Suppressor cells in the spleens of tumor-bearing mice: enrichment by centrifugation on hypaque-ficoll and characterization of the suppressor population.

Spleen cells from mice bearing methylcholanthrene-induced sarcomas or a mammary adenocarcinoma suppressed the mitogen responses of normal spleen and lymph node cells. Lymph node cells from tumor bearers had no suppressive effects. Centrifugation of spleen cells layered on Hypaque-Ficoll (specific gravity of 1.08) produced a dense fraction which pelleted and a light fraction which was retained at the Hypaque-Ficoll-medium interface. Suppressive activity was not found in either fraction of normal spleen cells. In tumor-bearer spleen cells suppressor activity was greatly enriched in the light fraction. Treatment of the suppressor fraction with anti-theta or anti-Ig serum and complement did not remove suppressor activity. However, the suppressor cells were removed by passage through nylon wool or by carbonyl iron treatment. Also, the population which adhered to plastic Petri dishes contained the suppressor cell activity.