The One-Four Plan

Abstract

Several isolates of Plasmodium vivax were cultured in vitro using a culture procedure specially modified to enhance the reinvasion rate of parasites. Between 30 and 40 h after start of the culture with blood containing mainly ringforms and young trophozoites, parasites were concentrated on Nycodenz gradients. Subsequently the parasites were mixed with reticulocyte-rich fractions from different blood sources and incubated in micro-well cluster plates. Reinvasion in different types of host cells was studied. The results suggest that reinvasion of P. vivax is, under in vitro conditions, restricted by the limited availability of reticulocytes. Multiplication rates of up to five times were occasionally obtained. The development during the second cycle was generally hampered, probably due to the presence of leucocytes, which could not be effectively removed from the initial (parasitized) material. As a general rule the parasitaemia after two-four schizogonic cycles was too low to justify further maintenance of the cultures. The system described here can be used for short-term experiments, e.g. for drug testing and for reinvasion experiments.