“Hierarchy” and “Holacracy”; A Paradigm of the Hematopoietic System

The mammalian hematopoietic system has long been viewed as a hierarchical paradigm in which a small number of hematopoietic stem cells (HSCs) are located at the apex. HSCs were traditionally thought to be homogeneous and quiescent in a homeostatic state. However, recent observations, through extramedullary hematopoiesis and clonal assays, have cast doubt on the validity of the conventional interpretation. A key issue is understanding the characteristics of HSCs from different viewpoints, including dynamic physics and social network theory. The aim of this literature review is to propose a new paradigm of our hematopoietic system, in which individual HSCs are actively involved.

Ranitidine Fails to Suppress the Growth in vitro of Haemopoietic Progenitors from Human Peripheral Blood or Bone Marrow

Ranitidine was added in various concentrations (25-1600 ng/ml) to clonal assays of haemopoietic progenitors of normal human peripheral blood or bone marrow. Although a significant reduction in colonies forming from granulocyte-macrophage progenitors (CFU-GM) was demonstrated at the lowest drug concentration, no significant growth suppression was seen at higher concentrations. There was no evidence for growth inhibition of either erythroid progenitors (BFU-E) or pluripotent progenitors (CFU-mix) at any of the drug concentrations studied. A direct toxic effect of ranitidine on normal haemopoietic progenitors thus appears an unlikely cause of cytopenias observed during treatment.