Preclinical Evidence and Mechanisms of Traditional Chinese Medicine Polysaccharides Regulating the Gut–Lung Axis via Gut Microbiota in Respiratory Diseases

Traditional Chinese medicine (TCM) polysaccharides are important active components of traditional Chinese medicine, and their anti-inflammatory, immunomodulatory, and mucosal barrier protective effects have attracted widespread attention. Since most traditional Chinese medicine polysaccharides are difficult to be completely digested and absorbed in the gastrointestinal tract, their interventional effects on respiratory diseases may be closely related to the selective utilization by gut microorganisms and the regulation of the gut–lung axis. Therefore, the structural and functional interactions between traditional Chinese medicine polysaccharides and gut microbiota have gradually become an important direction in traditional Chinese medicine pharmacology and microecology research. This review mainly explores two core questions: first, how traditional Chinese medicine polysaccharides that can act on the gut–lung axis drive candidate gut bacteria and metabolic networks; second, how polysaccharide-driven candidate bacteria and metabolic networks regulate pulmonary infection, allergic inflammation, chronic airway injury, and fibrosis through the intestinal mucosal barrier, immune cell reprogramming, and cross-organ signal transmission. Accordingly, this narrative mechanistic review examines selected preclinical studies on traditional Chinese medicine polysaccharides regulating the gut–lung axis, focusing on summarizing the continuous mechanisms by which different polysaccharides promote the proliferation of related microbial communities and metabolite production through selective feeding of gut microorganisms, stabilize intestinal mucosal immunity, and exert pulmonary interventional effects. This review aims to deepen the understanding of the interaction mechanisms among traditional Chinese medicine polysaccharides, microorganisms, and the host, provide some reference for establishing a mechanistic evidence framework for gut–lung axis research and screening potential active polysaccharides with relevant structures and microbiota effects.