Cell adhesion leukocyte receptor expressed by mucosal venules, helps to direct lymphocyte traffic into mucosal tissues including the Peyer patches and the intestinal lamina propria. It can bind both integrin alpha-4/beta-7 and L-selectin, regulating both the passage and retention of leukocytes. Isoform 2, lacking the mucin-like domain, may be specialized in supporting integrin alpha-4/beta-7-dependent adhesion strengthening, independent of L-selectin binding. Homodimer. Additional isoforms seem to exist. Highly expressed on high endothelial venules (HEV) and lamina propia venules found in the small intestine, and to a lesser extent in the colon and spleen. Very low levels of expression found in pancreas and brain. Not expressed in the thymus, prostate, ovaries, testis, heart, placenta, lung, liver, skeletal muscle, kidney or peripheral blood leukocytes. The Ser/Thr-rich mucin-like domain may provide possible sites for O-glycosylation. The number of repeats in the mucin domain varies between 5 and 8 repeats.