The Bubonic Plague resulted in long-term changes to human immunity

AURORA, Colo. — The Bubonic plague, or “Black Death,” wreaked havoc all over Europe for centuries during Medieval times. Interestingly, a new study finds that the awful disease left a lasting impression on humanity – and not just in the history books. Scientists from the University of Colorado have collected compelling evidence suggesting the plague sparked evolutionary, immune system changes in human DNA that remain to this day.

Researchers examined the remains of 36 bubonic plague victims buried in a 16th century mass grave in Germany to make these discoveries.

“We found that innate immune markers increased in frequency in modern people from the town compared to plague victims,” says the study’s joint-senior author Paul Norman, PhD, associate professor in the Division of Personalized Medicine at Colorado’s School of Medicine, in a university release. “This suggests these markers might have evolved to resist the plague.”

The team collected DNA from the inner ear bones of the remains, which had been residing in the southern German city of Ellwangen. This is worth noting because Ellwangen dealt with bubonic plague outbreaks in both the 16th and 17th centuries. In addition, study authors compared the DNA to samples from 50 modern residents of the area.

So how did the plague change in the human immune system?

Their analyses reveal modern residents have changes in their “allele distribution for two innate pattern-recognition receptors and four Human Leukocyte Antigen molecules.” These genes help the body trigger and and direct its immune response to an infection. Researchers believe exposure to Yersinia pestis, a pathogen that causes the bubonic plague, caused these changes to take place.

“We propose that these frequency changes could have resulted from Y.pestis plague exposure during the 16th century,” Norman adds.

This is the first study ever to suggest that Yersinia pestis caused long-term changes in immunity-relevant genes in Germany and probably many other European regions as well. Considering that the bubonic plague persisted across Europe for roughly 5,000 years, researchers speculate immunity genes could have been dormant in humans for a long time and only recently “activated” through epidemic events.

“Although the lethality of the plague is very high without treatment it remains likely that specific individuals are protected from, or more susceptible to, severe disease through polymorphism in the determinants of natural immunity,” researchers write. “In this case, any change in allele frequencies that occurred during a given epidemic crisis could be evident as genetic adaptation and detectable in modern day individuals.”

So does virus immunity still come down to survival of the fittest?

Additional simulations conducted by the team show that in all likelihood natural selection helped spark those allele frequency changes.

“I think this study shows that we can focus on these same families of genes in looking at immunity in modern pandemics,” Norman continues. “We know these genes were heavily involved in driving resistance to infections. It sheds light on our own evolution.”

“There will always be people who have some resistance. They just don’t get sick and die, and the human population bounces back. I wouldn’t want to discourage anyone from taking a vaccine for the current pandemic,” the study author concludes. “It’s a much safer bet than counting on your genes to save you.”

The study appears in the journal Molecular Biology and Evolution.

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