January 26, 2022

if Omicron is less virulent, it is also thanks to our T lymphocytes

12:25 p.m., January 12, 2022, modified at 2:50 p.m., January 12, 2022

The latest worrying variant, Omicron, has spread across the planet at unprecedented speed. And this expansion is not over: experts now claim that 40% of the world’s population will be infected with Covid-19 in the next two months. Chronicle of an announced disaster? This may sound quite surprising, but we do not yet know the exact degree of severity of the symptoms caused by Omicron compared to other variants of concern. This delay is normal.

So far, however, the signs are pretty good.

With the previous variant, Delta, there was a clear link between infection and hospitalization, and then, in some patients, admission to intensive care – even death. It doesn’t seem to be so obvious with Omicron. However, the Director-General of the World Health Organization (WHO), Tedros Ghebreyesus, said on January 6, 2022: “While Omicron seems less serious than Delta, especially in people who have been vaccinated, that does not mean that it should classify it in the category of benign diseases… “

The virus goes less into our lungs, but not only

The question is why it would be less dangerous than the dreaded Delta. Does Omicron, known for his many mutations, have any changes that would make him less aggressive?

There are two aspects to consider. First, Omicron appears to be less capable of infecting lung cells. Rather, it is confined to the upper respiratory tract, just like other coronaviruses that remain in the nose and throat. This is particularly the case with OC43, a coronavirus responsible for colds.

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This is consistent with the milder symptoms already associated with Omicron, which are mainly related to the nose and throat – sniffling and dry cough. It is only when SARS-CoV-2 infects the lungs that a serious form of the disease occurs, with a drastic increase in breathing difficulties. Omicron seems less able to do this (ongoing studies seem to show that this variant also multiplies less well than its predecessors in the lungs when it reaches them, Editor’s note).

And there is a second aspect to be taken into account in explaining the lower proportion of severe illness currently observed. This is because other major players in the immune system besides antibodies, T cells, are able to manage Omicron.

Antibodies and T lymphocytes, the two vigilantes of our immune system

We first worried that Omicron, with all its mutations, could escape our immune system. This is also partly the case for antibodies. The Spike protein, present on the surface of the SARS-CoV-2 virus, is the key target for the latter: they attach themselves to it and block it, thus preventing it from interacting with the cells that the virus is trying to infect. and thus providing protection.

However, in Omicron, the parts of Spike that the antibodies recognize have changed: identifying him less well, they are less able to neutralize the virus.

With this line of defense, however, quantity can trump quality … So while they may not bind to Omicron as effectively as with previous variants, our immune system, especially when it is stimulated ( by vaccination in particular), can produce enough antibodies to do its job. This is one of the reasons why reminders are so important.

T cells attach to the infected cell and kill it

But the very good news comes from the second immune player mentioned above: our T lymphocytes, which can still recognize and eliminate Omicron. The “T” in their name comes from the thymus, an organ located in the upper part of our thorax where this family of “white blood cells” completes its development and maturation.

These lymphocytes work in a different way from antibodies. When one of our cells is infected with a virus, it takes a piece of its Spike protein and displays it on its surface … A bit like waving a red flag to say that it is occupied by the enemy. T cells have sensors that allow them to spot these warning signals. When they locate one, they attach themselves to the infected cell and kill it.

Our immune system can call on its T lymphocytes to destroy infected cells, for example by a virus (recognized by its antigens, the “red flags”, here yellow circles). This prevents the pathogen from multiplying and thus slows down its spread.

(Art of Science/Shutterstock, CC BY-SA)

(When our body is subjected to an unprecedented pathogen, the T lymphocytes participate in the defense by destroying the infected cells recognized by the antigens, the “flags” coming from the virus. In parallel, so-called “memory” T lymphocytes are generated. this pathogen and which will patrol our body. In the event of a second exposure, these memory cells are able to react very quickly and specifically as soon as they cross “their flag”, Editor’s note)

Thanks to T lymphocytes, the virus is slowed down

The method may seem a little extreme, but above all it is extremely effective. Because by killing the infected cell, the virus is also eliminated, which therefore cannot go on to infect new hosts. It’s like a controlled explosion. This process therefore makes it possible to control the virus by preventing it from colonizing and pirating more cells.

Antibodies are the “first line” of our immune system: they prevent the virus from entering our cells. The T lymphocytes are the “second line”: if the virus has managed to infect a cell, the T squadron arrives and kills it, thus stopping the virus in its tracks.

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And in this case, the T cells are still effective against the variant! Indeed, the parts of the Spike taken to be put on the surface of the infected cell – the red flags – have not changed much in Omicron, unlike those recognized by the antibodies.

The T lymphocytes recognizing previous versions of the Spike (via a previous infection or especially vaccines) therefore remain able to do their job well. Several studies have shown that the T lymphocytes generated by the vaccines retained their ability to fight Omicron.

Our immune system has been sculpted over millions of years of evolution. He’s got all kinds of tricks up his sleeve and luckily, at least so far, the T-cell one still holds up against Omicron. And like other parts of the immune system, they can remember each fight fought to be more effective at any subsequent infection … They may well stay in the race against possible future variants. Our T lymphocytes are a reason to be optimistic!

This article is republished from The Conversation under a Creative Commons license. Read the original article in French.

The original version was published in English