C1-INH is a member of the serpin family of proteases, as are alpha-antitrypsin, antithrombin III, and angiotensinogen.
These proteins stoichiometrically inactivate their target proteases by forming stable, one-to-one complexes with the protein to be inhibited.
Although synthesized primarily by hepatocytes, C1-INH is also synthesized by monocytes.
The regulation of the protein production is not completely understood, but, since patients respond clinically to androgen therapy serum levels of C1-INH increase, it is believed that androgens may stimulate C1-INH synthesis.
All C1-INH deficient patients are heterozygous; half the normal level of C1-INH is not believed sufficient to prevent attacks.
Although named for its action on the first component of complement (C1 esterase), C1-INH also inhibits components of the fibrinolytic, clotting, and kinin pathways.