THE MULTIFACTORIAL AND MULTISTAGE CHARACTER OF PROTECTIVE IMMUNITY TOPLASMODIUM-FALCIPARUM, NATURALLY ACQUIRED BY AN INDIGENOUS POPULATIONIN BURKINA-FASO

In malaria-endemic areas, protective immunity is acquired gradually. S ome authors have proposed that different stages can be distinguished d uring development. To test this hypothesis, several in vitro assays of the host immune response to P. falciparum were performed in three gro ups of individuals: 'unprotected' children with clinical attacks, 'sem i-immune' children, without clinical attacks but with transient high p arasitaemias during the transmission period, and 'protected' adults wi th low residual parasitaemias. By comparison of immune responses in th ese groups and multifactorial analyses, discriminant factors and poten tial protective mechanisms were identified. Anti-RESA antibody levels were lower in 'unprotected' than in 'semi-immune' children, while spec ific cellular responses, TNF levels and percentage of activated T lymp hocytes were higher. Low humoral immunity and high cellular activation in children were followed by high humoral immunity and low cellular a ctivation in adults. Therefore, protective immunity seems to pass thro ugh different stages and to result from the association of different i mmune mechanisms according to the level and duration of the individual experience of malaria.