Alteration of the complement system in children with acquired thyroid disease

Abstract

The complement system was studied in detail in 23 children with acquired thyroid disease of various etiologies. Seventeen patients had elevated titers of antithyroglobulin and/or antimicrosomal antibodies; 16 had complement abnormalities. Five of 6 patients with thyromegaly, but without circulating antibodies, also had alterations in serum complement. Of the 21 children with complement abnormalities, 13 had alterations in the classical pathway consisting of decreased serum levels of C4 or C2. Serum levels of C1 and the ability of these sera to lyse an antibody-coated target cell or consume C3–C9 with a preformed immune precipitate were normal. Alternative pathway abnormalities were also present in 8 of these 13 patients while isolated alternative pathway changes were found in another eight patients. Alternative pathway abnormalities were varied and consisted of depressed serum levels of factor B, properdin, and/or properdin convertase. In addition, various sera failed to support the lysis of rabbit erythrocytes or C3–C9 consumption with zymosan and/or cobra venom factor. Analysis of multiple specimens from 10 patients over a period of one year revealed the persistence of the original complement abnormalities. Complement changes were independent of the diagnostic classification of the thyroid disease, the presence or type of antithyroid antibody, abnormalities in thyroid function, or the response to therapy. These data indicate a diffuse alteration of the complement system in most children with acquired thyroid disease. Whether this alteration reflects the involvement of complement in the pathogenesis of these disorders remains unclear.