Background and Objectives: Intestinal microbiota is involved in the development and maintenance of immune homeosta- sis. This study was conducted to investigate the levels of key immunoregulatory bacteria in the intestinal wall-associated microflora and its effect on the transcriptional activity of the Foxp3 and RORyt genes in the gut-associated lymphoid tissue (GALT) of rats with Salmonella-induced inflammation, both untreated and treated with vancomycin and Bacteroides fragilis. Materials and Methods: To determine the levels of immunoregulatory bacteria in GALT of rats Q-PCR was used to identify them by species-specific 16S rDNA genes. Transcriptional activity of Foxp3 and RORyt genes was determined using Q-PCR with reverse transcription. Results: In animals treated with both vancomycin and Salmonella, the levels of segmented filamentous bacteria (SFB) in- creased while Akkermansia muciniphila and Faecalibacterium prausnitzii decreased. In rats that received pretreatment with vancomycin and then were infected with S. Enteritidis and S. Typhimurium, the levels of SFB increased, and the number of Bacteroides-Prevotela group, A. muciniphila, Clostridium spp. clusters XIV, IV, and F. prausnitzii significantly decreased, decreasing Foxp3 and increasing Rorγt mRNA expression. Administration of B. fragilis to animals treated with S. Enteriti- dis or S. Typhimurium and pre-treated with vancomycin caused a decrease in SFB and Rorγt mRNA levels and conversely, increased the numbers of the Bacteroides-Prevotela group, Clostridium spp. clusters XIV, IV, A. muciniphila, F. prausnitzii and Foxp3 gene expression in GALT. Conclusion: Our results suggest that the commensal microorganism B. fragilis may provide a protective role against the development of experimental colitis, which has to be taken into consideration for further clarification of the effective thera- peutic strategy of inflammatory bowel diseases, irritable bowel syndrome and necrotising colitis.
Intestinal microbiome supports immune homeostasis. Segmental filamentous bacteria (SFB) induce differentiation of Th17-cells in enteric-associated lymphoid tissue (GALT). Clostridium (cluster IV and XIVa) and Bacteroidesfragilis (polysaccharide A) stimulate the formation of T-regulatory cells (Treg) and production of suppressor cytokine IL-10. METHODS: Metabolites of B. fragilis, short-chain fatty acids (SCFA), activate GALT cells through the FFAR2 receptor. Decrease in the concentration of SCFA decreases the number of Treg and disrupts the balance of Th17/Treg, which leads decreased level of FFAR2, Foxp3 mRNA and an increase in RORgt in GALT. Vancomycin and salmonella were given to rats and the levels of SFB assessed. RESULTS: SFB increased and A.muciniphila, F.prausnitzii decreased post Vancomycin and salmmonella. In rats infected with salmonella after pretreatment with vancomycin, the number of SFBs increased with a marked decrease in the Bacteroides-Prevotela group, A.muciniphila, Clostridium spp. clusters XIV, IV, and F.prausnitzii, leading to a decrease in the expression level of Foxp3 + gene mRNA and an increase in Rorgt +. The introduction of B. fragilis to animals receiving Salmonella on the background of pre-treatment with vancomycin caused a decrease in the level of SFB and mRNA of Rorgt +, and, conversely, increased the number of Bacteroides-Prevotela group, A.muciniphila, Clostridium spp. clusters XIV, IV, F.prausnitzii and expression of Foxp3 + genes, indicative of restoration of intestinal microbiome homeostasis. CONCLUSIONS: Salmonella-induced changes in immunoregulatory bacteria impacts transcriptional activity of the Foxp3 and Roryt genes in rat GALT.
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