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 the integrin alpha-4/beta-7 and L-selectin, regulating both the passage and retention of leukocytes. Both isoform 1 and isoform 2 can adhere to integrin alpha-4/beta-7. 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. Highly expressed on high endothelial venules (HEV) of organized intestinal lymphoid tissues like the Peyer patches and mesenteric lymph nodes, and in the lamina propria of the intestine. Some expression found in the spleen, and low levels of expression in the peripheral lymph nodes and the lactating mammary gland. No expression was detected in the liver, kidneys, lungs or in normal brain. Expressed as well in brain endothelioma cells, and mucosal tissues which are in a chronic state of inflammation, such as inflamed pancreas. By TNF-alpha, and chronic inflammation. O-glycosylated; contains syalic acid. The Ser/Thr-rich mucin-like domain may provide possible sites for O-glycosylation. Absence of Madcam1 in the spleen has been found in aly/aly mice, but normal expression is found in intestinal venules. This aberrant expression is a secondary defect and not the direct cause of aly alymphoplasia, an autosomal recessive mutation which induces total aplasia of lymph nodes and Peyer patches.