Impact of SARS-CoV-2 in the Ultrastructure of Non-Keratinized Oral Epithelium

The oropharyngeal cavity serves as a primary site for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission and infection. The non-keratinized epithelium lining of the buccal mucosa and ventral surface of the tongue facilitates critical functions, including barrier protection, secretion, and sensory perception. However, exposure to SARS-CoV-2 initiates a cascade of cellular and molecular responses, leading to ultrastructural modifications that compromise the functionality of oral epithelial cells. Advanced imaging modalities, such as immunofluorescence (IF), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been instrumental in elucidating the viral load, infectivity, localization, ultrastructural alterations, and pathogenesis within infected non-keratinized epithelial cells. SARS-CoV-2 predominantly targets the stratum intermedium, stratum spinosum, and the innermost stratum basale, as confirmed by IF signals generated from the interaction of primary and secondary antibodies with the viral spike (S) protein. Electron micrographs further reveal electron-dense, SARS-CoV-2-like particles both intra-cellularly and extracellularly. No evidence of SARS-CoV-2 infection has been observed in the outermost stratum superficiale, as confirmed by IF, SEM, and TEM analyses. These infected cells exhibit distinct ultrastructural changes, including the loss of surface microvilli, disrupted keratin filaments, mitochondrial shrinkage, nuclear degradation, and the presence of SARS-CoV-2 within double-membrane vesicles, suggesting active viral replication. This chapter explores the mechanisms by which SARS-CoV-2 affects oral health, focusing on cellular responses and ultrastructural modifications in the non-keratinized oral epithelium. A comprehensive understanding of these processes may provide valuable insights into disease progression and inform potential therapeutic interventions for managing coronavirus disease 2019 (COVID-19)-related oral complications. The diagram illustrates SARS-CoV-2 infection diagnosis. It details sample collection, histology, and microscopy techniques for viral localization and morphological changes in infected cells, indicating infection levels from no infection to least infected. https://www.w3.org/1999/xlink" content-type="colour" xlink:href=" https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003748908/550bc977-6f4b-4545-82bf-2735acee8d94/content/fig5_178_1_C.jpg "/>