The cell adhesion molecule L-selectin is highly expressed on mature bone 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 sepsis and septic shock. The present study was designed to test the hypothesis that the release of PMN from the bone marrow increases the expression of L-selectin on circulating PMN. Peripheral blood and bone marrow samples were obtained immediately after sternotomy (BM1) and during (BM2) 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 results 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 0.56 x 10(9)/L) (p < 0.01) and an increase in the percentage of PMN expressing 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 segmented PMN in the circulation (p < 0.01). Hypothermia (27 degrees C) prevented the release of band cells into the circulation and the increased expression of L-selectin on the PMN.(ABSTRACT TRUNCATED AT 250 WORDS)