SARS-CoV-2-Induced Formation of Single and Heterotypic Syncytial Cells: An Ultrastructural Confirmation

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been associated with the formation of syncytial cells. Coronavirus disease 2019 (COVID-19) disease is linked with various cytopathic effects, including the formation of syncytial cells. Syncytia are multinucleated cells, resulting from the fusion of infected cells, which can contribute to tissue damage and disease severity. This chapter provides ultrastructural evidence of single and heterotypic syncytial cell formation in SARS-CoV-2-infected cells. We discuss the implications of syncytia formation in the pathogenesis of COVID-19 and highlight the importance of ultrastructural analysis in understanding the cytopathic effects of SARS-CoV-2. Through transmission electron microscopy (TEM) and immunofluorescence (IF), this chapter reveals the distinct ultrastructural features of syncytial cells, including multiple nuclei, enlarged cytoplasm, and increased organelle content. The presence of SARS-CoV-2 spike protein on the surface of syncytial cells is confirmed, highlighting its crucial role in viral entry and fusion. Furthermore, this chapter also discusses the implications of syncytia formation for COVID-19 pathogenesis, including enhanced viral replication and transmission, as well as altered immune response and cytokine production. By elucidating the mechanisms of syncytia formation, this chapter provides valuable insights into the cytopathic effects of SARS-CoV-2 and informs the development of effective therapeutic strategies for COVID-19.