Abstract
Toll-like receptors (TLRs) are powerful molecular regulators by which the immune system may “sense” the environment and protect the host from pathogens or endogenous threats. In mammalian cells, several TLRs were identified with a tissue and cell type-specific distribution. Understanding the functions of specific TLRs is crucial for the development and discovery of compounds useful to maintaining or re-establishing homeostasis in the gastrointestinal tract (GIT). Due to their relevance in regulating the inflammatory response in the GIT, we will focus here on TLR2, TLR4, and TLR5. In particular, we describe (a) the molecular pathways activated by the stimulation of these receptors with their known bacterial ligands; (b) the non-bacterial ligands known to interact directly with TLR2 and TLR4 and their soluble forms. The scope of this minireview is to highlight the importance of bacterial and non-bacterial compounds in affecting the gut immune functions via the activation of the TLRs.
Highlights
Being in proximity to the largest interface between the body and the external environment, the gut immune system has evolved to distinguish the tiniest molecular difference that exists between pathogenic and non-pathogenic microorganisms
In the gastrointestinal tract (GIT), the immune system contributes to the maintenance of the delicate equilibrium that exists between bacteria, yeast, bacteriophages, and gut epithelium to guarantee homeostasis and the optimal health of the organism
We focus on TLR2, TLR4, and TLR5, since among all toll-like receptors (TLRs), these are the main (i.e., type I interferon (IFN)) [23]
Summary
Being in proximity to the largest interface between the body and the external environment, the gut immune system has evolved to distinguish the tiniest molecular difference that exists between pathogenic and non-pathogenic microorganisms. An early interaction point occurs between potentially pathogenic bacteria and the toll-like receptors (TLRs) present on the membrane of the gut immune cells, as well as on the cellular membrane of the gut epithelium [3,4]. The barrier function of the gut epithelium of the GIT and the immune system. Signaling cascades leading to the release of pro or anti-inflammatory cytokines or antiviral compounds In this minireview, we focus on TLR2, TLR4, and TLR5, since among all TLRs, these are the main (i.e., type I interferon (IFN)) [23]. Understanding the dynamic exists betweenhomeostasis microorganisms development and discovery of compounds critical toequilibrium maintainingthat or re-establishing in in the gut and the activity of the immune system regulated by TLRs is crucial for the development and the GIT such as pre- and probiotics, as well as pharma- and nutraceuticals. Discovery of compounds critical to maintaining or re-establishing homeostasis in the GIT such as preand probiotics, as well as pharma- and nutraceuticals
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