†These authors contributed equally.
Academic Editors: Amedeo Amedei, Edda Russo, Francesca Romano and Alessandra Fanelli
Background: SARS-CoV-2 is a positive-sense single-stranded RNA virus. It is enveloped by four structural proteins. The entry of the virus into the host cells is mediated by spike protein binding to the angiotensin converting enzyme 2 (ACE2) and proteolytic cleavage by transmembrane protease serine 2 (TMPRSS2). In this study, we analyzed the expression of the ACE2 receptor and TMPRSS2 in cases under investigation for SARS-CoV-2 infection. Methods: The study was carried out using the viral transport medium of consecutive nasopharyngeal swabs from 300 people under examination for SARS-CoV-2 infection. All samples underwent the SARS-CoV-2 transcriptase-mediated amplification assay (Procleix® SARS-CoV-2) to detect the virus. Immunocytochemistry was used in each sample to detect the presence of the SARS-CoV-2 nucleoprotein, the ACE2 receptor, and TMPRSS2. Results: An immunocytochemical study with monoclonal antibody against SARS-CoV-2 viral nucleoprotein showed positivity in squamous cells. ACE2 were not detected in the squamous cells obtained from the nasopharyngeal samples. Conclusions: SARS-CoV-2 predominantly localizes to squamous cells in cytology samples of patients with positive transcriptase-mediated amplification SARS-CoV-2 assay results. The immunocytochemical negativity for ACE2 evidenced in the present study could be related to the cellular heterogeneity present in the nasopharyngeal smear samples and could be related to variations at the genomic level. Our results suggest that SARS-CoV-2 might be present in the nasopharyngeal region because viral cell junctions are weaker. This facilitates viral concentration, infective capacity and migration to specific organs, where SARS-CoV-2 infects target cells by binding to their receptors and then entering.