14th century Black Death 'responsible for modern immune system disorders'

Pandemics, such as the Black Death 700 years ago, have left a genetic legacy in our modern population. A recent study published in the journal Nature showed that the modern prevalence of autoimmune disorders in Europeans may be linked to their ancestors surviving the Black Death. Overactive immune system disorders and allergies may be the price to pay from a brutal medieval past, where having an overactive immune system could have saved your life.

Analysis of DNA from victims and survivors of the Black Death has pinpointed genetic differences that would have meant survival in this devastating medieval pandemic.

Such variation in our immune systems is also evident in today's modern population, where plague survival is linked to an increased prevalence of autoimmune diseases such as rheumatoid arthritis or Crohn's disease. Such knowledge can now inform scientists of the mechanisms behind these immune disorders, as the link between them and the Black Death becomes more evident.

Samples were taken from burial sites in the United Kingdom and Denmark that were verified as Black Death burial pits and the skeleton remains of those who died in the years after the deadly pandemic swept through Europe.

London was particularly hard hit, with more than 300 samples taken from the city's East Smithfield plague pits. DNA was extracted from teeth, and scientists were also able to check for remnants of yersina pestis, the infamous bacteria responsible for the Black Death. Although the condition is now easily treated with modern antibiotics, in the 14th century, it wiped out half of Europe's population in just seven years.

One particular gene, known as ERAP 2, stood out in analysis. In Denmark, the prevalence of ERAP 2 in the 14th century population after the plague shot up from 40 percent to 70 percent, indicating a strong selection pressure for the gene.

Laboratory experiments in cell cultures indicate that ERAP 2 may trigger a white blood cell response to yersina pestis that is more effective at combating infection. White blood cell types called macrophages were able to kill the bacteria strain more effectively in experiments than those without the ERAP 2 variant.

The price we may now be paying for survival is that our modern immune systems occasionally work in overdrive and attack our own body.

It is unlikely that modern pandemics, such as the recent wave of COVID-19, will impact the gene pool anywhere near as much, considering most deaths from the disease took place in people older than the reproductive age. A genetic bottleneck event where humanity's genes are changed in just a few years is extremely rare, and only the most brutal selection pressures can trigger these kinds of changes.

Such rapid natural selection is, hopefully, not something any population in the modern world will ever have to experience, and currently isolated cases of the Black Death can be treated with modern medicine. It is, however, a reminder that our very genetic make-up is shaped by our vulnerability to such historic tragedies, and that we must stay vigilant lest our genes are once again forced to change rapidly over future generations.