COVID-19: Why aren’t antibodies the only defense against omicron?

In the fight against the COVID-19 coronavirus, a key component of the immune system garnered attention: antibodies.

These Y-shaped proteins have made headlines recently because COVID vaccines don’t make enough of them to fight the omicron variant of the coronavirus, unless something is introduced to stimulate them.

Trained by both vaccines and infection, the antibodies adhere to the spike protein, which gets into the coronavirus, preventing it from penetrating cells and making the host sick.

However, antibodies are not the only variable at play.

In fact, “there is a complex and coordinated response that is really beautiful from an evolutionary point of view,” explains Roger Shapiro, an immunologist at Harvard.

Here are some key points:

“Bombers” of the innate immune system

In the minutes and hours after the virus appears in the body, proteins send out alarms to recruit the tough but weak defense team of the “innate” immune system.

The first to appear are the “neutrophils”, which make up between 50% and 70% of all white blood cells, which are quick to fight, but also to die.

There are also “macrophages”, specialized in detecting and eliminating pathogens, releasing key molecules that activate more intelligent colleagues, the so-called “natural killer” cells or “dendritic” cells, which transmit information to elite fighting cells.

“It’s like bombarding the entire area and hopefully damaging the invader as much as possible and at the same time calling in the base so that their SEAL units are ready to operate,” explains John Wherry, an immunologist at the University of Pennsylvania.

B and T cells: intelligence agents and trained assassins

If the “innate” defense does not drive away invaders, the “adaptive” immune system enters the picture.

Within a few days of the first infection, the “B cells” realize the threat and begin to produce antibodies.

Vaccination also trains B cells, primarily within the lymph nodes in our armpits, near the injection site, to be vigilant and ready.

Shapiro compared them to intelligence agents, who have vital information about the threats.

The most powerful types of antibodies, known as “neutralizers,” are like chewing gum that sticks to the end of a key, preventing you from opening the lock.

There are other less famous antibodies that are not as sticky as the “neutralizers”, but that still help to catch the virus, dragging it towards immune cells or asking for help and increasing the general response.

The key partners of B cells are “T cells”, which can be divided into “helpers” and “killers.”

“The killers attack the cells that were infected,” Shapiro said, but they also cause collateral damage.

Helper T cells “are like generals,” Shapiro added: they enlist troops, stimulate B cells to increase production, and direct their lethal counterparts toward the enemy.

Stop a serious illness

Due to the important mutation of its spike protein, the omicron variant can slip away more easily by neutralizing the antibodies contributed by a previous infection or vaccination.

The bad news is that this makes people more prone to symptomatic infections.

But the good news is that T cells are not so easy to fool, as they have a “periscope” in infected cells, where they can look for constituent parts of the virus during its replication cycle, Wherry said.

They are much better at recognizing the signs of enemies they have already encountered, even if they disguise themselves to overcome the antibodies.

Killer T cells carry out search and destroy missions, piercing infected cells, opening them and triggering reactions so that inflammatory proteins known as “cytokines” join the fight.

Depending on the speed of response, a vaccinated person who becomes infected may have mild, cold-like, or moderate flu-like symptoms, but the chances of severe illness are drastically reduced.

None of this detracts from the application of boosters, since they trigger the production of all kinds of antibodies and also seem to train B and T cells even more.

“Ómicron is worrying, but the glass is still half full; It’s not going to totally evade our response, ”Wherry considered.