CD54 is a 90 kD immunoglobulin superfamily member also known as ICAM-1 and Ly-47. It is expressed on activated endothelial cells, high endothelial venules (HEV), T and B cells, monocytes/ macrophages, granulocytes, and dendritic cells. CD54 is an important intracellular adhesion molecule that participates in T cell-T cell, T cell-B cell, and T cell-target cell interactions via binding of LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18). CD54 has also been shown to be involved in lymphocyte trafficking, making it an important molecule in many immune reactions and inflammation. CD54 is also a receptor for rhinovirus. The YN1/1.7.4 antibody has been reported to block binding of mouse CD54 to LFA-1 and Mac-1, inhibit cell-cell adhesion, and function in antigen presentation to T cells and leukocyte migration to inflammatory tissues.