Soluble intercellular adhesion molecule-1 provokes polymorphonuclear leukocyte elastase release by CD18

Background. Elevated levels of soluble intercellular adhesion molecule-1 (sICAM-1) correlate with the development of postinjury multiple organ failure. Soluble ICAM-1 secretion is known to be induced in endothelial cells and monocytes by diverse inflammatory stimuli. We have found the incubation of quiescent polymorphonuclear leukocytes (PMNs) with sICAM-1 elicits elastase release and, more recently, that cross-linking CD18 receptors on PMNs also produces elastase release. Consequently, our study hypothesis was that sICAM-1 provokes PMN elastase release through its interaction with CD18. Methods. To obtain sICAM-1, Chinese hamster ovarian cells transfected with human ICAM-1 were lysed and centrifuged at 150,000 g for 1 hour; the supernatant was passed over an ICAM-1 affinity column, eluted with 0.1 mmol/L glycine HCl, and concentrated with dialysis filter. Human PMNs (2.5 x 10(5)) were saturated with specific monoclonal antibodies for the beta(2) subunits (CD11a, CD11b, CD18) or nonspecific monoclonal antibodies for 30 minutes on ice before a 1-hour incubation with sICAM-1 (75 ng/ml) at 37 degrees C. Elastase activity was measured by the cleavage of n-methoxysuccinyl-A-A-P-V-p-nitroanilide. Results. Neutrophil incubation with sICAM-1 resulted in 19.2% +/- 2.8% of total PMN elastase, compared with 2.4% +/- 0.5% in the controls. Blockade of CD18 abrogated sICAM-1 provoked elastase release with monoclonal antibodies to CD18 (TS1/18, 31H8) resulting in 4.3% +/- 1.0% and 5.5% +/- 1.4% elastase release, respectively. Blockade of CD11a, CD11b, and nonspecific antibody controls had no effect on sICAM-1-induced elastase release. Conclusions. In vitro, sICAM-1 provokes PMN elastase release through CD18. This may represent a mechanism by which elevated levels of circulating sICAM-1, released from local injury sites, provoke distal organ dysfunction.