Immune depression in trypanosome‐infected mice. III. Suppressor cells

Spleen cells from trypanosome‐infected mice strongly suppressed lymphocyte stimulation induced in normal spleen cell populations by lipopolysaccharide, concanavalin A or allogeneic (H‐2‐different) stimulator cells. This suppression was not H‐2‐restricted, as responses of spleen lymphocytes both allogeneic and syngeneic to the suppressors were inhibited. Irradiation or mitomycin C treatment of suppressor populations markedly reduced but did not eliminate suppressor activity. Suppressor populations were effective when present in very low numbers. Addition of suppressor cells to mixed lymphocyte cultures at various intervals after initiation of the cultures showed that the suppressors require 48 h to manifest their activity. Cell depletion or enrichment experiments indicate that the mechanism of suppression is complex and involves more than one cell type.