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How the body’s immune system tries to fight COVID-19

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Vaccines have been shown to be the best defense against severe cases of COVID-19.According to the US Centers for Disease Control and Prevention, about unvaccinated adults 13 times more likely As of late November, I will be hospitalized for this disease more than vaccinated adults.

However, vaccines and the antibodies they produce are only part of the puzzle when it comes to fighting the coronavirus. The immune system has other defenses that find and kill infected cells and keep a living record of viruses, bacteria, or other infectious pathogens. This will allow your body to react faster the next time it is attacked.

And he said speed is essential E. John Welly, Director, Institute of Immunology, University of Pennsylvania.

“During infection, it’s a race,” he explained, urging the immune system to stop the virus before it has grown to levels that are debilitating. This is especially true for Omicron variants. At a great rate.

Here’s a breakdown of how the body’s immune system worked and how it was tested by Omicron.

B cells, T cells, NK and DC

Think of the immune system as having three layers of defense. It keeps hostile molecules, or pathogens, on the outside and tries to look inside. Its work is done by the skin, the body’s largest organ, whose cells defeat invaders and warn that the rest of the immune system is having problems.

The second layer attempts to stop the attacker after it has entered the body and before it infects the cells. This is where the bone marrow comes in. “Natural killer” Or NK cells and B cells (cells that produce antibodies). Both are types of white blood cells or lymphocytes.

Colored electron micrographs of natural killer cells.

The tonsils, lymph nodes, and spleen have “natural killer” or NK cells that are ready to fight the attacker.

(National Institute of Infectious Diseases)

NK was named because it was not created for an attacker. They already exist and are ready to kill cells that do not belong to the body, such as tumor cells. NK is scientifically part of the innate immune system.according to Rockefeller University Researcher, NK hangs in the tonsils, lymph nodes, and spleen and rushes to confront the attacker.

Antibodies, on the other hand, are produced after the attacker is discovered and become part of what scientists call the adaptive immune system. They attach to certain pathogens and are swallowed and destroyed by other members of the immune system.

In the case of SARS-CoV-2, the coronavirus that causes COVID-19, different antibodies bind to different parts of the virus, such as the spike protein that the virus uses to enter healthy cells and replicate multiple times. increase. If the peplomer is aggregated by an antibody, the virus cannot infect cells.

Virologist Trudy U. Rey says that if a new vaccination or booster is given, it may be ready to attack so many antibodies that it will not be infected. Science communicator. This is called “sterile immunity”, but in the case of COVID-19 it is only temporary. However, that is not the goal of COVID-19 vaccination. (This will be explained in detail later.)

A more common scenario is that some of the invading coronavirus passes through the antibody.There are several in the cell Congenital defense It can defeat the intruder, but SARS-CoV-2 shows that it can avoid the intruder by itself. Fortunately, there is a third line of defense: T cells.

A color image of T cells as seen with a scanning electron microscope.

T cells in the upper thymus can detect pathogens after they have invaded cells where antibodies cannot be detected.

(National Institute of Infectious Diseases)

Like B cells and NK cells, T cells are white blood cells derived from the bone marrow, Develops in the thymus and emanates from the thymus At the top of the chest. Their special power is the ability to detect viruses and other bacteria after entering cells that are hidden from antibodies.

T cells have two basic flavors: killer and messenger. The lethal version detects cells infected with the virus and kills them (by releasing a toxic version of the granules called cytokines), blocking the replication of the virus. Welly called this “destroying the village to save the country.” Messenger alerts B cells to new threats and responds by creating antibodies designed to respond to those threats.

This is a complex molecular dance with many other important parts of the immune system, such as dendritic cells and DCs that act as sentinels and courier services. In particular, DC tells T cells which specific threats they are hunting down and killing.

When the infection is overcome, the immune system spontaneously weakens, excreting some antibodies and T cells. However, some T cells survive as memory T cells and are ready to respond by killing infected cells and stimulating the production of new antibodies when the same attacker returns. In addition, some B cells remain as memory cells for processing antibody production.

How the vaccine stimulates the pump

Daniela Weiskov, Immunology scientists at the La Jolla Institute for Immunology have stated that the body’s adaptive immune system is highly specific. “Otherwise, you’ll always be inflamed,” she said, which is a good thing. However, it also means that what the antibody and T cells can bind to or recognize is limited. They need to learn the enemy before they can defend it.

The pharmacist prepares the syringe with the Pfizer-BioNTech COVID-19 vaccine.

Vaccines help create antibodies and memory T cells that recognize viruses and infected cells, allowing the immune system to react more quickly. Booster shots enhance this process.

