Although there is some debate in exactly what type of chemical produced by the body constitutes a cytokine, there is general agreement among medical biochemists regarding their function. The primary role of cytokines includes regulation and communication. Cytokines are often produced by the body in reaction to conditions of imbalance, including illness and physical trauma, and is an attempt to marshal other parts of the body to help restore proper balance.
There is certainly agreement that cytokines are proteins. One primary role of cytokines is essentially regulatory, and in this regard, they bear a close functional resemblance to hormones. The latter, however, are secreted by specialized discreet glands, whereas cytokines are secreted by more generalized tissue spread throughout the body. These include cells of the immune system, so-called glial cells of the nervous system, and both the inner wall and outer wall cells that form and protect organs. Most hormones also have system-wide effects, whereas most cytokines have but one specific and purposeful effect.
Biochemists have identified and classified a large variety of compounds, each a unique regulator of specific body functions. A regulatory function is one of modulation, feedback and reaction either up or down to maintain proper healthy balance. One of the more important is the body’s immune system, and two of its major cytokines are interleukins and interferons. In the event of infection or trauma, these distress signals will flood the bloodstream. Some medical researchers define the role of cytokines as immunomodulating agents.
A key role of cytokines is also to chemically communicate with other remote cells of the body, signaling or triggering them to perform their respective functions, and to regulate their function. Most cytokines are target-specific; their protein is structured precisely to match the wall structure of the cell it is trying to signal. The converse is not necessarily true; different cytokines may target the same cell and trigger the same reaction. Cytokines are also believed to have a role in initiating some stages of fetal development.
Typically, when these proteins find a match and latch on to their target, it causes the cell to alter its normal, stable functioning in some way. Usually, the instruction is simply to ramp up or suppress the cell’s metabolic rate, but the role of cytokines may also be to instruct remote cells to perform tasks beyond their normal bounds. Some appear to simply initiate a chain, or cascade, of cellular reactions. For example, a target cell may be told to produce another different cytokine, a sort of baton of cellular communication.
Among the most studied of the cytokines are the interleukins that primarily target and influence white blood cells, or leukocytes. They are produced by a benign but important type of white blood cell called T-helper cells, of which there are two different types, dubbed Th1 and Th2. One class of interleukins is responsible for the growth and proliferation of T-cells, the white blood cell which aggressively seeks to destroy invasive agents in the bloodstream as well as native body cells that have become abnormal, such as by viral infection or cancer. Another class of interleukins attracts yet another type of especially potent white blood cell called Natural Killer, or NK cells.