Aspects of Gut Microbiota and Immune System Interactions in Infectious Diseases, Immunopathology, and Cancer

Abstract

The microbiota consists of a dynamic multispecies community of bacteria, fungi, archaea, and protozoans, bringing to the host organism a dowry of cells and genes more numerous than its own. Among the different non-sterile cavities, the human gut harbors the most complex microbiota, with a strong impact on host homeostasis and immunostasis, being thus essential for maintaining the health condition. In this review, we outline the roles of gut microbiota in immunity, starting with the background information supporting the further presentation of the implications of gut microbiota dysbiosis in host susceptibility to infections, hypersensitivity reactions, autoimmunity, chronic inflammation, and cancer. The role of diet and antibiotics in the occurrence of dysbiosis and its pathological consequences, as well as the potential of probiotics to restore eubiosis is also discussed.

Metabolism at the centre of the host–microbe relationship

“…Antibiotic treatment-induced dysbiosis can have widereaching effects, for example on inflammation, infection and responses to vaccination [70][71][72]. Antibiotics have been shown to affect SCFA-producing bacteria causing a decrease in SCFA abundance [73,74].…”

Pre‐existing heterologous T‐cell immunity and neoantigen immunogenicity

“…In gastrointestinal infections, pathogens are captured by Peyer's patch‐resident M cells that allow pathogen‐derived antigens to be transferred across the epithelial cell layer and delivered to the peripheral immune system, specifically to antigen‐presenting cells such as dendritic cells (DCs), leading to the activation of T cells, and B cells, leading to the secretion of IgA antibodies. Interestingly, commensal antigens also use this mechanism to induce the production of low amounts of IgA antibodies through the modulation of their immunodominant epitopes to facilitate colonisation …”

Emerging Insights on the Interaction Between Anticancer and Immunosuppressant Drugs and Intestinal Microbiota in Pediatric Patients

“…There are evidences that gut microbiota plays a fundamental role in the healthy immune status maintenance. In particular, intestinal microflora and immune system are constantly shaping each other in a mutual aim to flourish and to keep the healthy individual in balance . The healthy state of the immune system in adulthood is related to the presence of a diversified microflora, which develops in early childhood thanks to a correct colonization sequence by different microorganisms.…”

“…Furthermore, commensal bacteria are responsible for triggering several pathways involved in the regulation of the immune system . A general consensus exists that Treg cells are key mediators of immune responses, maintaining both peripheral and mucosal homeostasis . Although the primary site of differentiation is the thymus, the induction of Treg cells can occur also in the gastrointestinal tract after the production of inducing factors by dendritic cells presenting antigens derived from commensal bacteria .…”