Immunologic and Biologic Characterization of Antisera

Sensitive immunologic techniques and more purified preparations of bovine pituitary thyrotropin have made it possible to re-examine the question of whether thyrotropin acts as an antigen upon injection into heterologous species. This possibility was first indicated by Werner (1, 2) in 1936, to explain the loss of responsiveness to thyrotropin which Collip and Anderson (3) previously had observed to follow repeated injection of crude pituitary extracts. These latter workers, having demonstrated that serum from such refractory animals could neutralize the effect of thyrotropin upon the thyroid in nonrefractory animals, postulated that thyrotropic stimulation had caused an increase in the titer of an antihormone acting to preserve homeostasis by exerting an effect opposite to that of the thyrotropin. In conflict with the antihormone thesis, however, were the observations (4) that a flavianic acid preparation of thyrotropin did not evoke refractoriness, could stimulate the thyroid of the refractory animal, and could not be neutralized by the serum of refractory animals-supporting the view that antibody to a foreign protein, rather than an antihormone, had been induced. To date, however, there has been no in vitro demonstration of a circulating antibody specific for thyrotropin (5), nor is it known whether highly purified thyrotropic preparations evoke antibody formation. The results of the present experiments suggest that in the rabbit, bovine thyrotropin itself, or a closely associated and as yet not separable protein, does induce the formation of precipitating antibody; and that antisera containing such antibodies can neutralize the thyrotropic effect of the hor-