Explained: Where does the COVID-19 virus attack first? Study Identifies Two Types of Cells in the Nose

Like all coronaviruses, SARS-CoV2 consists of a fat envelope with a “spike protein” on the surface. The spike acts as the “key” to “unlock” a protein in the human cell, called ACE2, that acts as the receptor for the virus. (File photo)

LAST WEEK, scientists reported that they have identified two specific types of cells in the nose as the likely initial infection points for SARS-CoV2, the new coronavirus that causes COVID-19 (briefly reported in The Indian ExpressApril 25th). A look at how this adds to emerging knowledge about the new virus:

The mechanism of infection was not known?

Yes, previous studies have shown what happens at the cellular level. The virus is entered through a “lock and key” effect. Like all coronaviruses, SARS-CoV2 consists of a fat envelope with a “spike protein” on the surface. The spike acts as the “key” to “unlock” a protein in the human cell, called ACE2, that acts as the receptor for the virus. Once inside the cell, the virus uses a second protein, called TMPRSS2, to complete its entry. TMPRSS2 has protein division capabilities, which allow the virus to reproduce and transmit within the cell.

So what has the new study found?

The new study has identified the specific cells where the entry mechanism likely comes into play when the virus begins to attack. These are goblet and hair cells in the nose, researchers from the Wellcome Sanger Institute (UK), the University Medical Center in Groningen, the University of the Cote d’Azur and the CNRS reported, according to Nice and colleagues in the journal Nature Medicine.

Goblet cells are mucus-producing cells on the surface of the organs, and are found along the respiratory tract, along the intestinal tract, on the upper eyelid, etc. Hair cells are hair-like cells, occurring again on the surface of various organs, and helping to sweep away mucus, dust, etc. to the throat, where it can be swallowed.

How did the study identify these cells as the likely points of initial infection?

The researchers looked for areas where the two key proteins, ACE2 and TMPRSS2, are most prominently expressed. For this, they turned to the Human Cell Atlas, an international consortium that aims to create comprehensive reference maps of all human cells. They looked at multiple data sets of more than 20 different tissues from uninfected people. These included cells from the lung, nasal cavity, eye, intestine, heart, kidney, and liver.

And what did the data show?

Both proteins were found in multiple organs. However, ACE2 expression was generally low, while TMPRSS2 was highly expressed with a wider distribution. This suggests that ACE2, rather than TMPRSS2, may be a limiting factor for viral entry at the initial stage of infection, the researchers wrote in the document.

“We found that … ACE2 and TMPRSS2 … are expressed in cells in different organs, including cells in the inner lining of the nose. We then revealed that mucus-producing goblet cells and hair cells in the nose had the highest levels of both COVID-19 virus proteins, of all cells in the airways. This makes these cells the most likely initial route of infection for the virus, “first author Dr. Waradon Sungnak of the Wellcome Sanger Institute said in a statement released by the institute.

Does this rule out other entry points?

The two input proteins were also found in the cells of the cornea of ​​the eye and in the lining of the intestine. The researchers said this suggests another possible route of infection through the ocular and tear ducts, and possible oral-fecal transmission. However, they note that:

* * The two types of cells in the nose, where proteins were expressed at the highest levels, are located in a place that is highly accessible to the virus.

* * The study also found that the production of ACE2 in nasal cells is likely activated at the same time as several immune genes that would be activated when cells fight infection.

* * The virus is believed to be transmitted through respiratory drops produced when an infected person coughs or sneezes.

The virus is believed to be transmitted through respiratory drops produced when an infected person coughs or sneezes. (Express photo / Amit Mehra)

How does knowledge help?

This is the first time that these two cell types have been identified as the probable initial entry points. The researchers believe that their identification could help explain the high transmission rate of COVID-19.

“This information can be used to better understand how the coronavirus spreads. Knowing which exact cell types are important for virus transmission also provides a basis for developing potential treatments to reduce the spread of the virus, “said Dr. Sarah Teichmann, lead author of the Wellcome Sanger Institute and co-chair of the Organizing Committee for the Cell. Human Atlas.

📣 The Indian Express is now on Telegram. Click here to join our channel (@indianexpress) and stay updated with the latest headlines

For the latest news explained, download the Indian Express app.