C1 Esterase Inhibitor

The 105-KDa glycoprotein C1-INH (CEI), a serine protease inhibitor, is the main inhibitor of the enzymes C1r and C1 esterase (C1s) belonging to classical pathway of complement system.
Moreover, CEI acts as inhibitor of the lectin pathway of complement activation via inactivation of mannan-binding lectin-associated serine protease-1 and -2 (MASP1 and MASP2), and inhibits the alternative pathway of activation by binding to C3b. Thus, CEI can be considered the major regulator of all three pathways of complement activation (doi: 10.1111/bjh.16938).
CEI deficiency in serum is associated with hereditary and acquired angioedema forms, characterized by the swelling of the deeper layers of the skin, caused by a build-up of fluid. Patients with hereditary angioedema (HAE) shows reduced levels of CEI, while the patients with acquired angioedema show normal or high levels of CEI but its enzymatic activity results impaired.
Low levels of CEI also predispose to autoimmune diseases, such as Lupus Erythematosus (SLE), due to excessive consumption of C3 and C4 complement components. (1)

Reference

• Cicardi M, Johnston D, T: Hereditary and Acquired Complement Component 1 Esterase Inhibitor Deficiency: A Review for the Hematologist. Acta Haematol 2012;127:208-220. doi: 10.1159/000336590

The C1q (Esterase) Inhibitor Reagent “IMG” Kit, when used in conjunction with Beckman Coulter Immage® Analyzer), is intended for the quantitative determination of C1q (Esterase) Inhibitor in human serum.