Pseudopod Projection and Cell Spreading of Passive Leukocytes in Response to Fluid Shear Stress

Abstract

Recent evidence suggests that circulating leukocytes respond to physiological levels of fluid shear stress. This study was designed to examine the shear stress response of individual leukocytes adhering passively to a glass surface. Human leukocytes were exposed to a step fluid shear stress with amplitude between 0.2 and 4 dyn/cm(2) and duration between 1 and 20 min. The response of the cells was determined in the form of projected cell area measurements by high-resolution observation before, during, and after fluid shear application. All cells selected initially had a round morphology. After application of fluid shear many cells projected pseudopodia and spread on the glass surface. The number of leukocytes responding with pseudopod projection and the extent of cell spreading increased with increasing amplitude and duration of fluid shear stress. Pseudopod projection after exposure to a step fluid shear occurs following a delay that is insensitive to the shear stress amplitude and duration. Leukocytes that did not project pseudopodia and spread in response to low shear stress could be shown to respond to a second shear step of higher amplitude. The spreading response requires an intact actin network and activated myosin molecules. Depleting the cell glycocalyx with protease treatment enhances the spreading response in sheared leukocytes. These results indicate that passive leukocytes respond to fluid shear stress with active pseudopod projection and cell spreading. This behavior may contribute to cell spreading on endothelium and other cells as well as to transendothelial migration of leukocytes in the microcirculation.

Fluid shear-induced cathepsin B release in the control of Mac1-dependent neutrophil adhesion

“…Notably, our prior results implicated FSS-related ctsB release and subsequent CD18 cleavage to not only prevent neutrophil binding to other cells (e.g., platelets) when suspended in a flow field [8] but also reverse it during pseudopod retraction when membrane-substrate attachments must be disengaged [6]. The principal evidence for neutrophils requiring a flow environment to remain nonadherent is that fluid stasis promotes projection of pseudopods and formation of attachments with various substrates involving CD18 integrins [2,42,43]. Once exposed to FSS, however, neutrophils retract pseudopods in a CD18-dependent fashion [44], even in the presence of low doses of inflammatory agonists, such as ,1 mM fMLP or ,10 mM PAF [1].…”

De-Activation of Neutrophils in Suspension by Fluid Shear Stress: A Requirement for Erythrocytes

“…6,7,22,27 The relatively low sensitivity to shear stress seen in this study may be the result of an antagonism between deactivation by the fluid shear stress and activation by collision with platelets in the shear field. The de-activation by fluid shear stress was enhanced by blockade of neutrophilplatelet binding (Fig.…”

“…This is a key requirement for normal circulation since leukocytes with pseudopods show enhanced resistance to flow in microvessels 36 to the point of complete capillary arrest. 32,38 Individual leukocytes respond to physiological shear stress, 5,7,10,13,26 as seen in other blood cells, like endothelial cells, 31 erythrocytes, 18 and platelets. 23 The response consists of a variety of cell reactions, including redistribution and shedding of surface adhesion molecules, 12 pseudopod retraction in migrating cells as well as pseudopod projection by non-activated leukocytes 7 and F-actin distribution.…”

Fluid Stresses on the Membrane of Migrating Leukocytes

“…The dimensionless variables were defined as: (4) (5) (6) where v i was the dimensional velocity in the i th direction. The viscosity of Plasma-Lyte, the shearing fluid, was measured with a viscometer to be 0.98 centipoise.…”