Induction of natural killer cells during murine influenza virus infection

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Cells which are cytotoxic for both virus-infected and uninfected target cells can be recovered from the spleens of mice injected with either infectious or non-infectious influenza A virus. Peak activity occurs at 1-2 days and decreases to low levels by day 6. The effector cells are insensitive to anti-Thy 1 antibody and complement treatment, are not H-2 restricted, do not adhere to plastic and are unaffected by silica or carrageenan. In this sense and in the pattern of susceptibility to lysis of a variety of cultured cell lines, these effector cells have the properties of natural killer (NK) cells and are referred to as such. They are present to an increased level of activity in nude (nu+/nu+) mice and to a low level of activity in beige (bg+/bg+) mice, but upon injection of virus there is a significant increase in activity in both hosts. Such cells were also recovered from the lungs of mice infected intranasally with a lethal or sublethal dose of virus. In the former case, maximum activity was reached 2 days post infection and the activity remained high until death; in the latter case, peak activity was reached 4 days after virus inoculation and by day 11 the activity had decreased to pre-infection levels. After intranasal inoculation of influenza virus, both beige mice and their heterozygous littermates contained similar levels of infectious virus in their lungs. However, this result does not eliminate the possibility that these cells may help to limit virus infection.