Abstract
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor, angiotensin-converting enzyme 2 (ACE2), transmembrane protease serine 2 (TMPRSS2), and furin, which promote entry of the virus into the host cell, have been identified as determinants of SARS-CoV-2 infection. Dorsal tongue and gingiva, saliva, and tongue coating samples were examined to determine the presence of these molecules in the oral cavity. Immunohistochemical analyses showed that ACE2 was expressed in the stratified squamous epithelium of the dorsal tongue and gingiva. TMPRSS2 was strongly expressed in stratified squamous epithelium in the keratinized surface layer and detected in the saliva and tongue coating samples via Western blot. Furin was localized mainly in the lower layer of stratified squamous epithelium and detected in the saliva but not tongue coating. ACE2, TMPRSS2, and furin mRNA expression was observed in taste bud-derived cultured cells, which was similar to the immunofluorescence observations. These data showed that essential molecules for SARS-CoV-2 infection were abundant in the oral cavity. However, the database analysis showed that saliva also contains many protease inhibitors. Therefore, although the oral cavity may be the entry route for SARS-CoV-2, other factors including protease inhibitors in the saliva that inhibit viral entry should be considered.
Highlights
Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is an emerging infectious disease that has spread worldwide [1]
Hamming et al reported that angiotensin-converting enzyme 2 (ACE2) is localized in the basal layer of non-keratinizing stratified squamous epithelium, but these findings are not described in detail [4]
transmembrane protease serine 2 (TMPRSS2) was strongly expressed in the upper layer of the stratified squamous epithelium. These findings suggest that the tongue coating protease is derived from the stratified squamous epithelium of the dorsal tongue and saliva
Summary
Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is an emerging infectious disease that has spread worldwide [1]. Since SARS-CoV-2 is found in saliva, attempts have been made to use saliva samples in PCR tests for COVID-19, and there has been a great deal of interest in the oral cavity and saliva in associated research [2]. Few basic studies have been conducted on the association between the oral cavity and COVID-19. Xu et al reported the expression of angiotensin-converting enzyme 2 (ACE2) in the oral mucosa, especially the dorsal tongue [3]. ACE2 is a host receptor to which SARS-CoV-2 binds [3]. The expression of ACE2 in the taste buds remains unclear, taste impairment has received particular attention as a symptom of COVID-19 [5]
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