Cross-linking of ICAM-1 induces co-signaling of an oxidative burst from mononuclear leukocytes.

Cell adhesion molecules were first described as accessory molecules simply to bridge one cell to another. More recently, it has been realized that these molecules also transmit signals from outside of the cell to inside. We show that cross-linking of the ICAM-1 on the cell membrane with anti-ICAM-1 mAb and F(ab')2 fragments of goat anti-MIgG in the presence of suboptimal levels of the bacterial peptide FMLP results in co-stimulation of an oxidative burst from CD14 expressing PBMCs. The amplitude of the oxidative response was less than the oxidative burst induced by CD18 cross-linking, whereas the response was more prolonged. On the other hand, cross-linking by anti-L-selectin mAb plus F(ab')2 fragments of goat anti-MIgG induced a minimal oxidative burst that was not significantly greater than the response generated by anti-L-selectin mAb alone. The addition of an excess of soluble ICAM-1 to compete for the anti-ICAM-1 mAb inhibits the oxidative burst in response to ICAM-1 cross-linking but not to CD18 cross-linking. These results suggest that ICAM-1 is capable of delivering a transmembrane signal into CD14-positive PBMC.