Black Death altered our immune response, caused autoimmune disease

Fast & Furious presents: Hobbs & Shaw is a lot of things. It’s utterly ridiculous, mindless fun, and there’s nothing wrong with that, but it’s also an exploration of what it means to change ourselves and those around us. Whether it’s the rather obvious juxtaposition of ordinary – albeit unusually muscular – humans versus the scientifically enhanced Idris Elba or the slightly lesser-known Snowflake virus, which can be reprogrammed to either kill humanity or effortlessly dispense vaccines it’s all about change.

Either way, by the time the cars skid to a halt and the credits roll, the fate of humanity will be decided. Sorry for the spoilers if you haven’t seen it Hobbs & Shaw in the past three years, but Elba’s Brixton lore has been defeated and the world has been saved. Hurrah! Score one for the good guys, we’ll need it to feel better about the fact that nature has been kicking dirt in our eye for centuries. Longer.

An international team of scientists led by researchers from McMaster University and the University of Chicago argue that infectious disease is one of the greatest selective pressures facing humanity, especially during particularly vicious disease outbreaks. Their new study, published in the journal Naturefocuses on what scientists call “the greatest mortality event in recorded history,” the Black Death pandemic that spread around the world in the fourteenth century.

RELATED: DNA from an ancient tomb reveals patient zero of the Black Death

Given that the disease wiped out large swathes of the human population, with some regions losing more than half their population at one time, it makes sense that we’ve undergone some adaptive changes as a result of exposure to Yersinia pestis, the bacteria that causes Black Death.

To find out, researchers collected DNA samples from 206 Europeans from two different populations. One group was in Denmark, the other in London, and both groups had representatives from before, during, and after the Black Death swept through the area. Of the total of 206 individuals represented in the DNA data, 67 lived before the pandemic, 97 lived after it ended, and the remaining 42 lived during the plague and died from the disease.

Scientists compared the DNA samples over time, looking for genes that may have changed due to natural selection, particularly genes that may have mutated in response to the plague. They initially found hundreds of potential candidates, but were able to refine the search by looking for genes with frequencies that were opposed before and after the pandemic.

The thinking here is that any beneficial mutation would necessarily be rare among people who died of the plague, but we would expect their frequency to increase among survivors. Of the hundreds they initially identified, narrowing it down to genes with that trait reduced the total list to 35. From there, scientists compared changes in both populations, in Denmark and London, to see what changes showed up in both places, another thing we would expect if the changes were caused by a common disease. That narrowed the list down to four genes, all of which appear to have improved in response to the plague pandemic.

Later lab tests suggested that the mutated versions of those four genes helped protect our medieval ancestors against Y. pestis, as well as a host of other diseases. Among the modifications were changes that make the immune system better at detecting proteins on the surface of the bacteria. That makes it easier to identify and kill. Another adaptation makes immune cells better able to talk to each other, so that as soon as a cell learns about the intruder, it can tell everyone. Researchers estimated that people with two good copies of this beneficial mutation were 40% more likely to survive an infection than their peers. In the midst of a deadly disease, our immune system was busy not only keeping our ancestors alive, but making them better suited to survive into the future. The only problem is that they didn’t consider the cost.

Those same genes that may have helped our ancestors avoid death as the world collapsed around them have also been linked to a buffet of modern autoimmune diseases. In the calculus of the moment, it kind of makes sense. Even if those people, surrounded by their deceased and dying loved ones, could have known that evolving would mean inflammatory bowel disease for their descendants, would they have cared? Would they care? And would we blame them if they didn’t?

In the end, it probably doesn’t matter. They did what they did. They survived. And now we are paying the price for our ancestors surviving the Black Death with creaky joints and chronic pain.

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