Eimeria tenella: use of a monoclonal antibody in determining the intracellular fate of the refractile body organelles and the effect on in vitro development

A monoclonal antibody, which recognizes the refractile body of Eimeria sporozoites, was used to study the developmental fate of this organelle during asexual development of E. tenella and to determine the effect of this monoclonal antibody on in vitro development of the parasite. Through use of immunofluorescent antibody and gold-labeling techniques at the light and electron microscopy level, the refractile body at 48 to 96 hr postinoculation was found to separate into 6 to 10 small globules, then diffuse throughout the schizont cytoplasm, and eventually reconcentrate as a small dot of material in each of the mature first-generation merozoites. The schizont did not develop to maturity if diffusion of the refractile body did not occur. The refractile body material was quickly lost as the merozoite left the schizont and invaded new cells and was not detected in any later developmental stages. The in vitro development of first- and second-generation schizonts of E. tenella was greatly inhibited (up to 100%) with exposure to the monoclonal antibody. There was an increase in the number of schizonts with nondispersed refractile body in the monoclonal antibody-treated cells when compared to the untreated controls, and the few mature schizonts seen had up to a 50-fold decrease in the number of merozoites. Immunofluorescent antibody labeling of the refractile body of intracellular sporozoites and schizonts treated in vitro with the monoclonal antibody for 24-96 hr postinoculation indicated that the antibody had crossed the host cell and parasite plasma membrane during incubation.