Possible role of gut microbes and host’s immune response in gut–lung homeostasis

Abstract

The vast diversity of microbial communities reside in various locations of the human body, and they are collectively named as the ‘Human Microbiota.’ The majority of those microbes are found in the gastrointestinal and respiratory tracts. The microorganisms present in the gastrointestinal and the respiratory tracts are called the gut microbiota and the airway microbiota, respectively. These microbial communities are known to affect both the metabolic functions and the immune responses of the host. Among multiple factors determining the composition of gut microbiota, diet has played a pivotal role. The gut microbes possess enzymatic machinery for assimilating dietary fibers and releasing different metabolites, primarily short-chain fatty acids (SCFAs). The SCFAs modulate the immune responses of not only the gut but other distal mucosal sites as well, such as the lungs. Dysbiosis in normal gut flora is one of the factors involved in the development of asthma and other respiratory disorders. Of note, several human and murine studies have indicated significant cross-talk between gut microbiota and lung immunity, known as the gut–lung axis. Here, in this review, we summarize the recent state of the field concerning the effect of dietary metabolites, particularly SCFAs, on the “gut–lung axis” as well as discuss its impact on lung health. Moreover, we have highlighted the role of the “gut–lung axis” in SARS-CoV-2 mediated inflammation. Also, to analyze the global research progress on the gut–lung axis and to identify the knowledge gap in this field, we have also utilized the bibliographic tools Dimension database and VOS viewer analysis software. Through network mapping and visualization analysis, we can predict the present research trend and the possibility to explore new directions.

The “Asthma-Polycystic Ovary Overlap Syndrome” and the Therapeutic Role of Myo-Inositol

“…Alterations in microbiota can be also present in asthma patients [ 60 , 61 ]. Recent studies showed that gut and lung microbiota are closely interconnected (“gut–lung axis”) and can be involved in the pathogenesis of asthma [ 62 ]. In particular, a significantly reduced presence of Lactobacillus can be of great importance [ 57 , 60 , 61 , 62 , 63 ].…”

“…Recent studies showed that gut and lung microbiota are closely interconnected (“gut–lung axis”) and can be involved in the pathogenesis of asthma [ 62 ]. In particular, a significantly reduced presence of Lactobacillus can be of great importance [ 57 , 60 , 61 , 62 , 63 ]. If gut microbiota is altered, endotoxins are generated that may contribute to chronic inflammation in asthma patients by activation of NF-κB pathway [ 64 , 65 ].…”

Demonstration of safety characteristics and effects on gut microbiota of Lactobacillus gasseri HMV18

“…Normal flora benefits human health through mucosal homeostasis maintenance, promoting immune status, and being reactive in drug metabolism and metabolite utilization [1,2]. Multiple probiotic strains have been isolated and identified from human flora [3].…”

Bifidobacterium animalis subsp. lactis BL-99 ameliorates colitis-related lung injury in mice by modulating short-chain fatty acid production and inflammatory monocytes/macrophages

“…Various genetic and environmental factors contribute to the increasing incidence of UC. [1][2][3] Extraintestinal manifestations (EIM) may occur in up to 24% of patients with IBD before the onset of intestinal symptoms. EIM most commonly occur in joints, skin, eyes, and other parts, but numerous studies have shown that lung injury caused by IBD should not be ignored.…”

“…9 On the other hand, intestinal microbiota and microbial metabolites are also involved in maintaining immune homeostasis in distal mucosal sites, especially in the lungs. 3,10 We have previously found that intestinal microbial diversity and composition in mice with colitis and concurrent lung inflammation are dramatically different from those in their controls. 9 Short-chain fatty acids (SCFAs), as important microbial metabolites from the microbial fermentation of dietary fiber, are also a major bridge for metabolic and immune signaling within the gut-lung axis.…”