TheSalmonella entericaSerotype Typhi Vi Capsular Antigen Is Expressed after the Bacterium Enters the Ileal Mucosa

Abstract

Salmonella enterica serotype Typhi, the etiological agent of typhoid fever, produces the Vi capsular antigen, a virulence factor absent in Salmonella enterica serotype Typhimurium. Previous studies suggest that the capsule-encoding viaB locus reduces inflammatory responses in intestinal tissue; however, there are currently no data regarding the in vivo expression of this locus. Here we implemented direct and indirect methods to localize and detect Vi antigen expression within polarized intestinal epithelial cells and in the bovine ileal mucosa. We report that tviB, a gene necessary for Vi production in S. Typhi, was significantly upregulated during invasion of intestinal epithelial cells in vitro. During infection of bovine ligated loops, tviB was expressed at levels significantly higher in calf tissue than those in the inoculum. The presence of the Vi capsular antigen was detected in calf ileal tissue via fluorescence microscopy. Together, these results support the concept that expression of the Vi capsular antigen is induced when S. Typhi transits from the intestinal lumen into the ileal mucosa.

In Vivo Regulation of the Vi Antigen in Salmonella and Induction of Immune Responses with an In Vivo -Inducible Promoter

“…In the gut lumen, where the osmolarity is approximately 300 mM, the bacterium expresses very little or no Vi antigen (2,40). The low osmolarity of the blood and of the intracellular compartment is predicted to favor Vi expression, as also suggested by detectable Vi expression within bovine epithelial cells (33). This is in contrast to the very low or absent immune responses to Vi seen in the majority of typhoid patients, with anti-Vi antibodies found more frequently in the sera of chronic carriers and rarely in individuals with acute infection.…”

Non-animal models of epithelial barriers (skin, intestine and lung) in research, industrial applications and regulatory toxicology

“…Immortalized human adenocarcinoma cell lines such as Caco-2 or T84 (Khare et al, 2009;Raffatellu et al, 2005;Tran et al, 2010;Khare et al, 2012) have been extensively used to study absorption mechanisms, as such cell lines have been shown to act as acceptable models for the investigation of enterocyte differentiation and function (Cencič and Langerholc, 2010). Cells are commonly grown on semi-permeable Transwell ® inserts, where they form a polarized monolayer and exhibit villi formation.…”

Molecular Mechanisms Used by Salmonella to Evade the Immune System

“…The human pathogen S. Typhi expresses the Vi capsular polysaccharide during transit through the intestine (Tran et al, 2010). This polysaccharide has anti-inflammatory properties, (Sharma and Qadri, 2004) and also inhibits complement deposition (Looney and Steigbigel, 1986;Wilson et al, 2011).…”