Epidemiological correlation between levels of antibodies promoting merozoite phagocytosis of Plasmodium falciparum and malaria-immune status.

A phagocytosis assay was used to measure the prevalence of cytophilic antibodies directed against Plasmodium falciparum merozoites in three groups of subjects from Africa: preimmune (individuals aged 2 to 15 years), immune (adults), and postimmune (African adults residing out of the endemic area). Results show that levels of antibodies promoting merozoite phagocytosis (APMP) increase slowly and gradually with age. The production of high levels of APMP requires about 15 years of continuous exposure to malaria and concurs with the ability of exposed individuals to control a high parasitemia and its pathological consequences, such as spleen enlargement. In the absence of antigenic restimulation for more than 1 year (postimmune subjects), APMP titers decrease abruptly. No correlation was found between APMP levels and levels of antimalarial antibodies detected by fluorescence and precipitation assays. Low levels of APMP in subjects susceptible to clinical manifestations of the disease and high levels in subjects in a state of premunition suggest that the results of the merozoite phagocytosis assay more closely reflect clinical immunity than do other markers of antimalarial humoral immunity.