Chronic stress, gut microbiota, and immunity: interconnections and implications for health

Psychological stress influences the hypothalamic-pituitary-adrenal (HPA) and the sympathetic-adrenal -medullary (SAM) axes which directly impact the immune system. Stress not only affects hematopoietic stem cell activity but also increases the circulating levels of inflammatory cells, thereby potentially exacerbating pathogenic conditions. Moreover, stress affects hormone release, inflammation, and autonomic changes, which can modify the composition of the gut microbiota and indirectly alter the immune system. This review aims to summarize the research that demonstrates the relationships among stress, the gut microbiota, and hematopoiesis to increase our understanding of the intricate connections among them, while also highlighting the bidirectional influences among chronic diseases, systemic inflammation, and stress.