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 b y mothers giving birth to babies with or without neonatal alloimmune t hrombocytopenic purpura (NAITP) and patients with post-transfusion pur pura (PTP). All these individuals produced an antibody specific for th e HPA-1a allotype present on the platelet glycoprotein IIb-IIIa (GPIIb -IIIa). Sera from mothers who gave birth to thrombocytopenic babies (g roup 1, n = 36), non-thrombocytopenic babies (group 2, n = 4) or from PTP patients (group 3, n = 3) were tested by an indirect-ELISA. Result s indicated no evident differences in the isotype composition or titre of the antibodies from the three groups of sera. The antibody titre r anged from 1:120 to 1:3500. Antibodies with the IgG1 subclass were pre sent in all sera. Most sera contained IgG1 alone (24/43 sera tested) o r in combination with IgG3 (10/43). IgG2 was never present and only th ree sera showed intermediate reactivity with anti-IgG4 MAb. Few sera ( nine sera from groups 1 and 2) were weakly positive when tested with t he anti-IgM antibodies. These results suggest that neither the titre n or the isotype composition can be used to predict the severity or the occurrence of thrombocytopenia in newborns.