A large cell with densely granular cytoplasm that is found in connective tissues, for example around blood vessels and in the skin. Mast-cell granules contain mediators of inflammation (e.g. histamine) and lipid mediators (such as prostaglandin D₂ and leukotriene C4), as well as various cytokines, which cause a local increase in blood flow and attract white blood cells to the area. The granule contents are released from the cell in response to tissue injury or as part of an allergic response. Release is triggered by binding of antigen to a type of antibody (IgE) that is bound to the mast cell. The cell also releases heparin, an anticoagulant that prevents clot formation. See also allergy.