The gut–organ axis: Clinical aspects and immune mechanisms

The gut-brain axis exemplifies the bidirectional connection between the intestines and the brain, as evidenced by the impact of severe stress on gastrointestinal symptoms including abdominal pain and diarrhea, and conversely, the influence of abdominal discomfort on mood. Clinical observations support the notion of the gut-brain connection, including an increased prevalence of inflammatory bowel disease (IBD) in patients with depression and anxiety, as well as the association of changes in the gut microbiota with neurological disorders such as multiple sclerosis, Parkinson's disease, stroke and Alzheimer's disease. The gut and brain communicate via complex mechanisms involving inflammatory cytokines, immune cells, autonomic nerves, and gut microbiota, which contribute to the pathogenesis in certain gut and brain diseases. Two primary pathways mediate the bidirectional information exchange between the intestinal tract and the brain: signal transduction through bloodstream factors, such as bacterial metabolites and inflammatory cytokines, and neural pathways, such as neurotransmitters and inflammatory cytokines within the autonomic nervous system through the interaction between the nerve cells and beyond. In recent years, the basic mechanisms of the pathophysiology of the gut-brain axis have been gradually elucidated. Beyond the gut-brain interaction, emerging evidence suggests the influence of the gut extends to other organs, such as the liver and lungs, through intricate inter-organ communication pathways. An increasing number of reports on this clinical and basic cross-organ interactions underscore the potential for better understanding and novel therapeutic strategies targeting inter-organs networks. Further clarification of interactions between multiorgans premises transformative insights into cross-organ therapeutic strategies.