Expression of duodenase-like protein in epitheliocytes of Brunner’s glands in human duodenal mucosa

A duodenase, a protease structurally related to human cathepsin G, was found earlier in bovine duodenal mucosa. It was demonstrated that under the influence of duodenase an enteropeptidase zymogen is activated in vitro showing the possible participation of duodenase in the cascade of activation of digestive enzymes. To identify a duodenase functional analog in human duodenum, an immunofluorescence study of duodenal mucosa was conducted by confocal microscopy using antibodies to human cathepsin G and to bovine duodenase. The previously unknown place of synthesis and secretion of cathepsin G — Paneth cells located at the bottom of Lieberkuhn crypts — was revealed. Binding of cathepsin G-specific antibodies in a rough endoplasmic reticulum zone and in the cryptal duct was observed. Duodenase-specific immunofluorescence but not that of cathepsin G was found in the epitheliocytes and secretory ducts of Brunner’s glands, which are characteristic sites of duodenase biosynthesis in cattle. Binding of CD14-specific antibodies in the Brunner’s glands, where the antibodies co-localized with the antibodies to duodenase, was also demonstrated. These data indicate the presence of a protein immunologically similar to duodenase in the human duodenal mucosa. Our study demonstrated the absence of its colocalization with cathepsin G in Brunner’s glands.