on intact or on solubilized platelets. Neither was there any correlation of the increase in PAIgG between intact and solubilized preparations. 3 out of 4 children who received high-dose i.v. gammaglobulin showed a concomitant normalization of the platelet count and of the PAIgG concentration both on intact and lyzed platelets. The remaining child did not respond to gammaglobulin and continued to have abnormal PAIgG.