Role of Interferon and Partial Immunity in Influenza Virus Infection of Mouse Lung

Summary The mechanism of recovery from infection with the PR8 strain of influenza virus in nonimmune mice and in mice partially immunized with formalin-inactivated PR8 vaccine, was investigated. The results demonstrated that in the lungs of immunized mice limitation of virus growth is mediated primarily by specific serum NT antibody. ITF was not detected in the lungs of the immunized group challenged with a sublethal dose of virus but was demonstrated in the lungs of control mice from day 3 through day 5. It was not detected on day 7 when NT antibody appeared in the serum. Pulmonary virus growth, as indicated by tests for infectious, lethal and HA virus, was maximal from day 2 to day 5 at which time ITF content reached a peak. Thereafter, virus titers remained at a high level though declining when ITF was no longer demonstrated. The time of maximum lung consolidation was subsequent to these events. Partially immunized mice survived a lethal challenge of 106 EID50 and ITF was detected in the lung on day 5, whereas in the lungs of infected controls, higher ITF titers were present over a longer period but the mice did not survive. The implication of these findings is discussed.