Relative importance of total versus external platelet-associated IgG

We present measurements of total platelet-associated immunoglobulin G following platelet lysis (PAIgG tot) and surface-restricted IgG (PAIgG ext) on intact, gel-filtered platelets from 36 normal human donors and 9 patients with human immunodeficiency virus (HIV) infection (CDC stages IIb-IV). For this purpose, an indirect micro ELI-SA technique was developed involving competition between PAIgG and solid-phase absorbed IgG for fixation of conjugated anti-human IgG antibody. In normal donors, the mean values of PAIgG tot was 8.3 +/- 7.4 (mean +/- 2 SD) and of PAIgG ext 4.2 +/- 4.4 fg/platelet. In HIV-infected subjects, PAIgG tot was 37.2 +/- 62.8 and PAIgG ext 17.1 +/- 23 fg/platelet. In healthy subjects the comparison of individual levels of PAIgG tot and PAIgG ext revealed a significant correlation (r:0.763; p: 0.003). These results are compared to those which have been reported in the literature. In addition, the major immunopathological mechanisms considered responsible for immune-mediated idiopathic thrombocytopenic purpura are discussed.