Abstract: AIM:To cultivate the exoerythrocytic stage of Plasmodium yoelii in vitro and to study
some involved affecting factors. METHOD:In vitro cultivation.RESULTS:The monolayer hepatocytes grown in 16 - mm plastic cell culture dishes were inoculated with sporozoite suspension prepared from
Anopheles stephensi mosquitoes for 48 hours. At a final density of2×10⁴ cells per well, the infection
rate of hepatocyte, cultured in medium supplemented with 15 % bovine serum, was 0.035± 0.013%, the
diameter of the nearly mature EEF of Plasmodium yoelii was up to 40.3×31.6 μm, and contained more than 100 nuclei, the number of EEF might be 4- 10/cm². An intraperitoneal inoculation of the EE schizonts to mice could induce parasitemia. At a final density of 0.5×10⁴ or 4×104 cells per well or the hepatocytes cultured in medium supplemented with 10% bovine serum, no EEF could be observed. CONCLUSION: The density of hepatocytes and culture medium are important for the cultivation of the EE stage of Plasmodium yoelii. This procedure will lay foundation for the further studies of the sporozoite invasion, the development of EEF and the affecting factors involved.

Key words: Plasmodium yoelii, exoerythrocytic stage, cultivation in vitro, hepatocytes, Wistar rats, bovine serum