Cytokines are small proteins that act as chemical messengers for communication between cells. Almost every cell in the body is capable of secreting cytokines, the many families of which are made up of proteins, peptides, or glycoproteins. Each family is produced for a specific function and matches a receptor on the surface of its target cell type. The functions of these proteins include regulating immune responses or inflammation and stimulating blood cell production. Cytokines have both local and systemic effects and may act on the same cell from which they were released, or other nearby cells.
Chemokines, one type of cytokine, send messages to other cells through a process called chemotaxis. The messengers initiate the immune response by alerting other cells of threats and guiding them to the site of injury or infection. Interferons are proteins secreted in response to bacteria, viruses, parasites, or cancer cells. They inhibit virus replication by immediately signaling nearby cells to shield themselves from the virus and activating natural killer T-cells to destroy infected cells.
Tumor necrosis factor, or TNF, are cytokines that act on abnormal cells and attack cancer cell lines. They produce rapidly in response to infection by gram-negative bacteria and may cause fever and inflammation lasting up to 24 hours. TNF activates the liver to produce proteins the body needs for systemic immune responses to severe or widespread infection.
Interleukins are a large and varied category of cytokines produced by leukocytes, especially T-cells. Their function depends on the type of white blood cell with which they interact. Lymphokines coordinate the immune response through communication with other cells. Monokines come from monocytes or macrophages and fulfill many of the same functions as lymphokines. Cytokines secreted by T-cells and macrophages coordinate the entire network of interacting cells during an immune response.
Erythropoietin or hemopoietin is a cytokine secreted by the kidneys to trigger red blood cell production in bone marrow. A constant supply of erythropoietin is secreted to compensate for normal turnover of red blood cells. Red blood cells carry oxygen, so when oxygen levels are too low, the body tries to correct this by stimulating the production of additional blood cells. Colony-stimulating factors, or CSFs, are another type of cytokine necessary for differentiation of blood cells from stem cells in the bone marrow.
They cause acute inflammation as part of the healing process by pulling leukocytes, such as neutrophils, monocytes, and macrophages, from circulating blood. The body also activates other leukocytes known as mast cells at the site of infection or injury. Interactions between cytokines and leukocytes cause nearby blood vessels to widen and become porous so additional white blood cells and blood components can reach the site quickly.
T-helper cells identify pathogens or foreign substances in the body then release cytokines into the bloodstream. As they travel through, they trigger other cells to mount an immune response and activate T- and B-cells. Activated macrophages surround and break down foreign material, engulf and kill microorganisms, and remove dead cells. This is the start of the cascade induction that results in many cytokine cells being released from multiple cell types; a continuous feedback loop escalates an immune response until the compounds can eliminate the threat.
Anti-inflammatory cytokines regulate inflammation. For example, some interleukins prompt inflammation while other types reduce inflammation to maintain balance during an immune response. Arthritis, joint disease, and chronic pain can result from excessive cytokine production, unbalanced cytokines, or erroneous production without a pathogen or injury to target. Excessive pro-inflammatory cytokines correlate with osteoarthritis, while anti-inflammatory cytokines, especially TNF, that damage tissue appear to be a cause of rheumatoid arthritis.
Cytokine interaction with cells and each other is complex. Pleiotropism refers to different effects from the same cytokine, depending on the target cell type. Redundancy occurs when multiple cytokines have the same effect, while synergism means the combined effects are greater than either one individually. Antagonism is the action of one cytokine inhibiting other cytokines. They locate and attach to designated cell receptors quickly and function for a short time, so new cytokines can be released as the immune response adapts to changing circumstances.
Cytokines are part of cancer immunotherapy or natural cancer treatment, which some doctors use to treat leukemia, lymphoma, melanoma, bladder, and kidney cancer. Scientists manufacture these cytokines in a laboratory; then, doctors administer them to cancer patients. The treatment requires giving patients more cytokines than the body would produce naturally, with the goal of augmenting the immune response to overcome cancer cells. Immunotherapy is an option for other illnesses and medical conditions, as well.
A healthy, nutrition-rich diet is essential to maintaining a proper balance of cytokines. Lack of sleep, nutritional deficiencies, and a sedentary lifestyle contribute to poorly balanced cytokine production, which could compromise the immune system. Acute stress over a short time lowers production of inflammatory cytokines while increasing anti-inflammatory cytokines, but chronic stress results in higher levels of pro-inflammatory cytokines. Chronic stress is a risk factor for many negative health conditions including inflammatory disease, depression, and fatigue.
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