The implementation of surface plasmon resonance technique in monitoring pregnancies with expected fetal and neonatal alloimmune thrombocytopenia

Background Maternal anti-HPA-1a alloantibodies are responsible for most cases of severe fetal and neonatal alloimmune thrombocytopenia (FNAIT). The presence of HPA-1a alloantibodies in maternal blood alone does not predict the fetal platelet (PLT) count, and the predictivity of antibody titers determined by enzyme immunoassays (EIAs) is debated. In contrast to EIA, surface plasmon resonance (SPR) provides information on antibody-binding properties. Study Design and Methods Sequential sera from pregnant women with expected FNAIT were assessed for HPA-1a alloantibodies using SPR. GroupI (n=6) was treated with intravenous immunoglobulin (IVIG) and steroids beginning at 19 weeks of gestation (w.g.), and GroupII (n=4) received intrauterine PLT transfusions (IUT) beginning at 22w.g. Maternal alloantibodies were quantified using an HPA-1a monoclonal antibody (MoAb) as a standard. Antibody avidity was determined as the ratio of B-700 (end of the dissociation phase) to B-350 (end of the association phase); the area under the curve (AUC) was calculated to determine overall antibody binding. Results After 22w.g., alloantibody characteristics remained stable in both groups, while there was a steep decrease in B-700 and B-350 values between 16 and 22w.g. (assessed only in GroupI), indicating a decrease in anti-HPA-1a alloantibody concentrations. Interestingly, the AUCs of the last maternal sample before elective delivery appeared to be correlated with fetal and neonatal PLT counts (p=0.014 and 0.017, respectively). Conclusion SPR provides quantitative information on HPA-1a alloantibody characteristics in addition to monoclonal antibody-specific immobilization of platelet antigens. SPR results can be calibrated using a MoAb standard and should be further assessed for a potential correlation with fetal PLT count.