Attenuated portal hypertension in germ-free mice: Function of bacterial flora on the development of mesenteric lymphatic and blood vessels

Intestinal bacterial flora may induce splanchnic hemodynamic and histological alterations that are associated with portal hypertension (PH). We hypothesized that experimental PH would be attenuated in the complete absence of intestinal bacteria. We induced prehepatic PH by partial portal vein ligation (PPVL) in germ-free (GF) or mice colonized with altered Schaedler's flora (ASF). After 2 or 7 days, we performed hemodynamic measurements, including portal pressure (PP) and portosystemic shunts (PSS), and collected tissues for histomorphology, microbiology, and gene expression studies. Mice colonized with intestinal microbiota presented significantly higher PP levels after PPVL, compared to GF, mice. Presence of bacterial flora was also associated with significantly increased PSS and spleen weight. However, there were no hemodynamic differences between sham-operated mice in the presence or absence of intestinal flora. Bacterial translocation to the spleen was demonstrated 2 days, but not 7 days, after PPVL. Intestinal lymphatic and blood vessels were more abundant in colonized and in portal hypertensive mice, as compared to GF and sham-operated mice. Expression of the intestinal antimicrobial peptide, angiogenin-4, was suppressed in GF mice, but increased significantly after PPVL, whereas other angiogenic factors remained unchanged. Moreover, colonization of GF mice with ASF 2 days after PPVL led to a significant increase in intestinal blood vessels, compared to controls. The relative increase in PP after PPVL in ASF and specific pathogen-free mice was not significantly different. CONCLUSION In the complete absence of gut microbial flora PP is normal, but experimental PH is significantly attenuated. Intestinal mucosal lymphatic and blood vessels induced by bacterial colonization may contribute to development of PH.

The bilateral responsiveness between intestinal microbes and IgA

The immune system has developed strategies to maintain a homeostatic relationship with the resident microbiota. IgA is central in holding this relationship, as the most dominant immunoglobulin isotype at the mucosal surface of the intestine. Recent studies report a role for IgA in shaping the composition of the intestinal microbiota and exploit strategies to characterise IgA-binding bacteria for their inflammatory potential. We review these findings here, and place them in context of the current understanding of the range of microorganisms that contribute to the IgA repertoire and the pathways that determine the quality of the IgA response. We examine why only certain intestinal microbes are coated with IgA, and discuss how understanding the determinants of this specific responsiveness may provide insight into diseases associated with dysbiosis.

[Smoking and digestive tract: a complex relationship. Part 2: Intestinal microblota and cigarette smoking]

The digestive tract is colonized from birth by a bacterial population called the microbiota which influences the development of the immune system. Modifications in its composition are associated with problems such as obesity or inflammatory bowel diseases. Antibiotics are known to influence the intestinal microbiota but other environmental factors such as cigarette smoking also seem to have an impact on its composition. This influence might partly explain weight gain which is observed after smoking cessation. Indeed there is a modification of the gut microbiota which becomes similar to that of obese people with a microbiotical profile which is more efficient to extract calories from ingested food. These new findings open new fields of diagnostic and therapeutic approaches through the regulation of the microbiota.

Eosinophilic esophagitis is characterized by a non-IgE-mediated food hypersensitivity.

Eosinophilic esophagitis (EoE) is a chronic disease characterized clinically by symptoms of esophageal dysfunction and histologically by eosinophil-predominant inflammation. EoE is frequently associated with concomitant atopic diseases and immunoglobulin E (IgE) sensitization to food allergens in children as well as to aeroallergens and cross-reactive plant allergen components in adults. Patients with EoE respond well to elemental and empirical food elimination diets. Recent research has, however, indicated that the pathogenesis of EoE is distinct from IgE-mediated food allergy. In this review, we discuss the individual roles of epithelial barrier defects, dysregulated innate and adaptive immune responses, and of microbiota in the pathogenesis of EoE. Although food has been recognized as a trigger factor of EoE, the mechanism by which it initiates or facilitates eosinophilic inflammation appears to be largely independent of IgE and needs to be further investigated. Understanding the pathogenic role of food in EoE is a prerequisite for the development of specific diagnostic tools and targeted therapeutic procedures. This article is protected by copyright. All rights reserved.