Negative Side Effects of Immune System Evolution Described

Some of the mutations that allow humans to fend off deadly infections also make us more prone to certain inflammatory and autoimmune diseases. In an article published today in Trends in Immunology, Radboud University researchers describe how ancestral origins impact the likelihood that people of African or Eurasian descent might develop immune-related diseases. The authors also share evidence that the human immune system is still evolving depending on a person's location or lifestyle.

One of the body's best defenses against infectious diseases is inflammation. First author Jorge Dominguez-Andres and senior author Mihai Netea compiled data from genetics, immunology, microbiology, and virology studies and identified how the DNA from people within different communities commonly infected with bacterial or viral diseases was altered, subsequently allowing for inflammation. While these changes made it more difficult for certain pathogens to infect these communities, they were also associated with the emergence, over time, of new inflammatory diseases such as Crohn's disease, Lupus, and inflammatory bowel disease.

"There seems to be a balance. Humans evolve to build defenses against diseases, but we are not able to stop disease from happening, so the benefit we obtain on one hand also makes us more sensitive to new diseases on the other hand," says Dominguez-Andres. "Today, we are suffering or benefiting from defenses built into our DNA by our ancestors' immune systems fighting off infections or growing accustomed to new lifestyles."

For example, the malaria parasite Plasmodium sp. has infected African populations for millions of years. Because of this, evolutionary processes have selected people with DNA that favors resistance to infections by causing more inflammation in the body. In doing so, this has also contributed to making modern Africans prone to developing cardiovascular diseases, such as atherosclerosis, later in life.

The team also reported that early-human ancestors of Eurasians lived in regions still inhabited by Neanderthals and interbred. Today, people with remainders of Neanderthal DNA can be more resistant against HIV-1 and 'staph' infections, but are also more likely to develop allergies, asthma, and hay fever.

The negative side effects of changes in each population's immune systems are a relatively recent finding. "We know a few things about what is happening at the genetic level in our ancestry, but we need more powerful technology. So, next-generation sequencing is bursting now and allowing us to study the interplay between DNA and host responses at much deeper levels," says Dominguez-Andres. "So, we are obtaining a much more comprehensive point of view."