EFFECT OF ANTITHYROID PEROXIDASE (TPO) ANTIBODIES ON TPO ACTIVITY MEASURED BY CHEMILUMINESCENCE ASSAY

A chemiluminescence method was developed to measure thyroid peroxidase (TPO) activity and the inhibitory effect of: anti-TPO antibodies in p urified porcine TPO. The TPO preparation was characterized kinetically and controlled by Western-blotting technique, The chemiluminescence m ethod proved to be reproducible and much more sensitive than the widel y used guaiacol method, being able to detect TPO concentrations of 2.2 3. x 10(-5) g/L vs 6.63 x 10(-2) g/L with the latter. Otherwise, the d eterminations with tile two methods correlated well (r = 0.76). Invest igating the effect of IgGs from 23 hypothyroid patients on measured TP O activity, we detected inhibition in 19 cases with the chemiluminesce nce technique (15 with the guaiacol method). Anti-TPO antibodies showe d competitive inhibition of TPO activity with respect to the substrate guaiacol. In both systems, the inhibition is present in the IgG F(ab' )(2) fragment. We conclude that the high sensitivity of chemiluminesce nce detection allows routine determination of the inhibition of TPO ac tivity by anti-TPO antibodies.