THYROID PEROXIDASE AUTOANTIBODIES AND THEIR EFFECTS ON ENZYME-ACTIVITY IN PATIENTS WITH SYSTEMIC LUPUS-ERYTHEMATOSUS

Thyroid microsomal antibodies (Ms-Ab) are recently proved to be direct ed to thyroid peroxidase (TPO). The aim of this study was to investiga te whether the sera of patients with systemic lupus erythematosus (SLE ) contain anti-TPO antibodies (TPO-Ab) and whether these antibodies in fluence enzyme activity. Sera from patient with Hashimoto's thyroiditi s was also studied. Serum samples were obtained from 37 patients with SLE, 20 patients with Hashimoto's thyroiditis and 20 healthy subjects. TPO-Ab were detected by immunoprecipitation using crude microsomal pr eparations or enzyme-linked immunoabsorbent assay (ELISA) with recombi nant TPO. positive TPO-Ab by ELISA were found in 11 (61%) of 18 patien ts with lupus whose serum contained Ms-Ab. Low levels of TPO-Ab also w ere found in three (16%) of 19 lupus sera that did not contain Ms-Ab. All patients with Hashimoto's thyroiditis had high levels of TPO-Ab in serum. When measured by ELISA, TPO-Ab were highly correlated with the results of a TPO immunoprecipitation assay and with the titers of Ms- Ab in patients with lupus (r = 0.83, n = 18, P < 0.01; r = 0.63, n = 1 8, P < 0.01) and in Hashimoto's thyroiditis (r = 0.89, n = 20, P < 0.0 1; r = 0.75, n = 20, P < 0.01). When evaluating the direct influence o f TPO-Ab on the activity of TPO, we found no significant inhibition of enzymatic activity in both guaiacol and iodide assays by lupus sera i n contrast with sera from Hashimoto's thyroiditis. Our findings raise the possibility that the specificities of TPO-Ab in SLE are distinct f rom those in patients with Hashimoto's thyroiditis.