White blood cells (WBC) protect the body from infectious pathogens. They are recruited to the site of infection, and respond quickly and potently. There have been many studies of WBC, but the mechanism of leukocyte arrest in pulmonary capillary has not been brought to a consensus even though the pulmonary capillary bed is a key site of neutrophil recruitment and sequestration in the lung and is important to prevent damage to healthy tissue and fight infection [1]. It has been shown that the selectins are responsible for early adhesion steps in the recruitment of leukocyte into the sites of inflammation in venules, but the role of adhesion molecules in leukocyte arrest in the pulmonary capillaries is still controversial.
In this study, we aimed to determine the mechanical and biochemical properties of neutrophils for understanding of neutrophil arrest, using micropipette aspiration with various sizes of micropipettes coated with soluble P-selectins and heat-treated BSA used as a control. Our observations demonstrate that very small concentrations of sP-selectin have an effect on neutrophils motion and arrest in non-tapered micropipette. The larger contact area formed by the aspirated cell leads to greater adhesion with higher disrupting forces in capillaries than in venules. The gap width between the neutrophil surface and the micropipette wall varies from 3 nm to 228 nm and this gap thickness decreases with increasing concentration of sP-selectin. Higher concentrations of sP-selectin produce more bonds, which leads to closer contact and smaller gap width than in lower concentrations or BSA. Additionally, it was shown that high concentrations of anti-P-selectin F(ab΄)2 fragments are effective to inhibit the P-selectin mediated adhesion.
There is no mechanical arrest observed in tapering vessels with taper angles of up to 9°. However, there is a transit point where cells slow down, which does not depend on the endothelial cell adhesion molecule concentration, taper rate, or aspiration pressure. From these results, leukocyte arrest may be mainly influenced by adhesion rather than mechanical trapping.
This research was extended to study the mechanical and adhesive properties of the breast cancer cell lines, BT-20 and Hs578t. It was found that both breast cancer cells exhibit solid-like behavior and some of the cells have more than one apparent trend of Young’s modulus in a cell. Both cell lines show adhesion to P-selectin and the velocity of BT-20 cells was dependent on sP-selectin concentration.