Plasmodium gallinaceum: effect of insect cells on ookinete development in vitro

In vitro culture conditions affecting the transformation efficiency from zygote to ookinete for Plasmodium gallinaceum were examined, as a step toward improving the overall efficiency of in vitro culture systems for sporogonic stages. Gametocytes from infected chickens were allowed to fertilize in vitro and the resulting zygotes were purified and cultured. The time course for ookinete development in vitro was similar to that seen in Aedes aegypti mosquitoes. Supplementing a basal M-199 culture medium with heat-inactivated chicken serum and glucose did not affect transformation efficiency, but resulted in a four-fold increase in infectivity to mosquitoes when fed back to Ae. aegypti. Transformation from zygote to ookinete increased 5- to 10-fold when zygotes were cocultured with one of six different mosquito cell lines or a Drosophila cell line. Under optimal conditions, transformation efficiencies of up to 75% were observed. The presence of insect cells also increased the longevity of ookinetes in culture up to 42 h, while in acellular cultures ookinetes degenerated after about 24 h. The stimulatory effect was apparently not due to a factor secreted into the medium by the cells.