The lung-gut crosstalk in respiratory and inflammatory bowel disease

Both lung and gut belong to the common mucosal immune system (CMIS), with huge surface areas exposed to the external environment. They are the main defense organs against the invasion of pathogens and play a key role in innate and adaptive immunity. Recently, more and more evidence showed that stimulation of one organ can affect the other, as exemplified by intestinal complications during respiratory disease and vice versa, which is called lung-gut crosstalk. Intestinal microbiota plays an important role in respiratory and intestinal diseases. It is known that intestinal microbial imbalance is related to inflammatory bowel disease (IBD), this imbalance could impact the integrity of the intestinal epithelial barrier and leads to the persistence of inflammation, however, gut microbial disturbances have also been observed in respiratory diseases such as asthma, allergy, chronic obstructive pulmonary disease (COPD), and respiratory infection. It is not fully clarified how these disorders happened. In this review, we summarized the latest examples and possible mechanisms of lung-gut crosstalk in respiratory disease and IBD and discussed the strategy of shaping intestinal flora to treat respiratory diseases.