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Measles wipe immune system's memory of other illnesses, studies find

08 November 2019

Two detailed studies of blood from unvaccinated Dutch children who contracted measles now reveal how such infections can also compromise the immune system for months or years afterward, causing the body to "forget" immunity it had developed to other pathogens in the past. The studies each investigated different branches of the immune system, and both found evidence to support the immune amnesia hypothesis.

A measles infection can wipe our immune system's memory and even leave us weaker against new infections.

By comparing the children's antibody repertoire before and after a measles infection using Virscan, the researchers could clearly see whether their immunology memory was being damaged. In Science Immunology, Petrova and colleagues sequenced antibodies produced by B cells - one of the primary immune cells able to recognize a virus and deploy attacks against it - from 77 unvaccinated children. Or, as Mina puts it, "measles seems to be punching holes in the immune memory".

Before the introduction of the measles vaccine, almost every child experienced measles infection. Using data from a group of unvaccinated children in the Netherlands, both studies revealed what scientists have long suspected: that the measles virus cripples the immune system in a profound and lasting way.

Professor Colin Russell, senior author from the University of Amsterdam, said: "For the first time we see that measles resets the immune system and it becomes more baby-like, limiting how well it can respond to new infections".

The notorious measles virus not only makes people sick, it also sneaks inside important immune cells in the body and wipes their "memories", new research suggests.

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This was not observed in infants vaccinated against measles, mumps and rubella (MMR), they found.

"Not only does natural infection expose the children to the potentially devastating consequences of measles infection, but also as highlighted here, will weaken rather than strengthen their immune systems, so that even if they are lucky enough to escape serious consequences of the primary infection, they are still left prone to catching other infections due to the long-term immune suppression mediated by the primary infection", says Petrovsky, who did not work on this current research.

Getting measles is even more risky than doctors had realised, because it destroys immunity that the victim has acquired to other diseases, researchers say. A new analysis of 77 unvaccinated children from the Netherlands carried out by an global team of researchers led by scientists at Harvard has found that the virus erases the body's memory of previous pathogens - effectively wiping its immunity memory. All children lost a large part of their so-called memory cells - the immune cells that the body created after an infection and that are ready to fight the same infection if it strikes again. It sometimes leaves children with brain damage or hearing loss, and while deaths are rare in the USA, measles killed 110,000 people globally in 2017.

Over the last decade, evidence has mounted that the measles vaccine protects in not one but two ways: Not only does it prevent the well-known acute illness with spots and fever that frequently sends children to the hospital, but it also appears to protect from other infections over the long term.

"Measles essentially takes away their ability to efficiently protect themselves", said Michael Mina, an epidemiologist at Harvard University and co-author of the new study, published today (Oct. 31) in the journal Science.

"The (measles) virus is much more deleterious than we realised, which means the vaccine is that much more valuable", Mr Elledge said.

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A two-dose vaccine has helped to slash measles cases since 2000, saving an estimated 21.1 million lives between 2000 and 2017, World Health Organization said.

"Every time we see a pathogen, our immune system recognizes this pathogen, builds immunity to it and then stores it in the form of immune memory", explains Velislava Petrova, a postdoctoral fellow in immunogenetics at the Wellcome Sanger Institute in the United Kingdom and first author of the report published in Science Immunology. After infection, immature B-cell populations did not recover to their pre-infection levels, leaving the body with a smaller pool of options for fighting future infections of any kind.

The studies' findings also emphasize the importance of vaccines.

Researchers then tested this "immunological amnesia" directly in ferrets, showing that infection with a measles-like virus reduced the level of flu antibodies in ferrets that had been previously vaccinated against flu.

"He just sent a one-line sentence that said: 'It's amusing, we saw a big drop in antibodies to everything other than measles, '" Mina says. "We show that measles directly causes the loss of protection to other infectious diseases".

"The measles vaccine is really a superhero", he says.

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Measles wipe immune system's memory of other illnesses, studies find