Neonatal thymus grafts. I. Studies on the regulation of the level of circulating thymic factor (FTS).

The level of circulating thymic factor (FTS) tested by its action on spleen rosette-forming cells from adult thymectomized mice, has been shown to be stable in young animals. This stability suggests a regulatory mechanism. An approach of this regulation has been attempted by disrupting the FTS level either by neonatal thymus grafting in adult normal and thymectomized animals, or by injections of synthetic thymic factor into normal, thymectomized mice, grafted or ungrafted. In all cases, after an initial increase over the normal value, FTS levels returned close to the previous range, indicating the existence of some homeostatic mechanism of FTS secretion.