The influence of thyroxine and insulin on the share of cell populations, involved in erythro- and myelopoiesis in bone marrow and blood of 1-10-day old pigs, was investigated. After durable injections of thyroxine (4mg per kg body weight every 12 h from the 2nd day of life) a relative share of erythroid cells in haemopoetic tissue of animal bone marrow was seen to increase, while the proliferative activity of myeloid precursors decreased. Under the influence of insulin (after injections 0.15 U insulin per kg body weight every 12 h for 3 days) a relative share of proliferating erythroid cells increased, while that of myeloid cell did not change significantly.

We present evidence about the functional activity of factors produced by cortisol-resistant thymocytes. Experiments in vivo have shown that the administration of the supernatant prepared from cortisol-resistant thymocytes leads to a strong stimulation of endogenous colony formation, significantly prolongs survival of sublethally irradiated mice, increases the rate of restoration of the number of thymocytes in the thymus after sublethal irradiation, and contributes to the recovery of the humoral immune response of nude mice to T-dependent antigens. The results obtained suggest that along with other cytokines, cortisol-resistant thymocytes spontaneously produce a chemotactic factor inducing migration of stem cells from the bone marrow to the periphery.

An interspecific marker of mammalian erythroid cells, which was called the erythroblast antigen, was identified in 1974, using polyclonal monospecific antibodies. Further studies have demonstrated the expression of this antigen in a variety of nonhemopoietic organs and tissues, which have the following common feature: they have a barrier location; that is, they are located at the boundary. It has been proposed that the erythroblast antigen participates directly or indirectly in the transport of various substances and specifically transport of iron. The present review deals with this topic.

Like bones and other tissues in the organism, hemopoietic tissue is a constantly regenereting system in which stem hemopoietic cells (SHC) are involved in mitosis like stem cells of other tissues, this suggesting a universal mechanism of cell repopulation. Hemopoietic connective tissue is a special structure for autoregeneration and differentiation of stem cells. It forms hemopoiesis as the environment in which cells develop. Cell repopulation is the function of connective tissue and bone marrow. In leukemia involvement of the stroma creates conditions for tumor cell growth. Connective tissue disease at first manifests by imbalanced cell-to-cell interactions and then disorders cell repopulation and leads to appearance of abnormal cell forms. Abnormalities in cell development involve alteration of their biological properties. Fibrosis is a common biological phenomenon. It is one of manifestations of connective tissue functions. Fibrous tissue overgrowth in leukemia is to be regarded from a general biological viewpoint. Normally extension of the function of bone marrow hemopoiesis involves or is parallel with connective tissue growth which does not impair balanced interactions between cellular structures, their regeneration and degradation. Myelofibrosis, a form of fibrosis manifestations, is observed (in different measure) in all leukemias and is their integral component. Hemopoietic connective tissue is an "incubator" of SHC, and therefore, development of fibrosis is determined by the initial connective tissue involvement (disease) of nontumorous origin. In leukemia the same biological regularities, maintaining the organism viability, are in force, but their effect is distorted, because in leukemia the bulk of cells is many times higher than in health or even in disease. Moreover, increase of the bulk of cells occurrs under conditions of deficient bone marrow hemopoiesis, present to this or that measure in leukemia.

Radioprotective action of MIGI-K hydrolysate on adaptive response was studied. It was shown that this preparation protecting animals under lethal and sub-lethal doses of irradiation can also modify adaptive response. It was supposed that adaptive response model can be applied for studying possibilities of radioprotectors' use under low doses irradiation.

Perspective chemical classes of prophylactic radioprotecting compounds were found from analysis of proper experimental data. Preparations effective in a wide range of radiation doses of various intensity were synthesized. Their activity are due to combination of antiradiation and many other pharmacological properties. During acute radiation these preparations protect stem cells pul of critical tissues but under prolonged radiation they normalize the hematological, immune and lipid peroxide oxidation systems. There is no strong correlation between radioprotection and increasing of functional reserve of organism.

We present a review of experimental studies performed at the Laboratory of Histogenesis of the Institute of Developmental Biology, Russian Academy of Sciences, on the problem of cell interactions during hemopoiesis. Special attention has been given to original experimental models, such as production of hemopoietic foci on underlayers of fibroblasts encapsulating a foreign body in the peritoneal cavity of rodents (after intraperitoneal transplantation of hemopoietic cells) and repopulation of ectopic hemopoietic territories under the kidney capsule of mice by syngeneic or xenogeneic hemopoietic cells. We describe the competitive interactions of genetically different hemopoietic cells after the transplantation of their mixtures to irradiated mice (multicomponent radiation chimeras). Xenogeneic and multicomponent chimeras have also been obtained in long-term bone marrow culture. We have examined characteristics of hemopoiesis on stromal cell underlayers produced by cells of various origins in vitro and then transplanted into the peritoneal cavity of irradiated mice. We discuss the results obtained and possible mechanisms of these phenomena.