Gut microbiota: A new insight into lung diseases

The human gut microbiota is a complex ecosystem involved in the metabolism, immunity, and health of the host. The microbiome plays a key role in the development of the host's innate and adaptive immune system, while the immune system orchestrates the maintenance of host-microbe symbiosis. Lung diseases are usually accompanied by dysbiosis of the intestinal flora and an immune-inflammatory response. The intestinal flora and its metabolites are directly or indirectly involved in the immune regulation of the host in lung disease. However, the exact mechanism of action of the gut-lung axis crosstalk remains unclear. This review is aimed to summarize the latest advances in gut microbiota and their metabolites in typical lung diseases, such as pulmonary hypertension, COPD, and lung cancer. Especially COVID-19, a problem troubling the world, is also discussed in it. Moreover, it is concentrated on the action mechanisms between the identified gut microbiota or their metabolites and the specific lung diseases, and on the link among the gut microbiota, its metabolites, and immune regulation, which could be used as a breakthrough to find new mechanisms and targets for some diseases without specific therapeutic drugs in clinic. It is also discussed a new therapeutic tool "drug-bacterial interaction" and the potential of therapeutic applications in clinic. This review would provide a clear direction for future research on gut microbiota and lung diseases, and propose a new therapeutic strategy targeting "drug-bacterial interaction" in clinic.