The enzyme is distributed in cells of the gastrointestinal tracts, lymphoid tissues, blood cells, urinary organs and microglia. Its intracellular localization in different mammalian cells is different to that of its analog Cathepsin D. Cathepsin E associates with the membrane tissue in the intracellular canaliculi of gastric parietal cells, bile canaliculi of hepatic cells, cells of the rinal proximal tubule in the kidney, epithelial cells in the intestine, trachea and bronchi, osteoclasts and even in erythrocytes. Its localization in the endosome structures can be seen in many different cell types such as antigen-presenting B cell lymphoblasts, gastric cells and microglia.