The control exerted by thymic hormone (THF) on cellular cAMP levels and immune reactivity of spleen cells in the MLC assay.

We have shown previously that THF induces immunocompetence in lymphoid cells through the control of cellular cAMP levels and DNA synthesis. By the use of a one-way MLC assay it was now shown that the exposure of spleen cells to THF is accompanied by an increase, in the proliferative response of the responding cells. These effects are mediated by regulation of cellular levels of cAMP during the course of the MLC response. Thus, substances which modify cellular levels of cAMP such as DBcAMP, theophylline, and imidazole change the reactivity of cells exposed to THF in the MLC assay. It was also found here that cellular cAMP levels are critical in controlling the reactivity of normal spleen cells in the absence of THF. It is suggested that THF increases the number of competent cells in the spleen cell population capable of responding to antigenic stimulation in the MLC assay.