The gut-lung axis and viral pneumonia: Unrevealing the gut microbiota.

Viral pneumonia is often accompanied by gastrointestinal symptoms, highlighting the central role of the gut-lung axis in the disease process. Despite mounting evidence that links viral pneumonia to gut microbiota dysregulation, the precise function of gut microbiota remains controversial, especially regarding the bidirectional modulation of host immunity driven by microbial metabolites and the systemic immune effects regulated through the gut-lung axis. This review focuses on the period from 2020 to 2025 and systematically elaborates on the emerging advances surrounding the bidirectional crosstalk between respiratory viruses and gut microbiota via the gut-lung axis. It provides a detailed discussion on the gut-lung axis, covering the fundamental roles of gut microbial composition, key metabolic mediators and signaling pathways, and immune cell migration coupled with systemic inflammatory reactions. Additionally, the regulatory effect of traditional Chinese medicine (TCM) as a prebiotic is emphasised, with a detailed explanation of how TCM compound preparations modulate bacterial metabolism, repair the intestinal barrier and activate antioxidant and anti-inflammatory responses in order to regulate the gut-lung axis and combat viral pneumonia. This review incorporates newly reported experimental evidence, elaborates the concentration- and time-dependent effects of essential metabolic mediators including short-chain fatty acids (SCFAs) and the state-dependent dynamic shifts of host immune responses, with an aim to clarify existing discrepancies across relevant studies. Accumulating mechanistic knowledge regarding the gut-lung axis highlights promising therapeutic values targeting the intestinal microecology. Future investigations are prioritized to identify characteristic biomarkers related to the gut microbiota and develop a standardized intervention system tailored to different stages of viral pneumonia.