Objective: To explore the changes of L-selectin protein expression on peripheral blood polymorphonuclear leukocytes (PMN) and their role during PMN sequestration in the lungs of rats with acute lung injury (ALI).
Methods: The model of ALI in rat was established by intravenous injection of E. Coli endotoxin (ET). The protein expression of L-selectin on peripheral blood PMNs was measured by immunofluorescence and flow cytometry. Myeloperoxidase (MPO) enzyme analysis and histology were employed to estimate the quantity of PMN sequestration in lungs of rats during ALI.
Results: (1) The protein expression of L-selectin on PMN after injection of ET (7.8 +/- 1.6) was all significantly lower than that in control group (10.5 +/- 2.1, P < 0.05). (2) MPO activity increased significantly after injection of ET in comparison with the control group [0.069 +/- 0.011) U/mg lung tissue, P < 0.01]. The difference was not significant between the fucodin treated 5 min group [(0.391 +/- 0.071) U/mg lung tissue] and ET-treated 5 min group [(0.359 +/- 0.074) U/mg lung tissue]. But MPO activity was significantly lower in fucodin-treated 15 min group [(0.396 +/- 0.061) U/mg lung tissue] than that in ET-treated group at same time point [(0.490 +/- 0.069) U/mg lung tissue, P < 0.05].
Conclusions: (1) In physiological state, L-selectin are consistently expressed on the surface of PMN membrane. The protein expression of L-selectin on PMNs reduces rapidly after injection of ET and is the lowest at 15 min, then gradually increases. (2) The early stage of PMN sequestration in lungs is not dependent on L-selectin, but L-selectin is still important for maintaining a continual PMN sequestration in lungs of rats with ALI.