ANALYSIS OF IMMUNOGLOBULIN CLASS, IGG SUBCLASS AND TITER OF HPA-1A ANTIBODIES IN ALLOIMMUNIZED MOTHERS GIVING BIRTH TO BABIES WITH OR WITHOUT NEONATAL ALLOIMMUNE THROMBOCYTOPENIA

We analysed the titre and isotype composition of antibodies produced by mothers giving birth to babies with or without neonatal alloimmune thrombocytopenic purpura (NAITP) and patients with post-transfusion purpura (PTP). All these individuals produced an antibody specific for the HPA-1a allotype present on the platelet glycoprotein IIb-IIIa (GPIIb-IIIa). Sera from mothers who gave birth to thrombocytopenic babies (group 1, n = 36), non-thrombocytopenic babies (group 2, n = 4) or from PTP patients (group 3, n = 3) were tested by an indirect-ELISA. Results indicated no evident differences in the isotype composition or titre of the antibodies from the three groups of sera. The antibody titre ranged from 1:120 to 1:3500. Antibodies with the IgG1 subclass were present in all sera. Most sera contained IgG1 alone (24/43 sera tested) or in combination with IgG3 (10/43). IgG2 was never present and only three sera showed intermediate reactivity with anti-IgG4 MAb. Few sera (nine sera from groups 1 and 2) were weakly positive when tested with the anti-IgM antibodies. These results suggest that neither the titre nor the isotype composition can be used to predict the severity or the occurrence of thrombocytopenia in newborns.