The time during which transplated lymphocytes block proliferation and differentiation of non-syngeic stem cells has been determined by retrasplantation of immuno-competent cells from one lethally irradiated recipient to another one. It was established that process of inactivation of CFU by allogeneic lymphocytes proceeds itwo stages. At the first stage, the colonization of recipient's tissues takes place. The colonization of tissues and processes of early recognition are completed during the first hours after transplantation of cell mixtures. At the second stage, the processes of redistribution of injected cells occur and a complete inactivation of stem cells take place. These events are completed in bone marrow and spleen 4-5 days after transplantation of cells mixture, possibly with the participation of lymphocytes sensibilized with the target-cells.

Erythrocytic inhibitor from the polycythemic rats depressed the mitotic activity of the cells of the erythroid series in mice by 40%. The inhibitory effect lasted about 12 hours. The inhibitor acted on the G2-period. Not only the blast forms of the erythron, but also the stem hemopoietic cells served as the points of the inhibitor "application".

The action of vinblastine and colchicine on the populations of antibody-forming cells, their precursors and stem cells using a model of primary immune response and in the transplantation system was studied using techniques by Jerne and Nordin (1963), Kennedy et al. (1965), and Till and McCulloch (1961). It was discovered that vinblastine and colchicine, at single administration 48 hours after immunization, inhibited immune response completely. The administration of colchicine and vinblastine to a donor gave an exponential decrease of in foci-forming cell number in a recipient in the system of syngenic transfer. But at the same time, vinblastine at small doses stimulated population of antibody-forming and stem cells, whereas at large doses it was not effective. Colchicine, in contrast, strongly inhibited both antibody-forming and haemopoietic cells in the recipient.

The study is based on the analysis of 10 cases of sarcomatosis of the brain and spinal pia mater. A progressive development of the disease, cachaxia, the existence of focal symptoms, radicle pain, xantochromia in the CSF, protein-cell dissociation and some other signs are characteristic of primary sarcomatosis of the pia mater. On the basis of clinical symptoms and CSF changes it is possible vitaly to perform a differential diagnosis with chronic infectious diseases and especially with tubercular meningitis and polyradiculomyelitis. Pathomorphological studies revealed tissue infiltration of the surrounding intracerebral vessels by tumors cells without proliferation into the dura mater and radicles of the spinal cord.

By means of two different markers of differentiation, using immunofluorescene method, the authors have characterized changes in the population of hepatic cells 1-8 weeks following the start of 3'-methyl-4-dimethyl-aminoazobenzene or 2-acetyl-aminofluorene action. Alpha-fetoprotein served as a marker of embryonic hepatocyte differentiation; while ligandin-as a marker of high-differentiated mature hepatocytes. The toxic effect of the carcinogens on hepatic stem cells was accompanied with a decrease of ligandin content in centrilobular hepatocytes. Among newly proliferating elements "oval" cells, cells of bile tract epithelium and most of basophilic hepatocyte-like cells fail to contain either alpha-fetoprotein or ligandin. Small groups of basophilic hepatocyte-like cells would contein alpha-fetoprotein. In cells of high cylinder-shaped epithelium of intestinal type ligandin was found, but alpha-fetoprotein was not found. The latter was absent in oxyphilous hepatocytes of hyperplastic nodules. In terms of ligandin content three types of morphologically identical nodules were differentiated; a) ones not containing this protein, b) ones containing it in amounts common to normal mature hepatocyte, and c) hyperdifferentiated nodules containing abnormally high concentrations of ligandin. Within one nodule cell all cells were identical in ligandin content. Thus, it is shown that at early stages of chemical carcinogenesis there occure in the liver multiple foci of differentiation of various kind. These intensive processes are assumed to be essential for tumor evolution in the tissue.

The peculiarities of carefully studied immunoglobulin receptors of the specialized clones of B-lymphocytes are described. These latter are precursors of antibody-forming cells but play only a limited role in the recognition of foreign antigens which is realized by T-lymphocytes. The differentiation of T- and B-lymphocytes from the single precursor, a bone marrow stem hemopoietic cell, proceeds in the bone marrow itself, thymus and peripheral lymphoid organs in several discrete stages. At each of these stages the cells have definite properties and, in some cases, may be separated one from another. The modern data are given concerning the properties of cells at every stage of antigen-independent differentiation of T- and B-lymphocytes which proceeds during embryonic and postnatal development, its alternative pathways, factors of regulation, role of local microenvironment and possibilities of modelling in vitro.

When transplanting the bone marrow cells from adult C57BL mice to the lethally irradiated (CBA X C57BL) F1 hybrids of different age, the decrease of the colony forming activity of the stem haemopoietic cells was observed in the spleen of the older recipients, as compared with the 3 months old ones. The joint transplantation of the bone marrow and thymus cells resulted in both the cases in the stimulation of the growth of colonies. The number of endogenous colonies of haemopoietic cells arising in the spleen of animals following the sublethal irradiation was greater in younger hybrids. After the induction of the "transplant versus host" reaction by the lymph node or spleen cells from the CBA mice, the relative weight of spleen and regional lymph node, respectively, in the older recipients exceeded those in the younger ones.

A study was made of the effect of the hybrid resistance abrogation by means of the lymphoid cell administration on the survival of the lethally irradiated mice protected by the transplantation of the semiallogeneic bone marrow. Injection to the C57BLxCBA recipients of the C57BL lymphoid cells one day before the irradiation and the transplantation of the bone marrow of the same genotype (C57BL) increased the chimera survival in comparison with the untreated recipients; such pretreatment 7 days before the irradiation decreased the chimera survival. Parental spleen lymphocytes administration produced but an insignificant effect on the radioresistance both of the stem hemopoietic cells (by the endocolonisation test) and of the organism as a whole (by the 30-day survival test) of the F1 hybrid. On this basis a conclusion was drawn that the differences in the splenocyte efficacy, when they were injected at different periods before the irradiation, could not be attributed to the changes in radioresistance.