Hygiene Hypothesis: How We Are Destroying Our Immune Systems, Causing Autoimmune Diseases By Decimating Evolved Gut Microbiomes

Hygiene hypothesis is a highly supported idea that claims that early exposure to pathogens is crucial to the development of the human immune system, and that our modern, over-sterilized, over-medicated lifestyles are directly contributing to the abundance of autoimmune diseases and allergies. In the last few decades, our healthcare system has seen diseases like type 1 diabetes, food allergies, and asthma overcome our youth in countries where modern economies with thriving medical communities are the envy of developing countries, but these developing countries are barely touched by such bodily self-attacks. Hygiene hypothesis is one of the strongest-supported theories for how we got here.

Erika von Mutius studied asthma in the 1980s in Munich. Most researchers thought that asthma was the result of air pollution, but after years of research into that theory, there was little evidence that pollution was causing Munich’s increasing rates of asthma, Smithsonian Magazine reported. In 1989, the Berlin Wall fell and for the first time, researchers had an amazing opportunity to study groups of genetically similar children, divided by the Iron Curtain, which created distinctly different childhoods. The results showed a significant difference in prevalence of asthma, which only made sense when von Mutius found a paper by a British physician who, after examining the medical records of 17,000 British children, suspected that exposure to a multitude of germs from siblings during infancy might be linked with lower rates of hay fever and eczema.

“The immune system is programmed within the first two years of life,” Mikael Knip, a Finnish physician explained to a Smithsonian Magazine reporter. Finland has one of the highest rates of Type 1 diabetes. “With less early infection, the immune system has too little to do, so it starts looking for other targets.”

“Exposure to bacteria may play a pivotal role in the immune system, and that we might be able to understand what that role is by studying the human microbiome,” Aleksandar Kostic, a postdoctoral fellow in the lab of Ramnik Xavier at the Broad Institute of MIT and Harvard, explained. Kostic’s work is a collaborative effort that involves researchers at Aalto University, Broad Institute, University of Helsinki, the Novartis Institute of Biomedical Research, and many other health organizations all around the world. They are all working together on a project called the DIABIMMUNE Study Group.

These researchers are examining the gut microbiomes of infants from three different countries in order to better learn how our gut microbiomes might affect the prevalence of immune disorders. What they’ve learned is that interactions between bacterial species might account for the enormous spike in these autoimmune diseases, and that our seeming obsession with sanitary environments and killing germs might be directly causing the soaring rates of health conditions like type 1 diabetes, asthma, atopy and food allergies.

The DIABIMMUNE Study Group collected monthly stool samples from infants in Finland, Estonia and Russian Karelia for its latest research. After evaluating the gut microbiomes of the babies along with information about breastfeeding, diet, allergies, infections, and family history, they discovered a significant difference in the babies’ guts depending on where they were raised.

“According to the hygiene hypothesis, the increasing incidence of autoimmune diseases in western countries may be explained by changes in early microbial exposure, leading to altered immune maturation. We followed gut microbiome development from birth until age three in 222 infants in Northern Europe, where early-onset autoimmune diseases are common in Finland and Estonia but are less prevalent in Russia.”

The gut microbiomes of the Finnish and Estonian infants were rampant in Bacteroides species. The Russian Karelian babies had significantly more prevalent Bifidobacterium in their guts while they were infants and also a larger variety of microbiomes over the next three years.

“We can only speculate why this difference in bacterial populations exists; what we could show was what implications that difference in populations might have,” Tommi Vatanen, a co-first author of the research published in Cell, said.

Lipopolysaccharide (LPS) exposure has the ability to trigger the immune system, but all LPS don’t work in the same way, according to Medical News Today. LPS signaling in the Russian Karelian’s babies’ microbiome was led by E. coli, performing its typical role triggering the immune response. In the Finnish and Estonian babies’ microbiomes, they found that the LPS from the Bacteroides species was in charge due to its prevalence, only it failed to activate the immune systems of the babies. Actually, not only did it fail where E. coli succeeded, it actually wrecked the infants’ immune systems’ chances of ever activating LPS from E. coli or other bacteria that usually is able to trigger the effect.

“We believe that E. coli, which lives in the infant gut in all three countries, might be one of the immune educating bacteria responsible for training the immune system early in life. But, we found that if you mix Bacteroides with E. coli it can actually inhibit the immune-activating properties of E. coli, and we suspect this might have consequences on the development of the immune system,” Vatanen explained.

In the Finnish and Estonian babies, the Bacteroides rules the guts and in preventing the activation, it leads to an immunologically very “silent” system, which is not a good thing. The researchers said that this silence probably makes the babies prone to significant inflammation in childhood. They say that the Finnish and Estonian babies’ systems have altered from the natural state of microbiota that has developed over the entire course of human evolution. In the meantime, Russian Karelian infants have gut microbiota that more closely resembles the relationship that humans have developed with bacteria in our guts since the dawn of mankind. The researchers say that improved sanitation and improved standards of living have caused the prevalence and dominance of Bacteroides.

They don’t know exactly how and why this happened, but they are fairly comfortable saying that there is a connection between the altered microbiome within the guts of children in modern countries and the development of immune-related disease.

Interestingly, one theory for eliminating food allergies includes adding specific bacteria to back into children’s guts. For a study published in The Journal of Allergy and Clinical Immunology, researchers gave mice food allergies by simultaneously administering to them a protein found in egg whites and alum, an adjuvant known to induce allergic traits. Then, they treated the food allergies that they had artificially induced. The treatment involved giving the mice Bifidobacterium longum KACC 91563 and Enterococcus faecalis KACC 91532. These strains of bacteria were able to actually suppress the food allergies that they had induced in the mice when they were administered the egg whites protein and the adjuvant at the same time. This offers some hope to children with unnatural gut microbiomes, that they may be able to recover from their autoimmune diseases, but more research is still called for on the hygiene hypothesis front.

[Image via Pixabay]