Deformabejty of younger polymorphonuclear leukocytes (PMN) released from the bone marrow

We have previously demonstrated that PMN newly released from the bone marrow preferentially sequester in pulmonary capillaries (1). To test the hypothesis that PMN newly released from the bone marrow (PMN^BrdU) are less deformable than their circulating counterparts, PMN were labeled in the bone marrow with BrdU (100mg/kg, i.v.) 24 hr before BM release was induced by either saline (control), granulocyte colony stimulating factor (G-CSF, 12.5μg/kg, s.c.), or lipopolysaccharidefLPS, 10μg/kg i.v.) administration. Both G-CSF and LPS cause a significant increase in circulating PMN, band cell and PMN^BrdU counts within 8 hr (p<0.05). Blood leukocytes harvested at 8 hr were filtered through a polycarbonate filter (pore size of Sum) by continuous infusion pump. The ratio of PMN^BrdU present before and after filtration was determined by immunocytochemistry. In control animals PMN^BrdU ratio approached unity (99.3± 3.6%, n=4). but it decreased significantly in the G-CSF (73.3±3.3%, p<0.01, n=4) and LPS (51.5±6.6%, p<0.01, n=4) treated animals. These results suggest that PMN released during active bone marrow release are less deformable than their circulating counterparts that may account for their preferential sequestration in pulmonary capillaries.