Role of Toll-like receptors in the development of immunotolerance mediated by probiotics

Abstract

Commensal bacteria are important in intestinal homeostasis and appear to play a role in early tolerance to foreign antigens. The requirement for homeostatic balance between tolerance and immunity poses a unique regulatory challenge to mucosal immune systems. Dysregulation of this balance can contribute to the pathogenesis of numerous inflammatory conditions such as inflammatory bowel diseases. The primary response to these bacteria is triggered by pattern recognition receptors (PRR), which bind pathogen-associated molecular patterns (PAMP). PRR comprise Toll-like receptors (TLR), nucleotide-binding oligomerization domains, adhesion molecules and lectins. Probiotics are living commensal micro-organisms of the intestinal tract with clinically documented health effects in human subjects. They are known to affect the gastrointestinal tract and the associated immune system and to have numerous effects on intestinal function and immune responses, including immunotolerance. This last effect appears to be mediated via regulatory T-cell activation by intestinal dendritic cells and the low activation of T-helper 1 and 2 (Th1 and Th2) cell inflammatory responses. However, the precise mechanisms of probiotic activity remain poorly understood. The aim of the present work was to review the function of TLR in the development of immunotolerance and examine the specific role of probiotics in the regulation of tolerance to antigens.

Probiotic Mechanisms of Action

“…The adaptive immune response depends on B and T lymphocytes, which are specific for particular antigens. In contrast, the innate immune system responds to common structures called pathogen-associated molecular patterns (PAMPs) shared by the vast majority of pathogens [132]. The primary response to pathogens is triggered by pattern recognition receptors (PPRs), which bind PAMPs.…”

La adición de Enterococcus faecium aumenta la respuesta inmune intestinal en cerdos en crecimiento

“…Existen varias células encargadas de la presentación de antígenos en el GALT, incluyendo los enterocitos y otras células epiteliales intestinales (CEI), tales como células M, células dendríticas (CD), macrófagos y linfocitos T y B (Gómez-Llorente et al, 2010). Las bacterias activan las CD directamente a través de los receptores de reconocimiento de patrones (PRR) o indirectamente por la captura de los productos apoptóticos/necróticos de otras células que están muriendo en respuesta a la exposición microbiana (Bermúdez-Brito et al, 2012).…”

Bacterial translocation: gap in the shield

“…Ismert továbbá, hogy a bélfl óra esszenciális szerepet játszik az immunrendszer kifejlődésében, többek között a Toll-like receptorok indukcióján keresztül [5]. Ugyanakkor az immunrendszer fejlődéséhez a bélrendszer kedvező mikroökológiai konstellációja is hozzájárul, amely lehetővé teszi a lumenben jelen lévő mikrobiális antigé-nek "mintavételezését" ("sampling").…”