Altered lymphocyte functions in rats bearing syngeneic Moloney sarcoma tumors. II. Suppressor cells.

Spleens from tumor-bearing rats contained a population of adherent cells that suppressed lymphocyte responses to Con A and LPS and cell-mediated cytotoxicity (CMC). By use of various fractionation procedures, Ig+ cells, T cells, and null cells were excluded as candidates for the suppressor cell activity. Procedures that removed macrophages abolished the suppressive activity whereas those procedures that enriched for or involved direct addition of macrophages resulted in augmented suppression. On the basis of these results, we conclude that the suppressor elements in spleens of tumor-bearing rats were macrophages.