Selectins with a catch

Not content simply with a good fit, evolution has apparently designed adhesion molecules that stick optimally only when tugged upon. This property, say Bryan Marshall and Cheng Zhu (Georgia Institute of Technology, Atlanta, GA), and Tadayuki Yago and Rodger McEver (University of Oklahoma, Oklahoma City, OK), and colleagues, may stop leukocytes and platelets from lingering in stagnant backwaters in the blood where there is little or no flow.

Blood is a medium dominated by flow and shear forces. “If you think flow is disruptive, then greater flow should make cells roll faster,” says Zhu. “That's the case at the high end, but at the low end it reverses.”

The Georgia Tech group found that this effect could be attributed to the behavior of individual adhesion molecules such as P-selectin and its partner P-selectin glycoprotein ligand-1...