Measles causes immune amnesia

02 November 2019

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Measles erases the immune system's memory of past infections, two new studies revealed this week...

Infection with measles virus is known to leave victims with a weakened immune system for several years afterwards. This is manifest as a loss of immunity to infections an individual has fought off previously, and  skin tests for tuberculosis can switch to a negative result in patients known to have been exposed in the past. Doctors have also documented cases of autoimmune diseases reducing in severity post-measles, an observation in line with reduced immune function.

All this points to a state of "immune amnesia" induced by measles infection. Scientists suspected some sort of immune memory erasure was occurring, although they had no idea why. Now, thanks to two studies out this week, one from Velislava Petrova at the UK's Sanger Centre and the other by Michael Mina at Harvard University in the US, a clearer picture is forming of what happens in the measles aftermath.

“Cells that were there before, that could generate this memory of other pathogens, were lost after measles,” Petrova told the Naked Scientists. “In addition, after measles, we have only a small amount of those available new immune cells that can respond to a new infection.”

The new insights emerged when the research teams were able to compare blood samples collected from a group of unvaccinated children in the Netherlands, both before and after they naturally caught measles. One of the teams looked at the profile of antibodies in the blood samples, while the other group looked at the memory B cells that make those antibodies. The two studies were in strong agreement: measles infection in the children had wiped out up to 70% of their immune memories. This is the immunological equivalent of waking up one morning to discover you've forgotten over two thirds of what you had ever learned.

This is the immune equivalent of waking up one morning to discover you've forgotten over two thirds of what you had ever learned...

Fortunately, the immune system does bounce back, although the recovery period is prolonged and leaves a person in a vulnerable state for up to 5 years.

What the studies do not tell us though, is why measles should make this happen in the first place. The paradox is that measles infection results in a powerful lifelong immunity to the virus itself, despite its disabling effect on immune memories for other infections. Presumably, this is one side effect of the natural history of measles as it targets and grows in immune cells after it infects. But understanding this crucial missing piece of the puzzle will take more time. 

Reassuringly, none of the documented immune-disabling effects were seen in individuals who received the measles, mumps and rubella (MMR) vaccine, which contains a live, weakened form of the measles virus and achieves strong lifelong protection by producing a limited infection in vaccinees. This has the effect of educating the immune system about the structure and appearance of the virus but without any of the damaging consequences of the wild-type infection.

Worryingly, MMR vaccination rates have dropped significantly in some geographies in the wake of public safety fears fuelled by misinformation, and the "anti-vax" movement. This has undoubtedly contributed to the 300% rise recently in measles cases in the US, UK and other developed countries, where vaccination uptake has dropped below the 95% required to maintain the "herd immunity" that prevents the virus from circulating in the community.

The reticence to vaccinate, based on no evidence other than hearsay, seems surprising given an annual measles disease burden in the millions and a death toll that still exceeds 100,000 people per year. Perhaps these new results, indicating that the consequences of measles infection are even more far-reaching than we had first realised, will help to change minds...

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