Plasmodium falciparum Inhibitory Capacities of Paired Maternal-cord Sera from South-west Province, Cameroon

In malaria endemic areas, young children are protected against malaria attack during the first few weeks of life partially by transplacentally acquired antibodies. In this study, we show, using an in vitro assay, that part of these antibodies are involved with blocking the re-invasion of host red blood cells by erythrocytic merozoites. One hundred consecutive paired maternal-cord blood samples were collected at delivery and their plasma assayed for total IgG antibodies against crude blood stage antigens by the ELISA. The Ig fraction were precipitated from the plasma samples with (NH4)2SO4, purified on PD10 columns and used in vitro in determining the re-invasion inhibitory capacities. The mean (±SD) ELISA OD405 IgG antibodies to crude blood stage antigens of maternal (0.476 ± 0.48) and cord (0.421 ± 0.39) plasma samples was not significantly different. However, the mean total protein concentration of the Ig fractions for maternal samples (15.82 ± 3.85) was significantly higher (p = 0.005) than that of paired cord samples (12.87 ± 2.86 mg/ml). There was no correlation between anti-Plasmodium falciparum-specific IgG levels and total protein concentrations of the Ig fractions of both maternal and cord samples. The entire test Ig fractions were strongly inhibitory (>50 per cent) except for four paired maternal cord samples, which were moderately inhibitory (21–50 per cent) at the highest concentration tested (1:2 dilution). Furthermore, there was no correlation between maternal IgG levels and percentage re-invasion inhibition at the 1:2 dilution. The results suggest that mothers resident in malaria endemic areas possess naturally acquired re-invasion inhibitory antibodies and their foetuses can acquire these antibodies transplacentally, which may contribute to the relative protection observed in infants during their first few weeks of life.