Ultrastructural analysis of nasopharyngeal epithelial cells from patients with SARS-CoV-2 infection

Abstract

The nasal epithelium is an initial site for SARS-CoV-2 infection, responsible for the ongoing COVID-19 pandemic. However, the pathogenicity and morphological impact of SARS-CoV-2 on the nasopharynx cells from symptomatic patients with different viral loads remain poorly understood. Here, we investigated the ultrastructure of nasal cells obtained from individuals at distinct disease days and with high and low SARS-CoV-2 loads. Squamous and ciliated cells were the main cells observed in SARS-CoV-2 negative samples. We identified virus-like particles (VLPs) and replication organelles (RO)-like structures in the squamous cells from high viral load samples after 3- and 4-days of symptoms. Ultrastructural changes were found in those cells, such as the loss of microvilli and primary cilium, the increase of multivesicular bodies and autophagosomes, and signs of cell death. No ciliated cells were found in those samples. Squamous cells from low viral load sample after 5 days of symptoms showed few microvilli and no primary cilium. VLPs and RO-like structures were found in the ciliated cells only. No ultrastructural alterations were seen in the cells from low viral load individuals after 10- and 14-days of symptoms. Our results shed light on the ultrastructural effects of SARS-CoV-2 infection on the human nasopharyngeal cells.