HEMATOPOIESIS
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.
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