A cytokine and a chemokine are both small proteins made by cells in the immune system. They are important in the production and growth of lymphocytes, and in regulating responses to infection or injury such as inflammation and wound healing. Cytokines are the general category of messenger molecules, while chemokines are a special type of cytokine that direct the migration of white blood cells to infected or damaged tissues. Both use chemical signals to induce changes in other cells, but the latter are specialized to cause cell movement.
Cytokines are a class of proteins secreted in the mammalian immune system, used as messenger molecules to control the duration and strength of the immune response to foreign microorganisms. Many cytokines produced by T cells direct the immune response of various white blood cells (leukocytes) to a foreign microorganism in the body. Among the important varieties are the interleukin (IL) molecules and interferon alpha and beta. The ILs help regulate inflammation, fever, and wound healing, among other things, while the interferons block the replication of viruses.
These proteins heal wounds by signaling blood cells, endothelium, and clotting enzymes to coagulate. There is significant overlap among many cytokines in the healing responses that they facilitate, particularly in response to wounds. They attract various lymphocytes to consume and destroy microorganisms, while guiding skin cells to regrow over the wound, and lead new collagen, blood vessels, and other cells to grow in areas of lost tissue. The various receptors that bind cytokines are called cytokine receptors. Categorizing these receptors has become an important field of research in immunology.
Chemokines are cytokines that induce chemotaxis, which is the movement of a cell or group of cells that follow a chemical messenger to a new location. Unlike cytokines, chemokines have just one major role: to direct the chemotaxis of leukocytes toward foreign, potentially disease-causing microorganims so that these cells are labeled and destroyed by the immune response. Both proteins will act on system target cells, but only chemokines specifically control the chemotaxis of leukocytes during the inflammation that initiates immune response to a pathogen.
Upon binding to receptors on their target, chemokines cause the cells to change their shape and adhere to the endothelial walls inside vessels. Like some other cytokines, they also induce cells to make compounds that kill bacteria, though this is a secondary characteristic of chemokines. Cytokines and chemokines at the site of injury or infection will have similar overall effects: getting different lymphocytes to prevent the increase of bacterial populations.