C1-inhibitor: more than a serine protease inhibitor

C1-inhibitor (C1-inh) is a crucial regulator of the activation of plasmatic cascade systems involved in inflammation contributing to the homeostasis in the generation of proinflammatory mediators. The importance of C1-inh is illustrated by patients with hereditary angioedema where decreased levels of C1-inh lead to an uncontrolled generation of vasoactive peptides resulting in potential life-threatening subcutaneous edema. Recent publications, however, suggest that the anti-inflammatory properties of C1-inh do not strictly depend on its capacity to regulate the complement and contact phase system. This review summarizes the biochemical characteristics of C1-inh and its role in the regulation of plasmatic cascade systems as well as the role of the nonserpin domain.