C5a
Chapter: 2
A split product of the complement protein, C5. It is an exceptionally important and potent proinflammatory mediator, because it has both anaphylatoxic and chemotactic effects. Therefore, it is active in engendering both the vascular and cellular phases of the inflammatory response. Because it is a plasma protein and, therefore, almost instantly available at the site of an inciting stimulus, it is probably the most important mediator in terms of initiating the complex series of events that results in augmentation and amplification of the initial inflammatory stimulus.