Why is the immune system so forgetful?

measles appears to be more harmful than scientists once suspected.
virus is one of the most contagious human pathogens and is inherently dangerous, sometimes causing fatal complications such as pneumonia and encephalitis.
now, the effects of measles extend further - it can make the immune system suffer from amnesia.
researchers analyzed the blood of children infected with measles and unvaccinated before and after the measles outbreak in the Netherlands, and found that the virus erased the body's memory of previous pathogens. The papers were published recently in Science-Immunology and Science.
two studies reveal how the infection damages the immune system months or years later, causing the body to "forget" past antibodies to other pathogens.
these antibodies, children lose most of their immune defenses and become vulnerable to the viruses they have encountered and defeated," he said. "We've found strong evidence that the measles virus is actually destroying the immune system," said Stephen Elledge, a researcher at the Howard Hughes Institute of Medicine in the United States. It
the extent to which this "immune amnesia" increases the risk of infection death. But infectious disease experts say the findings are a good reason to immunized children against the virus. Measles cases are on the rise due to inadequate vaccinations and misdirected vaccine safety issues - a global increase of more than 30 per cent between 2017 and 2018.
if we allow an outbreak, we are deliberately creating people who are also susceptible to other diseases, " he said. Verislava Petrova of the Wellcome Sanger Institute in the UK, who led one of the studies, said.measles virus is one of the most contagious viruses scientists have ever seen. Before the vaccine was developed in 1963, measles caused 3 to 4 million cases a year in the United States. But over the next few decades, that number plummeted - in 2000, when the United States announced the eradication of the disease, only 86 cases were reported.
but since then, measles has made a comeback and is often endemic in unvaccinated communities. On October 3 this year, the U.S. Centers for Disease Control reported 1,250 cases.
the World Health Organization, measles still infects more than 7 million people worldwide each year, killing more than 100,000 people, because of lack of access to and denial of vaccination.
previous studies have suggested that the disease's effects extend far beyond infection.
Michael Mina, a virologist at Harvard University who was involved in the study, published a study in 2015 that suggested measles could suppress the immune systems of infected people for two to three years, making them susceptible to other diseases. The researchers hypothesized that measles could lead to an "immune amnesia" in which the body forgets the pathogens it has encountered.
, however, the hypothesis is still controversial, and the key questions include: If immune amnesia is real, how does it happen and how serious is it?
now, an international team of researchers led by researchers from Harvard Medical School, Brigham and Women's Hospital and the University of Rotterdam Medical Center in the Netherlands has the answer.
researchers analyzed blood samples from 77 unvaccinated Dutch children before and after measles. The results showed that the measles virus removed 11 to 73 percent of the protective antibodies in these children. These antibodies could have "remembered" previously infected pathogens to avoid re-infection, from flu to herpes viruses to a range of viruses and bacteria that cause pneumonia and skin infections. The paper was published in Science.。 VirScan, reported by Elledge and colleagues in 2015, can identify antibodies to hundreds of viruses, including influenza and herpes, with just a drop of blood, but for people who were vaccinated against measles decades ago, the number of measles antibodies in the blood may be too low to be detected.
, in 2013, the Rik de Swart team at the University of Rotterdam Medical Center collected blood from an unvaccinated child in the Netherlands with parental consent. Later, measles spread and the researchers took another set of blood samples. The average time between sample collections was 10 weeks.
years later, Elledge, Mina and Swart worked together to analyze samples of these infected children using VirScan. They effortlessly found measles antibodies, but also noticed something strange: other antibodies in children seemed to be disappearing.
measles, the number of antibodies previously accumulated in children decreased or even decreased sharply. "We started by trying to figure out how VirScan works with measles. But we found that when measles struck, the antibodies disappeared. Elledge told China Science Daily.
researchers repeated the experiment in four macaques -- this time collecting blood samples from five months before and after the measles infection-- with even more obvious results. The monkeys lost an average of 40 to 60 percent of their antibodies, which protected them from other pathogens. However, Elledge says it takes time for antibodies to disappear from the bloodstream.
"Imagine that your immunity to pathogens is like carrying a picture of a criminal with you that has been poked a few holes in it." Mina said, "If you see criminals, it's harder to recognize them, especially when important features like eyes or mouths are holed." The
Petrova team also performed different analyses of the blood of Dutch children. The team directly found the source of the antibody, B-cells, and the measles virus is known to infect B-cells. They found that measles infection reduced the diversity of memory B cells. The virus kills B-cells targeting other pathogens and replaces new B-cell memory for measles.
also reduces the diversity of another class of B cells, nonse specific childish B cells in the bone marrow, which are ready to fight unfamiliar infections. The study was published in Science-Immunology. The researchers say the measles virus not only removes immune memories, it also makes it harder for the immune system to respond to new pathogens in the future. the study measured the immune damage caused by the measles virus for the first time and highlighted the value of preventing measles infections by vaccination, the researchers said.
Bryan Grenfell, a population biologist at Princeton University, said the two studies provide further strong evidence of the high immunosuppressive effect of measles infection and the anti-measles vaccine.
"the only way to prevent measles from eliminating immune memory is obvious - to vaccinate." Mina told reporters, "In fact, after your child has measles, doctors should consider revaccinated them against all common pathogens." But
recent years, the "anti-vaccine" movement has been on the rise in some Western countries, with some anti-vaccine campaigners spreading false information about the triple vaccine for measles, mumps and rubella. Some people choose not to vaccinate against measles or even if they are eligible.
found that getting the measles, mumps and rubella vaccine did not compromise children's overall immunity. These results are consistent with decades of research. Petrova said ensuring widespread measles vaccination would not only help prevent measles, which has killed 120,000 people this year alone, but could also prevent hundreds of thousands of deaths from persistent damage to the immune system.
"this raises awareness of the importance of understanding and preventing the long-term effects of measles, including invisible effects that doctors and parents do not pay attention to." If your child has measles and pneumonia two years later, you may not be able to link the two. But the symptoms of measles may really be just the tip of the iceberg. Mina said. (Source: Tang Feng, China Science .)