Measles Causes "Immune Amnesia"
Sun, April 11, 2021

Measles Causes "Immune Amnesia"

Measles accounts for more than 100,000 deaths a year, and studies have associated the disease with a higher risk of death among survivors / Photo by: luanateutzi via 123RF

 

Measles accounts for more than 100,000 deaths a year, and studies have associated the disease with a higher risk of death among survivors. This higher risk is because measles makes those affected with it vulnerable to other infections, especially in children, but the reasons for this remain poorly understood.

That is until a pair of recently published studies looked into the specific mechanism that causes this side effect. The studies compared blood samples from unvaccinated children in the Netherlands before and after they were exposed to measles. The results of the study showed how measles exposure causes the body to "forget" the immunity it developed against other pathogens.

Killing Immune Cells

Harvard virologist Michael Mina found that children are more likely to catch other diseases if they were exposed to measles. These post-measles infections could be attributed to half of all infectious disease deaths among children living in measles-plagued areas, reported the New Scientist, a London-based weekly English-language magazine that keeps readers up to date with the latest science and technology news from around the world.

Measles accounted for an estimated 100,000 deaths among children in 2017 and Mina believed two or three times that number will likely die later on due to other infections—infections that they would've been immune to if they hadn't had measles.

This is because the measles virus kills the specialized immune cells that children develop when they were exposed to pathogens. Each of these specialized cells learns to produce antibodies to fight against a certain pathogen, and the absence of these cells makes children more vulnerable to other diseases.

The New Scientist reported that Mina and his team established the antibodies made by 77 unvaccinated Dutch children who later caught measles. Prior to them having measles, the children developed antibodies against many viruses and bacteria. But catching measles led to the loss of up to 73 percent of their library of antibodies for all types of pathogens.

"The worst-affected 20 percent lost more than half the antibodies they could make against more than half the pathogens we tested," Mina said.

Immune Amnesia

Mina's study was based on a 2012 study published in PLOS Pathogens. The 2012 research determined how a measles virus can wipe out immune memory cells—the cells that record and catalog a person's lifetime of infections and help them fight against succeeding invaders.

The researchers, led by virologist Rik de Swart, examined how a virus invades a cell and hijacks the mechanism to copy itself. They did so by injecting a gene in the measles virus and presented the modified virus into macaques, a subspecies of monkey.

The scientists monitored the movement of the virus at various stages as it invaded cells to make copies and light up its host. "Glowing green speckles" would appear in places where the monkey has lymphoid tissues, which host immune cells, according to National Geographic.

"These winks of light revealed that the virus favors what’s known as immune memory cells,” it added. The virus was found to settle later into the surface lining of the nose and lungs, allowing it to launch into the air when a person coughs. The viral constellation vanished when the immune system took action to clear the infection, which emphasized an important step in immune amnesia.

According to National Geographic, the sudden darkness meant the virus wiped out some of the body's immune recollections as well as turned the system against itself when it infected memory cells. It did so by forcing healthy immune cells to eliminate the infected cells.

"If the virus didn’t kill those memory cells already, the immune system would finish the job off," de Swart said. "We could literally see it happening under our hands."

A similar mechanism is likely found in humans, but de Swart noted that how much immune memory vanished may vary from person to person.

The 2012 research determined how a measles virus can wipe out immune memory cells—the cells that record and catalog a person's lifetime of infections and help them fight against succeeding invaders / Photo by: Maxim Lupascu via 123RF

 

Importance of Vaccination

The studies further highlighted the importance of vaccination. Before children were vaccinated, there was no doubt that every one of them would get measles and about 2.6 million would die due to the disease each year.

The vaccine for measles is usually combined with mumps and rubella, hence the MMR vaccine, and is incredibly effective. With just two doses, a child will have nearly 97 percent protection against the said diseases, which resulted in significant declines in deaths due to measles around the world.

The number of measles cases dropped when vaccine use became widespread, along with other diseases such as pneumococcus and diarrhea. In fact, regions deprived of good resources saw dramatic declines of up to 50 percent while impoverished areas plummeted by as much as 90 percent.

"We actually saw the whole overall baseline for childhood mortality drop precipitously," Mina said.
This shows how crucial vaccination is to maintaining and upholding children's health—and comes at a time when more and more people begin to question the effectiveness of these immunity boosters. In this case, not only does a measles vaccine protect populations against a single disease, but it also helps in keeping a hoard of other infections at bay by preventing immune amnesia.

The vaccine for measles is usually combined with mumps and rubella, hence the MMR vaccine, and is incredibly effective / Photo by: Jovan Mandic via 123RF