Salmonella typhimurium translocates flagellin across intestinal epithelia, inducing a proinflammatory response

Abstract

This study investigated whether soluble paracrine factors mediated Salmonella-induced IL-8 expression in polarized model intestinal epithelia. We found that the basolateral media of model epithelia that had been apically infected with Salmonella typhimurium for a short period (10 minutes) could activate IL-8 secretion in virgin model epithelia, demonstrating that a proinflammatory factor (PIF) was indeed present. Initial characterization found that PIF was a heat-stable protein with a molecular mass of about 50 kDa that acts on the basolateral, but not apical, surface of model intestinal epithelia to elicit IL-8 secretion. PIF was not present in the media of model epithelia stimulated with other inducers of IL-8 secretion (TNF-α or carbachol) but was present in S. typhimurium supernatants, indicating PIF is of bacterial origin. PIF was purified from bacterial culture supernatants by anion/cation exchange chromatography and SDS-PAGE and found by using microsequencing to be the protein flagellin. In support of this finding, flagellin-deficient S. typhimurium mutants did not secrete detectable levels of PIF (i.e., a bioactivity that induced IL-8 secretion when placed basolaterally on model epithelia). Furthermore, viable flagellin-deficient mutant organisms (fliC/fljB and flhD) failed to elicit IL-8 secretion when added apically to model intestinal epithelia. These findings indicate that translocation of flagellin across epithelia, subsequent to apical epithelial-S. typhimurium interaction, is likely a major means of activating a mucosal inflammatory response.

Anti-flagellin antibody responses elicited in mice orally immunized with attenuated Salmonella enterica serovar Typhimurium vaccine strains

“…Recent findings confirmed that bacterial flagellins do not elicit inflammatory responses in the normal gut epithelium, a behavior explained by the lack of functional TLR5 expression at the apical surface of enterocytes (Gewirtz et al 2001), the activation of apoptotic responses by flagellin-exposed antigenpresenting cells (Ren et al 2006) and/or the activation of suppressive CD4 + CD25 + T regulatory cells (Crellin et al 2005). Although our findings indicate that the expression of chimeric flagellins by recombinant attenuated S. Typhimurium strains has an inherently reduced immunogenicity as an oral bivalent vaccine approach, stimulation of specific immune responses triggered by purified flagellins delivered via the nasal or parenteral routes (Honko et al 2006) represents more promising alternative for the use of Salmonella flagellins in vaccine development.…”

Radioresistant cells expressing TLR5 control the respiratory epithelium's innate immune responses to flagellin

“…Consequently, our study reinforces the hypothesis whereby the epithelium has a key role in in vivo mucosal, pro-inflammatory processes. In the literature, there are some divergences on how TLR5 is exposed on epithelial cells [36]. Because TLR5 is active when flagellin is administered i.n., we assume that apical/luminal signalling induces the epithelial response, as described previously [37].…”

Contribution of FliC to Epithelial Cell Invasion by Enterohemorrhagic Escherichia coli O113:H21

“…A recent study of fliC expression in serovar Typhimurium showed that fliC was transcribed by bacteria in Peyer's patches but not in the mesenteric lymph nodes or spleen, indicating that flagellin may contribute to early stages of host infection (6). Serovar Typhimurium can also translocate FliC across the intestinal epithelium in SPI-1-induced vesicles, where it stimulates a potent inflammatory response via Toll-like receptor 5 (TLR5) signaling (15). Proinflammatory chemokine production is also upregulated by FliC through TLR5 signaling during EHEC O157:H7 and EPEC O127:H6 infection of intestinal tissue (22,31,35).…”