Effects of Hormones and Cysteine Protease Modulators on Infection of HEPG2 Cells by Plasmodium berghei Sporozoites In vitro Determined by ELISA Immunoassay

Abstract

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.

Proteases in host cell invasion by the malaria parasite

“…Some of the earliest studies soon revealed that this is sensitive to protease inhibitors, and that work has been fully reviewed previously (Blackman, 2000). Similar phenomena were subsequently recorded in other stages and other pathogenic Apicomplexa, and there is now abundant evidence that invasion by the Plasmodium sporozoite (Kumar et al ., 1994; Silvie et al ., 2004), the Toxoplasma tachyzoite (Conseil et al ., 1999; Que et al ., 2002), and the Eimeria sporozoite (Fuller and McDougald, 1990) is also sensitive to protease inhibitors. Importantly, the bulk of this evidence implicates parasite‐derived proteases of just two mechanistic classes – serine and cysteine.…”