Studies on an experimental system for the invasion of Theileria sergenti merozoite into erythrocytes.

The entry of Theileria sergenti merozoite into erythrocytes was examined to establish an in vitro experimental system for merozoite invasion. Free merozoites (1 x 10(8)) were incubated with erythrocytes (2 x 10(7)) in RPMI-1640 containing various concentrations of fetal bovine serum (FBS). The invasion assay was examined at various temperatures and pH concentrations. The results showed that merozoite invasion was accelerated by the addition of FBS and by incubation at 37 degrees C at pH 6.5-7.5. To investigate how enzymatic activity contributes to the entry of T. sergenti merozoites, the inhibitory effect on the merozoite invasion was examined by using protease inhibitors. An inhibitory effect on the invasion of merozoites was observed in the medium containing 1,10-phenanthroline and ethylenediaminetetraacetic acid disodium salt which are classified as metalloprotease inhibitors. The results suggest that FBS plays an important role in the effective invasion of merozoite into erythrocytes and that enzymatic activity may affect the invasion of merozoite into the host cell.