The present studies were designed to test the hypothesis that mechanical deformation of polymorphonuclear leukocytes (PMN) leads to functional changes that might influence their transit in the pulmonary capillaries. Human leukocytes were passed through 5- or 3-μm-pore polycarbonate filters under controlled conditions. Morphometric analysis showed that the majority of PMN were deformed and that this deformation persisted longer after filtration through 3-μm filters than through 5-μm filters (P < 0.05) but did not result in the cytoskeletal polarization characteristic of migrating cells. Flow cytometric studies of the filtered PMN showed that there was a transient increase in the cytosolic free Ca2+ concentration after both 3- and 5-μm filtration (P < 0.01) with an increase in F-actin content after 3-μm filtration (P < 0.05). Although L-selectin expression on PMN was not changed by either 5- or 3-μm filtration, CD18 and CD11b were increased by 3-μm filtration (P < 0.05). Priming of the PMN with N-formyl-methionyl-leucyl- phenylalanine (0.5 nM) before filtration resulted in an increase of CD11b by both 5 (P < 0.05)and 3-μm (P < 0.01) filtration. Neither 5- nor 3-μm filtration induced hydrogen peroxide production. We conclude that mechanical deformation of PMN, similar to what occurs in the pulmonary microvessels, induces both structural and functional changes in the cells, which might influence their passage through the pulmonary capillary bed.
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