Measles Erases 'Immune Memory' Of Other Illnesses


 
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By Molly Walker

Measles infection in unvaccinated children was associated with up to a 70% decline in antibodies to other pathogens following infection, researchers found.

After cases of severe measles, unvaccinated children lost a median of 40% (range 11-62%) of their already existing pathogen-specific antibodies and after a case of mild measles, children lost a median of 33% (range 12-73%) of these pre-existing antibodies, reported Michael Mina, MD, PhD, of the Harvard T.H. Chan School of Public Health in Boston, and colleagues.

By contrast, controls retained over 90% of their antibody repertoires over similar time periods, the authors wrote in Science.

In addition, the 20% of children most affected by measles lost over half of their pathogen-specific antibodies to most pathogens, and in some children, up to 70% antibody loss against specific pathogens was detected, the researchers noted.

"Imagine that your immunity against pathogens is like carrying around a book of photographs of criminals, and someone punched a bunch of holes in it. It would then be much harder to recognize that criminal if you saw them, especially if the holes are punched over important features for recognition, like the eyes or mouth," Mina said in a statement.

This statement from Harvard Medical School also attempted to provide numerical context for the findings -- saying that if a person had 100 different antibodies against chicken pox prior to contracting measles, they might emerge with only 50, cutting their protection against chicken pox in half.

Peter Hotez, MD, PhD, of Baylor College of Medicine in Houston, who was not involved with the research, noted a 2015 paper on this subject, which showed that measles has a prolonged effect on host resistance that can last 2-3 years, and even can drive an increase in non-measles deaths in children.

"This is providing further mechanistic data describing that phenomenon," he explained.

"We know that measles has a lot of devastating effects [such as] measles pneumonia, measles encephalitis, and measles deafness -- severe acute morbidities that often result in ICU admissions. There are other chronic, debilitating effects from measles that go beyond ICU admissions, and is yet another reason why there's an urgency to vaccinate against measles in order to protect kids," Hotez noted.

Indeed, Mina and colleagues said that this study is the first to measure the immune damage caused by the virus and is further evidence for the immune amnesia hypothesis (that by depleting antibody repertoires, measles partially obliterates immune memory to previously encountered pathogens).

The researchers examined blood from 77 unvaccinated children infected with measles in the Netherlands during a 2013 outbreak. Children were a mean age of 9. Of these children, 34 had mild measles and 43 had severe measles. The researchers then compared these samples with the blood of 115 uninfected children and adults using the VirScan system, a tool that detects antiviral and antibacterial antibodies in the blood.

Samples were taken prior to and after measles infection. The mean time between sample collections after measles infection was 7 weeks, the authors said.

Examining the diversity of the antibody repertoire, the team found that measles infections were linked with a reduction of about 20% in the overall diversity of the antibody repertoire as measured by VirScan. While Mina and co-authors said this was consistent across individual pathogens, effect sizes varied -- with 12 of the 77 children losing over 40% of their antibody repertoire diversity. However, the authors noted no changes in immunoglobulin (Ig)G, IgA, or IgM levels.

"These results suggest that, rather than a simple loss of total IgG, there is a restructuring of the antibody repertoire after measles," the team wrote.

Hotez discussed the importance of vaccinating against measles, saying that the study "ramps up the urgency for insuring measles does not return."

"If we slow or reverse public health gains when it comes to measles, this will have catastrophic consequences," he said.

Mina and colleagues also emphasized the importance of vaccination, and suggested that given these findings, booster shots against other illnesses, such as hepatitis or polio, may be necessary for children infected with measles.



 
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