[In vitro cultivation of Plasmodium falciparum. Applications and limits.- Methodology]

Abstract

Five years after Trager and Jensen fixed the requirements for a continuous culture of exo-erythrocytic stages in a semisynthetic medium, major advances have been realized. However all practical applications of this method have not yet been investigated. Its main interest is to offer the observation of the intraerythrocytic asexual multiplication and the beginning of the sexual cycle in monitored conditions, beyond the organism regulating processes, and with endless possibility to modify these conditions according to the necessities of the experiment. Compared with the previous use of expensive monkeys, this culture allows a study of P. falciparum in its natural host, cell, the human erythrocyte. It has been already applied for several investigations: - ultrastructure, metabolism, ADN and ARN sequencies of the parasite itself; - the relations between host and parasite (invasion of the erythrocyte by the merozoïte); - constitutional factors of resistance to malaria (hemoglobin S, C, E, deficiency in G6PD, elliptocytosis); - nutritional factors and immunologic defenses (antibodies, cytotoxic cells, ADCC...); - production of plasmodial antigens at the various erythrocytic stages; - chemotherapy (resistance to antimalarial drugs, screening of new drugs and study of their mode of action). The main disadvantages of Trager's and Jensen's method are for one part it concerns the sole erythrocytic stages and for the other part the parasite growth requires components of human origin (serum and erythrocytes). Human serum is hardly adapted to a standardization and appears as the main cause of variations observed in the in vitro proliferation of the parasite. Erythrocytes have a short survival and their metabolism is difficult to separate from that of the parasite. The minor disadvantages of the culture are: - a relative lack of reproductibility which raises difficulties for interpretation of inhibition tests either by antibodies or by antimalarial drugs; - a low output; - a rather expensive cost. Besides, adapting a strain to culture conditions probably induces clone selection (i.e.; loss of protuberances on the erythrocyte membrane). Paradoxically, the successful cultivation of erythrocytic stages raised a need to cultivate the other stages of parasite, that is to say, mainly, the exo-erythrocytic intra-hepatic stages and the sporogonic stages which take place in the mosquito. Somes valuable advances have been recently made in these two ways with animal parasites. The method of culture of P. falciparum has given to all laboratories, even to those out of the endemic area the most valuable opportunity to extend their investigations towards human malaria.