Homeostatic T helper 17 cell responses triggered by complex microbiota are maintained in ex vivo intestinal tissue slices

Segmented filamentous bacteria (SFB) are members of the commensal intestinal microbiome. They are known to contribute to the postnatal maturation of the gut immune system, but also to augment inflammatory conditions in chronic diseases such as Crohn's disease. Living primary tissue slices are ultrathin multicellular sections of the intestine and provide a unique opportunity to analyze tissue-specific immune responses ex vivo. This study aimed to investigate whether supplementation of the gut flora with SFB promotes T helper 17 (Th17) cell responses in primary intestinal tissue slices ex vivo. Primary tissue slices were prepared from the small intestine of healthy Taconic mice with SFB-positive and SFB-negative microbiomes and stimulated with anti-CD3/CD28 or Concanavalin A. SFB-positive and -negative mice exhibited distinct microbiome compositions and Th17 cell frequencies in the intestine and complex microbiota including SFB induced up to 15-fold increase in Th17 cell-associated mediators, serum amyloid A (SAA), and immunoglobulin A (IgA) responses ex vivo. This phenotype could be transmitted by co-housing of mice. Our findings highlight that changes in the gut microbiome can be observed in primary intestinal tissue slices ex vivo. This makes the system very attractive for disease modeling and assessment of new therapies.