Description: Intercellular Adhesion Molecule-3 (ICAM-3) is a member of the immunoglobulin supergene family and functions as a ligand for the Lymphocyte Function-Associated Antigen-1 (LFA-1). ICAM-3 is a heavily glycosylated, integral membrane protein with five immunoglobulin-like domains. It shares high homology to ICAM-1 and ICAM-2 in the extracellular region. In contrast to ICAM-1 and ICAM-2, ICAM-3 is absent on endothelia. ICAM-3 is expressed on resting lymphocytes, monocytes and neutrophils, representing the major LFA-1 ligand on these cells. The finding that adhesion of resting T lymphocytes to LFA-1 occurs primarily via ICAM-3 combined with the fact that ICAM-3 is much better expressed than other LFA-1 ligands on monocytes and resting lymphocytes implies an important role for ICAM-3 in the initiation of immune responses.