Reduced C4 in HLA-B8 positive patients with Graves' disease.

We studied the serum concentration of C3 and C4 in 50 controls and 49 patients suffering from Graves' disease. No difference was observed in C3 or C4 levels between the patient and control groups as a whole nor when HLA-B8 positive or negative patients were compared with the corresponding control group. Nevertheless, C4 concentrations were significantly lower in HLA-B8 patients with Graves' disease compared to antigen negative patients (30.6 +/- 10.3 vs. 36.9 +/- 10.2 mg/100 ml, p less than 0.05). This difference in C4 levels was even more pronounced when only treated euthyroid patients were compared (27.2 +/- 6.4 mg/100 ml, for B8 positive vs. 35.9 +/- 10.7 mg/100 ml for B8 negative patients, p less than 0.02). These results suggest that reduction in C4 concentration may play a role in the pathogenesis of Graves' disease.