Effect of phytohemagglutinin on skin allograft survival in mice.

Single or repetitive i.p. injections of Phytohemagglutinin (PHA) induced a selective marked decrease in blood and bone marrow lymphocytes in mice, suggesting that PHA might have a specific immunosuppressive effect. To test this hypothesis, parallel' experiments were conducted using female C57Bl/6J (H-2b) mice as recipients and either female C3H/HeJ (H-2k) or female (C57Blx C3He) Fl (H-2b,k) hybrid mice as donors of full-thickness skin grafts. lmmunosuppression, as indicated by prolonged graft life, was induced by 4s little as a single injection of 0.1 mg and increased with the dose to the maximum tolerated dose of 3.0 mg PHA. Several time and dose responses were tested. Maximal immunosuppression was induced using a regimen of 3.0 mg i.p. 24 hrs. before grafting, followed by daily injection of 0.5 mg PHA i.p. These results lend support to the hypothesis that PHA, like anti-lymphocyte serum, has a specific suppressive effect on cel1-mediated immunity.