Clones of the malaria parasite Plasmodium falciparum obtained by microscopic selection: their characterization with regard to knobs, chloroquine sensitivity, and formation of gametocytes.

Abstract

A culture line of P. falciparum (FCR-3/Gambia) was used to select and place in culture [human blood] cells containing a single parasite. The method depends on examination of minute droplets of dilute cell suspensions with oil immersion phase-contrast microscopy. Droplets found to contain a single parasite were maintained under appropriate culture conditions until detectable numbers of parasites were present (generally by day 21). Of 9 clones that develoed, 7 were knobless and 2 were knobby. The clones differed somewhat in chloroquine sensitivity. Their 50% inhibition point under 1 set of conditions in vitro ranged from 0.02-0.06 .mu.g of base/ml, compared with only 0.003 .mu.g for the highly sensitive line FCR-8/West Africa. All 3 tested clones formed gametocytes under appropriate in vitro conditions.