Increase in neonatal suppressor cell activity resulting from the graft-versus-host reaction.

Suppressor cell activity in the spleen of 4-5-day-old mice is high and can be assayed in mixed lymphocyte cultures. The suppressor cells inhibit the proliferation of adult mouse spleen cells responding in vitro to an allogeneic stimulus. This suppressor cell activity can be increased by injecting the mice, on the day of birth, with 10(7) allogeneic spleen cells from adult mice. The suppressor cell activity in alloantigen stimulated neonatal mice is sensitive to treatment with anti-Thy-1.2 and complement. The increased neonatal suppressor cell activity after alloantigen stimulation has been demonstrated in a number of strain combinations. Preirradiation of the allogeneic adult donor spleen cells with 2,000 rads eliminates the ability of the spleen cells to increase neonatal suppressor cell activity. Nylon-wool-nonadherent (T-cell-enriched) spleen cells are most effective, and treatment of these cells with anti-Thy-1.2 and complement eliminates their activity. By using the appropriate strain combinations it was determined that the increase in neonatal suppressor cell activity is primarily due to a graft-versus-host reaction.