Eimeria tenella sporozoites: the method of excystation affects the surface membrane proteins

Eimerian sporozoites can be recovered from intestinal washings after oral administration of oocysts to chickens but suspensions of sporozoites are usually prepared in the laboratory by incubation of sporocysts or fractured oocysts in vitro, at body temperatures, with relatively high concentrations of trypsin and bile salts. Since these agents affect membrane structure, the surface membrane of proteins of Eimeria tenella sporozoites excysted in vivo and in vitro have been compared. Surface radio-iodination followed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that more 125I was incorporated into polypeptides on sporozoites excysted in vivo than on sporozoites excysted in vitro. The 125I-polypeptide profile of sporozoites excysted in vivo was more resistant to subsequent incubation with pure trypsin than that of sporozoites excysted in vitro, but incubation with bile salts resulted in the loss of some iodinated polypeptides from both preparations of iodinated sporozoites. Reaction with combinations of crude trypsin and bile salts led to the lysis of sporozoites. The method of excystation had no effect on the reaction of convalescent chicken serum with Western blots of sporozoites but the results of immunofluorescent staining carried out with mouse monoclonal antibodies indicated that the structure of the cell surface was altered and some antigenic determinants were lost from sporozoites excysted in vitro. In contrast, neither the infectivity of sporozoites determined in vivo, nor their invasion of cultured cells was changed by the method of excystation.