Measles ‘resets’ human immune system back to an immature state, study reports

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For the first time, scientists from the University of Amsterdam (Netherlands), Wellcome Sanger Institute (Hinxton, UK) and their collaborators demonstrated that measles ‘resets’ the human immune system back to an infant-like state by removing part of the immune systems memory resulting in limited ability to respond to new infections.

In the study, published in Science Immunology, the authors explained why children often catch other infections after measles and highlighted the importance of vaccination against measles.

Measles is the cause of more than 10,000 deaths per year worldwide. Despite the complete elimination of measles in the UK in 2017, the falling vaccination rates has caused the recent loss of the UK’s WHO measles elimination status. This could result in an increase of other dangerous infections; therefore, this research has great implications for public health.

The researchers took blood samples from a group of non-vaccinated individuals in the Netherlands, then follow-up samples were taken after the 2013 measles outbreak.

After the team sequenced antibody genes from 26 children, before and 40–50 days after their measles infection, they discovered that immune memory cells for other diseases that were present before the measles infection had disappeared after. Therefore, leaving the children at risk to diseases that they were once immune to.

“This study is a direct demonstration in humans of ‘immunological amnesia’, where the immune system forgets how to respond to infections encountered before. We show that measles directly causes the loss of protection to other infectious diseases,” explained lead author Velislava Petrova (Wellcome Sanger Institute and Cambridge University, UK).

The researchers tested for this ‘immunological amnesia’ in ferrets and demonstrated that infection with a measles-like virus reduced the level of flu antibodies in ferrets who had previously received a flu vaccine.

Study author, Paul Kellam (Imperial College London, UK) commented: “We showed that measles-like viruses can delete pre-existing flu immune memory from ferrets. Even after the ferrets had been successfully vaccinated against flu, the measles-like virus reduced levels of flu antibodies resulting in the animals becoming susceptible to flu infection again and experiencing more severe flu-like symptoms. This shows that measles could reverse the effects of vaccination against other infectious diseases.”

Furthermore, the team also discovered that the measles virus reverses the immune system back to an immature state that can only produce a limited repertoire of antibodies against disease – increasing the risk of secondary diseases.

“In some children the effect is so strong it is similar to being given powerful immunosuppressive drugs. Our study has huge implications for vaccination and public health as we show that not only does measles vaccination protect people from measles, but also protects from other infectious diseases,” explained senior author, Collin Russell (University of Amsterdam).

For some children signs of immunosuppression are still present 5 years after measles, despite them having healthy white blood cell counts. This study demonstrated how genetic techniques can display new mechanisms of disease that are otherwise undetectable using routine clinical tests and will assist in further understanding of the disease.

“Measles is highly contagious and its potentially devastating consequences are well known. This study finds that measles also has the potential to weaken our body’s existing immune response to other diseases, leaving us vulnerable to infections. These findings further strengthen the vital role the MMR vaccine plays in public health and protecting us from deadly disease. It is yet another reminder of how important vaccines are as a vital resource in eliminating infectious disease,” commented Charlie Weller, Head of Vaccines at Wellcome.

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Sources: Petrova VN, Sawatsky, Han AX et al. Incomplete genetic reconstitution of B cell pools contributes to prolonged immunosuppression after measles. Sci. Immunol. 4(41) eaay6125 (2019); www.sanger.ac.uk/news/view/measles-infection-wipes-our-immune-systems-memory-leaving-us-vulnerable-other-diseases; https://hms.harvard.edu/news/inside-immune-amnesia

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