Characterization of Cells Infiltrating the Lungs of X‐Irradiated and Nude Mice after Influenza Virus Infection

After X‐irradiated and nonirradiated mice (C3H/He) as well as athymic nude mice and haired littermates (BALB/c) were infected with influenza A virus (Kumamoto strain, H2N2), they were examined for survival period, the development of consolidation in the lungs and the characteristics of the cells infiltrating the lung tissues. In two different T‐cell deficient groups, there was a definite delay in the development of consolidation compared with their respective controls and this was reflected in prolonged survival periods: 5 days longer for irradiated mice and 6 days longer for nude mice. In both T‐cell deficient and normal groups, about 70% of the cells obtained from consolidated lung tissues after virus infection were found to be small lymphoid cells and there were no morphological differences between the T‐cell deficient and normal groups. None of these small lymphoid cells from the peripheral blood or the spleens of T‐cell deficient mice responded to concanavalin A. In the lungs of both X‐irradiated mice and nude mice, however, a definite increase in cells having natural killer activity was found at the late stages of the influenza infection, suggesting their participation in the development of consolidation.