**Author details**

*Some RNA Viruses*

this review [72].

**7. Final marks**

pathologies.

**Acknowledgements**

**Conflict of interest**

implicated in lung inflammation [80].

array of metabolites drives the crosstalk between the host and its microbiome. The three currently most studied categories of metabolites involved in host-microbiota interactions are short-chain fatty acids produced by bacteria from the fermentation of fibbers, bile acids produced in the liver and transformed by the gut microbiota before re-affecting the host, and tryptophan metabolites, which are the topic of

Tryptophan is an essential aromatic amino acid composed of a b carbon connected to the 3 position of an indole group and it is a biosynthetic precursor of a large number of microbial and host metabolites [78]. It's metabolism follows three major pathways in the gastrointestinal tract: the direct transformation of Tryptophan into several molecules, including ligands of the (AhR) by the gut microbiota [78]; the kynurenine pathway in both immune and epithelial cells via IDO-1 [79]; and the serotonin (5-hydroxytryptamine [5-HT]) production pathway in enterochromaffin cells via Tryptophan hydroxylase 1 (TpH1) [72]. The AhR is

The gut microbiota influences the health of the host, especially with regard to gut immune homeostasis and the intestinal immune response. In addition to serving as a nutrient enhancer, L-tryptophan plays crucial roles in the balance between

These lessons derived of SARS-CoVs infections outbreaks (2003 and 2019) can explain the role of the two antagonistic RASs pathways on the hypoxic pulmonary vasoconstriction an homeostatic mechanism in response to alveolar hypoxia secondary to acute lung injury in SARS, optimizing ventilation, perfusion and systemic oxygen delivery. Moreover, the new knowledge about the role of RAS proteins, namely, ACE-2 in gut with pleiotropic actions on the metabolism of tryptophan in the crosstalk microbiota–intestine, intestine-kidney and probably intestine-lung can help in designing new, based on probiotics and prebiotics or repurposing ancient therapies for disorders involving those organ crosstalk resultant physio

The authors would like to acknowledge the Instituto de Investigação Científica Bento da Rocha Cabral and Sociedade Portuguesa de Papillomavírus for support.

The authors declare that they have no competing interests.

intestinal immune tolerance and gut microbiota maintenance.

**46**

Andreia Matos1,2,3,4\*, Alda Pereira da Silva5,6, Joana Ferreira1,2, Ana Carolina Santos1,2, Maria Clara Bicho7,8 and Manuel Bicho1,2

1 Genetics Laboratory and ISAMB - Environmental Health Institute - Ecogenetics and Human Health Unit, Faculty of Medicine of University of Lisbon, Av. Prof. Egas Moniz, Piso 1C, 1649-028 Lisboa, Portugal

2 Instituto de Investigação Científica Bento da Rocha Cabral, Lisbon, Calçada Bento da Rocha Cabral, n°14, 1250-047, Portugal

3 Tumor and Microenvironment Interactions Group, i3S - Instituto de Investigação e Inovação em Saúde/INEB-Institute of Biomedical Engineering, University of Porto, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal

4 Abel Salazar Institute for the Biomedical Sciences (ICBAS), University of Porto, Rua de Jorge Viterbo Ferreira No. 228, 4050-313 Porto, Portugal

5 ISAMB - Environmental Health Institute - Ecogenetics and Human Health Unit, University Clinic of General and Family Medicine, Institute for Preventive Medicine and Public Health, Faculty of Medicine, University of Lisbon, Av. Professor Egas Moniz, Piso 1C 1649-028, Lisboa, Portugal

6 CBIOS - Biosciences Research Center, School of Health Sciences and Technologies, Universidade Lusófona, Campo Grande 376,1649-024, Lisboa, Portugal

7 Institute of Preventive Medicine and Public Health and Genetics Laboratory and ISAMB - Environmental Health Institute of University of Lisbon Faculty of Medicine; Av. Prof. Egas Moniz, Piso 1C, 1649-028, Lisboa, Portugal

8 Dermatology Research Unit, Instituto de Medicina Molecular, Av. Prof. Egas Moniz, 1649-028 Lisboa, Portugal

\*Address all correspondence to: andreiamatos@medicina.ulisboa.pt

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
