Cathepsin G in the Immune Protection of the Human Duodenum: New Sources of Biosynthesis
Proteases play a key role in all physiological processes in the small intestine and provide the functional activity of this division of the gastrointestinal tract, where nutrients are hydrolyzed and absorbed. High concentration of antigens in the intestine stimulates the immune system and results in chronic inflammatory response in normal gastrointestinal tract. Cathepsin G is a serine protease that participates in the regulation of immuno-cyte behavior and in the maintenance of complex balance between physiological and pathological inflammatory processes. In order to determine the role of cathepsin G in the small intestine, we performed a confocal immunofluorescence assay of bioptates of duodenal mucosa using human cathepsin G antibodies. This is the first study that has showed that cathepsin G, which is traditionally considered as one of inflammatory effectors, is a constitutive enzyme of the human duodenum, which is constantly present in normal duodenal mucosa. We also found new cellular sources of cathepsin G biosynthesis: intraepithelial lymphocytes (IEL), lamina propria lymphocytes, CD14-positive intestinal macrophages and specialized epitheliocytes of intestinal glands (Paneth cells). Our data on cathepsin G expression by duodenal immunocytes and Paneth cells suggest that cathepsin G is one of the main proteases of local intestinal immunity. It indicates that this enzyme plays an important role in the functional regulation of human digestive tract.