F. Moazzam et al., THE LEUKOCYTE RESPONSE TO FLUID STRESS, Proceedings of the National Academy of Sciences of the United Statesof America, 94(10), 1997, pp. 5338-5343
Leukocyte migration from a hemopoietic pool across marrow endothelium
requires active pseudopod formation and adhesion, Leukocytes rarely sh
ow pseudopod formation while in circulation, At question then is the m
echanism that serves to minimize leukocyte pseudopod formation in the
circulation, We tested the hypothesis that fluid shear stress acts to
prevent pseudopod formation, When individual human leukocytes (neutrop
hils, monocytes) spreading on glass surfaces in vitro were subjected t
o fluid shear stress (approximate to 1 dyn/cm(2)), an instantaneous re
traction of pseudopods was observed, Removal of the fluid shear stress
in turn led to the return of pseudopod projection and cell spreading,
When steady shear stress was prolonged over several minutes, leukocyt
e swelling occurs together with an enhanced random motion of cytoplasm
ic granules and a reduction of cytoplasmic stiffness, The response to
shear stress could be suppressed by K+ channel blockers and chelation
of external Ca2+, In rat mesentery microvessels after occlusion, circu
lating leukocytes project pseudopods in free suspension or when attach
ed to the endothelium, even though immediately after occlusion only fe
w pseudopods were present, When flow was restored, pseudopods on adher
ing leukocytes were retracted and then the cells began to roll and det
ach from the endothelium. In conclusion, plasma shear stress in the ci
rculation serves to reduce pseudopod projection and adhesion of circul
ating leukocytes and vice versa reduction of shear stress leads to pse
udopod projection and spreading of leukocytes on the endothelium.