A molecular model of histamine, an organic compound produced by basophils and mast cells triggering the inflammatory response to foreign antigens. Histamine also regulates gastric acid secretion and can act as a neurotransmitter. During an immune response, histamine acts as a vasodilator to increase blood flow and capillary permeability for white blood cells to an injured or infected area. In an allergic reaction, histamine is released by IgE antibodies when stimulated by an allergen, causing an abnormal hypersensitive reaction resulting in an inflammatory response.