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Immune System
Iron is an essential nutrient for humans, as well as microorganisms and pathogens that may invade the body. Tight regulation of iron within the body is one method the immune system uses to fight infection. During infection, hepcidin is released. Hepcidin is the regulatory hormone that induces the storage of iron within the cells as ferritin or hemosiderin. The storage of excess iron prevents pathogens from having access to adequate iron for essential biological processes, causing the pathogen to die. The proteins involved in iron regulation also play important roles within the immune system. The protein transferrin, which is responsible for binding iron within the bloodstream, is also required for T-cell differentiation. Transferrin is also present in macrophages, cells responsible for engulfing pathogens and mature red blood cells for breakdown. The iron content of macrophages can effect their ability to fight infection by altering the activity of NADPH oxidase within the cell. NADPH oxidase is what allows the macrophage to kill the engulfed pathogen by releasing a burst of reactive oxygen species (ROS) destroying the invader. An increased concentration of iron within the macrophage makes the macrophage cell more susceptible to bacterial infection. A decreased concentration of iron within the macrophage, in turn, decreases the macrophage cell's susceptibility to bacterial infection.