The number of transient endogenous spleen colonies (TEC) formed on days 4-6 postirradiation was found to be greatly increased in mice inoculated with M. arthritidis 1 day prior to sublethal irradiation. In irradiated plethoric mice, TEC formation was reduced (about 10-fold), but preinfection with M. arthritidis reversed the effect of plethora, and TEC formation in infected plethoric mice was almost as high as in infected normal mice. An abortive wave of 59Fe uptake was revealed as early as 5-6 days postirradiation in the spleen of control and infected mice. At day 6 a similar transient peak of erythropoiesis was observed in the marrow of mice infected with M. arthritidis. The data attest to the possible existence of the erythropoietin-independent mechanisms of the mycoplasma-induced activation of transient endogenous colony-forming units. The latter may play a major role in the development of various impairments of hematopoiesis and immune reactivity, which were often observed in mice infected either with mycoplasma or dually infected with mycoplasma and virus species.

The experimental data have been analyzed on the labeled cell distribution related to the grain count over the nucleus in autographs of histological sections (5 mcm) made of the rat brain subependymal zone and of epididymis duct epithelium at different time after 3H-thymidine injection and X-irradiation in the dose of 300 cGr. These results served some additional grounds to the recently established conclusion that a repeated successive decrease in the rate of DNA synthesis is occurring in the cell system starting from stem cell (level I) to semistem cell (levels II-VII) (Gracheva, 1982 r). 5 days after irradiation, at the peak of reparative proliferation, the cell reproduction was intensified, these cells having normally both middle and high levels of DNA synthesis. This process is running of the background of the inhibition of reproduction of cells with the inherent low level of DNA synthesis which are to start differentiation after mitosis. All this makes for the increase in the mean grain count over the nuclei, without changes of the inherent rates of DNA synthesis in the successive generations of the stem cells.

Presence of cells having hemopoietic origin in an intact tissue and in the lesion focus in the brain of xenogenic (a rat and mice) radiative chimeras has been studied in order to elucidate the sources of phagocytes in the CNS and their relation to the microglial elements. To identify the cells of the hemopoietic origin in the xenogenic radiative chimeras, an indirect immunofluorescent method has been applied using a specific antiserum against nonsoluble antigens of the rat bone marrow cells. In the intact cerebral tissue of the xenogenic radiative chimeras no cells of the donor type have been revealed during one year after irradiation and bone marrow transplantation. The cells having hemopoietic origin (macrophages, leucocytes) are revealed in the lesion locus (inflammatory granuloma) and in the surrounding cerebral tissue. A suggestion is made that phagocytes in the CNS lesion focus are of hematogenic origin and that there is not any histogenic connection between the microglia and the system of mononuclear phagocytes.

Changes in DNA synthesis rate were studied during the S-phase in the rat brain subependymal cells. The experimental data related to the distribution of cells depending on the silver grain count over nuclei were obtained from autoradiographs of the rat brain histological sections (5 mcm) during the first 4 hours after the intraperitoneal injection of 3H-thymidine. Recently it has been established that after the whole body X-irradiation of the rats subependymal cells were blocked independently on the irradiation dose in one of the three points along the S-phase (Gracheva, 1982b). It was postulated that these three points were boundaries of the four subphases into which the S-phase was divided. The durations of subphases SI-SIV were found to be 25, 40, 20 and 15% of ts values. The experimental cell distribution curve, in dependence of the grain count over the nuclei, was reproducible theoretically in condition of lineal and stairway increase of DNA synthesis rate during the S-phase in the boundaries of the four subphases. Among the cell population in the S-phase seven cell fractions were found, recognized by their decreasing levels of DNA synthesis and by the progressively (1 : 2 : 4 : 8 : 16: 32 : 64: increasing portions of cells from the 1st towards the VIIth level. DNA synthesis rates of the adjacent levels were overlapping. The pauses in DNA synthesis at each subphase of the S-phase in the cells of the I-VI levels are regarded as a compensation for the high rate of DNA synthesis. The results obtained are discussed in terms of cell subordination to the DNA synthesis levels, within the following sequence: stem cells--semistem cells--differentiating cells from the I towards the VII level.

The claster- and colony-forming capacities (CFF) of cells-precursors of granulomonopoiesis (CPGM) in the livers and spleens of 37 human embryos and 9 foetuses were studied in the agar system. The CFC of CPGM in the liver and spleen of 6-8 week old embryos were higher than those during the later embryogenesis. In haemopoietic cell suspension, separated from liver cells, the CFC of CPGM were lower than in the total cell suspension from the liver of 6-8 week old embryos to constant within 6-16 weeks of embryogenesis. The discussion involves stem cell heterogeneity in human embryogenesis, a possible role of the embryonal liver in regulating the number of granulopoietic cells-precursors and their functional activity.