Role of complement in the pathogenesis of postpartum thyroiditis: relationship between complement activation and disease presentation and progression
Authors: Parkes Arthur B , Othman Sakinah , Hall Reginald , John Rhys , Lazarus John H 
Published: December 2008

Parkes AB, Othman S, Hall R, John R, Lazarus JH, Role of complement in the pathogenesis of postpartum thyroiditis: relationship between complement activation and disease presentation and progression. Eur J Endocrinol 1995;133:210–5. ISSN 0804–4643

The aim of this study was to assess whether the presentation and progression of autoimmune postpartum thyroiditis (PPT) was related to the degree of thyroid peroxidase autoantibody (TPO-ab)-mediated activation of the complement cascade. One hundred and forty-eight thyroid autoantibodypositive women have been followed during their postpartum year. Seventy-five women remained euthyroid during this time whilst the remaining 73 showed one or more episodes of thyroid dysfunction. Fourteen women showed hyperthyroid PPT, 23 showed a biphasic PPT and the remaining 36 showed hypothyroid PPT. Hyperthyroid PPT was always transient but 29 of the 59 women with hypothyroidism remained hypothyroid or still required thyroxine replacement therapy at the conclusion of the study. Thyroid autoantibodies were measured by enzyme-linked immunosorbent assay (ELISA), free triiodothyronine and free thyroxine by the Amerlex M methods and thyrotrophin by the Amerlite TSH (monoclonal) assay. Complement component C3b, immobilized as a result of classical complement pathway activation in the presence of TPO/TPO-ab complexes in vitro, was measured by ELISA. Bioactive TPO-ab were calculated as the product of the C3 index and TPO-ab level. Basal levels of complement C3 activation were seen in the euthyroid TPO-ab-positive women (C3 index 0.06 at delivery rising to 0.36 at 12 months postpartum; bioactive TPO-ab activity 0.4kIU/l at delivery rising to 10.4kIU/l at 12 months' postpartum (N = 75). These parameters were elevated progressively as the severity of the clinical syndrome increased. In 14 hyperthyroid PPT women the C3 index was 0.47 at 8 months' postpartum (bioactive TPO-ab activity=20kIU/l; p vs euthyroid group, NS). In 23 biphasic PPT women the C3 index had risen to 0.65 by 7 months' postpartum (p < 0.005 vs euthyroid group), with bioactive TPO-ab activity 81kIU/l (p < 0.005), and in 36 women with hypothyroid PPT the C3 index was 0.7 by 6 months' postpartum (p < 0.005), with bioactive TPO-ab activity 76kIU/l (p < 0.005). In women with persistent PPT the C3 index had risen to 0.76 by 5 months' postpartum, with bioactive TPO-ab activity 116kIU/l; both parameters were statistically higher in the persistent group than in the remaining 44 cases where the C3 index was 0.56, with bioactive TPO-ab activity 33 kIU/l (p < 0.005 vs euthyroid; p < 0.05 vs transient). This study of the role of complement in the pathogenesis of PPT shows that the severity and duration of the thyroid dysfunction correlates with the degree of complement activation by TPO-ab measured in vitro.

AB Parkes, Autoimmunology Research Unit, Section of Endocrinology, Metabolism and Diabetes, Department of Medicine, University of Wales College of Medicine, Heath Park, Cardiff CF4 4XN, UK