The current understanding of lymphocyte migration across the endothelium includes four steps: attachment, rolling, arrest and diapedesis. In June Nature Immunology new evidence from researchers at The Weizmann Institute of Science, Rehovot, Israel, suggests the involvement of another step — chemorheotaxis.

Cinamon et al used cytokine–activated human umbilical vascular endothelial cells as an in vitro model of inflamed endothelium. They showed that apical endothelial chemokines are not only required to stop the cells rolling but are also needed for white blood cells to migrate across endothelial cells. In addition, continuous force or shear stress from fast flowing fluid must be applied on adherent white blood cells in order to facilitate migration. Lymphocyte integrins, intact actin cytoskeleton and G_i protein–mediated chemokine signalling, but not a chemotactic gradient, were mandatory for lymphocyte migration (Nature Immunol 2001, 6:515-522).

These data indicate that both molecular and mechanical signals operate to allow...