The long‐acting thyroid stimulator

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Abstract
When iniected into suitably prepared guinea pigs or mice, the serum of some patients with thyrotoxicosis causes a prolonged discharge of radioiodine from the thyroid. There is chemical and immunological evidence that the long‐acting thyroid stimulator (LATS) responsible for this effect is distinct from pituitary thyroid‐stimulating hormone, and that the activity is inherent in specific immunoglobulin G molecules. The distribution of thyroid‐stimulating activity in the polypeptide chains of the IgG parallels antigen‐binding activity in known antibodies. As a result of these findings and the specific absorption of LATS by human thyroid endoplasmic reticulum, it has been suggested that LATS is an autoantibody to a thyroid component. This hypothesis is discussed. Using suitable concentration methods LATS can be detected in the serum of 85 per cent of thyrotoxic patients, and the level correlates with several parameters of thyroid activity. High levels of LATS are also frequently associated with localized myxedema, but the relation of LATS to the eye signs associated with thyrotoxicosis is less clear.