Mary A. Maloney

BONE MARROW RESTORATION AFTER LOCALIZED DEPLETION

Studies have been made of marrow restoration after localized depletion of the rabbit femur by dextran perfusion. Restoration was shown to involve an initial period of reorganization which blends with a more prolonged period of hemic cell repopulation. Cellularity returned to normal levels by 35 days, the recovery of myeloid cells being somewhat more rapid than that of the erythroid elements. In either case, the evolution of immature hemic cells was soon followed by the appearance of more mature forms even at the earliest stages of marrow repopulation. 3H‐TdR uptake per cell increased rapidly to a level approximately twice normal after the first week. The augmented incorporation of thymidine, revealed by scintillation spectrometry and confirmed upon autoradiography, was shown to be due to an increase in DNA synthesis rate as well as in the fraction of participating cells. It is suggested that the enhanced cell production is brought about by a decrease in the proliferative cell cycle and an increase in the growth fraction. The origin of the repopulating cells remains a moot point. Cell migration from the epiphyseal marrow is apparently not involved. Irrespective of the source of stem‐type cells, the stimulus for regeneration appears to be locally determined.

RADIOSENSITIVITY OF THE PROCESS INITIATING BONE MARROW REGENERATION.

PATT, H. M., AND MALONEY, M. A. Radiosensitivity of the Process Initiating Bone Marrow Regeneration. Radiation Res. 41, 500-506 (1970). Studies were made of the radiosensitivity of the mechanism that initiates marrow restoration after localized depletion of the rabbit femur. The femur was x-irradiated, with the remainder of the body shielded, just prior to its depopulation by dextran perfusion. The status of marrow regeneration during the first 4 weeks was determined by the incorporation of tritiated thymidine into DNA and by the number of hemic cells in the mechanically ablated femur relative to the contralateral limb. A radiation dose-response curve was derived which has a form similar to that for mammalian cell survival, with a threshold region of about 200 R and a Do of approximately 325 R. It is emphasized that the parameters of the dose-response relationship for marrow regeneration cannot be equated necessarily with similar parameters derived specifically for cell survival. The present results provide further evidence for the local origin of the repopulating cells. However, whether the initiation of the various facets of marrow regeneration is due to uncommitted mesenchymal elements or to more than one cell type (for example, stromal stem cells and hematopoietic stem cells) in osseous tissue remains a moot point.

On the Origin of Hematopoietic Stem Cells after Local Marrow Extirpation

Summary The early hematopoietic regeneration in a depopulated segment of femur shaft is compared in +/+ and W/Wv mice and in W/Wv mice previously treated with +/+ marrow. Since the W/Wv mouse has an intrinsic CFU deficiency on spleen colony assay and since immigrant cells play a negligible role in the onset of regeneration after marrow extirpation, the W/Wv(+/+) chimera provides a model for evaluation of the contribution of residual cells to the regenerative program. There was little difference in the relative recovery of CFU in +/+, W/Wv, and W/Wv-(+/+) Moreover, +/+ derived CFU were responsible for nearly all of the CFU repopulation in chimeric mice. Thus, recovery of hemic cellularity must be due to residual stem cells rather than to stem cells derived by transformation of more primitive mesenchymal elements. The residual CFU are probably intimately associated with bone, most likely within the endosteum and haversian system.

A method for quantitative identification of canine erythrocytes.

Summary A procedure for the uantitative determination of injected canine erythrocytes by a differential agglutination technic utilizing lyophilized type-specific anti-sera is described. The method was applied in a study of erythrocyte survival after transfusion of blood. Approximately 20% of the blood of the recipient dogs was withdrawn and immediately replaced with an equal volume of donor blood. Determinations were made of red cell volume, plasma volume, donor and recipient red cell counts. Serial examinations of bone marrow and peripheral leucocytes were also made. Destruction of infused cells proceeded at a rate of about one per cent per day. No changes in bone marrow morphology or peripheral leucocytes were noted. Nitrogen balance was not significantly changed.