Local tissue complement synthesis--fine tuning a blunt instrument.

Complement is important to host defense and the regulation of inflammation. The liver is overwhelmingly the major source of circulating complement. However, many other organs are capable of synthesizing some or all of the complement components in a regulated tissue-specific manner. There is increasing evidence that this locally generated complement is biologically active and exerts powerful effects within the local environment. We review the role of local complement synthesis within different organs and speculate on its implication for immune and metabolic functions.