White blood cell (WBC) sequestration in lung capillaries is a key step in the inflammatory response to lung infection. P-selectin and ICAM-1 have well-defined roles in WBC adhesion in venules but their role in pulmonary capillaries is still unclear. Here, a novel in vitro Micropipette Cell Adhesion Assay used P-selectin, ICAM-1 or BSA-coated capillary-sized glass micropipettes as an in vitro model of a lung capillary. WBC were aspirated into adhesion molecule-coated vessels of varying diameters. Cell velocities and activation times were determined under pressures representative of lung capillaries. WBC velocities in this assay were significantly lower on P-selectin than BSA and decreased with increasing P-selectin concentration. These results demonstrate that P-selectin at low density mediates WBC adhesion in the pulmonary capillary geometry. WBC can also become activated upon aspiration into micropipettes and under some circumstances can be seen to exhibit a cyclic migratory behavior. This work was supported by grant BES-0547165 from the National Science Foundation and by an award from the American Heart Association.

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