[Observation of ultrastructure and drug sensitivity of in vitro cultured exoerythrocytic form of Plasmodium berghei].

The ultrastructure of in vitro cultured exoerythrocytic stage (EE) of Plasmodium berghei (P. b.) was observed under transmission electron microscope (TEM). The drug sensitivity of EE was also measured in vitro. The EE was cultured in monolayer host cell, fixed and embedded in situ. The ultrathin sections were prepared and examined by routine methods. The TEM pictures showed that the fine structure of in vitro cultured EE was similar with that of EE grown in rat hepatocytes in vivo, as described by Meis et al. The parasite was found within a parasitophorous vacuole, with nucleus, mitochondria, endoplasmic reticula and Golgi apparatus were observed inside the parasite. After 24 h cultivation, the EE was incubated for 48 h in medium containing a serial concentrations of primaquine or chloroquine, then examined under light microscope. The percentage of abnormal parasites was calculated. The preliminary results showed that the sensitivity of cultured P. b. EE to primaquine and chloroquine was significantly different. At the same concentration of 1 x 10(-5) mol/L, the percentage of abnormal parasites was 38.5 +/- 3.9% and 5.7 +/- 1.9%, respectively. These results demonstrated that the in vitro cultivation system of P. b. EE would have potential utility in antimalarial drug research. (Figs. 1-6).