Cellular and humoral inhibition of Plasmodium falciparum growth in vitro and recovery from acute malaria

Both mononuclear cell cytotoxicity and serum inhibition of Plasmodium falciparum growth in vitro were found to vary according to the stage of infection in Gambian children with clinical malaria. Cytotoxicity was displayed by mononuclear cells and serum from children with acute malaria but this form of parasite killing was more effective in children with low grade P. falciparum infections of at least 10 days duration. Parasite inhibitory antibody was not evident in sera from acutely infected children but was found in sera from children recovering from malaria and reached a peak in convalescent children when P. falciparum growth was inhibited by at least 50%. The humoral response in convalescent children was strain related, being more effective against the most recent infecting parasite strain than against other 'wild' P. falciparum isolates. In contrast, mononuclear cell cytotoxicity was not strain related; when effective, multiplication of all parasite isolates tested was retarded to the same degree. The discussion considers the role of mononuclear cell cytotoxicity in the development of protective immunity and suggests that it may be a 'front line' defense mechanism during each malaria attack.