No abstract

We present a short insight into the problem of parasitophorous vacuole (PV) formation as a most peculiar kind of cell vacuolization occurring in the course of intracellular development of coccidian pathogens of the genera Eimeria, Isospora, Toxoplasma, Sarcocystis, Cryptosporidium, Epieimeria, and Karyolysus. The review focuses on the morpho-functional diversity of PVs in these parasites. By the present time, the PVs containing different parasite genera and species have been examined to different extent. The membrane of the PV (PVM) obviously derives from the host cell plasmalemma. But soon after parasite penetration, the morphofunctional organization and biochemical composition of the PVM drastically changes: its proteins are selectively excluded and those of the parasite are incorporated. As the result, the PV becomes not fusigenic for lysosomes or any other vacuoles or vesicles, because host cell surface markers necessary for membrane fusion are eliminated from the PVM during parasite invasion. The pattern of the PVs is parasite specific and demonstrates a broad diversity within the same genera and species and even at different stages of the endogenous development. The PV is far from being an indifferent membrane vesicle containing the parasite. Instead, it represents a dynamic system that reflects the innermost events of host-parasite relationships, thus promoting the accomplishing of the parasite life cycle, which, in its turn, is a necessary prerequisite of the parasite eventual survival as a species.

Inflammation, malnutrition and growth retardation during critical time-windows of development play a powerful role in ontogenetic programming of the life-long risk to many adult diseases (including metabolic syndrome, obesity and diabetes). Cellular mechanisms and the accurate timing and duration of critical periods for the liver remain obscure. To resolve this problem, we developed a postnatal suckling-weanling rat model of mild, moderate, and acute gastroenteritis challenged by a protozoan parasitic spread throughout the whole world, namely Cryptosporidium parvum. The physiological state of the liver was evaluated by hepatocyte ploidy and protein content that were measured by cytophotometry and image analysis on isolated cells. Hepatocyte ploidy is known to irreversibly increase after stress and is associated with the decrease in liver physiological capacity. Hepatocyte hypertrophy reflects cell functional loading. From our results, cryptosporidiosis is able to provoke a burst in premature hepatocyte polyploidization and hypertrophy (in proportion to parasitic load), and thus plays an important role in epigenetic programming of hepatocyte structure and function. We revealed two sensitive periods in liver growth. The first period (the less sensitive) covers the time before the establishment of homoiothermy, i.e. 6-9 days after birth. The second period (the more sensitive) covers the time of weaning when the change of type of nutrition and the peak of hepatocyte polyploidization and differentiation occurs. Thus, our data provide direct evidence that phenomenon of ontogenetic programming is reflected at the cellular level.

No abstract

ABSTRACT. Two persisting stages in the life cycle of a hemogregarine Karyolysus sp. are described from the liver and blood cells of its intermediate host, the lizard Lacerta raddei nairensis. The tissue cell merozoites lie in a parasitophorous vacuole. Despite the protective role of the vacuolar membrane, the intracellular parasites are progressively destroyed and eliminated during the autumn and winter. Some of the merozoites that normally survive within the host cell even in cold seasons appear to be surrounded by another type of parasitophorous vacuole which is connected to the intercellular space by narrow channels. The intraerythrocytic gamonts that persist in the circulating blood are encapsulated and undergo progressive, obvious structural changes. The two persisting stages are compared with hypnozoites of other Sporozoa.