A DIFFERENTIAL ROLE FOR CELL-SHAPE IN NEUTROPHIL TETHERING AND ROLLING ON ENDOTHELIAL SELECTINS UNDER FLOW

We investigated the role of neutrophil microvilli in interactions with E-selectin and P-selectin in hydrodynamic shear flow by disruption wi th cytochalasin B, hypotonic swelling, and chilling. Cytochalasin B on ly marginally reduced microvilli numbers (from 30 +/- 6 to 16 +/- 6 pe r cell perimeter, p < 0.005) as shown by electron microscopy, complete ly disrupted tethering in shear flow to E-sesectin and P-selectin, inc reased the strength of rolling adhesions on E-selectin and P-selectin, and increased cell deformability in shear flow with a likely increase in the area of cell:substrate contact. Hypoosmotic swelling markedly reduced microvilli number (to 6 +/- 5 per perimeter, p < 0.005), almos t completely inhibited tethering on E- and P-selectin, and increased t he strength of rolling adhesions on P-selectin but not on E-selectin. Chilling almost completely abolished microvilli (to 3 +/- 3 per perime ter, p < 0.005), but pseudopod-like structures were present, and had l ittle effect on tethering in flow. Immunogold labeling of L-selectin, which is normally clustered on tips of microvilli, showed that in the absence of microvilli it remained in small clusters. Our studies show that alterations in cell morphology and viscoelasticity can have oppos ing effects on tethering and rolling, showing that they are independen tly regulatable. Furthermore, our results suggest that the association of molecules that mediate rolling with microvilli tips may be importa nt not just to enhance presentation, but for other functions such as t o promote resistance to extraction from the membrane or cooperative in teractions among clustered receptors.