Suppression of Cytolytic T-Lymphocyte Responses through Inactivation of Non-T Accessory Cells

The suppressive properties of nonspecific cytotoxic T lymphocyte (CTL) populations, derived from murine fetal calf serum (FCS)-precultured cells expanded in interleukin 2 (operationally defined as FCS-CM-expanded cells), were investigated on CTL responses generated by syngeneic alloreactive lymphoid cells. Our results suggest that the addition of FCS-CM-expanded cell populations can inhibit the CTL response by elimination of the bone marrow-derived macrophage (BM M phi) population used as non-T accessory cells. Indeed, in the culture conditions used, removal of IL-2 by the FCS-CM-expanded cells as well as a direct inactivating effect on the CTL precursors (CTL-P) could be excluded as a reason for inhibition. On the other hand, we were able to show that the BM M phi population was very sensitive to the cytolytic activity exhibited by the inhibiting cells in a 3 h 51Cr-release assay and that the suppressor effect observed could be partially circumvented by a second addition of BM M phi on the second day after the initiation of the culture.