Biomedical Engineering Reference
In-Depth Information
10
Growth factors
10.1 Introduction
The differentiation, growth and division of eukaryotic cells is modulated by various infl uences,
of which growth factors are amongst the most important for many cell types. A wide range of
polypeptide growth factors have been identifi ed (Table 10.1) and more, undoubtedly, remain to be
characterized. Factors that inhibit cell growth also exist. For example, interferons and TNF inhibit
proliferation of various cell types.
Some growth factors may be classifi ed as cytokines (e.g. interleukins, TGF-
and CSFs). Others
(e.g. IGFs) are not members of this family. Each growth factor has a mitogenic (promotes cell
division) effect on a characteristic range of cells. Whereas some such factors affect only a few
cell types, most stimulate growth of a wide range of cells.
The ability of growth factors to promote accelerated cellular growth, differentiation and/or divi-
sion has predictably attracted the attention of the pharmaceutical industry. Several such products,
most notably a range of haematopoietic growth factors, have now gained approval for general
medical use (Table 10.2), and such haematopoietic growth factors are considered directly below.
A number of additional polypeptide growth factors are considered subsequently (Table 10.3).
β
10.2 Haematopoietic growth factors
Blood consists of red and white cells which, along with platelets, are all suspended in plasma.
All peripheral blood cells are derived from a single cell type, i.e. the stem cell (also known as
a pluripotential, pluripotent or haemopoietic stem cell; see also Chapter 14). These stem cells
reside in the bone marrow, alongside additional cell types, including (marrow) stromal cells.
Pluripotential stem cells have the capacity to undergo prolonged or indefi nite self-renewal. They
also have the potential to differentiate, thereby yielding the range of cells normally found in
blood (Table 10.4). This process, by which a fraction of stem cells is continually 'deciding' to
differentiate (thus continually producing new blood cells and platelets to replace aged cells), is
known as haemopoiesis.
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