The genetic mutations that allow us to repel deadly infections have made us more vulnerable to inflammatory and autoimmune diseases such as Crohn’s disease.
Until a few years ago, the general public had never heard of Crohn’s disease. But recently, especially in developed countries, more and more people are complaining about this autoimmune disease that causes chronic inflammation of the intestine. There is also an increase in the number of cases of hemorrhagic rectocolitis, another chronic inflammatory bowel disease. Until now, science had not been able to determine the reason for this.
Today, a study provides a new perspective on these inflammatory diseases. According to an article published on 27 November in the journal Trends in Immunology, genetic mutations that allow us to repel deadly infections have made us more vulnerable to inflammatory and autoimmune diseases.
Dutch researchers Dominguez-Andres and Mihai Netea collected data from genetic, immunological, microbiological and virological studies and determined how the DNA of people from different communities infected with bacterial or viral diseases had changed to allow inflammation.
Since inflammation is one of the body’s best defenses against infectious diseases, these changes have complicated the infections of certain pathogens in these communities. However, over time, they have led to new autoimmune and inflammatory diseases, such as Crohn’s.
Do we suffer or benefit from the defenses embedded in our DNA by the immune system of our ancestors?
“In the past, people’s lives were much shorter, so some of these inflammatory and autoimmune diseases that may arise in the second half of life were not so relevant,” says Jorge Dominguez-Andres. Now that we live much longer, we can see the consequences of the infections that have occurred to our ancestors.
“There seems to be a balance. Humans evolve to build defenses against diseases, but we are not able to prevent diseases, so the benefit we get makes us even more susceptible to new diseases,” he continues. Today, we suffer or benefit from the defenses built into our DNA by the immune systems of our ancestors which help fight infections or adapt to new ways of life.
For example, people with residual Neanderthal DNA tend to be more resistant to HIV-1 and staphylococcal infections. On the other hand, they are more likely to develop allergies, asthma and hay fever.
Improved hygiene has led to a reduction in infections.
The negative effects of changes in the immune system in each population are relatively recent. “We know a lot about what is happening genetically in our ancestor’s DNA, but we still need more powerful technology to get to the bottom of it. Thus, the next-generation sequencing could allow us to study the interaction between DNA and host responses at much deeper levels,” says Dominguez-Andres.
This technology can also show how our immune system is changing in real-time due to changes in current lifestyles. For example, African tribes that still hunt have a greater intestinal bacterial diversity than African-Americans who live in cities and eat products purchased in supermarkets.
In addition, over the past two centuries, there have been many improvements in the collection of drinking water or waste, resulting in a significant reduction in exposure to infectious pathogens. As humans move towards processed foods and higher standards of hygiene, their bodies adapt by developing diseases of modernity, such as type 2 diabetes.
Lifestyles can influence immune responses
Researchers are currently planning to extend their research to non-Eurasian or African communities. “So far, all our studies have focused on populations of European and African origin, but should also be extended to indigenous and other populations to improve the representation of human genetic diversity,” explains Dominguez-Andrés. He concluded: “Lifestyles and ecology can really vary and influence immune responses. Therefore, there is still work to be done.
In general, chronic inflammatory bowel disease (IBD), Crohn’s disease and hemorrhagic rectocolitis are diagnosed in young people between the ages of 20 and 30. This disease can affect the rectum and colon and tend to relapse. In addition to painful bowel symptoms, it may also lead to rheumatic fever, skin lesions and inflammation of the internal structures of the eye.
Currently, this disease is more easily detected than Crohn’s disease, which takes a long time to diagnose due to the lack of specific symptoms. According to the Crohn’s & Colitis Foundation, Crohn’s disease may affect as many as 780,000 Americans who are strongly affected by diarrhea, sometimes abundant and watery, with possible loss of blood and mucus or pus in the stool. This is often accompanied by severe abdominal pain. When the anus is affected, cracks, abscesses, and fistulas may form. Patients sometimes also suffer from fever, weight loss, and severe fatigue.