Background: Autoantibodies directed against complement C1q (anti-C1q) have been described in a number of systemic autoimmune disorders. In systemic lupus erythematosus, they are strongly associated with proliferative lupus nephritis. However, no study has focused on the presence of anti-C1q in organ specific autoimmune disorders. The aim of this study was to determine the prevalence of anti-C1q in autoimmune thyroid disorders (AITD).
Methods: Serum levels of anti-C1q were measured using a commercially available ELISA kit (Bühlmann Lab. AG) in 23 patients with Graves disease (GD) and 51 patients with Hashimotos thyroiditis (HT). As controls, 16 patients with polynodular goitre and 72 normal blood donors were included. The patients underwent standard endocrinological evaluation.
Results: Positive serum concentrations of anti-C1q (>15 U/ml) were found in significantly more patients with AITD than in controls: 7/23 patients with GD (30.4%; P<0.005) and 10/51 patients with HT (19.6%; P<0.05), compared to 0/16 with polynodular goitre and 6/72 blood donors (8.3%). In patients with HT, anti-C1q correlated significantly with autoantibodies against thyroglobulin (Spearman r=0.3312, P<0.01) and against thyroid peroxidase (r=0.2339, P<0.05). Interestingly, in HT anti-C1q correlated also with thyroid stimulating hormone (TSH) (r=0.2684; P<0.05). In contrast, in patients with GD we found a negative correlation of anti-C1q with TSH (r=−0.4169, P<0.05) and a positive correlation with free thyroxine (r=0.4365, P<0.05).
Conclusions: Anti-C1q antibodies have an increased prevalence in patients with AITD. Their concentration correlates with autoantibodies against thyroid autoantigens and with some of the parameters of thyroid function.
Supported by the grant of the Czech Health Ministry IGA NR 8352-3.