Acute lung injury with endotoxin or NO₂ does not enhance development of airway epithelium from bone marrow

Adult marrow-derived stem cells can localize to lung and acquire immunophenotypic characteristics of lung epithelial cells. Lung injury increases recruitment of the marrow-derived cells. We speculated that comparing patterns of lung engraftment following different lung injuries would provide insight into potential mechanisms by which marrow-derived cells were recruited to lung. To evaluate this, adult female C57Bl/6 mice irradiated and engrafted with marrow from adult male transgenic GFP mice were exposed to either intranasal inhalation of endotoxin (25 μg/ mouse) or 3 days of 25 ppm NO₂ and then compared 1 or 3 months later to transplanted but otherwise uninjured mice. In all cases, the majority of marrow-derived cells recruited to lung were CD45⁺ leukocytes. In lungs of transplanted but otherwise uninjured mice, small numbers of CD45^- donor-derived cells in alveolar septae stained positively for pro-surfactant protein C. Rare donor-derived cells located in the airway epithelium stained positively with cytokeratin. Subsequent exposure of engrafted mice to NO₂ or endotoxin did not significantly increase the number or pattern of donor-derived CD45^- cells found in recipient lungs. These results suggest that NO₂ or endotoxin lung injury does not result in significant engraftment of marrow-derived cells in lung.