Over time, the human immune system has evolved to adapt to new environments and lifestyles. However, two Dutch researchers proposed that autoimmune diseases have (further) developed in parallel with the immune system.
In order to gain an overview of this dual development, Jorge Domínguez-Andrés and Prof. Mihai G. Netea evaluated various studies in the fields of virology, genetics, microbiology, and immunology. They focused on people of African and Eurasian origin to discuss whether and how the risk of autoimmune diseases was influenced by the lifestyle of their ancestors.
In their investigations, the study authors found that pathogens decreased their chance of survival over time due to genetic changes and the inflammation process. But the scientists also recognized that, in return, diseases such as IBD, Crohn's disease or lupus, which are related to inflammation, appeared.
Domínguez-Andrés notes: "There seems to be a clear balance. To protect against disease, people continue to develop their immune systems, but diseases will never cease to exist. So while we benefit from evolution in terms of health, we are also more susceptible to new diseases.
Many autoimmune diseases occur later in life. Due to the significantly lower life expectancy, they did not pose a problem for our ancestors. "Now we are seeing the effects of some of the infections that affected our ancestors," said Domínguez-Andrés.
The two researchers cite malaria as an example of their observations: "Of all infectious diseases, malaria has exerted the greatest evolutionary pressure on communities across the entire African continent. Plasmodium has been infecting people in Africa for thousands of years. By increasing inflammation, they say, our bodies evolved to improve the resistance to the infection.
However, the disadvantage is that the increased inflammation processes promote health problems that occur later in life. For this reason, people of African descent are nowadays more susceptible to arteriosclerosis and other cardiovascular diseases.
As another example, the researchers cite people whose roots go back to early Eurasiers and Neanderthals. In this case, the immune system is more resistant to staphylococcal infections and HIV-1, but more susceptible to asthma, hay fever or other allergies.
The researchers see another factor in the spread of autoimmune diseases with the changing lifestyles of the 21st century. The reduced contact with pathogens also appears to lead to reduced diversity of intestinal bacteria: "The falling number of intestinal microbes in western societies is related to "widespread diseases" such as cardiovascular diseases, diabetes, obesity or autoimmune diseases. Such diseases are very unusual in hunter-gatherer societies".
Domínguez-Andrés summed it up: "The immune system of our ancestors had to fight infections and adapt to new lifestyles over time. Today, we benefit from these defense mechanisms built into our DNA, but we also suffer from their consequences".
Domínguez-Andrés J & Netea MG, Impact of Historic Migrations and Evolutionary Processes on Human Immunity. Trends in Immunology 2019; doi:https://doi.org/10.1016/j.it.2019.10.001