Growth Factors And Cytokines Are Essential For The Normal Development Of The Human Body

Growth factors are naturally occurring substance capable of stimulating cellular growth

, proliferation and cellular differentiation. The sequence of amino acids has been determined for several growth factor polypeptides. This information permits a number of growth factors to be placed into families, members of which have related amino acid sequences, suggesting that they evolved from a single ancestral protein. Examples of growth factors are cytokines and hormones that bind to specific receptors on the surface of their target cells. The normal development of our tissues, body shape and size is strictly coordinated. Secreted growth hormones and cytokines signal between cells to regulate the key physiological processes of growth and differentiation as well as responses to injury and infection.

Growth factors are sometimes used interchangeably among scientists with the term cytokine. Historically, cytokines were associated with hematopoietic cells and immune system cells. Cytokines are soluble proteins produced and released by individual cells for the purpose of transmitting distinct messages of activation, inhibition, chemo attraction, apoptosis, etc. A message is received through a specific interaction of the cytokine with its corresponding receptor located on the plasma membrane of the receiving cell. This interaction triggers effector mechanisms within the responding cell which normally results in a beneficial outcome. However, these Signalling pathways are also a major cause of disease. Inappropriate growth control is a defining feature of human cancer, and is frequently associated with constitutive kinase activation. Excessive cytokine (interferon and interleukin) responses also underlie autoimmune and inflammatory diseases such as rheumatoid arthritis, diabetes and asthma. In some cases growth factor deficiencies can be managed by protein therapies, for example growth hormone (GH), insulin and interferon, although such treatments can be expensive and invasive.

Originating from a single fertilized egg cell, the mature human body contains some 85 trillion cells. Each of these cells has its own needs, as well as distinct duties, most of which requires the collaboration with other cells. For the dynamic system of the body to be in perfect health, this huge assembly of individual cells must act collectively and in total harmony. This necessitates an efficient and reliable system for intercellular communication. The fundamental elements of this complex communication network are cytokines and their cellular receptors. While growth factor implies a positive effect on cell division, cytokine is a neutral term with respect to whether a molecule affects proliferation. While some cytokines can be growth factors, such as G-CSF and GM-CSF, others have an inhibitory effect on cell growth or proliferation. Some cytokines, such as Fas ligand are used as "death" signals; they cause target cells to undergo programmed cell death or apoptosis.

Growth factors and cytokines are polypeptides with a wide range of potential therapeutic and diagnostic applications. They are complex biological molecules which cannot be completely characterized by physicochemical analysis alone, and require some form of bioassay to determine their potency. Bioassay systems are themselves inherently variable, so comparison of the potency of a growth factor or cytokine preparation with that of a common reference standard is necessary to permit inter assay and inter laboratory comparison of results.

The discovery of new growth factors and cytokines and the elucidation of their role in health and disease has become an area of extensive investigation in which remarkable advances have been made during the past ten years. The availability of recombinant growth factors and cytokines in significant quantities has stimulated both basic life science research and clinical studies aimed toward the development of improved tools to combat human diseases.

by: Barakat

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