Lung Surfactant Protein D (SP-D) Response and Regulation During Acute and Chronic Lung Injury

Abstract

Surfactant protein D (SP-D) is a collection that plays important roles in modulating host defense functions and maintaining phospholipid homeostasis in the lung. The aim of current study was to characterize comparatively the SP-D response in bronchoalveolar lavage (BAL) and serum in three murine models of lung injury, using a validated ELISA technology for estimation of SP-D levels. Mice were exposed to lipopolysaccharide, bleomycin, or Pneumocystis carinii (Pc) and sacrificed at different time points. In lipopolysaccharide-challenged mice, the level of SP-D in BAL increased within 6h, peaked at 51h (4,518ng/ml), and returned to base level at 99h (612ng/ml). Serum levels of SP-D increased immediately (8.6ng/ml), peaked at 51h (16ng/ml), and returned to base levels at 99h (3.8ng/ml). In a subacute bleomycin inflammation model, SP-D levels were 4,625 and 367ng/ml in BAL and serum, respectively, 8days after exposure. In a chronic Pc inflammation model, the highest level of SP-D was observed 6weeks after inoculation, with BAL and serum levels of 1,868 and 335ng/ml, respectively. We conclude that serum levels of SP-D increase during lung injury, with a sustained increment during chronic inflammation compared with acute inflammation. A quick upregulation of SP-D in serum in response to acute airway inflammation supports the notion that SP-D translocates from the airways into the vascular system, in favor of being synthesized systemically. The study also confirms the concept of using increased SP-D serum levels as a biomarker of especially chronic airway inflammation.