Direct cytotoxicity against chicken erythrocytes in mice. III. Degrees of radiosensitivity and cross-reactivity of cytotoxicity, delayed hypersensitivity and antibody production.

Exposure to 600 rad of X-irradiation 3 h after primary immunization with chicken erythrocytes (CRBC) abolished the production of antibodies and the generation of killer T cells, but scarcely affected the induction of delayed footpad reactions. Exposure to irradiation 3 h after secondary immunization reduced only slightly the generation of killer T cells and reduced slightly or substantially the production of antibodies. Delayed reactions persisted for long periods after elicitation in irradiated, boosted mice. Cross-reactivity between CRBC and quail erythrocytes (QRBC) was very weak with respect to the cytotoxicity, antibody and delayed reaction raised after primary immunization. Those raised after secondary immunization with the homologous antigen showed some degrees of cross-reactivity to another antigen. The booster with QRBC in CRBC-primed mice augmented the response to CRBC with respsect to the induction of cytotoxicity and delayed footpad reaction, but only weakly affected the response with respect to the production of antibody. Therefore, effector cells of cytotoxicity and delayed footpad reaction showed greater degrees of cross-reactivity than antibody-producing cells during an anamnestic response. The cross-reactive response raised after secondary immunization was radioresistant with respect to cytotoxicity and delayed footpad reaction but radiosensitive with respect to antibody production. Cytoxicity to immunizing antigen was inhibited by the unlabelled homologous antigen. Cytotoxicity to a cross-reacting antigen was inhibited by the same cross-reacting antigen and also by an immunizing antigen. There may exist heterogeneous populations of cytotoxic lymphocytes with different abilities to recognize antigens.