Researchers from the Wellcome Trust Sanger Institute (United States) have identified two specific types of cells in the nose as points of probable initial infection for the COVID-19 coronavirus. In their work, published in the journal Nature Medicine, they have found that goblet and cylindrical cells in the nose have high levels of the input proteins that the virus uses to enter cells.
This study also confirms that the cells of the eye and some other organs also contain the viral input proteins. In addition, the study also predicts how a key input protein is regulated with other genes in the immune system and reveals potential targets for developing treatments to reduce transmission.
The virus spreads through respiratory droplets that are produced when an infected person coughs or sneezes. While it is known to use a similar mechanism to infect cells as the one that caused the 2003 SARS epidemic, the exact cell types involved in the nose had not been previously identified.
To discover which cells might be involved in COVID-19 transmission, the researchers analyzed multiple data sets from the Human Cell Atlas consortium of single-cell RNA sequencing of more than 20 different tissues from uninfected people. These included cells from the lung, nasal cavity, eye, intestine, heart, kidney, and liver. The researchers looked at which individual cells both expressed from the two key entry proteins that are used by the COVID-19 virus to infect our cells.
The authors found that the ACE2 receptor protein and the TMPRSS2 protease that can activate SARS-CoV-2 entry are expressed in cells of different organs, including cells of the inner lining of the nose. They then revealed that mucus-producing goblet cells and hair cells in the nose had the highest levels of these two virus proteins, of all the cells in the airways. This makes these cells the most likely initial route of infection for the virus.
Furthermore, the two key entry proteins ACE2 and TMPRSS2 were also found in cells of the cornea of the eye and in the lining of the intestine. This suggests another possible route of infection through the eye and tear ducts, and also revealed a potential for fecal-oral transmission.
Link to the paper: https://doi.org/10.1038/s41591-020-0868-6
Editorial Disclaimer: information published during the 2020 COVID-19 pandemic may be updated frequently to reflect the dynamic nature of current understanding.