Expression of Lung Vascular and Airway ICAM-1 after Exposure to Bacterial Lipopolysaccharide

Airway instillation of bacterial lipopolysaccharide (LPS) into rat lungs induces neutrophil accumulation, which is known to be intercellular adhesion molecule-1 (ICAM-1)-dependent. In the present study, ICAM-1 messenger RNA (mRNA) of whole lung was found to increase by 20-fold in this inflammatory model. This increase was reduced by 81% after treatment of animals with anti-tumor necrosis factor-α (TNF-α) antibody and by 37% after treatment with anti-interleukin-1 (IL-1) antibody. The same interventions reduced whole-lung ICAM-1 protein by 85% and 25%, respectively. The studies were extended to assess the locale in lung of ICAM-1 upregulation. Lung vascular ICAM-1 content, which was assessed by vascular fixation of [¹²⁵I]anti-ICAM-1, rose 4-fold after airway instillation of LPS. This rise was also TNF-α-dependent. Under the same experimental conditions, fixation of [¹²⁵I]anti-ICAM-1 to airway surfaces increased 11-fold in a TNF-α-dependent manner. In situ hybridization and immunohistochemical analyses of lung tissue revealed ICAM-1 upregulation in the bronchiolar epithelium and in peribronchiolar smooth muscle. Soluble ICAM-1 could also be detected in bronchoalveolar lavage fluids (BALFs) of animals after intratracheal instillation of LPS. Retrieved alveolar macrophages showed a small, significant, and transient increase in surface expression of ICAM-1. These data indicate, at the very least, a dual compartmentalized (vascular and airway) upregulation of ICAM-1 after airway instillation of LPS. This upregulation requires TNF-α and IL-1. The functional significance of upregulated airway ICAM-1 remains to be determined.