The growth of macroscopic hemopoietic colonies was observed during postradiation regeneration in the spleen of dwarf hamsters (as well as of mice). The erythroid, granulocyte and megakaryocyte colonies were morphologically identified. The ratio between the erythroid and granulocyte colonies amounts to approximately 11. The formation of macroscopic spleen colonies and their morphology can be used for the functional characterization of hemopoietic microenvironment in the dwarf hamster.

A hypothesis of the use of hemopoietic stem cells with a view of satisfying the demand for mature cells depending on their generation age predicts that CFUs that survived after repeated treatment with hydroxyurea should have a greater capacity for self-renewal. It has been demonstrated that after repeated administrations of hydroxyurea according to the scheme devised by the authors of the hypothesis (3-4 times) and as a result of a more prolonged treatment (6 times, every other 12 or 15 h), the capacity of the survived hemopoietic stem cells for self maintenance was not only lower than normal but commonly significantly decreased. The generation-age hypothesis of the use of hemopoietic stem cells thus remains badly needing experimental support.

The paper deals with analysis of modern literature on origin of basophils and basophilic blood granulocytes. Data of radioimmunologic, electron-microscopic, cytochemical and morphological studies make it possible to conclude that these cells are of bonemarrow origin.

A high but limited capacity of haemopoietic stroma precursors to regenerate after irradiation and curettage was shown by the method of bone marrow implantation under the renal capsule of the syngeneic mice.

The bacterial mass, brucellar protective antigen and lipopolysaccharide (LPS) obtained from B. melitensis stimulated the formation of endogenous colonies in the spleen of mice belonging to different strains, subjected to irradiation in sublethal doses. The maximum stimulating effect was observed when the antigens were introduced 24 hours prior to irradiation. LPS introduced in the optimal dose induced an increase in the number of hemopoietic stem cells (HSC) in the s-phase of the cell cycle, thus stimulating the postirradiation survival of mice irradiated in a lethal dose. 24 hours after the injection of LPS the total number of HSC in the spleen increased 1.5 times. These data indicate that LPS has a stimulating effect on hemopoiesis in mice. The effect rendered by LPS is seemingly linked with an increase in the proliferation of HSC and, to a lesser extent, depends on changes in the migration of HSC.

It has been discovered that unlike animals with the intact thymus, thymectomized adult (CBA X C57B1)F1 mice did not demonstrate any reduction in the number of circulating colony-forming units (CFUs) induced by the elevated concentrations of endogenous glucocorticoids 2 weeks to 5.5 months following operation. It is assumed that the effect of glucocorticoids on CFUs is mediated by the T1 lymphocyte subpopulation.

Selective silver staining was used to study optimal conditions for demonstration of nucleolus organizer regions (NORs) of chromosomes in early embryogenesis of the laboratory mouse. The NORs were not observable during the first cleavage division. During the second cleavage, 1-7 NORs per metaphase were demonstrable. The time course of NORs demonstration was elucidated from the first cleavage till the 10th day of gestation.

To study the reasons for the failure of erythroid differentiation in a long-term organ culture of mouse embryonal liver, the development of erythroid colony-forming progenitors was examined. The "early" (BFUei) and "late" (CFUei) erythropoietin-independent erythroid progenitors were present in washes from organ cultures for at least 56 days and in the "rests" of the cultures for 46 days. The mean concentration and the correlation of the "early" and "late" progenitors were similar to those in the bone marrow and initial embryonal liver. The data suggest that the stopping of erythroid differentiation in organ culture of embryonal liver occurs after CFUei formation, interfering with their maturation to morphologically recognizable erythroid cells.

Hepatic tissues in 58 human embryos, 5-12 week-old have been investigated. At that time hemopoiesis is mainly presented by erythropoiesis. Ultrastructure of the hepatic parenchymal cells and that of the hemopoietic cellular elements have been studied. The cultural system used makes it possible to maintain hemopoiesis in the explants for 3.5 weeks. Under the conditions of cultivation in the organic culture, certain changes in architectonics of the explants are observed. As the time of the cultivation increases, the ultrastructure of the hepatic parenchymal cells, which make the hemopoiesis-inducing microenvironment, undergo further changes. A gradual substitution of erythropoiesis for granulomonocytopoiesis takes place.

