Identification of carbohydrates on Eimeria stiedai sporozoites and their role in invasion of cultured cells in vitro.

Invasion specificity of Eimeria stiedai sporozoites in cultured cells was examined. Intracellular sporozoites were observed in hepatobiliary epithelial cells, as early as 3 hours post inoculation (p.i.) but the infection rate was monitored for 6 hours. No intracellular parasites were found in rabbit parenchymal hepatocytes and rabbit kidney cells, even on prolonged culturing. In the hepatobiliary epithelial cells inoculated with fixed sporozoites, no intracellular parasite were found. Sporozoites attached on the cell surface of the hepatobiliary epithelial cells fixed with paraformaldehyde but did not penetrate. The carbohydrates present on Eimeria stiedai sporozoites and their functional role in the process of invasion of host cells were also examined. Lectin binding sites on the surface of sporozoites were detected by means of peroxidase-conjugated lectins. Sporozoites showed specific binding with UEA-I and PNA lectins, which bind L-fucose and D-galactose, respectively. Exposure of sporozoites to 100 microg/ml UEA-I significantly reduced their ability to invade primary rabbit hepatobiliary epithelial cells, but similar treatment with PNA had no such effect. Preincubation of these cells in Dulbecco's minimum essential medium containing 10% fetal bovine serum and 1% L-fucose suppressed the invasion activity of the sporozoites, but preincubation of the sporozoites in the same medium without L-fucose had no effect on cell penetration. D-galactose added to the medium had no effect on the invasion activity of sporozoites. These results indicate that L-fucose residues on E. stiedai sporozoites and L-fucose binding sites on host cells both are associated with recognition and/or invasion process.