Changes in natural killer activity in the influenza virus infection of mice and in treating lymphocytes with the influenza virus and its proteins in vitro

: Changes in the activity of natural cytotoxic lymphocytes (natural killers, NK) were studied in the course of infection of CBA mice with a mouse-adapted or unadapted (epidemic) variants of influenza A/USSR/90/77 virus. The activity of NK against K562 target cells in the peripheral blood, lungs, and spleens was found to increase considerably 18 hours after intranasal inoculation with any of the variants and to persist at a high level for up to 72 hours. Virus replication in the lungs and peripheral blood was observed only in mice infected with the adapted virus variant. A conclusion was drawn that the increase in NK activity in the organs of influenza virus-infected mice was nonspecific providing no protection against a fatal outcome after infection with the mouse-adapted (pathogenic) virus. Treatment of lymphocytes recovered from the peripheral blood, lungs, and spleens of infected and non-infected mice in vitro with preparations of intact viruses and isolated viral proteins exerted different effects on the NK activity: enhancement after treatment with intact viruses and inhibition by isolated viral proteins. The effect did not depend on the virulence of the strain from which viral proteins were isolated. The importance of the phenomenon of different modulating effect of influenza virus and its structural proteins on the NK activity is discussed.