C1-esterase inhibitor ( C1-INH, plasma protease C1 inhibitor ) is belonging to the serpin serine protease inhibitor, which controls the activation of the complement factor C1, and so regulates the complement system. The standard level in the blood is about 0.25 to 0.45 g / l


C1 -INH is the largest member of the serpin class of proteins. It is probably the most highly glycosylated protein. Remarkably, it has O -glycosylated residues that are unusual for non- membrane-bound proteins ( immunoglobulins IgA1 and IgD are other examples ).


Human C1 -esterase inhibitor gene is located on the eleventh chromosome ( 11q11 - q13.1 ).


Deficiency of this protein is called hereditary angioedema ( hereditary angioneurotic edema or ). Mostly it is presented with recurrent swelling ( edema ) of the skin, mucous membranes and internal organs, which can be life threatening. It is estimated that about one under 10,000-50,000 people are affected, but the actual number is probably much higher. In 85 % of cases, the level of C1 -INH is lowered, while in 15% of the protein circulates in normal amounts, but which is not functional.

Therapeutic benefit

Hereditary Angioedema

In patients with hereditary angioedema and frequent seizures prophylactic C1 -INH can be given. It can also reduce the duration or severity of seizures.

Other applications

The activation of the complement system can cause damage to cells. Therefore, the inhibition of the complement system under certain conditions may be of therapeutic benefit. For example, if someone has a heart attack, caused the lack of oxygen to the heart cell necrosis of cardiac cells: The sinking heart cells release their contents into the extracellular environment and thus activate the complement system. This activation attracts phagocytes, the peroxidase and other activators produce that can increase the damage to the surviving cardiac cells. The inhibition of the complement system could help to reduce this damage. Further may be used C1-esterase inhibitor in the treatment of vascular leak syndrome, an adverse effect of interleukin -2 therapy.

Currently, it is investigated whether recombinant C1 inhibitor, the survival of transplanted kidneys may be extended by treatment.


  • Protease inhibitor
  • ATC -B02