Hematopoiesis is mediated by a series of growth factors that act individually and in various combina-tions involving complex feedback mechanisms to stimulate the proliferation, differentiation, and function of hematopoietic cells.
Ten types of mature blood cells have been identified, each derived from primitive hematopoie-tic stem cells in the bone marrow. The most primitive pool of pluripotent stem cells comprises approximately 0.1% of the nucleated cells of the bone marrow, and 5% of these cells may be actively cycling at a given time. The stem cell pool maintains itself, seemingly without extensive deple-tion, by asymmetrical cell division. When a stem cell divides, one daughter cell remains in the stem cell pool and the other becomes a committed colony-forming unit (CFU). CFUs proliferate at a greater rate than the other stem cells and are more limited in self-renewal than pluripotent hematopoie-tic stem cells. The proliferation and differentiation are regulated by a number of things, including HGFs. These HGFs eventually convert the dividing cells into a population of terminally differentiated functional cells.
Cells committed to the myeloid pathway can develop into:
· red blood cells (erythrocytes)
· platelets (thrombocytes)
· monocytes and macrophages
· granulocytes (neutrophils, eosinophils, and basophils)
· tissue mast cells
Cells committed to the lymphoid pathway give rise to:
· B- or T-lymphocytes
· plasma cells
This chapter focuses on growth factors that are produced by recombinant DNA technology (identi-fied by the prefix “rh” which identifies a recombinant human form of the endogenous protein) and mar-keted in at least one country.