T-cell regulation of T-cell responses to antigen.

Parental thymocytes, inoculated into F mice which have been depleted of lymphoid cells by lethal irradiation, react to the host antigens which are contributed by the reciprocal parent in the F cross, by synthesizing DNA. The amount of DNA the parental thymocytes synthesize can be regulated by the addition of F thymocytes to the lethally irradiated F recipient. F thymocytes suppress the response of a highly responding inoculum of parental thymocytes and boost the response of an inoculum responding less well. These regulatory effects of F thymocytes are not abolished by 900 R of irradiation. 900 R-irradiated parental cells which are themselves incapable of DNA synthesis can also affect the response of DNA synthesizing cells. As with F thymocytes, the effect that 900 R-irradiated parental thymocytes has depends on the activity of the DNA synthesizing population; when it is high the effect is suppressive, when it is low there is augmentation. These results indicate that during the course of their response to antigen, T cells may transmit signals to other T cells which in turn transmit feedback signals to the primarily responding cells and in so doing alter their response. Such circular interactions between T cells may play an important role in immunological homeostasis.