Immunology

Slowing Things Down

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Science  20 Jun 2003:
Vol. 300, Issue 5627, pp. 1849
DOI: 10.1126/science.300.5627.1849d

In the course of an inflammatory response, lymphocytes enter the tissue bed from the microcirculation by squeezing through the blood vessel wall in a process known as extravasation. Yet normal blood flow within microvessels generates shear stress that would detach and sweep away any lymphocytes that had adhered to the vessel endothelium in the first place. So how do lymphocytes hang on?

Secomb et al. observe that microvessels can alter their local architecture to reduce shear stress substantially. Imaging of vessels in sheep skin was used to measure lymphocyte velocities after topical application of oxazolone—a hapten known to recruit lymphocytes; flow rates decreased in regions corresponding to apparent focal enlargements in the vessel walls. Scanning electron microscopy showed these to be balloonlike dilations between the capillary and postcapillary venules, and they were designated as microangiectasias. Estimates of shear wall stress within these regions yielded forces comparable to those mediating lymphocyte adhesion in vitro.—SJS

Proc. Natl. Acad. Sci. U.S.A. 100, 7231 (2003).

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