Evidence of suppresssor cell-mechanism of allograft tolerance induced by spleen extract and hydrocortisone.

The mechanism of allograft tolerance in mice induced by cell-free spleen extract in combination with hydrocortisone was investigated. HC potentiated tolerance induction when given after the spleen extract. When HC was given before, or during the first 2 weeks of antigenic treatment, it counteracted rather than potentiated the tolerance-inducing effect. Spleen or lymph node cells transferred from tolerant donors to untreated or sublethally irradiated syngeneic recipients suppressed the recipients' response to the particular alloantigens. The suppressive activity of lymphoid cells from tolerant donors was abolished when before their transfer the subpopulation of T cells was eliminated by means of anti Thy-1.2 serum and complement. This finding suggests that suppressor T cells may be involved in tolerance induced by spleen extract and hydrocortisone.