Activation of thyroid adenyl cyclase by antisera to thyroid plasma membrane preparations: effects of IgG and non-IgG antiserum components.

We have previously shown that IgG isolated from rabbit antibovine thyroid plasma membrane (anti-BTPM) antibodies exhibits properties similar to long acting thyroid stimulator (LATS) and HTS-lg in that it activates thyroid adenyl cyclase. In order to test whether another immunoglobulin class, eg, IgM, of anti-BTPM antiserum can also stimulate the bovine thyroid adenyl cyclase system, protein molecules of the antiserum were separated into different molecular sizes by gel filtration chromatography on Sephadex G-200. It was observed that the low molecular weight fraction, consisting predominantly of albumin, was inactive in stimulating adenyl cyclase of the thyroid gland. In contrast, both IgM-enriched and IgG-enriched fractions of the immune serum were fully active. Furthermore, the thyroid-stimulating activity of the IgM-enriched fraction can only be inhibited by anti-IgM and that of the IgG-enriched fraction by anti-IgG. Our data suggest that IgM, in addition to IgG, may also have LATS or LATS-like activities in terms of activating adenyl cyclase of the thyroid gland.