The leukocyte response to fluid stress

Area of Science:

• Cellular Biology
• Physiology
• Immunology

Background:

• Leukocyte migration is essential for immune response and requires pseudopod formation and adhesion.
• Leukocytes typically do not form pseudopods in circulation, suggesting a regulatory mechanism is at play.

Purpose of the Study:

• To investigate the role of fluid shear stress in regulating leukocyte pseudopod formation and adhesion in circulation.
• To test the hypothesis that fluid shear stress prevents leukocyte pseudopod formation.

Main Methods:

• In vitro experiments with human leukocytes (neutrophils, monocytes) subjected to controlled fluid shear stress.
• In vivo studies using rat mesentery microvessels to observe leukocyte behavior after occlusion and reperfusion.
• Pharmacological inhibition using K+ channel blockers and Ca2+ chelation.

Main Results:

• Fluid shear stress induced rapid pseudopod retraction in leukocytes on surfaces; removal of shear stress promoted pseudopod projection and spreading.
• Prolonged shear stress led to leukocyte swelling, increased cytoplasmic granule motion, and reduced stiffness.
• Shear stress-induced responses were inhibited by K+ channel blockers and Ca2+ chelation.
• In vivo, reduced flow (occlusion) allowed pseudopod formation, while restored flow caused retraction and detachment.

Conclusions:

• Plasma shear stress actively suppresses pseudopod projection and adhesion of circulating leukocytes.
• Decreased shear stress in post-occlusion microvessels promotes leukocyte pseudopod formation and endothelial interaction.
• Understanding shear stress regulation is key to controlling leukocyte behavior in vascular environments.