Stimulation by cyclic GMP of lymphocytes mediated by soluble factor released from adherent cells

Abstract

THE activation of lymphocytes by mitogens is a complex phenomenon which can be subdivided into reactions occurring on the surface of the cells¹ followed by a chain of intracellular reactions caused by biochemical alterations in the membrane². With respect to the mediation of the mitogenic signal from the membrane to the nucleus it has been claimed that 3′,5′ – cyclic GMP either directly fulfils a role as a ‘second messenger’³, or that a 3′,5′–cyclic GMP-dependent step is involved in the chain of intracellular reactions culminating in cell mitosis^3,4. These assumptions are based on the facts that after the addition of lectins to peripheral white blood cells depleted of granulocytes and monocytes, an increased intracellular concentration of 3′,5′–cyclic GMP was detected³ and that 3′,5′–cyclic GMP added exogenously activated DNA synthesis in spleen and thymus cells in vitro^4–6. The prerequisites for the validity of the above mentioned hypothesis, however, are that the 3′,5′–cyclic GMP levels are indeed increased in all cells entering the mitotic phase and that 3′,5′–cyclic GMP added exogenously acts directly on the lymphocytes, without the participation of other cells.