An expanding stage for commensal microbes in host immune regulation

Abstract

Gastrointestinal commensal microbiota is a concentrated mix of microbial life forms, including bacteria, fungi, archaea and viruses. These life forms are targets of host antimicrobial defense in order to establish a homeostatic symbiosis inside the host. However, they are also instrumental in shaping the functions of our immune system via a diverse set of communication mechanisms. In the gut, T helper 17, regulatory T and B cells are continuously tuned by specific microbial strains and metabolic processes. These cells in return help to establish a mutually beneficial exchange with the gut microbial contents. Imbalances in this symbiosis lead to dysregulations in the host's ability to control infections and the development of autoimmune diseases. In addition, the commensal microbiota has a significant and obligatory role in shaping both gut intrinsic and distal lymphoid organs, casting a large impact on the overall immune landscape in the host. This review discusses the major components of the microbial community in the gut and how its members collectively and individually exert regulatory roles in the host immune system and lymphoid structure development, as well as the functions of several major immune cell types.

Intestinal dysbiosis and probiotic applications in autoimmune diseases

“…Studies in germ‐free (GF) mice showed that the gut microbiota is required for normal immune system maturation, including gut‐associated lymphoid tissue development, which plays important roles in tolerance induction to autoantigens in the gut mucosa . These GF mice showed decreased numbers of CD4 + T cells, secreting IgA plasma cells and antimicrobial peptides, a thinner mucus layer and Peyer's patches .…”

“…Evidence from animal models has implied the direct involvement of gut microbiota in disease development, and some intestinal microbiota are associated with autoimmune diseases …”

T lymphocytes in the intestinal mucosa: defense and tolerance

“…14 While chemokines guide the migration of T cells, the integrins expressed on the T-cell surface, such as α4β7, interact with adhesion molecules expressed on endothelial and epithelial cells, such as mucosal vascular addressin cell adhesion molecule 1 (MAdCAM-1), to initiate attachment to and diffusion into the tissue. 15 Interestingly, more than 90% of lymphocytes in the small intestine are α4β7-integrin positive, and a deficiency in α4β7 leads to the disruption of GALT formation. 16 Furthermore, CD4 + CD8 + DP T cells have been described in several species, including humans.…”

Profiling of Human Gut Virome with Oxford Nanopore Technology

“…Yet, the advances in next-generation sequencing (NGS) technology and bioinformatic tools have also facilitated the development of human virome studies. Metagenomic analysis suggests that the gut of healthy humans harbors commensal virus, including phages, DNA virus and RNA virus[18–22]. Virome (phages and other host viruses) play roles in intestinal physiology, enteric immune system, host health and disease[23, 24].…”