This is the surprising title of an article written yesterday by Katherine Ellen Foley for Quartz. According to the article, our bodies store up many potential viruses and bacteria which could infect us. Our immune system’s job is to kick out the ones who start replicating and could get us sick.
But the question is: how does our immune system know when it’s time to react?
Geneticists from the University of Utah might have the answer. They found that some of the reasons behind our immune responses come from genomes of old infections from thousands of years ago.
Cédric Feschotte, lead author of the discovery, told Quartz that pieces of DNA found in these viruses function “as switches for regulating or turning on genes in the innate immune response.”
But how come these viruses in our body are so old? The team lead by Feschotte looked at some viruses called endogenous retroviruses, viruses which reproduce their own genetic material inside our cells, and then use our cells’ machinery to replicate. If this process occurs in egg or sperm cells, part of that viral genome end up being passed to future generations. And this is how millions of years later, this virus genetic material ends up being a big part of our own – around 8%.
Now the question remains: what is their function?
Researchers further examined the gene which is responsible for attacking the infected cells. This gene is called AIM2, and it reportedly produces a protein which can detect when a cell has been infected and can cause reactions which trigger the respective cells to self-sacrifice in order for the infection not to spread.
In order to prove that the old DNA bits coming from retroviruses are the ones causing this response, the researchers took human cells and deleted those sections. The result was that without those bits the cells kept on living.
So these old viral infections end up being relevant even millions of years later, and our immune system stores them for our own benefit.