Isotypic analysis of maternally transmitted Plasmodium falciparum-specific antibodies in Cameroon, and relationship with risk of P. falciparum infection.

In malaria-endemic areas, infants are relatively protected against malaria infection. Such protection is though to be related principally to the transplacental transfer of maternal antibodies. We measured total and Plasmodium falciparum-specific IgG (including subclasses), IgM, and IgE antibodies in 154 paired maternal-cord serum samples from an area of meso- to hyperendemic malaria in South Cameroon. Among peripheral mother blood samples, total IgG and IgM were detected in all samples, IgE in all but two. Plasmodium falciparum-specific IgG were detected in all serum samples, IgM and IgE in > 75% of samples. The prevalence rates of anti-P. falciparum IgG subclasses varied from 75% to 97%. With the exception of P. falciparum-specific IgG, all antibody class and subclass levels were lower in cord blood than in peripheral mother blood. Plasmodium falciparum-specific IgG1 and IgG3 isotypes were transferred to the offspring more often and more efficiently than IgG2 and IgG4. The detection of total and P. falciparum-specific IgM and IgE in some cord serum samples demonstrated that fetuses can mount humoral response against malaria parasites. We also determined whether transplacentally acquired antibodies protect against malaria infection by relating the antibody levels at birth to the risk of acquiring P. falciparum infection during the first 6 months of life. Among various classes and subclasses of P. falciparum-specific antibodies, only IgG2 were related to a decrease in the risk of acquiring a P. falciparum peripheral blood infection from birth to 6 months of age.