ICAM proteins are ligands for the leukocyte adhesion protein LFA-1 (integrin alpha-L/beta-2). During leukocyte trans-endothelial migration, ICAM1 engagement promotes the assembly of endothelial apical cups through ARHGEF26/SGEF and RHOG activation (By similarity). Homodimer. Interacts with MUC1 and promotes cell aggregation in epithelial cells. Interacts with ARHGEF26/SGEF. Interacts (on T cell side) with CD81, CD247 and CD9 at immunological synapses between antigen-presenting cells and T cells. Monoubiquitinated, which is promoted by MARCH9 and leads to endocytosis. Belongs to the immunoglobulin superfamily. ICAM family.