Sera containing anti-D, taken from 44 RhD-negative women with RhD-positive
infants, were tested in antibody-dependent cellular cytotoxicity (ADCC) and
monocyte monolayer assays (MMA) which used similar target and effector cell
populations. In addition, the anti-D concentration was measured in the Auto
Analyzer and the number of IgGl and IgG3 anti-D molecules bound to the target
red cells was measured by flow cytometry. The results of the functional assays
and AutoAnalyzer quantitation were examined for correlation with IgG subclass
quantitation and all results were compared for their ability to predict the severity
of haemolytic disease of the newborn (HDN). ADCC correctly predicted HDN in
39/44 (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 predictions was
highest when the maternal serum contained both IgGl and IgG3 anti-D. ADCC
activity and HDN were correlated with the number of cell-bound IgGl molecules
(r>0.58), but MMA activity was most closely correlated with the number of cellbound
IgG3 molecules (r = 0.68). Hence the superior predictive value of ADCC
is due to its ability to reflect the IgGl component of maternal anti-D, which has a
better correlation than IgG3 anti-D with the severity of HDN.