Microbiome and Gut Immunity: Innate Immune Cells
The innate immune system not only serves as a first line of defense against infections with pathogenic microorganisms but also plays an important role in the balanced interplay with the intestinal microbiota. Distinct subsets of innate immune cells such as macrophages, dendritic cells, granulocytes, mast cells, and innate lymphoid cells are found spread throughout the intestinal tissue as well as organized in tissue-specific lymphoid structures. These cells constantly survey the intestinal tissue for the presence of live microbes to prevent the spread of invading microbes and fine-tune the intestinal barrier. Specifically, metabolites from the commensal microbiota such as short-chain fatty acids have been identified to maintain tolerogenic conditions in the intestine, e.g., promoting regulatory T cells and down-modulating pro-inflammatory signaling pathways. In turn, aberrant recognition and handling of commensal microbes by the innate immune system or the excessive immune activation after pathogen sensing have been demonstrated to promote inflammatory conditions such as inflammatory bowel diseases in the intestine. Hence, the detailed understanding of the interplay between the microbiota and innate immune system may enable novel therapeutic interventions to promote human health and, specifically, to prevent auto-inflammatory diseases.
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