The transplantation of liver from the embryos and newborn C57BL-6 mice to the lethally irradiated hybrids (CBA X C57BL/6) F1resulted in 90% allogenic inhibition of the colony-forming activity of the donor elements. The degree of allogenic inhibition of liver cells of 19 days old embryos and newborn mice may be changed with the help of syngenic lymphocytes of adult mice or delayed transplantation of cells 72 hrs following the irradiation of recipients but these procedures proved to be ineffective with the liver cells of 13 and 16 days old embryos. A suggestion is put forward to the effect that the allogenic inhibition is based on the active reaction of recipient hybrids (CBAXXC57BL/6) F1 to the stem hemopoietic cells of C57BL/6 mice.

The maternal effect was shown to influence the degree of allogenic inhibition of stem hemopoietic cells of the embryonic liver and adult bone marrow in CBA and C57Bl/6 mice. The display of allogenic inhibition of stem cells of the embryonic liver and adult bone marrow proved to be similar in C57Bl/6 mice and dissimilar in CBA.

Bone marrow cells (0,5-10(6)) of female mice of CBA or C57BL strains were injected intravenously to lethally irradiated CBA, C57BL/6, (femaleCBA X maleC57BL/6)F1 and (femaleC57BL/6 X maleCBA)F1 mice. Spleen of recipients as assayed for colony count on the 9th day after bone marrow transplantation by the method of Till and McCullouch. Stem cells of CBA mice demonstrated failure of allogenic inhibition in (CBA X C57BL/6)F1 hybrid mice and formed the same number of colonies as in the spleen of syngenic recipients. The level of allogenic inhibition of CBA stem cells transplanted to (C57BL/6 X X CBA)F1 hybrid mice was 50%. Bone marrow cells of C57BL/6 mice formed colonies in spleen of (CBA X C57BL/6)F1 mice at least in 20 times less than in syngenic combination. In the transplantation of bone marrow from C57BL/6 mice to (C57BL/6 X CBA)F1 hybrid mice the allogenic inhibition was less pronounced (77-85%) as compared with the transfer of cells to (CBA X C57BL/6)F1 hybrid mice (95%). The sex of a recipient did not influence the number of formed colonies. The different level of allogenic inhibition of parental stem cells can not be explained by the effect of linkage with sex as the female of reciprocal hybrid mice have identical structure of sex chromosomes (X(CBA)XC57BL/6). The data obtained indicate that the maternal effect affects allogenic inhibition of stem cells in parent--F1 system. It is possible that the maternal influence may be determined by cytoplasmic factors of inheritance which affect the expressivity of recessive genes Hh, controlling the inheritance of specific haematopoietic cell antigens.

Using the method of exogenous cloning in vivo of the hemopoietic stem cells of the bone marrow and spleen in the femur and the spleen of mice it was shown that during hypokinesia the kinetics of the stem cells differed in both organs (the spleen and the bone marrow). Differentiation of transplanted stem cells from different sources was unchanged in the spleen, but stem cells of the bone marrow seeding in the femur changed the character of their differentiation in the direction of increase of the erythopoietic function, whereas stem cells of the spleen failed to alter the direction of differentiation.

It was found that the colony-forming capacity of parental bone marrow transplant (C57BL/6) was partially restored in the (CBA X C57BL/6) hybrid recipient irradiated with 800 rad when poly I -- poly C preparation was injected. The effect of poly I -- poly C injection on the colony formation was equivalent to addition of the thymus cells syngeneic with the marrow. In either case the number of splenic colonies was more than double that in the control. On the other hand, it was found that in a completely syngeneic system the number of splenic colonies was not influenced by the thymus cells and poly I -- poly C preparation. Poly I -- poly C doses ranging from 50 to 100 mug and thymus cell doses ranging from 4-10(6) to 8-10(6) did not increase the efficiency of the colony formation with a stable bone marrow dose transplant.

The experiments demonstrated that pretreatment of lethally irradiated recipient (CBA X C57BL/6) F1hybrid mice with cyclophosphamide (200 mg/kg of body weight) on day before the bone marrow transplantation (4 hours after the irradiation) suppressed the allogeneic inhibition of hematopoietic stem cells to 24% (while the inhibition in the untreated animals was 92.5%). It is suggested that cyclophosphamide acted on the recipient's radioresistant lymphoid cells effecting the allogeneic inhibition of stem cells.

