Effect of hyperbaric oxygen on neutrophil CD18 expression

Previous work has shown that treatment with hyperbaric oxygen significantly reduces neutrophil adhesion to postcapillary venules in a rat microcirculation model of ischemia-reperfusion injury. The mechanism of this process is unknown. The purpose of this study was to evaluate the effect of hyperbaric oxygen on neutrophil CD18 adhesion sites by flow cytometry in an animal model of ischemia-reperfusion injury. The gracilis muscle flap was raised in three groups of male Wistar rats: (1) a sham group (n = 25), (2) a group that underwent 4 hours of ischemia (n = 25), and (3) a group that underwent 4 hours of ischemia and received hyperbaric oxygen (100% 02, 2.5 atmospheres absolute, during the last 90 minutes of ischemia) (n = 25). Samples from one subgroup of each group (n = 5) were divided into two portions, and one portion was stimulated with phorbol-12 myristate 13-acetate (PMA). Samples from another subgroup of each group (n = 5) were treated in the same manner, and a flap flush was added at the end of reperfusion to determine the number of CD18 adhesion sites on adherent neutrophils remaining in the flap. Venous blood was drawn 10 minutes after the operation, at 5 minutes of reperfusion, and at 90 minutes of reperfusion. Hematocrit and white blood cell count were measured. Samples were analyzed by flow cytometry, and the antibody binding capacity was assessed using microbead standards and linear regression (antibody binding capacity was expressed as the mean number of sites per cell +/- SEM). Microbeads were used to align the flow cytometer and to provide external and internal standards. Ischemia-reperfusion injury increased the expression of CD18 by neutrophils (p < 0.05). Expression of CD18 was not decreased by hyperbaric oxygen treatment. Stimulation with PMA increased the expression of CD18 in all groups (p < 0.01). These results suggest that ischemia-reperfusion injury does increase the expression of CD18 by neutrophils. Hyperbaric oxygen, as administered in this experiment, did not prevent the increase in CD18 expression.