Angiotensin-converting Enzyme 2 Specific Cell Subset Identification in Oral Tissues: A Need of the Hour in COVID-19 Research.

It is well known that angiotensin-converting enzyme 2 (ACE2) is an important host factor responsible for the attachment of severe acute respiratory syndrome coronavirus clad 2 (SARS-CoV-2). ACE2 has been predominantly reported to be present in lungs and nasal mucosa, which is the most common site for the initiation of COVID-19. Apart from lungs, ACE2 is also expressed in heart, blood vessels, kidneys, brain, intestines, etc. Recently various locations of the oral cavity have been found to be associated with differential expression of ACE2 protein, with the tongue being the most common site. Moreover, the salivary glands have also been regarded as a potential source of SARS-CoV-2 infection due to the presence of the ACE2 receptor. However, till date there is no strong scientific evidence that has proved the existence and interaction of ACE2 protein and spike receptor of SARS-CoV-2 on oral mucosal and salivary gland epithelial cells.