Introduction: Beneficial commensal microorganisms and potential pathogens continuously challenge mucosal immune system. A number of physiological adaptations protect IECs from bacterial invasion such as glycoprotein layer of heavily glycosylated mucin-2 secreted by goblet cells. Deficit of the mucin layer could lead to the pathogenesis of numerous inflammatory conditions, including food allergies, IBD and intestinal cancer. Here we studied the effect of mucin layer depletion on microbiome, inflammation and macrophage programming using Mucin-2 knockout mice. We have also investigated the effect of its monosaccharides on the phenotypes observed.
Methods: The study was conducted at the Center for Genetic Resources of Laboratory Animals at the ICG SB RAS (RFMEFI61914X0005 and RFMEFI62114Х0010) using specific pathogen free C57BL/6 Muc2tm1Avel (Muc2-/-) and control C57BL/6 mice. Microbial communities of mouse fecal samples were analyzed by Shotgun sequencing and Single-Strand Conformation Polymorphism of 16S rRNA gene. We evaluated the effect of Mucin-2 depletion alone or in combination with the addition of Mucin-2 derived monosaccharides on the mucosal immune system. This included cytokine expression (INF-gamma, TNF-alpha, IL1-alpha and beta, IL-10, IL-12, IL-17, etc.) and histological analysis of the colon.
Results: The changes observed in intestinal flora of Muc2-/- mice were associated with up-regulation of the inflammatory cytokines, generation of IgG against own intestinal bacteria and development of Th2 and Th17 response as a results of continuous contact between microflora and IECs. Fucose and sialic acid restored gut flora such as Bacteroides spices, especially after antibiotics therapy. However, only fucose, but not sialic acid, suppressed Th2 and Th17 immune response with the decrease of M2 type macrophages and the increase of Th1 response in combination with proinflammatory factors.
Conclusion: Mucin-2 derived monosaccharides per ce or through regulation of the intesinal flora could modulate mucosal immunity in the experimental model of IBD.
Work was supported by RFBR grant 15-04-07653.