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Experiments in mice using syngeneic transfer of spleen cells and intraperitoneal inoculation of cyclophosphamide, levamisole, hydrocortisone, and anti-0 serum demonstrated that influenza virus may inhibit T-suppressors from the first days of infection. Then the T-helper system of lymphocytes is inhibited and the capacity of the animals to show delayed type hypersensitivity is reduced. In this period, higher activity of T-helpers is observed. It is assumed that inhibition of the T-helper system is associated with the affection by influenza virus of the cells which activate T-helpers.

Experiments in mice showed influenza virus and adenovirus to inhibit the secondary and the primary immune response to thymus-dependent antigens and not to influence production of antibodies to thymus-independent antigens.

In experimental influenza infection in mice, inhibition of generation of antibody and antibody-producing cells was observed against reduced activity of T-suppressors and activation of T-helpers. These data indicate that the immunosuppressive effect of influenza virus is associated with inhibition of some other elements in the lymphocyte T-system rather than T-helpers.

A comparative study of the potentials of enzyme-immunoassay (EIA) and lanthanide immunofluorescent assay (LIFA) for influenza virus detection in nasopharyngeal aspirates and nasopharyngeal washings was carried out. Monospecific and polyclonal antisera to hemagglutinin polyclonal antisera to matrix protein as well as polyclonal and monoclonal antisera to nucleoprotein were used. The nasopharyngeal aspirates were shown to contain virus-specific antigens in the amounts sufficient for influenza virus detection with polyclonal and monoclonal antibodies. There was a good correlation between chromophore results by EIA and fluorescence level in LIFA. The sensitivity of the test systems used (EIA and LIFA) was shown to be insufficient for the detection of virus-specific material in the nasopharyngeal washings. Besides, there was no correlation between the results obtained by different test systems. It was concluded that nasopharyngeal aspirates should be collected for rapid influenza diagnosis by EIA and LIFA.

The results of the study of persistent influenza infection in S57BL mice developing after inoculation with influenza virus enriched with defective-interfering (DI) particles are presented. Regular isolation of the virus from lung tissues of the infected animals for 45 days after infection was observed. At later intervals after infection (2-8 months), the lungs and spleens yielded 8 virus strains differing from the original by their pathogenicity for mice, and thermostability of hemagglutinin. Examinations by gel electrophoresis of a strain isolated 6 months after inoculation revealed changes in the mobility of M and NS proteins which could produce some phenotypic changes of the virus in the course of persistent infection.