title: Pathological examination of lung tissues in influenza a virus-infected mice.
abstract: This study examined pathological changes in the lung tissues of young and aged mice infected  with influenza virus. Young mice inoculated with influenza virus showed body weight loss at 4 days  post-infection (dpi), meanwhile body weight decrease started from 9 dpi in the aged mice. We  histopathologically examined the lungs of these mice. Immunohistochemical examination revealed that viral  antigen-positive bronchiolar and alveolar epithelial cell numbers at 3 dpi were significantly higher in  young mice than in the aged ones. Further, viral antigen-positive cells were observed at 9 dpi in the aged  mice, but not in the young ones. Diffuse and severe bronchointerstitial pneumonia characterized by the  accumulation of polymorphonuclear leukocytes (PMNs) was observed in young mice at 6 dpi. Histopathological  changes in the aged mice were milder than those in the young mice. Moreover, T cell and macrophage  accumulation in the lungs was significantly higher in the young mice than in the aged mice at 9 dpi. These  results suggest that there may be a correlation between the relatively low level of infiltration of PMNs,  macrophages, and T lymphocytes and the delayed body weight loss and longer lasting infections observed in  the lungs of the aged mice. These findings provide detailed insights into the age-specific course of  infection in young and aged populations with associated differences in lung pathology.
authors.affiliation: Division of Molecular Pathobiology, Research Center for Zoonosis Control, Hokkaido University, Sapporo, Japan.
authors.forename: Nilton Akio
authors.initials: NA
authors.lastname: Muto
authors.forename: Yuji
authors.initials: Y
authors.lastname: Sunden
authors.forename: Tomoe
authors.initials: T
authors.lastname: Hattori
authors.forename: Daisuke
authors.initials: D
authors.lastname: Fujikura
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Nakayama
authors.forename: Tadaaki
authors.initials: T
authors.lastname: Miyazaki
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Maruyama
authors.forename: Takashi
authors.initials: T
authors.lastname: Kimura
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Sawa
mesh_terms: D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D001835:Body Weight; D007150:Immunohistochemistry; D009980:Influenza A virus / Q000502:physiology*; D008168:Lung / Q000473:pathology* / Q000821:virology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009976:Orthomyxoviridae Infections / Q000473:pathology* / Q000503:physiopathology; D011024:Pneumonia, Viral / Q000473:pathology* / Q000503:physiopathology; D016019:Survival Analysis