The nature of leukocyte shape changes in the pulmonary capillaries

The size discrepancy between leukocytes [white blood cells (WBCs)] and pulmonary capillaries requires WBCs to deform. We investigated the persistence of this deformation on cells leaving the capillary bed and the role played by the cytoskeleton. Isolated rabbit lungs were perfused in situ via the pulmonary artery with effluent fractions collected from the left ventricle. Washout curves from cell counts in each fraction confirmed that WBCs are preferentially retained over erythrocytes. WBC deformation present on exit from the circulation was compared with that present after recovery in paired fractions, fixed either immediately or 60 min later. These cells were compared with cells recovered from the capillary in perfused fixative or fixed in peripheral blood. Our results show that leukocyte deformation persisted after the cells exited the pulmonary circulation. This deformation was associated with minimal submembranous F-actin staining, and microtubule distribution and cell polarization were unchanged. We conclude that cytoskeletal changes that occur during WBC deformation in the pulmonary capillaries are minimal and differ from those known to occur in actively migrating cells during chemotaxis.