Disgusting but helpful: “We underestimate how important mucus is for us”

Disgusting but helpful: “We underestimate how important mucus is for us”
Photo: CC0 Pixabay / Mojca-Peter

Mucus is much more than just a disgusting secretion. It is an underestimated body fluid that plays an important role in our health. Mucus protects us from pathogens, houses beneficial microbiomes and ensures smooth body functions

Whether as snot from the nose, sputum from the lungs or secretion from a weeping wound: when many people see mucus they think “Yuck!” But this often underestimated body fluid plays a crucial role in our health. It acts as a first line of defense against pathogens, a habitat for our microbiomes and a conveyor belt for our digestion so that everything literally runs smoothly.

Slime: lubricant and protection

Even in ancient times, mucus was assigned a central role: as one of the four body humors alongside blood, black and yellow bile, which were supposed to be in balance for health and well-being. Nowadays, the sticky secretions are considered to be disgusting pathogens.

Mucus – or mucus – is much more than just a sputum product of the body: as a natural lubricant, it is of great importance for swallowing and digestion, for example, prevents the penetration of pathogens in the form of nasal secretions or cervical mucus, protects the stomach wall from stomach acid and houses a large part of the human microbiome, for example in the intestinal flora.

More than a liter of mucus a day

Overall, the human body produces on average around one to one and a half liters of mucus per day. The composition of the gel-like substance, which mainly consists of water, proteins, antibodies and enzymes, varies depending on the region of the body. Certain glycoproteins, the so-called mucins, are responsible for the structure of the mucus. In interaction with their respective environment, they determined whether the mucus was thin, like in the lungs, or more viscous, like in the stomach.

Prevented infections

These same mucins probably play a major role in neutralizing dangerous germs that try to enter the body through the nose. Contrary to what was previously thought, the mucilage may not act like a barrier – rather, the sugar molecules in the mucins could disrupt the signal transmission of the germs and thus render them harmless. At least that’s what a study published in 2019 in the journal “Nature Microbiology” suggests by the German biophysicist Katharina Ribbeck, who researches mucus at the Massachusetts Institute of Technology in the USA.

According to the study, it is not yet possible to answer exactly how the mucins tame germs. However, if the corresponding bioactive sugar molecules were identified, this could probably allow the development of a “class of therapeutics for the treatment of persistent bacterial infections”.

Bioink made from slime

This is not the only conceivable application: In a study published in the journal “ACS Applied Bio Materials” in June of this year, an Indian research group presented a mucin-based bioink for 3D printing of lung tissue. Such ink could one day be used to create 3D lung models to study lung diseases and test possible treatments.

At the Technical University of Munich, under the direction of Oliver Lieleg, research is also being conducted into medical applications of mucins, including bioink made from mucins. Lieleg, who has been working on the topic for 15 years, attributes the great potential of the complex slime molecules to their diverse properties: They could, for example, bind a lot of water, stick to many surfaces, but suppress the adhesion of other objects quite well . “But there is also the opposite case: viruses, for example, are bound very well by mucins and that is part of the job of mucus so that we don’t constantly lie in bed with a cold.”

Contact lens lubricant

In addition, mucins are well tolerated as the body’s own material – an important property for possible medical use, which includes special coatings for contact lenses or intubation tubes. For this, Lieleg’s team took advantage of the fact that mucins are a good lubricant: “Contact lenses and intubation tubes are hard materials that, in the worst case scenario, can cause damage to soft tissue.” Mucin-based coatings could minimize such irritations – and in the case of contact lenses also ensure that lipids from the tear film of the eyes do not settle on the lenses.

Lieleg’s group obtains the mucus molecules used from mucus from pig stomachs, which is diluted and chemically cleaned until the end result is pure mucin with a cotton candy consistency.

In addition, the researchers have developed a wound healing patch specifically for injuries to soft tissue such as the tongue or intestines. The prototype contains a mucin-based side that has an antibacterial effect and thus prevents the wound from becoming contaminated.

Lieleg and his team are also researching possible disorders of the mucus system and were able to show that fine dust particles can influence the barrier effect of mucus. The group is currently carrying out similar studies on microplastic particles. “Mucus absorbs a lot of what hits our mucous membranes from the external environment,” summarizes Lieleg. “If contaminants weaken that barrier, things might get through that shouldn’t.”

Slime has an unjustified bad image

The scientist emphasizes: “I think we simply underestimate how important mucus is for us.” Without mucin in the tear film, blinking would become difficult over time. Certain clinical pictures were shown by reduced mucin production, for example in saliva. “If it doesn’t lubricate properly, speaking and swallowing are painful,” says Lieleg.

We owe the fact that we don’t get sick all the time to the mucus molecules, which absorb a lot: “What comes out of the nose may not look so nice, but that’s because the fine dust particles or a large part of the flu viruses from my office neighbor. Luckily hanging in there.” Slime has far too bad an image. “I think many people don’t realize how important it is to our everyday well-being.”

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