L-SELECTIN EXPRESSION INCREASES ON PERIPHERAL-BLOOD POLYMORPHONUCLEARLEUKOCYTES DURING ACTIVE MARROW RELEASE

The cell adhesion molecule L-selectin is highly expressed on mature bo ne marrow polymorphonuclear leukocytes (PMN), and the release of these cells from the bone marrow could produce a population of circulating PMN expressing high levels of L-selectin. Because L-selectin initiates the interaction of PMN with activated endothelium, these cells could be important in the pathogenesis of multiorgan failure following sepsi s and septic shock. The present study was designed to test the hypothe sis that the release of PMN from the bone marrow increases the express ion of L-selectin on circulating PMN. Peripheral blood and bone marrow samples were obtained immediately after sternotomy(BM1) and during (B M2) and just before closing the sternum (BM3) in five normothermic and five hypothermic cardiopulmonary bypass (CPB) procedures. L-selectin was measured using both immunocytochemistry and flow cytometry. The re sults showed that L-selectin expression on bone marrow PMN was greater than on peripheral blood PMN (p < 0.01) in all patients at baseline. Bone marrow release of PMN during normothermic CPB was associated with a rise in peripheral blood band cells (0.18 +/- 0.7 versus 2.98 +/- 0 .56 x 10(9)/L) (p < 0.01) and an increase in the percentage of PMN exp ressing high levels of L-selectin (9 +/- 3.3 to 36 +/- 6.6%, p < 0.03) and the L-selectin mean fluorescence intensity (MFI) on PMN (p < 0.05 ). The expression of L-selectin on band cells was higher than on segme nted PMN in the circulation (p < 0.01). Hypothermia (27 degrees C) pre vented the release of band cells into the circulation and the increase d expression of L-selectin on the PMN. We conclude that PMN released f rom the bone marrow express high levels of L-selectin and speculate th at these newly released PMN may be preferentially recruited to inflamm atory sites.