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Original Article |
Correspondence to: Scott L. Diamond, Institute for Medicine and Engineering, Department of Chemical Engineering, University of Pennsylvania, 1010 Vagelos Research Laboratories, 3340 Smith Walk, Philadelphia, PA 19104. Tel:(215) 573-5702 Fax:(215) 573-2093 E-mail:sld{at}seas.upenn.edu.
Adhesion and subsequent aggregation between neutrophils and platelets is dependent upon the initial binding of P-selectin on activated platelets to P-selectin glycoprotein ligand 1 (PSGL-1) on the microvilli of neutrophils. High speed, high resolution videomicroscopy of flowing neutrophils interacting with spread platelets demonstrated that thin membrane tethers were pulled from neutrophils in 32 ± 4% of the interactions. After capture by spread platelets, neutrophil membrane tethers (length of 5.9 ± 4.1 µm, n = 63) were pulled at an average rate of 640 µm/s as the wall shear rate was increased from 100250 s-1. The average tether lifetime decreased significantly (P < 0.001) from 630 to 133 ms as the shear rate was increased from 100 s-1 (Fbond = 86 pN) to 250 s-1 (Fbond = 172 pN), which is consistent with P-selectin/PSGL-1 bond dynamics under stress. Tether formation was blocked by antibodies against P-selectin or PSGL-1, but not by anti-CD18 antibodies. During neutrophil rolling on P-selectin at 150 s-1, thin membrane tethers were also pulled from the neutrophils. The characteristic jerking motion of the neutrophil coexisted with tether growth (8.9 ± 8.8 µm long), whereas tether breakage (average lifetime of 3.79 ± 3.32 s) caused an acute jump in the rolling velocity, proving multiple bonding in the cell surface and the tether surface contact area. Extremely long membrane tethers (>40 µm) were sometimes pulled, which detached in a flow-dependent mechanism of microparticle formation. Membrane tethers were also formed when neutrophils were perfused over platelet monolayers. These results are the first visualization of the often hypothesized tethers that shield the P-selectin/PSGL-1 bond from force loading to regulate neutrophil rolling during inflammation and thrombosis.
Key Words: thrombosis, P-selectin, PSGL-1, hemodynamics, tether
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