Polyclonal autoantibodies against C1 inhibitor in a case of acquired angioedema

Background: Angioedema attributable to acquired C1 inhibitor (C1-INH) deficiency is a rare disease related to lymphoproliferative disorders or autoantibodies to C1 inhibitor. We describe a patient with angioedema and autoantibodies to C1 inhibitor. Objective: To study the characteristics of autoantibodies to C1-INH in a patient with acquired angioedema. Methods: Autoantibodies to C1-INH were measured by enzyme-linked immunoadsorbent assay. Immunoglobulin (Ig)G autoantibody was purified by affinity chromatography on a protein G agarose column. We developed an enzyme-linked immunoadsorbent assay to determine whether the autoantibodies were directed against the C1-INH active center. Results: IgM and mainly C1-INH I-G autoantibodies were detected; both had K and a chains. No monoclonal component was detected. The autoantibodies were directed against the C1-INH active center. After various treatment strategies were attempted, an effective clinical response was attained with antifibrinolytic therapy. Conclusion: A case of acquired angioedema because of C1-INH deficiency was found to be attributable to the presence of polyclonal autoantibodies to C1-INH.