Zurich - It is not just contact with microbes on the farm that protects children from asthma and allergies. According to study in the Journal of Allergy and Clinical Immunology (2017; doi:), the sialic acid Neu5Gc, which is released by many farm animals and which children ingest by touch or through food, could be involved in the preventive effect.< p> Sialic acids are part of glycopeptides and glycolipids. They occur on the cell membranes of the mucous membranes and their secretions. Sialic acids play an important role in cell contacts. By binding bacteria and viruses, they are also involved in the immune system. Sialic acids occur almost exclusively in animals and humans. A certain sialic acid, Neu5Gc, is absent in humans. An enzyme for its production failed about 2 to 3 million years ago due to mutation.
Humans can, however Ingest Neu5Gc through contact with the mucous membranes of animals and through food. It is absorbed by cells in the body and then also appears on the surface of mucous membranes. Since Neu5Gc is not present from birth, an antibody reaction occurs.
Remo Frei from the University of Zurich and employees can now show that children who live on the farm and have contact with animals have increased antibody titers against Neu5Gc. The researchers found this by examining serum samples collected from two EU-funded epidemiological studies (PARSIFAL and PASTURE studies).
The Swiss researchers also found that the children with the highest antibody titers against Neu5Gc are the least likely to develop asthma. Was this coincidence or could it be that the uptake of Neu5Gc and its appearance on the mucous membranes has protective function against allergic diseases?
The researchers examined this hypothesis in mouse model. Genetically modified mice that do not produce Neu5Gc themselves were exposed to Neu5Gc through their diet. The animals were then immune to allergies: In provocation tests with ovalbumin and house dust, there was reduced reaction of the respiratory tract and the asthma symptoms were less pronounced.
To understand the mechanism of how Neu5Gc affects the human immune system, The researchers analyzed various cells of the immune system that play role in an inflammatory reaction. With an interesting result: Contact with Neu5Gc does not reduce the immunoglobulins E, i.e. the antibodies that occur more frequently in allergic reactions. Rather, an anti-inflammatory reaction of the immune system was triggered, mediated by so-called regulatory T cells. These cells were more active in both the mice and the children after exposure to Neu5Gc. Regulatory T cells are known to dampen excessive immune system reactions, including allergies.
The new findings, if confirmed, could lay the foundation for effective allergy prevention. Children at increased risk of asthma could be treated with Neu5Gc from early childhood. Should this prevent the development of allergies, the hypothesis put forward by Frei and colleagues would ultimately be proven. It remains to be seen whether the idea will be taken up and examined clinically.