Chemokines are small protein molecules that are produced by the cells of the immune system. These act as chemoattractants, leading to the migration of immune cells to an infection site so they can target and destroy invading bodies such as microbes.
In short, chemokines are cell signalling molecules that guide immune cells during the body's response to infection. Chemokines are present in all vertebrates as well as some viruses and bacteria.
Some of the functions of chemokines include:
Acting as chemoattractants to help immune cells migrate to the site of microbial invasion.
Chemokines activate immune cells by binding to receptors displayed on their surfaces. The chemokine receptor is one of the G protein-coupled receptors, with a G-protein component on the inside of the cell that induces cell signalling pathways when the receptor is activated. This causes cellular responses such as the cell moving towards an infection site and releasing cytotoxic antimicrobial substances. This chemically induced movement of cells is referred to as chemotaxis. Most chemokines are proinflammatory, that is they help mount an immune or inflammatory reaction in response to a bacterial, viral or other infection or in response to tissue damage.
Some immune cells have a homeostatic role, continually surveying bodily tissues and organs to ensure their growth or maintenance.
For example, lymphocytes may migrate to the lymph nodes in order to screen the lymphatic channels for microbes infecting the body. Chemokines that induce or guide this process of surveillance are termed homeostatic chemokines. Unlike other forms of chemokines, these homeostatic chemokines do not require a stimulus to trigger their function.
Some chemokines induce angiogenesis or the formation of new blood vessels.
Further Reading
Hyperinflammation triggers long COVID headaches