Immunoglobulin G subclasses of anti‐human platelet antigen la in maternal sera: relation to the severity of neonatal alloimmune thrombocytopenia

Abstract: The monoclonal antibody immobilization of platelet antigen (MAIPA) technique was employed to detect and semiquantitatively assess total IgG anti‐HPA‐1a and its subclasses in sera of mothers who gave birth to severely thrombocytopenic (<50×10 9 platelets/L) ( n = 14) or mildly thrombocytopenic/unaffected (>50×10 9 platelets/L) ( n = 13) neonates. There was no statistically significant difference between the IgG anti‐HPA‐1a subclass composition of the 2 groups of sera. The majority of sera (26/27,96%) showed IgG1+IgG3 while 17/27 (63%) had all 4 subclasses of the antibody. No significant differences between the severely thrombocytopenic and mildly thrombocytopenic/unaffected groups were detected in the levels of IgG, IgG1, IgG2 or IgG4 of the antibody. However, the values of IgG3 anti‐HPA‐1a were significantly higher in the severely thrombocytopenic than in the mildly thrombocytopenic/unaffected group of sera with only little overlap (median 2.94 vs. 1.68, range 1.36–9.71 vs. 1.50–2.84, respectively; p <0.01). The results suggest that maternal IgG3 anti‐HPA‐1a has predictive value for severe thrombocytopenia of the neonate. However, a prospective study of IgG HPA‐1a subclasses in a greater number of maternal sera at different times of pregnancy is needed to test if IgG3 anti‐HPA‐1a is predictive of the degree of fetal/neonatal thrombocytopenia.