Studies on the Induction and Expression of T Cell-Mediated Immunity

Abstract

Abstract Purified thymus-derived (T) cytotoxic lymphocytes were inhibited from mediating cytolysis of 51Cr-labeled target cells by alloantiserum directed against the target cell. Sensitization of BALB/c (H-2d) thymocytes was obtained in one way-mixed lymphocyte cultures against mitomycin C-treated C57BL/6 (H-2b) spleen lymphocytes and in vivo after injection into lethally irradiated C57BL/6 mice (educated T cells). EL-4 (H-2b) tumor cells were used as target cells. Several criteria for optimizing the blocking effect were investigated. Blocking was obtained with antibody-coated target cells but was absent when the lymphocytes were pretreated with the antiserum before admixing with the target cells. The blocking activity was dependent on the concentration of antiserum. It was estimated on a target cell basis that 50- to 200-fold increase in antibody concentration was required to mediate blocking than was necessary to induce lysis by complement. The blocking effect was observed with different ratios of effector to target cells (E:T) and was found to be independent of the concentration of effector cells present. Eluates obtained from antibody-coated target cells behaved very much like the original antiserum by reacting again with fresh target cells but not with the effector cells. When the cytotoxic assay was run for shorter incubation periods (90 min vs 180 min), more blocking activity was detected, and significant inhibition of cell-mediated cytotoxicity (CMC) was obtained with high dilutions of antiserum which were not inhibitory in longer incubation periods. Maximum blocking was obtained when the antiserum was present at the beginning of the assay; at 30 min or after, the addition of antiserum had no blocking effect. These results demonstrated that damage of target cells occurs rapidly after effector-target cell interaction long before the radioactive chromium marker is released.