Studio dell'effetto dei probiotici sulla modulazione della risposta immunitaria intestinale
Author(s)
Britti, Maria Serena
Date Issued
January 31, 2006
Type
Doctoral Thesis
Abstract
The gut immune system has to be able to protect the mucosa against pathogens but also must avoid hypersensitivity reactions to food proteins, normal bacterial flora and other environmental macromolecules. Oral tolerance is a specific suppression of cellular and humoral cell-mediated immune responses to orally administered antigen or to local microflora to prevent immune reactions to dietary antigens. Breakdown of oral tolerance may lead to the development of adverse reactions to food, mucosal immunopathologies directed against environmental antigens or autoantigens and thus to autoimmune disease. A large number of studies suggested that probiotics are able to exert numerous beneficial effects such as: mantenance of a balanced indigenous microflora, protection against intestinal pathogens and modulation of immune response that seem to ameliorate food allergies, autoimmune diseases and oral tolerance. Up to now, the mechanisms by which probiotics modulate intestinal immune response are not yet clarified.
In this study, it was verified whether oral feeding with probiotics may induce an anti-inflammatory and tolerogenic response at intestinal site. For such pourpose, two experimental models were used: rats tolerant to the feed antigen ovalbumin (OVA), normally not present in their diet, and rats immunized for the same antigen. The probiotics used were Bifidobacterium animalis MB5 (Ba), a strain not widely studied, and Lactobacillus casei subsp. rhamnosus GG (LGG), a well known probiotic strain, with numerous beneficial effects. Proliferation of splenic and mesenteric lymphocytes after in vitro stimulation with OVA or with a polyclonal mitogen, Concanavalin A (ConA), and the delayed time hypersensitivity (DTH) reaction were assayed. Expression of cytokines involved in oral tolerance induction and of some pro-inflammatory cytokines was also evaluated. Moreover, the principal subpopulations of intestinal lymphocytes were analized.
The results indicate that proliferation of mesenteric lymphocytes of immunized rats after in vitro stimulation with OVA was lower in probiotics fed animals than in unfed rats. Probiotics exert this effect only at intestinal level, in fact the proliferative response at splenic level and DTH response were not modified by probiotic treatment. The proliferative response after in vitro stimolation with the polyclonal mitogen ConA was high and similar in all groups of animals, suggesting that the reduction of proliferative response observed at intestinal level is antigen specific. LGG treatment induced an increase of interleukin (IL)-10 gene expression and an increase of basal secretion of IL-10 in mesenteric lymphocytes of immunized rats, compared to untreated rats. With LGG treatment, the regulatory subpopulation CD4+-CD25+ of intestinal lymphocytes reaches a middle level between the levels of tolerized and immunized rats. The gene expression of IL-4 and transforming growth factor (TGF)-β was not influenced by probiotic treatment, whereas gene expression of interferon (IFN)-γ and cytokine induced neutrophil chemoattractant (CINC) was reduced in splenic lymphocytes of immunized rats treated with Ba or LGG.
The conclusions of this study highlight a new role for probiotics in inducing a tolerogenic response at intestinal level, and contribute to clarify the mechanisms by which some probiotics can exert their immunomodulatory activities. It is possible that LGG exerts its tolerogenic activity throught in vivo induction of a Tr1-like lymphocytes population, with a low antigen specific proliferative response and high IL-10 production. Moreover Ba and LGG are able to modulate inflammatory response at splenic level, reducing the gene expression of pro-inflammatory cytokines.
Additional information
Dottorato di ricerca in Genetica e Biologia Cellulare. XVIII ciclo
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