Ultrastructural study confirms the formation of single and heterotypic syncytial cells in bronchoalveolar fluids of COVID-19 patients

Abstract

Background SARS-CoV-2 was reported to induce cell fusions to form multinuclear syncytia that might facilitate viral replication, dissemination, immune evasion, and inflammatory responses. In this study, we have reported the types of cells involved in syncytia formation at different stages of COVID-19 disease through electron microscopy. Methods Bronchoalveolar fluids from the mild (n = 8, 2–8 days), moderate (n = 8, 9–16 days), and severe (n = 8, after 17th days) COVID-19 patients were examined by PAP (cell type identification), immunofluorescence (for the level of viral infection), scanning (SEM), and transmission (TEM) electron microscopy to identify the syncytia. Results Immunofluorescence studies (S protein-specific antibodies) from each syncytium cell indicate a very high infection level. We could not find any syncytial cells in mildly infected patients. However, identical (neutrophils or type 2 pneumocytes) and heterotypic (neutrophils-monocytes) plasma membrane initial fusion (indicating initiation of fusion) was observed under TEM in moderately infected patients. Fully matured large-size (20–100µm) syncytial cells were found in severe ARDS patients of neutrophils, monocytes, and macrophage origin under SEM. Conclusions This ultrastructural study on the syncytial cells from COVID-19 patients sheds light on the disease's stages and types of cells involved in the syncytia formations. Syncytia formation was first induced in type II pneumocytes by homotypic fusion and later with haematopoetic cells (monocyte and neutrophils) by heterotypic fusion in the moderate stage (9–16 days) of the disease. Matured syncytia were reported in the late phase of the disease and formed large giant cells of 40 to 100 µm.

A Nanobody Interaction with SARS-CoV-2 Spike Allows the Versatile Targeting of Lentivirus Vectors

“…Our results are consistent with observations that SARS-CoV-2-infected cells form syncytia, indicative of activated Spike proteins on infected cell surfaces (11)(12)(13)(14)(15)(16)(17)(18). Our results also demonstrate that perturbations of host cell functions by SARS-CoV-2 infection are not sufficient to prevent lentivirus vector delivery and expression (19)(20)(21).…”

“…Another implication of our results is that it should be possible to target Spike with lentiviruses decorated with Spike-binding hACE2 fragments (24)(25). We also believe that specific lentivirus delivery will not be limited to SARS-CoV-2-infected Vero E6 cells because of reports that SARS-CoV-2 infections result in syncytia formation in other cell types, and in vivo: such observations are indicative of fusion-competent Spike proteins on the surfaces of infected cells (11)(12)(13)(14)(15)(16)(17)(18). Another consideration is that our results are likely not limited to lentiviral delivery vectors.…”

Age-specific nasal epithelial responses to SARS-CoV-2 infection

“…Such functional changes facilitate disease progression and potentially enhance viral spread 45,46 . Ultrastructural and immunofluorescence studies confirm significant SARS-CoV-2 infection in shed cells in severe COVID-19 cases 47 . Elevated vimentin levels, an EMT and basaloid cell marker, are also present in these cultures.…”