Regulation of mouse immuno-responses by a natural suppressor cell clone from bone marrow.

Natural suppressor (NS) activity is mediated by several kinds of cell lineages in bone marrow. We demonstrated that a NS cell, clone 7-31, was obtained after limiting dilution with bone marrow culture supplemented with WEHI supernatant. Clone 7-31, was capable of non-specific suppression of the generation of cytotoxic T lymphocytes without major histocompatibility complex restriction. Suppression of cytotoxic thymus-dependent lymphocyte (CTL) generation was also induced with a cell-free supernatant from the 7-31 cells. Interleukin-2 (IL-2) containing concanavallin-A-conditioned medium could not reverse the suppression. The supernatant did not inhibit the proliferation of IL-2-dependent CTLL-2 cells and rapidly growing tumour cells and fibroblasts. Thus, this bone marrow suppressor cell produces a soluble factor that inhibits the generation of CTL in vitro, and prolongs the acceptance of skin allografts in in vivo.