The production of white blood cells is stepped up, as is creation of new red blood cells to compensate for any loss of blood. When there is damage to blood vessels, the coagulation system becomes engaged. The cells of ruptured blood vessels emit chemokines and other cytokines that attract masses of platelets to plug up the holes, stop any bleeding, and, if necessary, start the clotting process. But blood coagulation and the elimination tissues damaged by injury or infection are only the beginning. As the danger wanes, permanent repairs begin.
Cytokines even influence the brain and the nervous system.
When serious infection arises, some cytokines tell the brain to raise the body's metabolic level and bring on fever, which both inhibits the growth of many pathogens and enhances the activity of inflammatory and immune cells. The brain even makes its own cytokines to influence host defenses. And indeed, some cytokines have shown benefit in clinical trials. But there is an inherent property of cytokines that will most likely limit the number of individual cytokines that might have clinical use. They bind to and trigger responses only in cells within the immediate vicinity of the cells that produce them, including even the producing cells themselves.