(Gary Coronado / Los Angeles Times)

Vaccination “is nothing more than training the immune system without getting sick,” Weiskopf said. The COVID-19 vaccine produces antibodies that recognize the SARS-CoV-2 spike protein and other properties. Memory T cell It can recognize cells infected with a virus.

“The more often the immune system sees the threat, the more detailed it reacts,” Weiskov said. It’s also faster — she said that if the system had these memory cells, it could react “much, much, much faster” the next time the same pathogen knocks. therefore, The value of booster shots.

When a virus mutates, the area to which the antibody attaches may change. If they change too much, the antibodies will bind to them and are not very good at preventing them from entering the cells.Or It seems to be the case of the Omicron variant, There are multiple mutations that affect peplomer.

However, the Omicron mutation did not soften the response of memory T cells, Weiskov, Ray, and Welly said. This is because the mutation has little effect on the part of the virus that T cells recognize.

Beyond that, Weiskopf said that each person has several different T cells, and their T cells are different from others. She said that due to rare misfortune, many effective T cells would be encountered in the rest of the population, even if the new variant could dodge all memory T cells.

Ray added that much of the talk about “weakened immunity” is based on the diminished presence of what is known as a neutralizing antibody that can block the virus from adhering to and replicating cells. However, other types of antibodies remain in the system.

“Some studies have even shown that just because an antibody doesn’t neutralize doesn’t mean it can’t do anything,” Ray said. For example, she said, just binding to some of the peplomers could encourage other immune cells to participate in the fight.

COVID-19 and unvaccinated

If you have never been exposed to the SARS-CoV-2 or COVID-19 vaccine, the coronavirus will not encounter customized antibodies or T cells on its way to the respiratory system. Welly said it takes a week to 10 days to convert undifferentiated T cells into killer and place them to confront infected cells, even if the immune system is healthy. During that time, the virus replicates exponentially and spreads throughout the body.

However, if immunized, killer T cells can be prepared within four days, Wheely said. That lucrative start makes a big difference in preventing the infection from getting out of control.

Nonetheless, unvaccinated people may have some T cells that are ready to defend against the first signs of infection, Weiskopf said.Researchers have found several T cells that respond to SARS-CoV-2 in samples taken from Those who have never been exposed to the virus, She said. She said these cells were created in response to a common cold that could be caused by other types of coronavirus and helped accelerate and enhance the immune response.

Not everyone who catches a cold has T cells with this kind of diversity, she added. However, this finding suggests to some researchers that scientists may be able to devise vaccines that can attack coronavirus variants by encouraging the immune system to make T cells like these. I am. (The Times owner, Dr. Patrick Soon-Shiong, has another company exploring this possibility.)

In any case, the more the virus replicates in the body, the greater the response from killer T cells. It raises a second issue, Wheely said: T cells cannot continue to kill tissue forever. At some point, the system needs to go into repair mode. Therefore, he said, there are regulatory T cells that “act as a counterweight for the entire system” and help suppress killer cells.

However, the system may not immediately throw the “off” switch. According to Welly, in some seriously ill COVID-19 patients, the virus has spread to many parts of the body and a huge number of killer T cells flood the system with “very harmful” cytokines. That is. Clinicians are helping these patients by suppressing the immune system and suppressing this response, he said.

If they recover from COVID-19, unvaccinated people have antibodies and memory cells that help protect them from their next encounter with SARS-CoV-2. However, Ray said that a person’s immune response after vaccination is far superior to the “innate immunity” provided by the infection. She said the reinfection rate for unvaccinated people with only innate immunity is twice that of vaccinated people.

Immunological age

During the pandemic process, older people tend to be affected by COVID-19, which is much more serious than children. There seem to be at least several reasons for that.

Ray study This study, led by researchers at Charité-Universitäts medizin Berlin, has certain innate protections in the nasal passages of children that may help destroy the virus before it replicates violently.

“This type of innate immune response seems to be delayed in the elderly and can cause excessive inflammation and ultimately more serious damage to’catch up’,” she writes. I have. Blog post.

According to Welly, the immune system, like other parts of the body, is susceptible to aging.

“One of the important things is to lose the production of these new, so-called” naive “T cells,” he said. These act as blank slate and are ready to learn new threats. In his later years, Welly said, “They will be much smaller parts of the cells that you can put into action.”

As we grow older, he said, problems also appear in other elements of the immune system. Overall, these problems “make it harder for the immune system to get out of the gate,” he said.

Sources

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2/ https://www.latimes.com/science/story/2022-01-19/how-the-bodys-immune-system-tries-to-fight-off-covid-19

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