Regulatory mechanisms controlling hematopoiesis: Principles and problems

Abstract

Hematopoiesis is regulated by the combined action of specialized stromal cells and a consortium of hematopoietic regulatory factors. The multiplicity of these regulatory controls does result in overlapping regulator action, but multiple regulators are required to stimulate stem cell proliferation and are more efficient than single regulators when stimulation of progenitor cells is required. Gene inactivation studies have indicated that despite overlapping actions each hematopoietic regulator does have unique functions. Delayed elevations of stem and progenitor cells in the blood are a feature of enhanced hematopoiesis induced by the injection of regulators. These cells are not a random sample of marrow cells in such situations and may well be selected to rapidly amplify hematopoiesis by seeding previously inactive hematopoietic regions.