Trypsin-like activity released by intestinal mucosa of IBD patients or by intestinal epithelial cells after ER stress-stimulation. [A] Biopsies from Control [Control, n = 14], Crohn’s disease [CD, n = 28] and ulcerative colitis [UC, n = 10] were incubated for 1 h in HBSS medium and trypsin activity released by biopsies in culture supernatants was monitored. IBD-NI, non-inflamed tissue; IBD-I, inflamed tissue. Data are expressed as mean ± SEM and were compared using Student’s t-test. ***p < 0.001 vs Control group. [B] Biopsies from Controls [Control, n = 14], Crohn’s disease [CD, n = 28] and ulcerative colitis [UC, n = 10] were embedded in optimal cutting temperature [OCT] milieu before cutting slices for in situ trypsin activity measures. Representative confocal photomicrographs of in situ zymography assays performed in colonic tissue slices [scale bar: 50 μm]. Graph representation of mean fluorescence intensity quantified from 10 to 28 patients per group. Data are expressed as mean ± SEM and were compared using Student’s t-test. *p < 0.05 vs Control group. [C] Monolayers of differentiated Caco-2 cells cultured on a transwell system were stimulated with Tunicamycin [Tm; 10 µg/mL] or Thapsigargin [Tg; 10 µg/mL], two classic ER stress inducers, and/or pre-treated with 1 mM 4PBA, a chemical chaperon that inhibits ER stress activation. [C,D] Trypsin-like activity was measured in [C] apical and basal [data not shown] supernatants recovered from Control or ER stress-treated Caco-2 cells and in [D] apical supernatant of ER stress-treated Caco-2 cells pre-incubated with PBA for 6 h. [E] Relative gene expression of ER stress markers [XBP1s, ATF6, ATF4] was measured. Data are expressed as mean ± SEM and were analysed by Student’s t-test. *p < 0.05, **p < 0.01 and ***p < 0.001 vs Control group and ^ϕϕϕp < 0.001 vs Thapsigargin group.