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Young F mice spontaneously generate cytotoxic T cells against parental targets.

Spleen cells from young (AKR/J female x BALB/c) or (BALB/c female x AKR/J)F1 mice can spontaneously generate effector cytotoxic T lymphocytes (CTL), in a 5-day primary in vitro culture, which lyse target cells from AKR/J and BALB/c but not allogeneic mice. These spontaneous CTL responses first appear when spleen cells are taken from F1 mice at 3 to 4 weeks of age, are maximum at about 5 weeks, and have declined by week 7. The fact that these spontaneous CTL responses are never detectable in the spleen cell cultures from any ages of parental AKR/J and BALB/c mice makes them unique properties of the F1 mice.