What are additional details on the pathophysiology of acquired angioedema (AAE) due to C1 inhibitor (C1-INH) deficiency (C1-INH-AAE)?

Updated: May 20, 2020
  • Author: Amanda T Moon, MD; Chief Editor: William D James, MD  more...
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Although the current classification of acquired angioedema is being readdressed, in acquired angioedema type I, the associated disorders (usually lymphoproliferative malignancies) produce complement-activating factors, idiotype/anti-idiotype antibodies, or other immune complexes that destroy C1-INH function. Neoplastic lymphatic tissue has been found to play an active role in the consumption of C1-INH and the complement components of the classic pathway.

The most commonly associated malignancy, B-cell lymphoma, has shown that anti-idiotypic antibody attached to immunoglobulin on the surface of B-cells causes C1-INH deficiency. Increased consumption of C1q followed by C2 and C4 results in subsequent release of vasoactive peptides that act on postcapillary venules.

In acquired angioedema type II, a normal 105-kd C1-INH molecule is synthesized in adequate amounts but, because of an unknown event, a subpopulation of B cells secretes autoantibodies to the C1-INH molecule. This autoantibody, which may be of any of the major immunoglobulin classes, binds to the reactive center of C1-INH. After binding to C1-INH and altering its structure, its regulatory capacity is diminished or abrogated.

In all reported cases of C1-INH deficiency caused by an autoantibody, C1-INH circulates in the blood in a form that has been cleaved by target proteases from its native molecule to a 95-kd fragment. Because of the higher affinity of the autoantibody for native C1-INH, the 95-kd antibody/C1-INH complex dissociates, and the freed antibody can bind to another native C1-INH molecule, further depleting C1-INH.

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