Hypoxia-induced upregulation of CD11b expression in granulocytes

The aim of this study is to evaluate leukocyte-endothelial adhesion during ischemia/reperfusion injury. Polymorphonuclear neutrophils (PMN) were isolated from healthy volunteers and incubated in the presence of 2% O₂ (hypoxia) or 21% O₂ (normoxia) at 37°C for two hours. In some experiments, whole blood was subjected to hypoxia or normoxia prior to PMN isolation. Flowcytometric analysis and adhesion assays were carried out using these PMN. Moreover, adhesion assay was carried out using PMN, prepared from the patients who underwent infrarenal aortic aneurysmectomy with aortic clamping at various time points as an in vivo model of ischemial reperfusion injury. Flowcytometric analysis revealed an increased expression of CD11b in PMN subjected to hypoxia compared with those subjected to normoxia prior to isolation. Interestingly, these phenomena were not observed with PMN isolated prior to being subjected with hypoxia. Enzyme-linked immunosorbent assay (ELISA) using serum prepared from whole blood subjected to hypoxia revealed elevated levels of tumor necrosis factor (TNF)- compared with those subjected to normoxia. PMN obtained during aneurysmectomy exhibited an increased adhesion to activated human umbilical vein endothelial cells (HUVEC), compared with those taken from the same patients prior to the operation. In contrast, PMN prepared after aortic clamp, exhibited a significant reduced adhesion to activated HUVEC. Hypoxic condition, induced CD11b expression on PMN in vitro. PMN subjected to hypoxic condition in vivo exhibited an increased adhesion to activated endothelium. Elevated level of serum TNF- may be involved in this phenomenon.