CD54 is an 85 kD protein also known as ICAM-1. It is a member of the immunoglobulin superfamily that is expressed on high endothelial venules in lymphoid tissue, peripheral blood monocytes, dendritic cells, granulocytes and thymic stromal cells. CD54 is weakly expressed on T and B cells, although expression can be increased by activation (especially on endothelial cells). ICAM-1 is an important protein in cell adhesion, inflammation and immune responses. CD54 has been shown to bind to CD11a/CD18 (LFA-1), CD11b/CD18, CD11c/CD18, CD43, fibrinogen, and hyaluronan. The 1A29 antibody has been reported to block T cell aggregation and binding of lymphocytes to HEV-derived endothelial cells and purified ICAM-1 protein.