Avidity enhancement of L-selectin bonds by flow: shear-promoted
rotation of leukocytes turn labile bonds into functional tethers

O. Dwir, A. Solomon, S. Mangan, G. S. Kansas, U. S. Schwarz and R. Alon

J. Cell. Biol. 163: 649-59 (2003)

L-selectin is a key lectin essential for leukocyte capture and rolling
on vessel walls. Functional adhesion of L-selectin requires a minimal
threshold of hydrodynamic shear. Using high temporal resolution
videomicroscopy, we now report that L-selectin engages its ligands
through exceptionally labile adhesive bonds (tethers) even below this
shear threshold. These tethers share a lifetime of 4 ms on distinct
physiological ligands, two orders of magnitude shorter than the
lifetime of the P-selectin-PSGL-1 bond. Below threshold shear, tether
duration is not shortened by elevated shear stresses. However, above
the shear threshold, selectin tethers undergo 14-fold stabilization by
shear-driven leukocyte transport. Notably, the cytoplasmic tail of
L-selectin contributes to this stabilization only above the shear
threshold. These properties are not shared by P-selectin- or
VLA-4-mediated tethers. L-selectin tethers appear adapted to undergo
rapid avidity enhancement by cellular transport, a specialized
mechanism not used by any other known adhesion receptor.