How measles wipes out the body's immune memory

Admin on 02 / 11 / 2019 under viruses and bacteria

Source: Harvard Medical School

Summary: A new study shows that measles wipes out 20 to 50 percent of antibodies against an array of viruses and bacteria, depleting a child's previous immunity. A measles-ravaged immune system must 'relearn' how to protect the body against infections. The study details the mechanism and scope of this measles-induced 'immune amnesia.' The findings underscore the importance of measles vaccination, suggesting those infected with measles may benefit from booster shots of all previous childhood vaccines.

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.

How does this work?

Some researchers have suggested that the vaccine gives a general boost to the immune system.

Others have hypothesized that the vaccine's extended protective effects stem from preventing measles infection itself. According to this theory, the virus can impair the body's immune memory, causing so-called immune amnesia. By protecting against measles infection, the vaccine prevents the body from losing or "forgetting" its immune memory and preserves its resistance to other infections.

Past research hinted at the effects of immune amnesia, showing that immune suppression following measles infection could last as long as two to three years.

However, many scientists still debate which hypothesis is correct. Among the critical questions are: If immune amnesia is real, how exactly does it happen, and how severe is it?

Now, a study from an international team of researchers led by investigators at Harvard Medical School, Brigham and Women's Hospital and the Harvard T.H. Chan School of Public Health provides much-needed answers.

Reporting Oct. 31 in Science, the researchers show that the measles virus wipes out 11 percent to 73 percent of the different antibodies that protect against viral and bacterial strains a person was previously immune to -- anything from influenza to herpesvirus to bacteria that cause pneumonia and skin infections.

So, if a person had 100 different antibodies against chicken pox before contracting measles, they might emerge from having measles with only 50, cutting their chicken pox protection in half. That protection could dip even lower if some of the antibodies lost are potent defenses known as neutralizing antibodies.

"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," said the study's first author, Michael Mina, a postdoctoral researcher in the laboratory of Stephen Elledge at Harvard Medical School and Brigham and Women's Hospital at the time of the study, now an assistant professor of epidemiology at the Harvard T.H. Chan School of Public Health.

"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," said Mina.

The study is the first to measure the immune damage caused by the virus and underscores the value of preventing measles infection through vaccination, the authors said.

"The threat measles poses to people is much greater than we previously imagined," said senior author Stephen Elledge, the Gregor Mendel Professor of Genetics and of Medicine in the Blavatnik Institute at Harvard Medical School and Brigham and Women's Hospital. "We now understand the mechanism is a prolonged danger due to erasure of the immune memory, demonstrating that the measles vaccine is of even greater benefit than we knew."

The discovery that measles depletes people's antibody repertoires, partially obliterating immune memory to most previously encountered pathogens, supports the immune amnesia hypothesis.

"This is the best evidence yet that immune amnesia exists and impacts our bona fide long-term immune memory," added Mina, who first discovered the epidemiological effects of measles on long-term childhood mortality in a 2015 paper.

The team's current work was published simultaneously with a paper by a separate team in Science Immunology that reached complementary conclusions by measuring changes in B cells caused by the measles virus. An accompanying editorial in Science Immunology, written by Duane Wesemann, Harvard Medical School assistant professor of medicine at Brigham and Women's Hospital, contextualizes that study.

Elledge, Mina and colleagues found that those who survive measles gradually regain their previous immunity to other viruses and bacteria as they get re-exposed to them. But because this process may take months to years, people remain vulnerable in the meantime to serious complications of those infections.

In light of this finding, the researchers say clinicians may want to consider strengthening the immunity of patients recovering from measles infection with a round of booster shots of all previous routine vaccines, such as hepatitis and polio.

"Revaccination following measles could help to mitigate long-term suffering that might stem from immune amnesia and the increased susceptibility to other infections," the authors said.