Effect of influenza virus on the immune responsiveness of animals.

Infection of mice with A/Hong Kong/1/68 (H3N2) and A/PR8/34 (H0N1) influenza virus strains resulted in a significant inhibition of the formation of antibody-producing cells in response to administration of sheep erythrocytes and a reduced capacity of spleen cells to induce "graft-versus-host" reaction. The immunosuppression caused by influenza infection was observed for a long period of time post infection (3--6 months). The extent of inhibition of antibody production depended on the dose of virus, route of inoculation, the sequence of infection and immunization and the internal between them. Heat-inactivated virus exerted no immunosuppressive effect.