| Abstract: | Tissue injury and inflammation in inflammatorybowel disease (IBD) are associated with enhancedmonocytic lysosomal enzyme release. In this study,peripheral monocytes and lamina propria mononuclearcells (LPMNC) were isolated from IBD patients andnormal controls. Cells were stimulated withlipopolysaccharide after treatment with IL-13, IL-4, andIL-10, and enzyme secretion was assessed by using thecorresponding p-nitrophenyl glycosides as substrates.Molecular forms of cathepsin D were examined to describethe mode of enzyme release. IL-10 and IL-4 stronglydown-regulate enzyme secretion in IBD monocytes. IBD monocytes showed a diminished responsiveness tothe inhibitory effect of IL-13. Impaired monocyteresponse was not found with combinations of IL-13 andIL-10 or IL-4 and IL-10. LPMNC from involved IBD mucosa showed significantly higher enzyme secretioncompared with LPMNC from noninvolved IBD mucosa butresponded inefficiently to either IL-4, IL-13, or IL-10alone. However, combined treatment with IL-10 and IL-4 or IL-10 and IL-13 strongly suppressedenzyme release by these cells. Both the precursor andmature forms of cathepsin D were elevated in IBDpatients. While IL-13 reduced mainly the precursor form, the effect of IL-4 and IL-10 concerns both theprecursor and mature form of cathepsin D. Our resultsfavor the potent clinical utility of combined treatment,thus improving chances of developing effective treatments for human IBD. |
