ICOS-ligand, expressed on human endothelial cells, costimulates Th1 and Th2 cytokine secretion by memory CD4+ T cells.

Endothelial cells (EC) play a central role in inflammatory immune responses and efficiently induce effector functions in T cells, despite lacking the classical costimulatory ligands CD80 and CD86. By using the mAb HIL-131 we now demonstrate that human inducible costimulator-ligand (ICOS-L), a molecule related to CD80/CD86, is constitutively expressed on human EC in vivo. In vitro, ICOS-L expression was strongly enhanced on human umbilical vein EC and microvascular EC by the inflammatory cytokines tumor necrosis factor alpha and IL-1beta, and to a lower extent by stimulation of EC by CD40 or lipopolysaccharide.