Role of specific cytotoxic lymphocytes in cellular immunity against murine cytomegalovirus.

Cytotoxic lymphocytes were generated in vitro against murine cytomegalovirus (MCMV)-infected cells by incubation with ultraviolet light-irradiated, infected fibroblasts. When passively transferred, they reduced virus titers in spleens of mice 1 day after infection with MCMV. Protection was abrogated by anti-theta serum and complement. Spleen cells from mice infected for 6 to 14 days protected mice better than cells from mice after infection for 1, 3, or 30 days. Protection by in vitro- and in vivo-generated cells was H-2K or H-2D restricted. Specific cytotoxic T lymphocytes are therefore present and operative during acute MCMV infection. However, MCMV infection inhibited the development of primary cytotoxic response against ectromelia virus. It also suppressed the ability of lymphocytes from mice with established memory for ectromelia to develop secondary cytotoxic cells in vitro, and it inhibited the development of memory cells for the cytotoxic response to ectromelia virus. In view of these data and the inability of animals recovering from MCMV infection to eliminate all infected cells, the cytotoxic response to MCMV may be qualitatively or quantitatively deficient.