Cyclic Hematopoiesis in Grey Collie Dogs: A Stem-Cell Problem

Studies were made to ascertain the possible basis of cyclic hematopoiesis in the grey collie. The results of ³H-thymidine and ⁵⁹Fe labeling in conjunction with other marrow parameters and peripheral counts suggest that the regular periodicity of blood neutrophil and reticulocyte levels is caused by a defect at the stem-cell—marrow interface. It is postulated that the ebb and flow of hemic cell production in the grey collie reflects competition for a limiting number of pluripotential stem cells with the alternating competitive pressure provided by activation and deactivation of a neutrophil feedback circuit from periphery to stem cell. This mechanism can account for the characteristic 12-day periodicity and contributes to the phase difference in the cycling pattern of neutrophils relative to reticulocytes.