Modulation of Mouse Natural Killer Cell Activity by the Serum Thymic Factor

Abstract

After mice were treated with serum thymic factor (FTS), an increase or a decrease in the NK activity was observed, depending on the duration of treatment and mouse strain: an increase for C57BL/6, BALB/c, A and nu/nu, and a decrease for NZB and CBA mice. The fact that treatment of C57BL/6 mice with FTS produces the same effect as thymectomy, that is, an increase.sbd.on the NK activity and returns the augmented NK activity of thymectomized mice to normal levels suggests that FTS has multiple effects with different results depending on the level of differentiation of the target cells. Different mechanisms of action of FTS on NK cells are discussed.