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A4478 - Alveolar Macrophage Numbers Are Decreased During Acute S. Pneumoniae Pneumonia, and Are Repopulated by Both Lung and Bone Marrow-Derived Cells During Recovery
Author Block: O. K. Giddings1, W. J. Brickey2, J. R. Martin1, J. C. Gomez3, J. C. Gomez3, C. M. Doerschuk4; 1Pulmonary and Critical Care Medicine, University of North Carolina, Chapel Hill, NC, United States, 2Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC, United States, 3Univ of North Carolina at Chapel Hill, Chapel Hill, NC, United States, 41Division of Pulmonary Diseases and Critical Care Medicine, Department of Medicine, Univ of N Carolina, Chapel Hill, NC, United States.
Rationale: During murine development, resident alveolar macrophages are derived from both fetal yolk sac and fetal liver, but not from bone marrow. During acute lung injury, the total number of alveolar macrophages in the lung decreases. Alveolar macrophages are capable of cell division. We sought to determine whether alveolar macrophages are reconstituted from remaining lung macrophages or from bone marrow-derived cells after injury induced by S. pneumoniae. Methods: 6-8 week old C57Bl/6 mice expressing CD45.2 were irradiated with 900 Gy with lead shields protecting the thorax to maintain native lung immune cell populations. After irradiation the mice were given 1x107 bone marrow cells from C57Bl/6 mice expressing the CD45.1 allele. After the bone marrows reconstituted for 8-10 weeks, the chimeric mice were given either PBS or a suspension of S. pneumoniae via tracheal instillation into the left lung. Chimeric mice that received no intervention were also studied. At 48 hours and 14 days after instillation, the lungs were digested to form a single cell suspension. Lung cells and blood leukocytes were immunolabeled and analyzed by flow cytometry. Cells were stained for CD45.2, CD45.1, Ly6G (neutrophils), NK1.1 (NK cells), CD3 (T cells), CD19 (B cells), CD64, Siglec-F and Ly6C. Alveolar macrophages were defined as CD45+Ly6G-CD64+Siglec-F+ and Ly6C low. Interstitial macrophages were defined as CD45+Ly6G-CD64+Siglec-F- and Ly6C-, and inflammatory macrophages as CD45+Ly6G-CD64+Siglec-F- and Ly6C+. Results: There was a significant decrease in the total number of alveolar macrophages in mice with acute S. pneumoniae infection (48 hours) compared to mice given PBS (48h or 14d) , infected mice studied 14 days after infection and mice with no stimulus. The percent of alveolar macrophages that were bone marrow-derived was significantly higher in mice with pneumonia for both 48h and 14 days compared to mice given PBS for either time or no stimulus (mean 37.58% and 48.03% compared to 8.1%, 13.66% and 18.26% respectively). There were no significant differences in the percent of bone marrow-derived interstitial or inflammatory macrophages, neutrophils or NK cells, each of which were predominantly bone marrow-derived. Conclusions: During acute lung injury the total alveolar macrophage population is diminished. Bone marrow derived cells contribute to restoring this population during resolution of acute pneumonia. Lung neutrophils, NK cells, interstitial macrophages and inflammatory macrophages are primarily derived from bone marrow cells. Support: R01 HL114388; T32 HL007106