The effect of soluble complement receptor 1 (sCR1) and human thyroid antibodies on the course of experimental autoimmune thyroiditis in rats.

Experimental autoimmune thyroiditis (EAT), induced by immunisation of rats with thyroid extract and complete Freund's adjuvant, has been used as a model to study the effects of complement inhibition mediated by soluble complement receptor 1 (sCR1) administration during the initial phase of the disease. There was no effect of sCR1 on the severity of thyroiditis at day 28 after immunisation or on the levels of thyroid antibodies, whether sCR1 was given during the first or second week after immunisation. Human IgG containing high levels of thyroid peroxidase antibodies given to rats at the time of immunisation caused significant worsening of thyroiditis severity (P < 0.01 compared to animals receiving normal IgG) but sCR1 again had no effect in this variant of the EAT model. The results indicate that complement does not play a major role in the initial phase of tissue injury in EAT and complement inhibition does not impair the generation of an autoimmune response against the thyroid, although it remains possible that complement activation is important during the chronic phase of disease maintenance in human autoimmune thyroid disease.