Possible Secretory Function of the Rhoptries of Eimeria magna during Penetration of Cultured Cells

Abstract

Ultrastructure of the penetration of Eimeria magna sporozoites into embryonic bovine trachea cells demonstrated that the host cell membrane was not broken during entry of the parasite. This membrane did, however, undergo alterations characterized by blebbing of vesicles, thickening, and eventual disorganization once penetration was completed. Concurrent with the entrance of the parasite into the cell, and the subsequent membrane alterations, was the appearance of empty membrane saccules, probably rhoptries, in the apical region of the sporozoite. It was proposed that rhoptry secretions aided penetration by changing cell surface characteristics which produced an eventual breakdown of the invaginated protion of the host cell membrane.

Toxoplasma gondii : an ultrastructural study of host-cell invasion by the bradyzoite stage

“…The association between the bradyzoite and host-cell membrane was close and resembled the interaction seen during phagocytosis of T. gondii Nichols and O'Connor 1981), invasion of E. magna (Jensen and Edgar 1976), endocytosis of Theileria parva (Fawcett et al 1984;Shaw et al 1997) or encapsulation of Cryptosporidium (Lumb et al 1988).…”

Fine Structure of Penetration of Cultured Cells by Isospora canis Sporozoites

“…canis were branched (Figs. 8,9,11 ) . Concurrent with entry of the sporozoites into the cells and the appearancc of the partially empty rhoptries, extensive vesiculations of the host cell cytoplasm were seen in apposition to the parasite's apical tip (Figs.…”

“…In fact, motility is required for the invasion by E . magna sporozoites of cultured cells ( 8 ) . Conversely, Plasmodium merozoites are reported to have limited motility and to become firniiy attached to the erythrocyte mernhrane before invasion occurs ( 3 ) .…”

Transmission Electron Microscopy of Intracellular Sporozoites of Eimeria vermiformis (Apicomplexa, Eucoccidiida) in the Mouse1

“…The rhoptry-microneme system has been suggested to function in secretion associated with host cell penetration (6). Rhoptries and micronemes were numerous in all of the sporozoites in the villus tips, but the sporozoites in the crypt cells usually had few of these organelles.…”