How the immune system and the microbiome interact in our nose

How the immune system and the microbiome interact in our nose

Microbes on the mucous membrane. © Michael Pelzer/University of Tübingen

Our nose is a gateway for bacteria and viruses from the air we breathe. To fight off these pathogens, beneficial bacteria and our immune system work together in the mucous membrane of our nose. A study now shows how the body’s own antibody immunoglobulin A influences the number and composition of the microbial inhabitants of the nose. A higher IgA level is therefore associated with fewer bacteria. The reactions of the antibodies to the bacteria apparently differ from person to person. The study also provides potential starting points for combating infections with the hospital germ MRSA.

The microbiome in our nose plays an important role in our health. Depending on which bacteria colonize our nasal mucosa, we may be more susceptible to allergies or certain respiratory diseases. In addition, helpful microorganisms and our immune system work together to keep harmful germs at bay. To combat unwanted bacteria on the mucous membrane, our body uses, among other things, the so-called secretory immunoglobulin A (sIgA). This antibody variant is able to bind bacteria and render them harmless. In addition to our nasal secretions, sIgA is found in saliva, sweat, intestinal fluid, tears and breast milk. However, how exactly it influences the nasal microbiome was previously unclear.

Immune system limits bacterial density

A team led by Rob van Dalen from the University of Tübingen has now investigated how the body’s immune system and the bacteria in the nose interact with each other. To do this, the researchers analyzed nasal swabs from 50 healthy people and recorded the secretory immunoglobulin A content and the composition of the bacterial communities. They also examined the interactions between these antibodies and the bacteria at the molecular level.

The result: “We found that the amount of sIgA that a person secretes into the nasal mucosa varied greatly from person to person,” report the researchers. “The amount of sIgA correlated negatively with the bacterial density. This suggests that sIgA in the nose limits the overall capacity of the bacteria to colonize.” The immunoglobulin A content of the nasal secretion differed from person to person, sometimes by more than a hundredfold, with people with less sIgA having significantly more bacteria the nose. However, the diversity of different bacterial species was not influenced by the amount of this antibody.

Individual differences

In addition, van Dalen and his team found that the bacteria in the noses of different people reacted differently to the secretory immunoglobulin A. While in some test subjects a clear reaction of these antibodies against certain bacteria was observed, the same bacteria in the nose of another person remained unaffected. The researchers therefore assume that the immune reaction depends on numerous factors, including probably the genetics of the person in question and the local conditions in the nose.

The researchers identified the bacteria Staphylococcus aureus as part of the nasal microbiome in eight of the 50 test subjects. This bacteria is usually harmless, but under certain conditions it can cause life-threatening infections. The variant methicillin-resistant Staphylococcus aureus (MRSA), which is resistant to many antibiotics, is feared as a hospital germ. To learn more about the interactions between S. aureus and the immune system, the research team analyzed at the molecular level how the secretory immunoglobulin A binds to the surface of the bacterium.

Potential for new treatment methods

The study revealed a specific interaction between sIgA and a surface protein of S. aureus called staphylococcal protein A (SpA). This protein has previously been linked to the bacterium’s resistance to various human antibodies. According to the researchers, manipulating the binding between SpA and sIgA could help in the future to strengthen the immune reaction against S. aureus. “We are beginning to understand the processes in our microbiomes better and better,” says van Dalen. “The interactions of the antibody sIgA with the nasal microbiome clearly show us how these microbial systems regulate themselves – and could be regulated. We have huge potential here for future treatment methods.”

An improved understanding of the antibody response to bacteria in the nasal microbiome could also help develop vaccines that are administered through the nasal mucosa. There are already flu vaccines for children and young people that are administered as a nasal spray. Nasal vaccines are also in development against Covid-19. However, according to the researchers, there is still a long way to go before the results that have now been published can actually influence clinical practice.

Source: Rob van Dalen (University of Tübingen) et al., Microbiome, doi: 10.1186/s40168-023-01675-y

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