Immune cells kill bacteria with “bleach”

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 a bacterium, you also 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), which is used to make bleach, or bleach, a well–known disinfectant and bleaching agent.

The composition of the oxidative antibacterial cocktail used by neutrophils was discovered relatively long ago, and it is also known which enzymes are needed to accumulate 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 does the bacterium receive a portion of chemicals, how quickly they act, and which of the chemicals is more important here. Neutrophils, having eaten a portion of microbes, die and collapse quite quickly – maybe the treatment of bacteria with oxidizing agents happens after their death?

To find out the details of what was happening, researchers from the Ruhr University and the University of Bonn injected a special fluorescent protein sensitive to oxidation into experimental bacteria: in its 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, the immune cells flooded the bacteria with an oxidative 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.

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, but 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 oxidative stress. a cocktail.

Author: Kirill Stasevich, “Science and Life”