10.01 Histamine and Cytokines

The highest concentrations of histamine in the body are stored in mast cells, a cell found in connective tissue that contains granules of chemicals including histamine. In the periphery, histamine is an autocoid. The two best characterised effects of histamine are its major roles in allergy and in gastric secretion. Histamine is stored in secretory granules in mast cells, and basophils (circulating equivalent of mast cells). The highest levels of histamine are found in lungs, followed by the mucous membranes, skin, stomach, and central nervous system. Histamine is released from mast cells and basophils in tissue damage or in hypersensitivity reactions. Histamine H₁- receptors mediate hypersensitivity, while histamine H₂- receptors mediate gastric acid secretion.