Morphological Analysis of Angiotensin-Converting Enzyme 2 Expression in the Salivary Glands and Associated Tissues

We evaluated localization of angiotensin-converting enzyme 2 (ACE2), the receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), in the salivary and associated tissues using immunohistochemistry. Fifty paraffin-embedded blocks from 48 anonymized patients, biopsied or operated on for diseases of the oral and maxillofacial region before 2010, were analyzed. ACE2-expressing cells were observed in the parotid, sublingual and the buccal glands, the conduits, the acinar regions of the serous glands, and sparsely in the mucous glands. Scattered ACE2-positive endothelial cells were also observed in nearby capillaries nourishing the salivary glands, as well as in the juxta-epithelial capillaries of the oral mucosa. ACE-2-positive adipocytes were scattered within the stroma of the parotid gland. These observations suggest the possibility that SARS-CoV-2 may travel through the bloodstream to the capillaries that nourish the salivary glands and oral mucosa, and inducing vasculitis and damage of oral tissues. SARS-CoV-2 infection of salivary glands through the bloodstream implies the main cause of salivary contamination. Similarly, ascending infection from oral fluid to the salivary gland conduit has been shown to be another possible mute. Moreover, infection of ACE2-positive parotid adipocytes may lead to parotid glands inflammation and contribute to systemic progression of coronavirus disease 2019.