Con A-induced suppressor cells in man. I. Introduction and characterization of suppressor cells.

Con A-induced suppressor cells were studied in autologous co-cultures of normal human lymphocytes. Lymphocytes pretreated with 5 microgram/ml, 20 microgram/ml, or 50 microgram/ml of Con A were cultured for 24, 48, 72 hours. Subsequently, the whole mononuclear (MN) cell subpopulation or T-enriched, B-enriched, and monocyte-enriched fractions were added to freshly obtained lymphocytes, stimulated with 5 microgram/ml of Con A and cultured for a further 96 hours. MN cells pretreated with 5 microgram/ml of Con A did not significantly affect the DNA synthesis in co-cultures with unfractionated MN cells, while cells pretreated with 20 microgram/ml or 50 microgram/ml for 48 and 72, but not for 24 hours, possessed the suppressive activity. The suppressor cells were found in T-, but not B-enriched subpopulations. Moreover, suppression was induced by T-enriched fraction from MN cells pretreated with 5 microgram/ml of Con A, while unfractionated cells failed to exhibit inhibitory activity. The degree of T-cell-induced suppression was dose-dependent. Irradiation with 3000 R diminished the suppressive activity of cells derived from 48-hour cultures and abrogated the activity of cells from 72-hour cultures. The present data indirectly prove that Con A-induced suppressor cells are radiosensitive T lymphocytes. The observation that induction of suppressor cells by Con A is dose-and time-dependent provides the further insight into regulatory immunological mechanism in humans.