Objective: To explore the effects of polymorphonuclear cells (PMN) on lung ischemia-reperfusion (I/R) injury in a canine model of pulmonary thromboembolism.
Methods: Fifteen dogs were divided into three groups: a sham group (n = 5), an ischemia group (n = 5) and a reperfusion group (n = 5). PMN in the whole blood were isolated with density gradient centrifugation. Apoptosis rates of the PMN was measured through flow cytometer after the cells were labeled by Annexin V-FITC before embolectomy and at 2, 4, 6 h after the operation. The myeloperoxidase (MPO) concentrations in lung homogenates were measured by ELISA. Alveolar PMN in the reperfusion lobar were observed by optical microscopy. The lung ultrastructure was studied by transmission electron microscopy.
Results: Alveolar PMN infiltration and the concentrations of MPO in the reperfusion group were significantly higher than those in the ischemia group (PMN (31 +/- 11) vs (8 +/- 4)/ten high power fields, MPO (11.7 +/- 1.6) vs (9.1 +/- 0.5) microg/L, P < 0.05). In the reperfusion group, abundant inflammatory cell infiltration was observed, predominantly with PMN in the alveoli. Apoptosis rates of the blood PMN at 6 h after reperfusion were much lower than before reperfusion (3.0 +/- 2.5)% vs (7.4 +/- 4.5)%, P < 0.05). At 4 and 6 h after operation, the PMN apoptosis rates in the reperfusion group were significantly lower than the ischemia group (4 h: (4.8 +/- 2.6)% vs (9.3 +/- 2.0)%, 6 h: (3.0 +/- 2.5)% vs (8.0 +/- 1.6)%, P < 0.05). PMN attaching firmly to the alveolar septum were observed by electron microscope.
Conclusion: PMN with enhanced activities and decreased apoptosis rate, are involved in the cellular mechanisms of the lung I/R injury in this model of pulmonary thromboembolism.