PREDICTION OF THE SEVERITY OF HEMOLYTIC-DISEASE OF THE NEWBORN - QUANTITATIVE IGG ANTI-D SUBCLASS DETERMINATIONS EXPLAIN THE CORRELATION WITH FUNCTIONAL ASSAY RESULTS

Sera containing anti-D, taken from 44 RhD-negative women with RhD-posi tive infants, were tested in antibody-dependent cellular cytotoxicity (ADCC) and monocyte monolayer assays (MMA) which used similar target a nd effector cell populations. In addition, the anti-D concentration wa s measured in the Auto Analyzer and the number of IgG1 and IgG3 anti-D molecules bound to the target red cells was measured by flow cytometr y. The results of the functional assays and AutoAnalyzer quantitation were examined for correlation with IgG subclass quantitation and all r esults were compared for their ability to predict the severity of haem olytic disease of the newborn (HDN). ADCC correctly predicted HDN in 3 9/44 (88.6%) cases, AutoAnalyzer quantitation in 35/44 (79.5%) and the MMA in 32/44 (72.7%). For all three assays, the number of correct pre dictions was highest when the maternal serum contained both IgG1 and I gG3 anti-D. ADCC activity and HDN were correlated with the number of c ell-bound IgG1 molecules (r greater than or equal to 58), but MMA acti vity was most closely correlated with the number of cell-bound IgG3 mo lecules (r = 0.68). Hence the superior predictive value of ADCC is due to its ability to reflect the IgG1 component of maternal anti-D, whic h has a better correlation than IgG3 anti-D with the severity of HDN.