Co-evolving immune system
But what might this have to do with our genes? Quite a bit. Mateo Fumagalli, a population genetics researcher at the Scientific Institute IRCCS Eugenio Medea in Italy, and his colleagues have found evidence that helminthes have played a role in the evolution of the human immune system. Looking at the geographical distribution of single nucleotide polymorphisms (SNPs), mutations that shape genetic variability, the group found that genetic variability was correlated with the diversity of an area’s parasites.
“Genetic variation is particularly important in the immune system, and genes in the immune system seem to be more polymorphic [variable] than genes with other functions,” says Manuela Sironi, one of Fumagalli’s colleagues. “It’s thought that pathogens have a strong selection pressure on the genes in our immune system. And with these correlations, we’ve found that helminthes have a very strong selective pressure on the evolution of our immune system.”
Sironi and Fumagalli’s data suggest that our immune systems have co-evolved with parasitic worms—living alongside helminthes for millions of years has shaped the way our immune systems react to pathogens, through a greater genetic diversity in our immune-related genes. In turn, helminthes have evolved the ability to mitigate the human immune response to their own advantage, as many worms need their human host healthy in order to propagate and survive.
Fumagalli’s research group then analyzed five interleukin genes, which encode for proteins involved in mediating the immune system’s response to disease. These genes have evolved to deal with a variety of different pathogens, including viruses, bacteria, fungi and worms.
“These genes are very involved with many autoimmune diseases like Crohn’s and multiple sclerosis,” Cooke says. “And these genes have evolved to deal with a lot of diverse pathogens. But when you take someone out of the environment where there is that diversity, all those different pathogens, it may result in an imbalance: an overactive response to pathogens and, ultimately, autoimmune disease.”
The work provides evidence that the human immune system likely co-evolved with helminthes. That makes perfect sense, Cooke says.
“A worm needs its host, and it’s important that they are able to harness our immune system in order to survive,” she says. “It’s happened over millions of years, but in evolving alongside us, these organisms have used our immune systems to facilitate their life cycle and in doing so have induced all kinds of regulation and fine-tuning that we’re only beginning to understand.”
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First Published in 2009
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