SARS-CoV-2 variants: “Our T cells are reason for optimism! »

The latest worrying variant, Omicron, spread across the planet at a speed unprecedented. And this expansion is not over: experts now claim that 40% of the world’s population will be infected within the next two months. Chronicle of a predicted disaster ? This may seem quite surprising, but we do not yet know exactly the degree of gravity from 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 varying, 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: If Omicron seems less severe than Delta, especially in vaccinated people, this does not mean that it should be classified as a mild disease.… »

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

There are two aspects to consider. First, Omicron seems less capable ofinfect lung cells. Rather, it is confined to upper respiratory tract, like other coronavirus which remain in the nose and throat. This is particularly the case of theOC43, a coronavirus responsible for colds.

This is consistent with the milder symptoms already associated with Omicron, which are mainly nose and throat related – sniffles and a dry cough. It is only when the SARS-CoV-2 infect the lungs that a serious form of the disease declares itself, with a drastic increase in breathing difficulties. Omicron seems less able to do this [des études en cours semble montrer que ce variant se multiplie également moins bien que ses prédécesseurs dans les poumons lorsqu’il les atteint, ndlr].

And there is a second aspect to take into account to explain the currently observed lower proportion of serious illness. It is about the fact that other major players in the immune system that antibody, the lymphocytes T, are able to handle Omicron.

The two guards of our immune system

We were initially concerned that Omicron, with all its mutations, could escape our immune system. It is moreover in part the case for antibodies. The protein Spike, present on the surface of the virus SARS-CoV-2, is the key target for the latter: they cling to it and block it, thus preventing it from interacting with the cells that the virus tries to infect and thus ensuring protection. However, at Omicron, the parts of Spike that the antibodies recognize have changed: identifying it less well, they are less able to neutralize the virus.

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

But the really good news comes from the second immune player mentioned above: our T cells, who can still recognize and eliminate Omicron. The “T” in their name comes from 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 by 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 allowing them to identify these warning signs. When they locate one, they attach to the infected cell and kill it.

[Lorsque notre corps est soumis à un pathogène inédit, les lymphocytes T participent à la défense en détruisant les cellules infectées reconnues grâce aux antigènes, les « drapeaux » venant du virus. En parallèle sont générés des lymphocytes T dits « mémoire », spécifiques à ce pathogène et qui vont patrouiller dans notre corps. En cas de seconde exposition, ces cellules mémoires sont capables de réagir très rapidement et spécifiquement dès qu’elles recroisent « leur drapeau », ndlr].

Like a controlled explosion

The method may seem a little extreme, but it is above all extremely effective. Because by killing the infected cell, the virus is also eliminated, which therefore cannot 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 ever 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 succeeded in infecting a cell, the T squadron arrives and kills it, thus stopping the virus in its tracks. momentum.

And in this case, 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 at Omicron, unlike those recognized by the antibodies.

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

Our immune system has been sculpted over millions of years of evolution. It has all sorts of tricks up its sleeve and fortunately, at least so far, the T cell one is still resistant to Omicron. And like other elements of the immune system, they can remember each fight they fight to be more effective against any subsequent infection… They could therefore well stay in the race against possible future variants. Our T cells are cause for optimism!