The Lymphocyte Function–associated Antigen 1 I Domain Is a Transient Binding Module for Intercellular Adhesion Molecule (ICAM)-1 and ICAM-3 in Hydrodynamic Flow

The I domain of lymphocyte function-associated antigen (LFA)-1 contains an intercellular adhesion molecule (ICAM)-1 and ICAM-3 binding site, but the relationship of this site to regulated adhesion is unknown. To study the adhesive properties of the LFA-1 I domain, we stably expressed a GPI-anchored form of this I domain (I-GPI) on the surface of baby hamster kidney cells. I-GPI cells bound soluble ICAM-1 (sICAM-1) with a low avidity and affinity. Flow cell experiments demonstrated a specific rolling interaction of I-GPI cells on bilayers containing purified full length ICAM-1 or ICAM-3. The LFA-1 activating antibody MEM-83, or its Fab fragment, decreased the rolling velocity of I-GPI cells on ICAM-1-containing membranes. In contrast, the interaction of I-GPI cells with ICAM-3 was blocked by MEM-83. Rolling of I-GPI cells was dependent on the presence of Mg2+. Mn2+ only partially substituted for Mg2+, giving rise to a small fraction of rolling cells and increased rolling velocity. This suggests that the I domain acts as a transient, Mg2+-dependent binding module that cooperates with another Mn2+-stimulated site in LFA-1 to give rise to the stable interaction of intact LFA-1 with ICAM-1.