Cytokines are a type of small proteins, which work as chemical messengers transmitting signals from one cell to another. Cytokines belong to many families that comprise proteins, glycoproteins or peptides. Nearly all the cells in the human body can secrete cytokines. Each family of cytokines is produced to undertake specific functions and they match with specific receptors located on the target type cells' surface. These proteins have several functions, including fuelling production of blood cells and controlling the immune responses. In fact, cytokines have local as well as systemic effects and they are also able to act on the very cells that released them. They can also act on other cells that are nearby.
Since the white blood cells (leucocytes) produce cytokines, these proteins are able to perform several vital functions that enable our body to function at best possible levels. Often, these proteins are produced in reaction to some form of bacterial infection. After these proteins released by the white blood cells serve as neurotransmitters transmitting messages all through our nervous system. In fact, cytokines are of many different types - prominent among them are interferons, interleukins and lumphokines.
As cytokines are basically chemical messengers, these proteins possess the ability to assist in regulating the nature as well as the intensity of the immune system's response of our body. The signals carried by cytokines helps the immune system to effectively produce the chemicals needed by our body to combat or neutralize infections. At the same time, they also help the body to initiate necessary measures that hold back the harmful bacteria from spreading to new areas.
For instance, cytokines affect the immune system because they encourage the immune system to augment T-cell production for a temporary period to combat bacterial infections. Subsequently the signals sent by the cytokines, the immune system stops producing excessive T-cell production after the bacteria has been neutralized. As the signals compound, these proteins maintains the functioning of the cells constantly.
The function of cytokines also includes hormones - which is yet another aspect of these proteins. To maintain a balanced and optimal health, it is important to regulate the human growth hormone (HGH). Hence, these proteins play a vital role to ensure that the growth rate is acceptable, without causing any problems that may result in the malfunctioning of the endocrine system. In fact, peptides present in the bloodstream facilitate in maintain the equilibrium by transmitting the right messages as well as responses to and back via the system.
Since it has been established that cytokines are capable of combating infections effectively, researchers have tried to produce these proteins in their laboratories. These researches are based on the fact that they aim to find treatments for people with weak immune systems that have been made vulnerable owing to HIV-related situations. In fact, creating conditions that are similar to those affected by HIV and, subsequently, stimulating cytokines production artificially may result in alternatives that would sooner or later help in restoring the cytokines production to repair the harmed immune systems.
It is worth mentioning here that production of cytokines is an indispensable process that is constant in our body. However, this may also lead to the production of some unwanted side effects. When there is too much stimulation to produce cytokines, it may often result in outbreak of fever, joint inflammation and even a sense of flittering pain that may sometimes be there and disappear after a while. Usually, the side effects of such stimulations are very temporary and they subside quickly as soon as the body decreases the production of cytokines.
Cytokines are of four types and this classification is done on the basis of their function. These types include chemokines, colony-stimulated factors (CSF), interferons and interleukins. Each of these types are discussed briefly below:
For the most part, chemokines work to kindle the white blood cells, especially leucocytes when the presence of bacteria, viruses and fungi are detected in the body. The primary work of the cytokines is to transmit signals to attract leucocytes to the infected areas of the body. Chemokines work by making the immune system alert about the location of infection in the body. Subsequently, the infection-combating cells target the area and eliminate the pathogens.
Colony-stimulating factors, also referred to as CSF, helps in increasing the white blood cell count in the body. These proteins send signals that facilitate the proliferation of white blood cells so that the body can defend itself from various infections. There are two types of CSFs - granulocyte colony stimulating factors, also known as G-CSFs, which send signals to the bone marrow to produce additional neutrophils - the most important variety of white blood cells. Similarly, granulocyte-macrophage colony-stimulating factors, also referred to as GM-CSF, kindle the bone marrow to enhance the production of two varieties of white blood cells, including the macrophages and neutrophils.
Interferons are another type of cytokines whose work is to activate the natural killer (NK) cells in the body, mainly to do away with any type of infection caused by viruses. The NK cells also specialize in obliterating tumour cells and, hence, they are considered to be the body's most important mechanism to shield the body's immune system from cancer.
The fourth type of cytokines is known as interleukins, which has a vital role in creating inflammatory response. These proteins transmit signals that results in multiplication of T lymphocytes, which, in turn, aids in containing infections. Scientists have identified more than 36 different types of interleukins, which aid in controlling the immune response. The interleukins are named in a numerical order and start from interleukin-1 (IL-1) and the last interleukin is named interleukin-36 (IL-36).
Transforming growth factors or TGFs are a collection of proteins, which mainly works to generate healthy cells. TGF-alpha is one variety of TGFs that is released by macrophages inside the brain cells. They help in generating epithelial tissue, which forms the lining of the body's internal cavities. On the other hand, TGF-beta promotes cellular growth. In addition, TGFs also work for cellular differentiation - which is basically a process that helps one type of cell to transform into another type of cell.
Tumour necrosis factor or TNF are basically a group proinflammatory cytokines and are secreted by macrophages in the brain cells. These proteins send signals to the cells and have a crucial role in generating systemic inflammation. Moreover, they also bring on fever when there is an infection and also take part in neutralizing viral proliferation and combating carcinogenesis.
There are two major groups of tumor necrosis factor or TNF - monokines and lymphokines. Their classification depends on the type of cell that produces these cytokines. While monocytes only secrete monokines, lymphocytes release lymphokines. In fact, monocytes as well as lymphocytes both form a variety of white blood cells, which assist in controlling the body's immune system.
Aside from the cytokines classifications mentioned above, these protein messengers can also be grouped as pro-inflammatory and anti-inflammatory. The pro-inflammatory cytokines bring on inflammation when there is any tissue injury. On the other hand, the anti-inflammatory cytokines such as IL-4, IL-10 and IL-13, work to the contrary. The anti-inflammatory cytokines work to reduce the inflammatory response. Any condition accompanied by chronic inflammation, for instance rheumatoid arthritis, is extremely detrimental to our health. As a result, anti-inflammatory cytokines like IL-4, IL-10 and IL-13 are secreted into the body to alleviate the inflammatory effects of such conditions.
Cytokines have various different functions and, depending on their functions, these protein messengers have three different biological actions. Their functions include serving as mediators and controllers of innate immunity, working as mediators and controllers of adaptive immunity and they also stimulate hematopoiesis.
Regulators and mediators of innate immunity: These cytokines are primarily produced by mono-nuclear phagocytes when any infectious agent is present in the body.
Regulators and mediators of adaptive immunity: These cytokines are primarily produced by T lymphocytes when the body specifically identifies any foreign antigen.
Stimulators of hematopoiesis: This type of cytokines is only produced by stromal cells in the bone marrow, white blood cells, especially leukocytes, and some other cells. They persuade the growth as well as differentiation of undeveloped leukocytes.