Soluble CD14 is essential for lipopolysaccharide‐dependent activation of human intestinal mast cells from macroscopically normal as well as Crohn's disease tissue

Abstract

SummaryMast cells are now considered sentinels in immunity. Given their location underneath the gastrointestinal barrier, mast cells are entrusted with the task of tolerating commensal microorganisms and eliminating potential pathogens in the gut microbiota. The aim of our study was to analyse the responsiveness of mast cells isolated from macroscopically normal and Crohn's disease-affected intestine to lipopolysaccharide (LPS). To determine the LPS-mediated signalling, human intestinal mast cells were treated with LPS alone or in combination with soluble CD14 due to their lack of surface CD14 expression. LPS alone failed to stimulate cytokine expression in human intestinal mast cells from both macroscopically normal and Crohn's disease tissue. Upon administration of LPS and soluble CD14, there was a dose-and time-dependent induction of cytokine and chemokine expression. Moreover, CXCL8 and interleukin-1b protein expression was induced in response to activation with LPS plus soluble CD14. Expression of cytokines and chemokines was at similar levels in mast cells from macroscopically normal and Crohn's disease-affected intestine after LPS/soluble CD14 treatment. In conclusion, human intestinal mast cells appear to tolerate LPS per se. The LPS-mediated activation in mast cells may be provoked by soluble CD14 distributed by other LPStriggered cells at the gastrointestinal barrier.

The role of mast cells in autoinflammation

“…45 Serumderived soluble CD14 may compensate for this effect. 46 Various studies, including ours, have demonstrated that MCs express all components of the NLRP3 inflammasome. Priming of MCs with LPS further enhances the expression of NLRP3.…”

“…On the other hand, it is also important for the recognition of the prototype TLR4 ligand LPS and endogenous TLR4 ligands . Serum‐derived soluble CD14 may compensate for this effect . However, in vitro, under serum free conditions, mouse BMMCs or peritoneal MCs (PMCs) are significantly less sensitive to TLR4 stimulation with LPS (smooth and rough variants) than bone marrow‐derived or peritoneal macrophages (J. Scheffel, unpublished data).…”

Antibiotics Suppress Activation of Intestinal Mucosal Mast Cells and Reduce Dietary Lipid Absorption in Sprague-Dawley Rats

“…Because MMCs are distributed in the lamina propria, it seemed unlikely that MMCs directly sense the fatty acids in the intestinal lumen. However, intestinal MMCs are well documented to contribute to colitis, secretory diarrhea, and food allergies, which reflects on the ability of MMCs to detect allergens or harmful bacterial products 44,45 through receptor interactions, such as complement receptor 3, 46,47 CD48, 48 soluble CD14, 13 and Toll-like receptors. 49–51 Activated MMCs in these pathological states impair the intestinal barrier 52–56 and increase permeability, which enhances the flux of bacterial products or food antigens into the intestinal tissue.…”

“…Fat absorption facilitates the absorption of bacterial lipopolysaccharide (LPS) from the gut, 7,11 which associates with chylomicron remnants. 12 Because intestinal MMCs are activated by bacterial products, such as LPS 13 or Escherichia coli hemolysin, 14 we hypothesized that the gut microbiota is responsible for the lipid-induced activation of intestinal MMCs.…”

Regulation of the pleiotropic effects of tissue-resident mast cells

“…98 Intriguingly, BMMCs and human intestinal MCs lack mCD14, with the consequence that they recognize R-chemotypes of LPS but not S-chemotypes. 99,100 In correlation, macrophages deficient in CD14 show an LPS recognition phenotype comparable with MCs. 101 Moreover, both murine BMMCs and murine peritoneal mast cells (PMCs) were found to lack the adaptor protein TRIFrelated adapter molecule, resulting in their inability to activate the TRIF pathway and hence to produce type I interferons on LPS stimulation.…”