Six to nine hours after the beginning of stress-reaction caused by a 6-hour immobilization there appeared, in the bone marrow of CBA mice, cells with the antigenic (theta-antigen) and functional (cells-helpers) characteristics of T-lymphocytes. Migration of T-lymphocytes into the bone marrow was regarded as the mechanism of increase in nonspecific resistance of the organism.

A mixture of the bone marrow cells and lymphocytes of the lymph nodes of C57BL mice was injected intravenously to A X C57BL mice irradiated in a dose of 850 R. It appeared that under the effect of syngenous lymphocytes of C57BL mice the colony-forming cells (CFC) of the bone marrow of the F1 hybrid mice proliferated as if they were in the syngenous organisms. Along with the restoration of the number of CFC capable of forming colonies in a genetically foreign organism these cells, under the effect of lymphocytes, altered the direction of differentiation which was characterized by increase in the number of granulocytic colonies. This process was accompanied by the development of the blast transformation reaction and hyperplasia of the lymphoid tissue of the recipient spleen.

Tests set up on male-mice of the CBA/I lineage demonstrated that fat carbohydrate rations of 1:7.3 and 1:3.8 in granulated combined fodder tend to increase the number of stem cells in a statistically fashion. Among mongrel mice kept on a ration with 7 per cent of fat a combination of mexamine with AET was found to loose some of its toxicity.

A study was made of the influence of hydrocortisone on the individual stages of immunogenesis: migration of the hemopoietic stem cells from the bone marrow, B-cell migration and cooperation between the T and B lymphocytes in the course of primary immune response to sheep red blood cells was studied. Experiments were carried out on (CBAXC57B1) F1 mice. In doses which failed to suppress the proliferation of hemopoietic cells hydrocortisone produced a marked immunosuppressive action which was a sum total result of its inhibition of various stages of immunogenesis--the stem cells and the B-cells migration and the T-B lymphocyte cooperation.

Studies dealing with the colony-forming cell as a subject of experimental research are reviewed. The techniques of cultivation of colony-forming cells, their proliferation, differentiation and self-renewal have been considered.

After a sublethal (200 rad) irradiation of mice there occurred during the first 24 hours in the bone marrow a marked reduction of the number of the stem (to 4%), committed precursors of granulocytes and macrophages (to 20%) and of the morphologically-identified cells (to 50%). Complete restoration of hemopoiesis was observed by the end of the 2 weeks after the irradiation and was primarily due to the exponential growth of the number of the stem cells and their intensified proliferation. An increase in the number of the committed precursors was retarded to the moment of restoration of the normal amount of cells in the bone marrow.

Cytochemical methods were applied for detecting of distribution and dynamics of dehydrogenase activity (H- and M-subunits of lactate dehydrogenase, malate and succinate dehydrogenase) during maturation of pigeon erythrocytes. In the erythroblasts the above enzymes were seen in the whole cell; in reticulocytes - only around the nucleus; in erythrocytes - on the border line between the nucleus and the cytoplasm. The cytophotometric data show a decrease in enzymatic activity during maturation being more significant in the period from the erythroblast to reticulocyte development than from the reticulocyte to erythrocyte development.

The nidi of hemopoiesis appeared in the liver and the lymph nodes of DBA/2, C57BL/6j and F1 (C57BL/6j X CBA) strains of mice of the 6th day after a single intraperitoneal injection of cyclophosphamide in a dose of 200 mg/kg. This process was accompanied by the appearance of stem hemopoietic cells in the liver. Their maximum number was observed on the 6th and the 9th days. On the 12th day their level decreased, but it still exceeded the one in the animals which received a suspension of normal liver cells. In myelosan exhaustion the pool of the bone marrow and splenic stem cells, the subsequent cyclophosphamide injection failed to induce the appearance of the nidi of hemopoiesis and stem cells in the liver.

In erythroid and myeloid cells of rabbit bone marrow the total activity of esterases and their isozyme spectrum in polyacrylamide gel disc electrophoresis were studied. Higher esterase activity was observed in the myeloid cells as compared with erythroid ones. In the isozyme spectrum of esterases from the myeloid cells an additional cathode fraction was observed, which was not found in extracts of erythroid cells. Experiments with inhibitors showed that the enzymes studied were carboxyl- and acetylesterases.