Sera from Cameroon induce crisis forms during Plasmodium falciparum growth inhibition studies in vitro.

Sera collected from 176 children and adults from 3 different regions of Cameroon were used in inhibition assays against Plasmodium falciparum in vitro. The individuals had been classified clinically as malarious or non-malarious. Of the 58 non-malarious persons questioned, 39 claimed never to have had symptoms of the disease. Sera were tested for inhibitory effects on either merozoite entry and retardation of growth or inhibition of intraerythrocytic growth. The sera from malarious individuals showed only 9% and 29% mean inhibition values at 24 and 48 h, respectively, while those from the non-malarious persons showed 59% and 73% inhibition for the same periods. Of the 58 sera from non-malarious persons, 34 produced typical crisis forms by 24-36 h. Some sera also inhibited merozoite entry into erythrocytes. Our data suggest an important relationship between acquired immunity to P. falciparum in Cameroon and the types of inhibition described here.