[Plasmodium yoeli 265 BY--new possibilities in the study of the resting stages of the malarial parasites]. / Plasmodium yoelii 265 BY--novye vozmozhnosti v izuchenii pokoiashchikhsia stadii maliariinykh parazitov.

When Swiss mice were experimentally infected with P. yoelii yoelii 264 BY sporozoites through bites of the mosquito Anopheles stephensi, there were no blood parasites in most (85%) animals after a short (on day 4-5) incubation period. The hepatic parenchymal cells from the animals without primary infection manifestation (following 2 months of the infection) or with the disease self-arrested (on day 26 of postinfection) were the first to display 5-11-microunits mononuclear parasites that are likely to be similar to the hypnozoites of some malaria parasite strains in man and primates. This suggests that rodent malaria parasites, as P. vivax, might cause infection with prolonged incubation and true relapses previously unknown for these parasites. Therefore, P. yoelii is a promising accessible model for studying the persistence phenomenon of malarial parasites at the tissue level.

[The dynamic activity of lymphocyte succinate dehydrogenase and its correlations in experimental malaria]. / Dinamika aktivnosti suktsinatdegidrogenazy limfotsitov i ee korreliatsionnykh sviazei pri éksperimental'noi maliarii.

Succinic dehydrogenase (SDH) activity in peripheral blood lymphocytes has been studied in progressing experimental malaria on a P. yoelii model, the strain 265 BY; the multinipple rats Mastomys natalensis. Cytochemical method employing n-nitrotetrazolium violet was used. Comparative analysis of changes in SDG activity in peripheral blood lymphocytes and changes in the level of parasitemia has demonstrated that day 10 was a critical period when there was an evident inverse correlation between the qualitative parameters. The findings give evidence of SDH participation in an adequate response of immunocompetent cells to malaria infection, thus leading to recovery.

[The relationship between the fate of the agent of toxoplasmosis, Toxoplasma gondii, in macrophages cultivated in vitro and the virulence of the parasites]. / Sud'ba vozbuditel'ia toksoplazmoza Toxoplasma gondii v makrofagakh, kul'tiviruemykh in vitro, v zavisimosti ot virulentnosti parazitov

Comparative light microscopic and electron microscopic studies of development of a highly-virulent RH strain and a less virulent Lagrave strain of Toxoplasma cultivated in macrophages in vitro were made. Contrary to active multiplication of the highly virulent strain most of toxoplasmas of a less virulent strain disintegrated the first hours, degenerating completely in 24-48 hours after the penetration into the macrophages. Submicroscopic study showed no marked cytological changes of macrophages infected with a less virulent strain in comparison with the marked changes of the nuclei in macrophages infected with the RH strain. Disintegration of parasites within the phagosome was accompanied by a gradual transformation of an originally double (or triple) vacuolar membrane to a single membrane and by the disappearance of an additional layer of mitochondria and endoplasmic reticulum elements surrounding the vacuolar membrane. It is likely that the capacity of toxoplasma to develop in macrophages in vitro could become an additional marker to its virulence for albino mice.

[Cytological study of a continuous swine embryonic kidney cell line with a persistent Toxoplasma infection]. / Tsitologicheskoe izuchenie perevivaemoi linii émbrionalnykh pochechnykh kletok svin'i pri persistirovanii v nikh toksoplazm

Invasion of the PEK cell culture by toxoplasma did not cause any sharp disruption of the vital activity of the cells and failed to lead to their rapid degeneration. The observed changes in the morphology of the host cells were apparently chiefly the result of a purely mechanical pressure of the vacuoles on the nucleus and the cytoplasm, although the extreme forms of disturbances of the cell morphology were possibly associated with their greater injury. No complete "selfpurification" of the cells apparently occurred, since despite the marked reduction in the number of parasites a possibility of reinfection with toxoplasma of the culture at the later periods after the infection could not be excluded.

Interaction between macrophages of various origin and Toxoplasma gondii under conditions in vitro.

The study of proliferation of a virulent strain of Toxoplasma in cultures of macrophages of various origin revealed a certain sequence in the development of the pathogen: penetration and phagocytosis of the parasite, the stage of disintegration of one part of population and active proliferation of the other, resulting in the destruction of host cells. It was found that the penetration and phacocytosis were more active if macrophages from resistant animals (rats) were used, in comparison with those isolated from susceptible animals (white mice, guinea pigs). The activity of proliferation of a virulent strain of Toxoplasma also differs with the host cells: the toxoplasma multiply more rapidly in macrophages from susceptible animals than in those from resistant animals. The following changes of macrophages due to proliferation of the parasite were observed: change of form of the cell accompanied with the loss of cytoplasmatic processes, vacuolation of the cytoplasm, displacement of the nucleus towards the periphery followed by its pycnosis and rupture of the cell.