Immune cells kill bacteria with "bleach"
After eating a bacterium, neutrophil immune cells instantly flood it with a strong oxidizer – hypochlorous acid
Kirill Stasevich, "Science and Life"
The immune system has a whole arsenal of ways to fight bacteria, and one of them is just to eat the enemy.
This is done, in particular, by neutrophils, or neutrophil granulocytes, which are among the first to encounter infection. But it's not enough to swallow the bacterium, you need to kill it somehow. The cells flood the absorbed bacterium with a complex chemical cocktail with strong oxidizing agents. The composition of oxidizing chemical weapons includes hydrogen peroxide and hypochlorous acid (hypochlorite), from which lime chloride is made, or bleach – a well-known disinfectant and bleaching agent.
The composition of the oxidative antibacterial cocktail used by neutrophils was revealed relatively long ago, it is also known which enzymes are needed for the accumulation of hydrogen peroxide and hypochlorous acid. But until now, it was not entirely clear what exactly happens in neutrophils when they absorb a bacterium: at what point the bacterium receives a portion of chemicals, how quickly they act, and which of the chemicals is more important here. Neutrophils, after eating a portion of microbes, die and collapse quite quickly – maybe the treatment of bacteria with oxidants happens after their death?
To find out the details of what is happening, researchers from the Ruhr University and the University of Bonn introduced a special fluorescent protein sensitive to oxidation into experimental bacteria: in a normal state, it glowed green when illuminated with blue light, but after oxidation, in order to achieve fluorescence, it had to be illuminated not with blue light, but with purple.
The bacteria were fed to immune cells, and it turned out that within a few seconds after they got inside the neutrophils, the glowing protein changed properties. In other words, immune cells flooded bacteria with an oxidizing cocktail almost instantly. An article in eLife says that, judging by the speed of the chemical reaction and the way the fluorescent protein inside the bacteria was oxidized, hypochlorite was the main oxidizer – so it's a stretch to say that neutrophils killed bacteria with "bleach".
However, in order to get hypochlorite, neutrophils need hydrogen peroxide. Therefore, when the gene responsible for the production of peroxide was turned off, the absorbed bacteria remained alive. On the other hand, if the gene responsible for the production of hypochlorite was turned off, the bacteria died, but very reluctantly – the peroxide itself also killed them, but it was definitely not enough here.
With the new data, we can not only better understand how immune cells fight infection and why some bacteria still manage to withstand chemical weapons - perhaps in the future it will be possible to create some new, more effective antibacterial drugs that will help the immune system kill microbes by acting on enzymes that create an oxidative cocktail.
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