Abstract
The gut epithelium constitutes an interface between the intestinal contents and the underlying gut-associated lymphoid tissue (GALT) including dendritic cells (DC). Interactions of intestinal epithelial cells (IEC) and resident DC are characterized by bidirectional crosstalk mediated by various factors, such as transforming growth factor-β (TGF-β) and thymic stromal lymphopoietin (TSLP). In the present study, we aimed (1) to model the interplay of both cell types in a porcine in vitro coculture consisting of IEC (cell line IPEC-J2) and monocyte-derived DC (MoDC) and (2) to assess whether immune responses to bacteria are altered because of the interplay between IPEC-J2 cells and MoDC. With regard to the latter, we focused on the inflammasome pathway. Here, we propose caspase-13 as a promising candidate for the noncanonical inflammasome activation in pigs. We conducted challenge experiments with enterotoxigenic Escherichia coli (ETEC) and probiotic Enterococcus faecium (E. faecium) NCIMB 10415. As potential mediators of IEC/DC interactions, TGF-β and TSLP were selected for analyses. Cocultured MoDC showed attenuated ETEC-induced inflammasome-related and proinflammatory interleukin (IL)-8 reactions compared with MoDC monocultures. Caspase-13 was more strongly expressed in IPEC-J2 cells cocultured with MoDC and upon ETEC incubation. We found that IPEC-J2 cells and MoDC were capable of releasing TSLP. The latter cells secreted greater amounts of TSLP when cocultured with IPEC-J2 cells. TGF-β was not modulated under the present experimental conditions in either cell types. We conclude that, in the presence of IPEC-J2 cells, porcine MoDC exhibited a more tolerogenic phenotype, which might be partially regulated by autocrine TSLP production. Noncanonical inflammasome signaling appeared to be modulated in IPEC-J2 cells. Our results indicate that the reciprocal interplay of the intestinal epithelium and GALT is essential for promoting balanced immune responses.
Highlights
Intestinal epithelial cells lining the intestinal mucosa are continuously exposed to a variety of potentially harmful antigens and build a physical interface that separates the luminal content from the host milieu [1]
IPEC-J2 cells secreted thymic stromal lymphopoietin (TSLP), which we proposed as being a promising candidate mediating the interactive intestinal epithelial cells (IEC)/dendritic cells (DC) crosstalk in addition to transforming growth factor-β (TGF-β), at levels of around 300 pg/ ml, but the detected levels did not show significant variations attributable to different cultivation variants and bacterial stimulation (Figure 5(b))
We investigated inflammatory reactions to selected bacterial agents and found a more tolerogenic phenotype of monocyte-derived DC (MoDC) cocultured with IEC
Summary
Intestinal epithelial cells lining the intestinal mucosa are continuously exposed to a variety of potentially harmful antigens and build a physical interface that separates the luminal content from the host milieu [1]. Within the dynamic communication system between enterocytes and mucosal immune cells, IEC direct the function of resident DC by releasing immune mediators, such as the regulatory cytokine TGF-β and TSLP [5, 6]. Intestinal DC and IEC are both pivotal for maintaining normal barrier function as they support the discrimination. Functional properties of the intestinal epithelium cannot be fully understood by using in vitro models in which epithelial cells are solely grown as monocultures [7]. Our objective was to reconstruct the intestinal environment in vitro by implementing the presence of MoDC in the subepithelial compartment of a porcine jejunum epithelial cell line grown on cell culture inserts of Transwell systems
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