This is the best-known chemical mediator in acute inflammation. It causes vascular dilatation and the immediate transient phase of increased vascular permeability. It is stored in mast cells, basophil and eosinophil leukocytes, and platelets. These are released from neutrophils and include cationic proteins, which may increase vascular permeability, and neutral proteases, which may activate complement. These are a group of long-chain fatty acids derived from arachidonic acid and synthesised by many cell types.
Some prostaglandins potentiate the increase in vascular permeability caused by other compounds.
These arc also synthesised from arachidonic acid, especially in neutrophils, and appear to have vasoactive properties. This is present in high concentration in mast cells and platelets. It is a potent vasoconstrictor. This family of chemical messengers released by Iymphocytes. Apart from their major role in type IV hypersensitivity, Iymphokines may also have vasoactive or chemotactic properties.