Effects of Trauma on Leukocyte Intercellular Adhesion Molecule-1, CD11b, and CD18 Expressions

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Abstract
Background During traumatic injury, a multitude of events, including ischemia, may cause leukocyte adhesion and margination. In this study, alterations of surface receptors involved in leukocyte adhesion were studied in traumatized patients. In an attempt to discern the role of hypoxia, additional experiments were conducted in which normal human leukocytes were subjected to hypoxic stress in vitro. Methods Venous blood was obtained from 10 trauma patients within 2 hours of blunt injury (mean Injury Severity Score of 17 +/- 8) and from 8 normal volunteers (controls). Leukocytes were isolated from patients and controls. To assess the effect of hypoxia, normal leukocytes were placed in hermetically sealed environments containing 100% nitrogen. All leukocytes were labeled with phycoerythrin- or fluorescein-bound monoclonal antibodies to intercellular adhesion molecule-1 (ICAM-1), or to integrins CD18 and CD11b. Receptor concentration was measured by flow cytometry. Results were expressed as percentage of receptor-positive cells (%) and mean fluorescence channel units, which directly correlate with monoclonal antibody cell surface density. Significance of differences was tested by analysis of variance/Kruskal-Wallis test. Results Compared with the normal controls, circulating leukocytes obtained from traumatized patients showed decreased expression of ICAM-1, CD11b, and CD18 2 hours after injury. In contrast, normal leukocytes exposed to hypoxic stress in vitro exhibited a marked increase in CD11b and CD18 expression and no change in ICAM-1 expression. Conclusions Leukocytes obtained from traumatized patients showed a significant decrease in cell surface expression of adhesion receptors. This phenomenon is unlikely to be a direct consequence of hypoxia alone, because exposure to isolated hypoxia in vitro actually increased expression of CD11b and CD18.