In vivo effector function of influenza virus-specific cytotoxic T lymphocyte clones is highly specific.

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Abstract
Cloned lines of murine cytotoxic T lymphocytes (CTL) directed to type A influenza virus confer complete protection upon adoptive transfer to syngeneic mice lethally infected by influenza virus. The exquisite specificity exhibited by a subtype-specific cloned CTL in culture is reflected in its capacity to eliminate pulmonary virus and mediate recovery only in those mice infected by the virus subtype recognized by this cloned line in vitro. A cross-reactive CTL cloned line protects mice infected by either of 2 influenza virus subtypes. In mice dually infected with 2 virus subtypes, the subtype-specific CTL clone reduces lung virus levels of the recognized virus subtype only and cannot prevent these mice from dying. Adoptive transfer of the cross-reactive CTL clone into mice simultaneously infected with 2 virus subtypes results in reduction of pulmonary titers of both subtypes and promotes complete recovery. These results directly implicate CTL as an important antiviral defense mechanism in experimental influenza infection, and indicate that both the induction and expression of antiviral effector activity by CTL in vivo is highly specific, thus favoring the concept that CTL express their antiviral effect in vivo by direct cytolysis of infected cells.