Stimulation of Granulocyte Macrophage Progenitors via Monocyte/Macrophage Activation: A Fundamental Regulatory Pathway of Terminal Differentiation

Abstract

The basic reason for testing a graft is to assure in advance its capacity to completely restore hematopoiesis, including early recovery and long-term production of mature cells of all lineages. Colonies growing in agar or methylcellulose after external stimulation indicate the most advanced, committed progenitors, which in vivo produce blood cells in the early recovery phase. Less differentiated precursor and multipotential cells capable of producing long-term recovery currently cannot be detected by simple assay systems in routine testing; probably they occur less frequently and must attach to feeder cells for self-renewal and production of advanced progenitors (see previous chapter). The feeder layer may represent an equivalent to their natural microenvironment in bone marrow, which provides not only attachment sites but also all necessary growth and differentiation factors.