Background: The 2019 novel coronavirus (2019-nCoV) has affected more than 72,000 people worldwide and caused more than 1,800 deaths so far. 2019-nCoV uses the angiotensinconverting enzyme 2 (ACE2) as the cell receptor to invade the human host and primarily causes pneumonia. Thus, ACE2 is the key to understanding the mechanism of 2019-nCoV infection.
Methods: We compared ACE2 expression levels across 31 human normal tissues, between males and females, and between younger (ages <= 49 years) and older (ages > 49 years) persons in these tissues. We also investigated the correlations between ACE2 expression and immune signatures in various tissues.
Results: ACE2 expression levels were the highest in small intestine, testis, kidney, heart, thyroid, and adipose tissue, and were the lowest in blood, spleen, bone marrow, brain, blood vessel, and muscle. In lungs, colon, liver, bladder, and adrenal gland, ACE2 showed the medium expression levels. ACE2 was not differentially expressed between males and females and between younger and older persons in any tissue. In skin, digestive system, brain, and blood vessel, ACE2 expression levels were positively associated with immune signatures in both males and females. In thyroid and lungs, ACE2 expression levels were positively and negatively associated with immune signatures in males and females, respectively.
Conclusions: Our data provide potential cues for the 2019-nCoV epidemic may infect other tissues outside lungs, affect males and females and young and old persons equally, and old age and male are associated with higher mortality risk for 2019-nCoV infection.