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. 2021 Dec:113:300-307.
doi: 10.1016/j.ijid.2021.09.013. Epub 2021 Sep 10.

Coronavirus disease 2019 and the gut-lung axis

Dan Zhou  1 , Qiu Wang  2 , Hanmin Liu  3
Affiliations

Coronavirus disease 2019 and the gut-lung axis

Dan Zhou et al. Int J Infect Dis. 2021 Dec.

Abstract

Gastrointestinal and respiratory tract diseases often occur together. There are many overlapping pathologies, leading to the concept of the 'gut-lung axis' in which stimulation on one side triggers a response on the other side. This axis appears to be implicated in infections involving severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), which has triggered the global coronavirus disease 2019 (COVID-19) pandemic, in which respiratory symptoms of fever, cough and dyspnoea often occur together with gastrointestinal symptoms such as nausea, vomiting, abdominal pain and diarrhoea. Besides the gut-lung axis, it should be noted that the gut participates in numerous axes which may affect lung function, and consequently the severity of COVID-19, through several pathways. This article focuses on the latest evidence and the mechanisms that drive the operation of the gut-lung axis, and discusses the interaction between the gut-lung axis and its possible involvement in COVID-19 from the perspective of microbiota, microbiota metabolites, microbial dysbiosis, common mucosal immunity and angiotensin-converting enzyme II, raising hypotheses and providing methods to guide future research on this new disease and its treatments.

Keywords: Coronavirus disease 2019; Dysbiosis; Gut–lung axis; Immunity; Microbiota.

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Conflict of interest statement

Declaration of Competing Interest None declared.

Figures

Figure 1
Figure 1
Bidirectional gut–lung axis. The gut microbiota and microbiota metabolites can regulate lung immunity through the lymphatic or circulatory systems, when the composition and diversity of the gut microbiota are changed, termed ‘microbial dysbiosis’. Similarly, the lung microbiota may also affect the gut microbiota through the lymphatic or circulatory systems, and dysbiosis of the intestinal flora can be caused by lung microbial dysbiosis and inflammatory cytokines through the lymphatic or circulatory systems.
Figure 2
Figure 2
The gut–organ axis. The gut microbiota shares a mutually beneficial relationship with its host, where it produces various metabolites that can further signal to remote organs in the body through neural, endocrine, immune, humoral and metabolic pathways, regulating the body's metabolic homeostasis and organ physiology. Complex interactions between the gut microbiota and the different organs result in formation of the ‘gut–organ axis’, such as the gut–lung axis, gut–brain axis, gut–heart axis, gut–liver axis, gut–kidney axis, gut–liver–kidney axis etc. Within these axes, any alterations in gut microbiota composition and diversity may not only trigger gut disorders, but may also influence other organs and cause associated diseases.
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