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Changes in the cytoplasmic elements of cultured cells infected with Eimeria vermiformis sporozoites
1Department of Parasitology, University of Queensland, St. Lucia, Brisbane, Australia.
Abstract:
Epithelial-type (PK-15) and fibroblast-type (MDBK) mammalian cell cultures were inoculated with purified Eimeria vermiformis sporozoites. Matched samples from 0 to 93 h after inoculation (HAI) were processed for electron microscopy; half of the sample preparations were extracted with non-ionic detergent prior to fixation. Specimens were examined by both transmission and scanning electron microscopy. Numerous sporozoites were attached to the cultured cells from 2 to 93 HAI, usually near the cell periphery. Some host cell microvilli extended up and appeared attached to the sporozoites. Sporozoites fixed during the penetration process were markedly constricted at the site of entry; however, no noticeable changes occurred in the host cell membrane or surface microvilli during sporozoite invasion or in sporozoite-infected cells. In cells extracted with 1% Triton X-100, the host cytoskeleton was progressively reorganized about the parasites but changes were limited to the immediate area of the sporozoite. Around resident sporozoites, the cytoskeleton became less dense but also more ordered, which contrasted with adjacent cell areas. Cytoskeletal elements passed both over and under the parasites. The appearance of the cytoskeleton suggested that the host cell formed a loose, basket-like net of cytoskeletal elements about the parasite.
Insights
Eimeria vermiformis sporozoites attach to mammalian cells, triggering reorganization of the host cell cytoskeleton into a basket-like net around the parasite. This interaction occurs without apparent damage to the host cell membrane during invasion.
Area of Science:
- Cell Biology
- Parasitology
- Microscopy
Background:
- Eimeria vermiformis is a protozoan parasite that infects mammalian cells.
- Understanding host-parasite interactions at the cellular level is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the ultrastructural changes in mammalian cells during Eimeria vermiformis sporozoite invasion.
- To examine the host cell response, particularly cytoskeletal rearrangements, following sporozoite attachment and entry.
Main Methods:
- Inoculation of PK-15 (epithelial) and MDBK (fibroblast) cell cultures with Eimeria vermiformis sporozoites.
- Processing samples at various time points (0-93 h post-inoculation) for transmission and scanning electron microscopy.
- Utilizing non-ionic detergent (Triton X-100) extraction to visualize host cell cytoskeletal organization around the parasites.
Main Results:
- Sporozoites attached to host cells, primarily near the periphery, with some microvillar interaction observed.
- Sporozoite penetration involved constriction at the entry site, but host cell membranes and microvilli showed no noticeable changes.
- Triton X-100 extraction revealed progressive reorganization of the host cytoskeleton around the parasites, forming a less dense yet more ordered, basket-like structure.
Conclusions:
- Eimeria vermiformis sporozoites interact with host cells without causing immediate membrane damage.
- Host cells actively reorganize their cytoskeleton to form a unique structure around invading sporozoites, suggesting a specific cellular response mechanism.