CONSTITUTIVE AND STIMULATED EXPRESSION OF ICAM-1 PROTEIN ON PULMONARYENDOTHELIAL-CELLS IN-VIVO

The expression of intercellular adhesion molecule-1 (ICAM-1) on pulmon ary endothelial cells after stimulus and subsequent binding of neutrop hils is a first step leading to lung injury. A similar process may dic tate the binding of tumor cells to the pulmonary endothelium during me tastasis. We report the development of a new technique that allowed us to monitor the location and relative expression of ICAM-1 levels on t he luminal surface of the pulmonary microvasculature in vivo. This tec hnique uses intravital microscopy together with a two-step labeling pr ocedure involving fluorescent microspheres. Constitutive expression of ICAM-1 was not detectable to a significant level by our model, but ex pression was observed after upregulation by the systemic administratio n of TNF alpha. Sprague-Dawley rats were injected with 0-5.0 mu g/kg T NF alpha and ICAM-1 expression was monitored through 24 hr. ICAM-1 exp ression was related to both the dose of TNF alpha administered and the time elapsed between injection of TNF alpha and observation, Injectio n of 5 mu g/kg TNF alpha caused upregulation of ICAM-1 protein express ion from 0.30 +/- 2.76 binding events/175,000 mu m(2) to 62.6 +/- 5.48 through 4 hr observation, after which levels returned to near baselin e within 24 hr. The delay required for maximal expression is likely re lated to the time required for the cell to respond to the stimulus and generate ICAM-1 protein, Reductions in the relative numbers of ICAM-1 protein expressed between 4 and 24 hr in vivo are likely a result of protein turnover after the initial stimulus. (C) 1997 Academic Press.