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. Expressed at low level on a subpopulation of lymphocytes, macrophages, and endothelial cells, but is strongly induced on these cells, and on fibroblasts and epithelial cells. Monoubiquitinated, which is promoted by MARCH9 and leads to endocytosis. Spontaneous onset of obesity in 16-week old mice with higher levels of white and brown fat and a slightly heavier liver. Enhanced susceptibility to high fat diet-induced obesity characterized by a weight increase and higher levels of white and brown fat. Belongs to the immunoglobulin superfamily. ICAM family. ICAM-1