Regulation of Intestinal Immune Responses through TLR Activation: Implications for Pro- and Prebiotics

Abstract

The intestinal mucosa is constantly facing a high load of antigens including bacterial antigens derived from the microbiota and food. Despite this, the immune cells present in the gastrointestinal tract do not initiate a pro-inflammatory immune response. Toll-like receptors (TLRs) are pattern recognition receptors expressed by various cells in the gastrointestinal tract, including intestinal epithelial cells (IEC) and resident immune cells in the lamina propria. Many diseases, including chronic intestinal inflammation (e.g., inflammatory bowel disease), irritable bowel syndrome (IBS), allergic gastroenteritis (e.g., eosinophilic gastroenteritis and allergic IBS), and infections are nowadays associated with a deregulated microbiota. The microbiota may directly interact with TLR. In addition, differences in intestinal TLR expression in health and disease may suggest that TLRs play an essential role in disease pathogenesis and may be novel targets for therapy. TLR signaling in the gut is involved in either maintaining intestinal homeostasis or the induction of an inflammatory response. This mini review provides an overview of the current knowledge regarding the contribution of intestinal epithelial TLR signaling in both tolerance induction or promoting intestinal inflammation, with a focus on food allergy. We will also highlight a potential role of the microbiota in regulating gut immune responses, especially through TLR activation.

Jian carp ( Cyprinus carpio var. Jian) intestinal immune responses, antioxidant status and tight junction protein mRNA expression are modulated via Nrf2 and PKC in response to dietary arginine deficiency

“…The fish intestine contains the largest part of the immune system, which is constantly exposed to potentially pathogenic bacteria and other toxic elements [1]. Moreover, it has been demonstrated that the impairment of the fish intestinal immune system could lead to pathogen translocation and inflammatory bowel disease [2], thereby decreasing fish growth performance [3].…”

The melatonin-sensitive circadian clock of the enteric bacteriumEnterobacter aerogenes

“…1,4 Microbial signaling affects both homeostatic maintenance of intestinal function as well as circadian control of gastrointestinal function. 5,6 Disruption of the circadian clock, either via dietary restriction or phase shifting (e.g. jet-lag) affects temporal distribution of the gut microbiome constituents.…”

Meat and fiber intake and interaction with pattern recognition receptors (TLR1, TLR2, TLR4, and TLR10) in relation to colorectal cancer in a Danish prospective, case-cohort study

“…Our analyses suggest that the meat carcinogenic pathway involves activation of TLR1 and TLR10 followed by activation of NF-ĸB-initiated transcription of inflammatory genes (Figure 1). Bacterial cell-surface lipopolysaccharides are ligands for TLR1 activation (48), whereas TLR10 has been suggested as a key mediator of Listeria monocytogenes-induced inflammation (49). L. monocytogenes has become a major foodborne pathogen that can be found in meat and processed foods due to its ability to survive the most common food-processing conditions such as extreme pH, high salt concentration, low water activity, and refrigeration temperatures (50).…”