Patients with
acute lung injury or
respiratory distress syndrome often require supplemental
oxygen to maintain tissue oxygenation; however, this treatment can cause or worsen
lung inflammation. CD44 is a transmembrane adhesion molecule that is present on a wide variety of cell types, including leukocytes and parenchymal cells, and is an important player in leukocyte trafficking. The aim of this study was to determine the role of CD44 during
hyperoxia-induced (> 95%
oxygen)
acute lung injury. Whereas all wild-type mice survived the 72-hour observation period, 37.5% of CD44 knockout (KO) mice died. CD44 deficiency was associated with a profound influx of neutrophils into the bronchoalveolar space, in the presence of similar or even lower neutrophil numbers in lung parenchyma, suggesting that CD44 is important for containing neutrophils in the pulmonary interstitium during
hyperoxia. In addition, CD44 deficiency resulted in increased
IL-6 and keratinocyte-derived
chemokine release into bronchoalveolar lavage fluid (BALF). CD44 KO mice further displayed evidence for increased vascular leak and injury of type II respiratory epithelial cells. CD44 protected against bronchial epithelial cell death, as shown by increased epithelial cell
necrosis and a trend toward increased BALF
nucleosome levels in CD44 KO mice. CD44 can bind and internalize
hyaluronic acid (HA), which acts proinflammatory. Concentrations of HA increased in BALF from CD44 KO but not wild-type mice during
hyperoxia. These data suggest that CD44 protects against
hyperoxia-induced
lung injury and mortality by a mechanism that at least in part relies on its ability to clear HA from the bronchoalveolar space.