Immune system: strong acid bombs against bacteria - then the pus turns green

Immune defense: why pus is green
Pus looks pretty gross because of its greenish color, but it has a very important function for the body. The secretion produces an aggressive acid against bacteria. These new study findings provide starting points for therapies to strengthen the immune system.

Certain enzyme is responsible for green color of pus
With a sinus infection, an abscess on the buttocks or an inflamed wound on the leg: No matter what the cause or where in the body there is pus, the secretion usually looks pretty disgusting. Sometimes the secretion is more yellowish, in other cases it is green. The color gives information about the processes in the body. For example, the enzyme myeloperoxidase, or MPO for short, is responsible for a green color. Scientists from Switzerland have now examined this enzyme in more detail and found astonishing results.

Extremely aggressive acid
As the University of Basel reports in a communication, university researchers have succeeded in clarifying the role of the MPO enzyme.

The enzyme, which gives the pus a greenish color, therefore produces an extremely aggressive acid in the fight against infections, with which it can kill pathogens without damaging the surrounding tissue.

According to the experts, the results of the study, which have now been published in the journal "Nature Microbiology", provide starting points for therapies to strengthen the immune system.

White blood cells against bacterial pathogens
White blood cells play a key role in the fight against bacterial pathogens. They identify intruders, eat them and then render the bacteria harmless with highly toxic substances.

It is important that these substances only affect the bacteria and cause as little collateral damage as possible in the surrounding tissue.

The Swiss scientists have now discovered how white blood cells solve this difficult task. Accordingly, the enzyme MPO sits directly on the surface of bacteria and produces an extremely aggressive acid there, which immediately reacts with the environment, eats a hole in the bacterial cell envelope and thus kills it.

MPO fights very precisely and precisely against bacterial infections without causing collateral damage in the area.

"Powerless against this acid bomb"
White blood cells use hydrogen peroxide to fight bacterial invaders. The enzyme MPO forms hypochlorous acid from it, a substance that, according to the researchers, is many times more effective and aggressive than hydrogen peroxide. The acid settles directly on the surface of the bacteria, reacts there immediately and kills the intruder.

"Bacteria are practically powerless against this acid bomb," said study author Prof. Dirk Bumann. “Because hypochlorous acid is so highly reactive, the bomb immediately reacts with the next biomolecule. It does not get into the wider environment, but is ignited locally. The bacteria die and the surrounding tissue is spared. "

Some people accumulate hydrogen peroxide
According to the information, the study also examined cells from humans who lack the enzyme MPO due to a genetic defect. According to the experts, this defect affects around one in 5,000 people, so it is very rare.

In these people, the hydrogen peroxide is not converted to hypochlorous acid, but accumulates until it finally flows into the blood cell and outwards.

“The bacteria are rendered harmless even without an MPO. However, this not only damages the bacteria, but also the blood cells themselves and the environment, ”said Bumann.

Co-author PD Dr. Nina Khanna added: "How strong inflammatory reactions without MPO and the associated death of blood cells are disadvantageous or whether they even lead to long-term damage has not been researched so far."

New forms of therapy in the fight against bacterial infections
According to Khanna, cellular collateral damage does not currently play such a major role in Germany, "because in our latitudes we struggle with infections much less often than in the past." However, it would be conceivable to develop new forms of therapy in the fight against bacterial infections, which could support the immune response by specifically strengthening the MPO mechanism.

“This approach is interesting in that so far there are only drugs that do the opposite and inhibit MPO. The reason is that MPO can also have negative effects on the body in the case of heart diseases, ”says Bumann.

However, if such MPO inhibitors were used widely, the disadvantages of infectious diseases could be more pronounced. (ad)

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