THE COMPLEMENT-ACTIVATING CAPACITY OF MATERNAL IGG ANTIBODIES TO BLOOD-GROUP-A IN PAIRED MOTHER CHILD SERUM SAMPLES/

Background and objectives: The aim of this study was to investigate wh ether IgG antibodies to blood group A bind or activate complement afte r crossing the placenta. Materials and methods: IgG anti-A concentrati ons as well as C1-q-binding and the capacity of anti-A to form the C5b -9 membrane attack complex were measured in sera of 61 mother/child pa irs. The enzyme-linked immunosorbent assay was used to quantitate anti -A or anti-B in maternal and neonatal serum samples. Results: The conc entrations of IgG anti-A in ABO-identical and ABO-compatible children born to type O or B mothers correlated significantly with maternal con centrations (p < 0.05), whereas type A or AB children had strikingly d iminished concentrations of IgG anti-A. The IgG anti-A concentrations were analyzed in two different groups: first, 44 mother/child pairs wi th mothers and children group O or B (group I), and second, 17 pairs w ith mothers group O or B and children group A or AB (group II). In gro up I, identical or compatible pairs with regard to IgG anti-A, a signi ficant correlation was found by Spearman's rank analysis, whereas the same analysis revealed no significant correlation in group II. The cap acity of anti-A to activate complement was also more marked in newborn s who were ABO-identical or ABO-compatible with their mothers, and thi s capacity was virtually absent in cord blood samples from incompatibl e babies. Conclusions: Tests for complement-dependent or complement-in dependent ABO blood group antibodies must be interpreted in the light of the blood group or the child.