Effects of Antiphagocytic Agents on Penetration of Eimeria magna Sporozoites into Cultured Cells

Abstract

Madin-Darby Bovine Kidney cells were treated with sodium flouride, iodoacetate, and 2-deosyglucose, reagents that block glycolysis, and thus reduce phagocytosis. Sporozoites readily entered cells whose ATP stores were largely depleted. They also entered cells treated with colchicine, colcemid, and vinblastine. These latter agents did not inhibit sporozite motility after 6 hr incubation. Cytochalasin B prevented penetration of cells by inhibiting the motility of sporozoites. This effect was reversible. Warm sporozoites entered cold cells 4 times more radily than cold sporozoites into warm cells. The above findings suggest that phagocytosis is not the mechanism for entry of E. magna sporozoites into cultured cells, but that sporozoite motility is of primary importance.

Gliding motility powers invasion and egress in Apicomplexa

“…cytochalasins (which are inhibitors of actin polymerization), indicated a key contribution of parasite actin filaments in motility 10,22 (FIG. 4a).…”

“…Moreover, in P. berghei, disruption of the αβ-heterodimer capping protein that regulates the growth of F-actin critically impairs the motility of sporozoites and the propagation of infection 45 . Finally, the F-actin-binding protein coronin contributes to the organization of the filaments for productive motility in Capping model of motility [11][12][13] Observation of the IMC by freeze-fracture electron microscopy 14 Cytochalasin B inhibits invasion 10 Apical microneme exocytosis in S. muris 17 Observation of the moving junction of P. knowlesi merozoites by electron microscopy 5 The rearward translocation of TRAP-related proteins that drive gliding motility and invasion is conserved in Apicomplexa 85 Identification of aldolase as the bridge between actin filaments and adhesins in T. gondii 87 Identification of MYOH as the motor that initiates gliding motility at the apical pole of T. gondii tachyzoite 76 Identification of glideosomeassociated connector, which bridges actin filaments and adhesins 40 Identification of the MYOA receptors in the IMC, the gliding-associated proteins GAP45 and GAP50 in T. gondii …”

“…The term 'capping' was first used to describe the redistribution of immune complexes on the surface of lymphocytes 9 and has been extended to refer to any polarized translocation of surface protein on a cell. Next, it was demonstrated that cytochalasin B blocks the motility of Eimeria magna sporozoites and also inhibits host cell invasion 10 . This suggested a possible role for actin in invasion, and a link between motility and invasion, both of which were eventually developed as paradigms for gliding motility in Apicomplexa.…”

Toxoplasma modifies macrophage phagosomes by secretion of a vesicular network rich in surface proteins.

“…The specialized endocytic compartment in which living Toxoplasma reside contains a prominent vesicular network that forms connections with the parasite plasma membrane and the phagosome membrane (14,21,22). The origin and function of this assembly are unknown; however, similar networks occur in host cell phagosomes containing other protozoa that subvert host cell endocytic processing (3,4,13,20,31).…”

Gliding motility in apicomplexan parasites

“…Earlystudies detailed the inhibitory effects of the cytochalasins, a family of actin disrupting drugs, on different manifestations of parasite motility [38,[48][49][50][51][52][53][54]. With actin implicated, a hunt for myosin motors logically ensued, andcircumstantial evidencedid suggestthat myosinsmight indeed be involved [51,54,55].Following the identification of the first bona fideapicomplexan myosins inToxoplasma gondiiand other parasites [56][57][58][59][60] the stage was set for the characterization of the actin-myosin motor complex, an assemblydubbed the 'glideosome' by Opitz and Soldati [61].The primary components of this locomotory apparatus have been identified and characterized over the course of many years using traditional biochemical and molecular approaches, coupled with ultrastructural and immunochemical studies, that have helped to define the interactions among components and lay out a molecular blueprint for how the parasite assembles the machinery necessary for motility (Fig 3).…”