WILD ISOLATES OF PLASMODIUM-FALCIPARUM MALARIA SHOW DECREASED SENSITIVITY TO IN-VITRO INHIBITION OF PARASITE GROWTH MEDIATED BY AUTOLOGOUS HOST ANTIBODIES

Antigenic diversity in field populations of Plasmodium falciparum para sites may delay the acquisition of protective immunity to malaria, the development of which may thus require repeated exposure to infection over a prolonged period of time. In this study we show that P. falcipa rum parasites may vary in their sensitivity to antibody-mediated invas ion/growth inhibition in vitro. Wild isolates of P. falciparum from ch ildren living in an endemic area of Burkina Faso were tested for their sensitivity to the growth inhibitory effects of antibodies originatin g from the same (autologous) and from other donors (heterologous). A s ignificantly lower invasion inhibition activity was obtained when the isolates and antibodies were tested in autologous compared with hetero logous combinations. The lower sensitivity to growth inhibition by aut ologous antibodies may be due to immune pressure in vivo, selecting fr om a heterogeneous parasite population those with a low expression of: he antigens recognized by the host's antibodies. Alternatively, the pa rasites cultured from each child might represent expanding parasite po pulations, mainly constituting strains not earlier seen by the immune system of that specific host. The results reinforce the concern about Plasmodium antigenic diversity as a major obstacle towards the develop ment of an effective malaria vaccine.