New insights into inflammatory resolution

Acute inflammatory reactions are usually self-limiting and resolve quite rapidly with complete removal of the injurious agent and little incidence of tissue damage. Chronic inflammatory reactions, on the other hand, fail to resolve and persist for long periods of time with varying levels of tissue injury. To identify the 'stop signals' that switch off acute inflammation and that may be absent or inactivated during the development of a chronic lesion, is of enormous interest. Using the experimental model of carrageenin-induced inflammation in the rat we have identified the need for the expression of inducible cyclooxygenase and its synthesis of the cycloopentenone prostaglandins for effective resolution in this model; inhibition of this cyclooxygenase prevented exudate and inflammatory cell clearance. Herein, we describe these findings and suggest a possible mechanism by which inducible cyclooxygenase derived cyclopentenone prostaglandins may be exerting their antiinflammatory effects during resolution.