Quantitative Studies of Mitoses and DNA‐Synthesizing Cells in Bone Marrow and Blood of Guinea‐Pigs Recovering from Sublethal Whole‐Body Gamma Irradiation*

Abstract

DIVISION by mitosis is confined to the more immature type of bone-marrow cell. However, the chances of observing mitoses in the least differentiated cells are considerably diminished by the low incidence of these cells in normal marrow.The study of the least differentiated cells may be fachtated by examining bone marrow in the early stages of regeneration after a temporary arrest of cell production. Provided that the arrest of haemopoiesis is of sufficient magnitude and duration, the more differentiated cells eventually mature and are discharged from the marrow. Then, until regeneration is relatively advanced, a period follows when immature cells predominate. Quantitative studies of bonemarrow in sublethally irradiated guinea-pigs (Harris, 1956(Harris, , 1960a have shown that immediately after an abortive recovery of granulopoiesis there is a short period between 12 and 14 days after irradiation, when immature cells are particularly evident and this precedes final erythropoietic and granulopoietic recovery. The proliferative activity of bone marrow at this early stage of regeneration has been studied before testing its ability to protect animals from the effects of a large dose of y-irradiation. Evidence that mitosis predominates in a particular cell group at this stage of regeneration would be of special interest.The purpose of this paper is to report quantitative studies of those cells in the bone marrow of young guinea-pigs which show evidence of proliferation at an early stage in the final recovery of haemopoiesis after sublethal whole-body irradiation. The identity of a cell may be more difficult to establish during mitosis but cells which are destined to divide can be easily recognized during the pre-mitotic stage of DNA-synthesis. Therefore, in each experiment, proliferation was studied by making concomitant observations of mitotic figures and DNA-synthesizing cells in smears prepared from the same sample of bone marrow. In addition, the size of each cell in mitosis or DNA-synthesis was recorded. Smears prepared from the buffy layer of centrifuged blood, obtained from the inferior vena cava, were examined for the presence of DNA-synthesizing cells.The discovery that bone-marrow cells from normal animals are able to colonize the haemopoietic tissues of lethally irradiated animals (Ford, Hamerton, Barnes and Loutit, 1956) emphasizes the need to identify the essential stem cells in bone marrow. The transplant may be of only short duration, being then replaced by the host's regenerating tissues, but the graft niay persist for a considerable time (Ford, 1961). The cells responsible for the persistence of a graft must be relatively immature and possess the ability to divide and to be a continuous source of progenitors. They could be blast cells which have already differentiated into early forms of granulocyte and red cell or, accepting the monophyletic theory of haemopoiesis, they might be cells of an even earlier order which still retain the ability to differentiate along various lines. The significance of the ...

Recovery of Haemopoiesis after Cyclophosphamide

“…These cells are known to be actively proliferating [6,17] and there is evidence suggesting that they may possibly function as stem cells [14],…”

“…The rise in marrow lymphocytes has been shown to depend on the dose of irradiation [12]. By means of studies of DNA-synthcsis H arris et al [6] also showed that a consider able proportion of the small lymphocytes in the irradiated marrow were newly formed.…”

An Investigation of Lymphocyte Production in Guinea-Pig Bone Marrow

“…Autoradiography: The method used was based upon the stripping-film technique described by PELC (17) and full details of the handling of bone marrow smears have been described elsewhere (7). The smears were stained through the stripping film with a 0.1% solution of New Methylene Blue.…”

“…Previous studies of bone marrow recovering from irradiation (7,8) have shown that at a certain stage during the recovery many of its dividing cells (%-]/2 of all telophases) appear to be forming small or medium-sized lymphocytes. Experiments were therefore planned in which the problem of lymphocyte production in guineapig bone marrow has been further investigated.…”

Studies on Hypoxia (Iii. The Differential Response of the Bone Marrow to Primary and Secondary Hypoxia)

“…Now the only obvious precursors are the transitional lym phocytes, and these virtually never undergo mitosis. Harris et al [1963] illustrate w hat they consider to be a transitional lym phocyte in mitosis. A part from the difficulty of accurately identi fying cells in mitosis, they give no inform ation about the m itotic index of these cells in norm al m arrow.…”