Effects of hormones and cysteine protease modulators on infection of HepG2 cells by Plasmodium berghei sporozoites in vitro determined by ELISA immunoassay.

An enzyme-linked immunosorbent assay (ELISA) detecting a Plasmodium berghei liver-stage-specific protein Pbl-1 is described. The quantitative detection limits ranged from 0.01 to 0.05 microgram of parasite protein. Qualitatively the assay detected as little as 0.001 microgram Pbl-1 per well. Using the ELISA dexamethasone and insulin together was shown to promote higher parasite infections in HepG2 cells compared to unsupplemented medium. Anti-cowpea-protease cysteine inhibitor significantly increased hepatocyte invasion as compared to controls, whereas a significant decrease was recorded in the presence of the protease inhibitor E64. Partial involvement of cysteine proteases in HepG2 invasion by P. berghei sporozoites is therefore suggested.