Integrative Biomedical Research
Integrative Biomedical Research (Journal of Angiotherapy) | Online ISSN 3068-6326
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Volume 10 Number 1 2026
REVIEWS (Open Access)
The Gut–Brain–Immune Axis in Chronic Disease: Mechanisms and Therapeutic Opportunities — A Narrative Synthesis
Mohamed Sadeq Al-Ibrahim 1, Ahmad Hamdy Ibrahim 2, Sawsan S. Al- Rawi 3*, Bayram Dawod Ahmed 4
Integrative Biomedical Research 10 (1) 1-8 https://doi.org/10.25163/biomedical.10110884
Submitted: 10 January 2026 Revised: 01 March 2026 Accepted: 11 March 2026 Published: 13 March 2026
Abstract
The gastrointestinal microbiota shapes host metabolism, immunity, and brain function through a tripartite gut–brain–immune axis, yet the field still lacks a unified synthesis linking barrier failure, immunometabolic signaling, and disease-specific outcomes. We conducted a structured narrative review of preclinical and clinical literature indexed largely through PubMed-listed sources, synthesizing evidence on neural, endocrine, immunological, and microbial-metabolite communication pathways and their dysregulation in Parkinson’s disease, Alzheimer’s disease, multiple sclerosis, and related chronic conditions. Across disorders, intestinal barrier failure and endotoxemia recur as a shared upstream trigger, converging on microglial activation, kynurenine pathway shunting toward neurotoxic quinolinic acid, and blood–brain barrier compromise, while each disease additionally shows a distinctive dysbiotic signature and cellular trafficking pattern—vagal alpha-synuclein propagation in Parkinson’s disease, amyloid cross-seeding in Alzheimer’s disease, and Th17-mediated demyelination in multiple sclerosis. Microbiome-directed interventions, including dietary modulation, psychobiotics, and fecal microbiota transplantation, showed measurable, if heterogeneous, benefit; a placebo-controlled fecal transplantation trial in Parkinson’s disease, for instance, reported meaningfully greater motor improvement than placebo. The evidence, taken together, supports the gut–brain–immune axis as a mechanistically coherent and therapeutically actionable framework, though translation remains constrained by engraftment variability and a scarcity of standardized, biomarker-guided trial designs. Personalized, multi-omics-informed strategies appear to be the most promising path toward clinical utility. Keywords: gut–brain–immune axis; gut microbiota; neuroinflammation; dysbiosis; kynurenine pathway; fecal microbiota transplantation; neurodegenerative disease
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