Cathepsin D is up‐regulated in inflammatory bowel disease macrophages

SUMMARY Down‐regulation of receptors involved in the recognition or transmission of inflammatory signals and a reduced responsiveness support the concept that macrophages are ‘desensitized’ during their differentiation in the intestinal mucosa. During inflammatory bowel disease (IBD) intestinal macrophages (IMACs) change to a reactive or ‘aggressive’ type. After having established a method of isolation and purification of IMACs, message for cathepsin D was one of the mRNAs we found to be up‐regulated in a subtractive hybridization of Crohn's disease (CD) macrophages versus IMACs from control mucosa. The expression of cathepsin D in intestinal mucosa was analysed by immunohistochemistry in biopsies from IBD and control patients and in a mouse model of dextran sulphate sodium (DSS)‐induced acute and chronic colitis. IMACs were isolated and purified from normal and inflamed mucosa by immunomagnetic beads armed with a CD33 antibody. RT‐PCR was performed for cathepsin D mRNA. Results were confirmed by Northern blot and flow cytometrical analysis. Immunohistochemistry revealed a significant increase in the cathepsin D protein expression in inflamed intestinal mucosa from IBD patients compared to non‐inflamed mucosa. No cathepsin D polymerase chain reaction (PCR) product could be obtained with mRNA from CD33‐positive IMACs from normal mucosa. Reverse transcription (RT)‐PCR showed an induction of mRNA for cathepsin D in purified IMACs from IBD patients. Northern blot and flow cytometry analysis confirmed these results. Cathepsin D protein was also found in intestinal mucosa in acute and chronic DSS‐colitis but was absent in normal mucosa. This study shows that expression of cathepsin D is induced in inflammation‐associated IMACs. The presence of cathepsin D might contribute to the mucosal damage in IBD.