|MadSci Network: Immunology|
A cytokine is a protein (generally a small one) that is used by various white blood cells to talk to each other. Other body cells will sometimes secrete cytokines; but, I generally think of a cytokine as one that is produced by a white blood cell or produced to communicate to a white blood cell and usually both. For example, some cytokines are used to promote inflammation near an infected cut. These cytokines will induce white blood cells in the area to leave the bloodstream to fight the infection. The area will also take up fluid (swell) mostly in order to support the immune response. Some cytokines are also growth factors that induce responding white blood cells to divide when it is useful for the body to have more of those particular white blood cells at a particular place. Erythropoietin wouldy fit the more general definition of a hormone or growth factor than the definition that I use above. The term cytokine is usually reserved for communication proteins of white blood cells. The distinction is a little bit arbitrary but useful to scientists. Precursors of erythrocytes in the bone marrow express a receptor that binds erythropoietin. When this receptor binds erythropoietin, these cells divide more quickly and live longer and thus produce more red blood cells. In some ways erythropoietin is related to cytokines, particularly in that its receptor is similar to some cytokine receptors and also is wired into the cell in a similar way. I am not familiar with the term "monokine." Feel free to email me if you have any more questions. Jeff
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