Expression of scavenger receptor class A and CD14 in lipopolysaccharide-induced lung injury

CD14 and macrophage scavenger receptor class A type I and II (MSR-A) are receptors for lipopolysaccharide (LPS). In this study, the expressions of both receptors in the lung after administration of LPS in aerosol to mice with a nebulizer were observed. Bronchiolar epithelial cells and alveolar macrophages immediately incorporated LPS and expressed CD14. CD14-positive neutrophils then appeared in the alveolar space followed by the appearance of MSR-A-expressing cells in the vascular lumen, pulmonary interstitium, and alveolar space. Numbers of apoptotic cells increased after 1 day, and MSR-A-expressing macrophages actively incorporated apoptotic bodies. Daily administration of macrophage colony stimulating factor (M-CSF) to the mice resulted in increased levels of MSR-A expression and reduced levels of CD14 as well as several cytokine expressions, leading to shortening of the inflammatory process. The numbers of apoptotic cells were reduced in M-CSF injected mice. These findings imply that CD14 acts as an immediate expressing receptor for LPS and MSR-A exerts a protective function by scavenging LPS and apoptotic cells in LPS-induced lung injury.