The Front Line of Enteric Host Defense against Unwelcome Intrusion of Harmful Microorganisms: Mucins, Antimicrobial Peptides, and Microbiota

Abstract

SUMMARY The intestinal tract is a complex ecosystem that combines resident microbiota and the cells of various phenotypes with complex metabolic activities that line the epithelial wall. The intestinal cells that make up the epithelium provide physical and chemical barriers that protect the host against the unwanted intrusion of microorganisms that hijack the cellular molecules and signaling pathways of the host and become pathogenic. Some of the organisms making up the intestinal microbiota also have microbicidal effects that contribute to the barrier against enteric pathogens. This review describes the two cell lineages present in the intestinal epithelium: the goblet cells and the Paneth cells, both of which play a pivotal role in the first line of enteric defense by producing mucus and antimicrobial peptides, respectively. We also analyze recent insights into the intestinal microbiota and the mechanisms by which some resident species act as a barrier to enteric pathogens. Moreover, this review examines whether the cells producing mucins or antimicrobial peptides and the resident microbiota act in partnership and whether they function individually and/or synergistically to provide the host with an effective front line of defense against harmful enteric pathogens.

Modulatory Effects of Gut Microbiota on the Central Nervous System: How Gut Could Play a Role in Neuropsychiatric Health and Diseases

“…24 Mucus is secreted by goblet cells and acts as a mechanical protective layer that also contains digestive and antibacterial enzymes and antibodies, and will hydrate the epithelial layer and helps it regenerate. 25 The epithelial layer, in addition to playing an important part in absorption of the nutrients, also serves as a physical barrier due to the tight junctions between the epithelial cells. Furthermore, enteroendocrine cells are distributed through the epithelial layer.…”

Microbiota and the control of blood-tissue barriers

“…In addition to its physical nature, this barrier contains a chemical component consisting of e.g., mucins, trefoil peptides and surfactant peptides. 65 The primary physical barrier is formed by a single layer of epithelial cells with the paracellular space being sealed by TJ. 66 The TJ regulate the flow of water ions and small molecules, as well as preventing antigens and pathogens from entering mucosal tissues.…”

Butyrate-producing Clostridium cluster XIVa species specifically colonize mucins in an in vitro gut model

“…Moreover, by locally excreting antimicrobials or competing with pathogens, mucosal microbes more effectively limit pathogen translocation. Besides host immune effectors (Lievin-Le Moal and Servin, 2006), microbial properties, such as mucus adhesion (Roos and Jonsson, 2002) or the ability to degrade host-derived glycans (Derrien et al, 2004), also impact the distinct surface-attached microbial composition, generally characterized by an enrichment of Firmicutes (especially Clostridium cluster XIVa) over Bacteroidetes (Eckburg et al, 2005;Frank et al, 2007;Hill et al, 2009;Shen et al, 2010;Willing et al, 2010;Hong et al, 2011;Nava et al, 2011). Moreover, the mucus layer is persistently colonized by all types of hydrogenotrophs: methanogenic archaea, sulphate-reducing bacteria and acetogenic bacteria (Nava et al, 2012).…”