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pppA2'p5'A2'p5'A(2'-5'P3A3) activates macrophages and increases the phagocytosis of macrophages from different species including human beings. This indicates that the activation of macrophages may be a general action of 2'-5'P3A3. This discovery broadens the effect of 2'-5'P3A3 beyond the antiviral field. alpha-Feto-protein (AFP) inhibits the phagocytosis of macrophages and may be involved in the development of hepatoma. Data presented here show that 2'-5'P3A3 can antagonize this suppressive effect of AFP. Methods used so far for introducing 2'-5'P3A3 into the cells were made with the aid of CaCl2, etc. under conditions which may not be the same as those used clinically. It was found that 2'-5'P3A3 can develop its biological effect without the aid of CaCl2, etc.

In this paper, the increase of cellular cAMP and cGMP levels in macrophages induced by ppA2'p5' A2'p5'A (briefly 2'-5'P3A3) is first reported. The optimal concentration of 2'-5' P3A3 for the elevation of cellular cGMP to the highest level is 10(-7)-10(-6) mol/L, while that for cAMP is 10(-7) mol/L. The time for cGMP to reach its peak value is 15 min and that for cAMP is 2 h, when the cells are treated with 2'-5' P3A3 at 10(-7) mol/L, which is the optimal concentration for developing biological effect of macrophages (phagocytosis). These results suggest that cGMP and cAMP may be related to, or may be the mediators for, 2'-5'P3A3 action.