An overview of primary and secondary tethers.

The left side shows a primary tether of a leukocyte as it moves from the mainstream of blood and binds to E-selectin expressed on the endothelium (A), whereas the right side shows a leukocyte tethering to a rolling leukocyte through L-selectin and PSGL-1 (B), which captures the free-flowing leukocyte and causes it to interact with E-selectin on the endothelium (secondary tether).