Human lymphocyte cytotoxicity against target cells infected with influenza A viruses of both recent and old strains

In vitro measurement of lymphocyte cytotoxicity (LC) reflects one aspect of human cell-mediated immunity against influenza. We studied peripheral blood LC against target cells infected with 1 of 3 strains of influenza A virus; these represent both recent and old strains. Positive LC responses were obtained in 94 % of subjects. Responses were significantly greater against the older strains, A/New Jersey/76 (Hsw1N1) and A/PR/8/34 (H0N1), than against A/England/42/72 (H3N2). LC reactivity occurred even in the absence of detectable HAI antibody titers. These results showed that positive LC responses to a variety of influenza A strains are common in normal adults and suggested that LC may be a more sensitive indicator of previous influenza exposure than conventionally measured HAI antibodies.