The number of children with allergies grows every year, but children growing up on a farm seem to be exempt from this trend. Past studies have linked exposure to microorganisms associated with farms and farm animals to a reduced risk of allergies, but now a non-microbial farm-associated molecule has also been identified to serve the same purpose: sialic acid.
Exposure to microorganisms found in farm life reduce the risk of allergies because they can “train” the immune system when to react and when not to react. While microorganisms are present and we are exposed to them in all sorts of environments, farms have a particularly dense and diverse population of microbes, making this exposure the best scenario for teaching the immune system the difference between a harmful infection and an allergic reaction.
On the other hand, sialic acids are non-microbial promoters of immune health. Sialic acids are a group of molecules that provide binding sites for some pathogens and toxins, and they are found in pets, farm animals, and “food of animal origin.” A recent study from the University of Zurich shows that early exposure to sialic acids can prevent asthma.
"Early childhood contact with animals and the consumption of food of animal origin seems to regulate the inflammatory reactions of the immune system," explained lead scientist Remo Frei. Humans are uniquely devoid of sialic acids; almost all other vertebrates, including farm animals, have a sialic acid called N-glycolylneuraminic acid (Neu5Gc) in their systems.
While a genetic mutation prevents humans from producing their own supply of Neu5Gc, exposure to the acid is possible through animals and animal food products. Upon first exposure to Neu5Gc, a person’s immune system responds by producing antibodies specific to Neu5Gc. During his studies, Frei found that farm children have many more antibodies against Neu5Gc in their blood - and children with more antibodies suffered considerably less from asthma.”
Neu5Gc provides protection by alleviating asthma symptoms associated with poor respiratory function by stimulating an anti-inflammatory immune response. "This takes place through so-called regulatory T-cells, which have an increased presence," Frei said. "These T-cells dampen incorrect responses of the immune system and have a strong anti-inflammatory effect.”
Regulatory T cells are at the center of immune function when it comes to maintaining a response strong enough to kill viral or bacterial infections, but gentle enough to avoid autoimmune diseases, like asthma. The connection between sialic acids and regulatory T cells makes perfect sense.
While Frei and his team have brought to light the importance of exposure to sialic acids to prevent asthma and other allergic reactions, not everyone - not even mostly everyone - grows up on a farm. So, their next goal is to bring the benefits of farm life to everyone, even cityfolk: “In this way, we can possibly lay an important foundation stone for effective allergy prevention."
The present study is published in the Journal of Allergy and Clinical Immunology.
Source: University of Zurich, Trends in Molecular Medicine
