The Black Death Still Affects Human Immune Systems Today

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The world’s most devastating plague outbreak, the Black Death, changed the course of human history by killing half of the population of medieval Europe in seven years in the 14th century.

But what about the survivors of the single biggest fatality ever recorded? New study published Wednesday The journal Nature suggests that more than luck determined who lived and who died.

Analysis of centuries of DNA from both Black Death victims and survivors has identified key genetic differences that help people survive the plague, according to a study published in the journal Nature. rice field.

These genetic differences continue to shape the human immune system today, and genes that once conferred protection against the plague are now more vulnerable to autoimmune diseases such as Crohn’s disease and rheumatoid arthritis. Related, says the study.

“We are the descendants of people who survived past pandemics … and understanding the evolutionary mechanisms that contributed to our survival is not only important from a scientific point of view, but also the mechanisms of susceptibility to current diseases. and genetic determinants,” study co-author Luis Barreiro, professor of genetic medicine at the University of Chicago, said in an email.

A seven-year study involved the extraction of isolated DNA from three different groups of excavated skeletons. London and Denmark: Plague victims, those who died before the Black Death, and those who died between 10 and 100 years after the plague hit.

More than 300 samples were obtained from particularly plague-affected London, including from individuals buried in the East Smithfield plague pits, which were used for mass burials at the height of the epidemic in 1348–1349. I was. Another 198 samples were taken from human remains buried at his five locations in Denmark.

DNA was extracted from the dentin at the base of the individual’s teeth, and researchers were also able to confirm the presence of Yersinia pestis, Yersinia pestis. We then looked for signs of a genetic adaptation to the disease.

“It’s a long process, but in the end we have sequences of the genes of people before, during, and after the epidemic, and we can ask: What genes did one population have? Do they look different than what the populations of the

identified by the team Mutations in a specific gene, known as ERAP 2, appear to be strongly associated with plague. Prior to the Black Death, variants of ERAP2 found to protect against plague were found in 40% of individuals included in the London study. After the Black Death he was 50%. In Denmark, the percentile disparity was more pronounced, varying from approximately 45% of samples buried before the plague to 70% of samples buried after the plague.

The team still don’t know exactly why this mutant conferred protection, but experiments with cultured cells showed that in people with ERAP2 mutants, immune cells known as macrophages were able to fight against Yersinia pestis. was shown to provoke very different responses, Barreiro explained. In laboratory experiments, macrophages from individuals with the variant were able to kill more bacteria than macrophages from individuals without the variant.

“I don’t know if it’s still protected from the plague given the very low number of cases in the current population, but I’m guessing it should,” he said. Variants are likely to be beneficial against other pathogens – this was not part of the study.

A disadvantage of this variant is that it is associated with an increased susceptibility to autoimmune diseases such as Crohn’s disease, in which the immune system becomes overactive.

“This suggests that the population that survived the Black Death paid. The price is to have an immune system that is more likely to react against itself,” Barreiro said.

He said the Covid-19 outbreak is unlikely to shape our immune systems in a similar way. This means that genes that confer protection are unlikely to be passed on to the next generation.

David Ennard, a professor in the Department of Ecology and Evolutionary Biology at the University of Arizona, said he was not involved in the study.

“The narrow time frame in which the samples were taken and the large number of samples analyzed were the selling points of this study, and in a commentary published alongside the study, he said, ‘I hope the authors will accurately date natural selection.’ make it possible,” he said.

“Evolutionary biologists have previously wondered about the possibility of natural selection in the Black Death, but without accurate dating of many samples, a proper investigation would have been impossible.”