Kryptosporídie: epicelulárne parazity v objatí membrány hostiteľskej bunky
| Title in English | Cryptosporidia: Epicellular parasites embraced by the host cell membrane |
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| Authors | |
| Year of publication | 2009 |
| Type | Conference abstract |
| MU Faculty or unit | |
| Citation | |
| Description | Cryptosporidia are significant pathogens of vertebrates with unique strategies for attachment to host epithelial cells, which, together with phylogenetic analyses suggest a close affinity to gregarines. Speculation that the genus Cryptosporidium represents a ‘missing link’ between the gregarines and coccidians is frequently discussed. Electron microscopic observations on two evolutionarily distinct gastric species, Cryptosporidium muris from experimentally infected rodents and C. fragile from naturally infected toads, allowed us to map ultrastructural aspects of the cryptosporidian invasion process along with the origin and architecture of parasitophorous sac, and to generalize these observations for gastric cryptosporidia. Both species exhibit a comparable strategy of host cell invasion, in which contact between the invading zoite and the host cell induces recruitment of the host microvillar membrane. The recruited part of the host cell membrane loses its microvillous appearance and forms a tight-fitting elastic membrane fold, encircling the contact zone between invading zoite and host cell, which gradually rises along the zoite, subsequently forming the parasitophorous sac. Thus, cryptosporidia do not penetrate under the host cell plasma membrane, nor do they come into close contact with the host cell cytoplasm. The only exception is a region of early tunnel connection between the parasite and the host cell; nevertheless, even this transient connection disappears when the feeder organelle forms and becomes limited by a dense line separating it from the filamentous projection, i.e. from the parasitophorous sac of host cell origin. The parasite remains attached to the host cell surface, only enveloped by the host cell membrane folds. Supported by data presented herein, the term epicellular more accurately defines the host compartment within which cryptosporidia reside than does the term intracellular-extracytoplasmic. Furthermore, the attachment strategy of cryptosporidia is similar to that of the eugregarines, in that they also adhere to the microvillous surface of host epithelial cells in an epicellular position, although eugregarines are not enveloped by the host cell membrane. Further analyses revealed the existence of pore-like structures in the surface of the cryptosporidian parasitophorous sac. As these structures were also seen in older developmental stages, they are not a priori considered initial non-fused areas before the rims of membrane folds completely coalesce. |
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