This study was pursued on hybrid (CBA X C57Bl)F1 mice at the ages of 17 and 27 months irradiated at a dose of 4 Gy. It was shown that the postirradiation recovery of haemopoiesis in old mice was the same as in the young (2-3 month-old), and in some respects (for instance, granulocytic and erythroid cells of the bone marrow, and CFUc) the recovery was even more active exhibiting a period of a pronounced hyperregeneration.

Radiosensitivity of hemopoietic stroma precursors from long-term bone marrow culture was measured by implantation of adherent cell layer under renal capsule of syngeneic mice. D0 was 4.86 +/- 0.15 Gy and n was 2.4, i.e. radiosensitivity of cultured cells was nearly the same as that of stromal precursors from fresh bone marrow.

After exposure in vitro and in situ CFUdc of CBA mouse bone marrow and spleen were characterized by the comparable parameters of radiosensitivity and oxygen-dependent modification: the values of D0 for bone marrow and spleen cells were 1.31 and 1.35 Gy (in vitro) and 1.36 and 1.37 Gy (in situ), and the values of the oxygen effect were 2.3 and 2.5, respectively.

The ability of CFUdc to repair radiation-induced lesions in the irradiated body was studied by the methods of dose fractionation and dose-rate reduction. With the dose-rate decreased from 1-0.5 Gy/min to 0.02 Gy/min, a mean lethal dose per cell increased from 1.35 up to 1.93 Gy. With fractionation of the dose, the known picture of repair of sublethal radiation lesions was obtained the second survival peak being insignificant. The authors discuss the possible causes of the distinctions in the repair parameters of CFUdc obtained by the two methods.

The influence of the T-system of immunity on the processes of the proliferation and differentiation of hemopoietic precursor cells outside the organs of the hemopoietic and lymphoid systems has been studied. Thymocytes have been found to regulate the formation of hemopoietic foci in the peritoneal cavity. The effects of the stimulation and suppression of colony formation, as well as the degree of their manifestation, depend on the initial level of the colonies. The thymectomy of the recipients or donors of hemopoietic cells leads to the increase of colony formation. Syngeneic thymocytes abolish the effect of thymectomy.

The number of colonies formed in the peritoneal cavity (on the artificial underlayer made of peritoneal cells) and in the spleen of lethally irradiated recipients, (CBA X X C57BL) F1 mice, after the intraperitoneal injection of marrow cells depends on the cell donor's genotype: syngeneic cells and cells from mice of the parent strain CBA form fewer colonies in the peritoneal cavity than in the spleen, while cells from C57BL mice produce the reverse distribution of colonies between the peritoneal cavity and the spleen. Allogenic lymphocytes, when transplanted simultaneously with hematopoietic cells, suppress colony formation in the peritoneal cavity from day 2 of cultivation and eliminate the already developed foci of hematopoiesis by day 5.

The ultrastructure of lipoblast-like cells produced by clones of transformed culture of strain in the medium with an increased (60%) concentration of bovine serum was studied. The aim of using the stimulator rich in adipogenous factors was the elucidation of the origin of lipid accumulation in some of cell types during heterogeneous differentiation of clones. In these conditions non-differentiated lipoblasts assumed the fine structure of mature lipid cells. The statement of the marker significance of lipid accumulation in non-differentiated cells of the clones and the conversion of these cells under the influence of non-specific stimulator to the mature lipocytes confirms the data on conservation of over-all cytogenetic potentials and the capacity of their realization in the cells of transformed cultures. It is suggested that the increased concentration of bovine serum in the cultural medium not only stimulates differentiation (by any way determined cells), but is also capable of acting on the stem elements produced by the clone. In that case the influence of the stimulator on the trends of heterogeneous differentiation is not unlikely.

It was shown on (CBA X C57Bl)F1 mice that a single intraperitoneal injection of a physiological solution (0.2 ml) reduced the number of haemopoietic stem cells in the bone marrow and increased concurrently the radioresistance of CFU.