The Black Death shaped our genes and our immune system, according to a study

The recent study is a first approximation to how pandemics, such as the Black Death

It can modify our genomes and how they contribute to our current susceptibility to disease.

The Black Death – the most devastating event in history – not only wiped out half of Europe ‘s population in less than five years, it also changed our genome and immune system.

According to a study published this Wednesday in the journal Nature , the same genes that once protected us against the Black Death are now associated with greater susceptibility to autoimmune diseases such as Crohn’s disease and rheumatoid arthritis.

The authors of the study, carried out by the University of Chicago (United States), McMaster University (Canada) and the Pasteur Institute (France), have studied the genetic impact of the bubonic plague that 700 years ago wiped out between 30% and 60% of the population of North Africa, Europe and Asia.

It has long been speculated that the Black Death pandemic , caused by the bacterium Yersinia pestis , might have exerted selective pressure on humans, but it was difficult to prove by studying modern populations because humans have faced many selective pressures since then. .

Ancient DNA samples sequenced

For this study, the team sequenced ancient bone DNA samples from more than 200 individuals from London and Denmark who died before, during and after the passage of the Black Death in the late 1340s.

Of 300 immunity-related genes , they selected four that, depending on the variant, protected or increased susceptibility to Y. pestis.

The team focused on a gene with a particularly strong association with susceptibility: ERAP2, which helps the immune system recognize the presence of an infection.

Individuals who possessed two copies of a specific genetic variant, designated rs2549794, were able to produce full-length copies of the ERAP2 transcript, and produced more of the functional protein.

“When a macrophage encounters a bacterium, it cuts it into pieces to present to other immune cells signaling that there is an infection. So having the working version of the gene probably improves our immune system’s ability to detect the invading pathogen.” explains Luis Barreiro, from the University of Chicago and co-author of the study.

“According to our estimates, having two copies of the rs2549794 variant would have made a person 40% more likely to survive the Black Death than those with two copies of the non-functional variant,” he says.

Then, in the lab, the team showed that the rs2549794 variant affected the ability of living human cells to help fight plague, and that macrophages expressing two copies of the variant were more efficient at neutralizing Y. pestis than macrophages. that they didn’t have it.

“These results support the ancient DNA evidence that rs2549794 is protective against the Black Death, ” according to Javier Pizarro-Cerda of the Pasteur Institute.

Susceptibility to current diseases

But over time, our immune systems have evolved to respond to pathogens, and what was once a protective gene against plague is now associated with increased susceptibility to autoimmune diseases. It is the balancing act with which evolution plays with our genome, the authors point out.

This study is a first approach to how pandemics can modify our genomes and go unnoticed in modern populations.

Future research will expand the project to examine the entire genome, not just a set of immunity-related genes .

“Understanding the dynamics that have shaped the human immune system is key to understanding how past pandemics, such as the plague, contribute to our susceptibility to disease today,” said co-lead author Hendrik Poinar of McMaster University. of the studio. 

(With information from EFE)

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