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Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the causative agent of the 2019 Coronavirus Disease (COVID-19) pandemic, enters host cells through contact between the projected droplets and the cells of the nose, oral cavity or eyes. The infectivity of SARS-CoV-2 depends on the ability of the virus to enter host cells.
The virus binds to the host cell’s receptor, the angiotensin-converting enzyme 2 (ACE2), which is abundantly expressed in the epithelial tissue that lines the airways; it is in this sense that SARS-CoV-2 is primarily considered to be a respiratory virus. The ACE2 receptor interacts with the viral spike protein, thereby facilitating entry into cells.
Study: Oral mucosa could be an infectious target of SARS-CoV-2. Image Credit: wavebreakmedia / Shutterstock
COVID-19 is associated with several clinical conditions, such as dysosmia and dysgeusia. Dysgeusia can result from the effect of SARS-CoV-2 on the taste buds of the tongue. A previous study suggested that the distribution of the SARS-CoV-2 virus in the oral cavity was thought to be in the saliva. Yet recent research has shown an even distribution of the virus in the gum line.
A recent study suggested that ACE2 receptors are expressed in oral tissues, making the oral cavity a potential important entry point for SARS-CoV-2 into the respiratory and gastrointestinal tract. Thus, a recent study published in the journal Health care reports for the first time the expression of ACE2 receptors in human oral tissue which includes the gum, tongue and palate.
About the study
The current study involved twenty volunteers with a median age of 36, with an equal number of males and females. The medical histories of all volunteers, as well as the history of smoking and alcohol consumption, were recorded.
The expression of ACE2 at various sites in the oral cavity was assessed by performing liquid cytology, which has advantages over liquid cytology as there are fewer contaminants and fewer artifacts. air dried. The cells were taken from the tongue, palate and gum line of each participant and subjected to liquid cytology.
Study results
The results of the current study indicate that in terms of site-specific cytology, the median number of cells taken from the tongue was 2129.0. Among these cells, the median number of cells positive for the ACE2 receptor was 478.0 and the median proportion positive for the ACE-2 receptor was 18.2.
The median number of cells in the palate was 2597.5, of which the median number of ACE2 receptor positive cells was 44.5, and the median proportion of ACE2 receptors was 2.0. The median number of cells in the gingiva was 7,923.5, of which the median number of cells positive for the ACE2 receptor was 1323.4, the proportion positive for the ACE2 receptor being 14.6.
ACE2 expression values were tongue, 18.2%, gingiva, 14.6%, and palate, 2.0%. Thus, the results of the study showed that the expression of ACE2 was highest in the tongue, followed by the gum and palate. The proportion of ACE2 was much higher in the gingiva and tongue than in the palate.
Contextual factors in volunteers such as gender, alcohol consumption, and smoking were not associated with the distribution of ACE2 in the tongue, palate, or gum tissue.
Ultimately, the results indicate that the inflammatory gingival sulcus is a novel route of excretion for SARS-CoV-2. Binding of SARS-CoV-2 to ACE2 receptors can be avoided by special periodontal treatment by dental professionals aimed at decreasing the distribution of ACE2 in the cells of the gingival sulcus.
Conclusion
The present study indicates that the gingival sulcus may be a new entry point for the SARS-CoV-2 virus due to the high expression of ACE2 receptors. However, the expression of ACE2 in the human oral cavity and their difference in distribution between different ethnicities have yet to be evaluated.
The use of liquid cytology in the study is advantageous because it is a useful and non-invasive method that can help to assess important clinical topics.
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