Crohn's disease-derived monocytes fail to induce Paneth cell defensins

Abstract

Crohn's disease (CD) is associated with a multitude of genetic defects, many of which likely affect Paneth cell function. Paneth cells reside in the small intestine and produce antimicrobial peptides essential for the host barrier, principally human α-defensin 5 (HD5) and HD6. Patients with CD of the ileum are characterized by reduced constitutive expression of these peptides and, accordingly, compromised antimicrobial barrier function. Here, we present a previously unidentified regulatory mechanism of Paneth cell defensins. Using cultures of human ileal tissue, we showed that the secretome of peripheral blood mononuclear cells (PBMCs) from healthy controls restored the attenuated Paneth cell α-defensin expression characteristic of patients with ileal CD. Analysis of the Wnt pathway in both cultured biopsies and intestinal epithelial cells implicated Wnt ligands driving the PBMC effect, whereas various tested cytokines were ineffective. We further detected another defect in patients with ileal CD, because the PBMC secretomes derived from patients with CD were unable to restore the reduced HD5/HD6 expression. Accordingly, analysis of PBMC subtypes showed that monocytes of patients with CD express significantly lower levels of canonical Wnt ligands, including Wnt3, Wnt3a, Wnt1, and wntless Wnt ligand secretion mediator (Evi/Wls). These studies reveal an important cross-talk between bone marrow-derived cells and epithelial secretory Paneth cells. Defective Paneth cell-mediated innate immunity due to inadequate Wnt ligand stimulation by monocytes provides an additional mechanism in CD. Because defects of Paneth cell function stemming from various etiologies are overcome by Wnt ligands, this mechanism is a potential therapeutic target for this disease.is characterized by intense gastrointestinal inflammation, including infiltration of immune cells, such as granulocytes and mononuclear cells. The pathogenesis is complex and not fully understood, although a combination of microbial and other environmental elements, as well as host genetics, is known to influence susceptibility (1, 2). Although CD may principally affect the whole gastrointestinal tract, predilection sites are the terminal ileum and/or colon, where the location remains stable during the course of disease, suggesting local rather than systemic immunebased susceptibility factors.In patients who have CD with small intestinal involvement, different pathophysiological defects and genetic associations are described that focus on the Paneth cell (2). This cell type is normally located on the bottom of small intestinal crypts, where it is the main source for antimicrobial peptides, predominantly the human α-defensin 5 (HD5) and HD6. One main molecular characteristic of patients with ileal CD is reduced expression of these defensins, resulting in an impaired defense barrier through reduced antimicrobial killing (3). However, the impact of inflammation on Paneth cell function in the small intestine is so far poorly investigated. It also remains unclear whether the...

Expression of human cathelicidin peptide LL-37 in inflammatory bowel disease

“…The reason for different observations between the previous and current studies remains unclear, but our findings indicate that LL-37 is induced in the inflamed mucosa of IBD patients and suggest that LL-37 may act as one of the protective factors against microbial invasion which aggravate gut inflammation. In contrast to reduced expression of HD5 and HD6 in the small intestine in patients with ileal CD [31,32], antimicrobial activity in the colon might be enhanced through increased expression of LL-37 in colonic SEMFs.…”

“…Patients with CD of the ileum are characterized by reduced constitutive expression of HD5 and HD 6 and, accordingly, compromised anti-microbial barrier function [31,32]. Epithelial cells have been reported to be a major expression site of LL-37 in various tissues [33].…”

Altered pattern of tumor necrosis factor-alpha production in peripheral blood monocytes from Crohn's disease

“…Notably, the paradoxical efficacy of GM-CSF in some cases of CD may be due to the correction of such defects in epithelial monocytes, for example by rescuing their epithelial repair function[37]. Another critical function for mucosal monocytes may concern the induction of antimicrobial peptide production by Paneth cells[38]; indeed, a defective production of defensins after bacterial translocation may result in altered shaping of gut microbiota, leading to inflammatory amplification in a vicious circle.…”

Improvement of a ‘Leaky' Intestinal Barrier

“…For this reason, we have suggested the term 'Paneth's disease' for ileal Crohn's disease [9] . Finally, monocytes have recently been demonstrated to enhance the Paneth cell function by Wnt-factors, but this mechanism is defective in monocytes from Crohn's disease patients [10] .…”

“…In the experimental colitis model, this works quite well. Since recent data [10] suggest that the genetic defects in the Paneth cell may be bypassed by monocyte-derived Wnt factors, their application may be promising although still very speculative. Moreover, high Wnt activity may unfortunately induce colonic or small intestinal tumors.…”