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On the Mechanism of Action of Phytohemagglutinin in Cellular Immunity

Summary To study the mechanism of action of phytohemagglutinin in cellular immunity, preparations of phytohemagglutinin were made to separate its mitogenic, erythroagglutinating, and immunogenic properties. Boiled phytohemagglutinin (PHA-P, Difco), which had lost its mitogenic and erythroagglutinating activities, was used to test the immunogenic properties of phytohemagglutinin. A purified mitogenic fraction of phytohemagglutinin was isolated chemically which stimulated the lymphoid system in vivo. Untreated PHA-P was able to prolong graft rejection and block the delayed hypersensitivity reaction. Neither boiled PHA-P nor the mitogenic fraction of phytohemagglutinin was able to mimic the actions of the untreated compound. The mechanism of action, therefore, does not appear to rest in either of these properties alone. In the delayed hypersensitivity reaction, intraperitoneal injection of N-acetyl-D-galactosamine and D-galactose was able to block partially the effect of phytohemagglutinin on the reaction. These sugars, however, were not similarly effective in blocking the action of phytohemagglutinin on graft rejection.