Killer T cell responses to influenza A during a drift period: studies in mice

After intravenous immunization of mice with any influenza A H3N2 drift strain attempts to restimulation of cytotoxic T cell (CTL) activities with the same virus or other drift period variants were unsuccessful for up to 6 weeks. Cross-stimulation 4-5 months after primary sensitization yielded, in most situations, positive but lower--as compared to primary--secondary cytotoxic T cell responses. Homotypic challenge was also effective after priming with some influenza A subtypes (A/E/72, A/PC/73, A/T/77) at this time.