A video about the shooting of a microbe
Scientists filmed how the immune system kills bacteria
Nikita Shevtsev, Naked Science
Scientists filmed how the immune system kills bacteria
Scientists at University College London were able to capture this process on video. An article about the study is available on the Preprints website BioRxiv.org (Parsons et al., Single-molecule kinetics of pore assembly by the membrane attack complex).
In earlier studies, scientists found signs of damage in living bacteria that faced the effects of the immune system. "Bullet holes" were found in the walls of bacteria. And although they were incredibly small – only 10 nanometers – it was enough to neutralize most of the pathogens.
In the new work, the researchers modeled the process of immune cells attacking foreign cellular organisms. It turned out that these deadly holes are formed thanks to a single molecule – the membrane-attacking complex (MAC). By tracking each step of the process, the scientists found that the process stops shortly after the hole begins to form.
Scientists say that the process is suspended because 18 copies of the same protein are needed to complete the hole. Initially, there is only one copy, which is inserted into the bacterial surface, after which other "clones" of the protein take their place nearby, but much faster. That is, the introduction of the first protein molecule into the surface of a pathogenic bacterium is the slowest stage, which determines the speed of the entire process.
Formation of "bullet holes" in bacterial walls / ©Edward S. Parsons et al., UCL
"This introduction of the first MAC molecule is a bottleneck in the killing process. It is curious that more than one molecule of this protein does not appear on our own healthy cells, the process does not move further. Thus, healthy cells remain intact," says one of the authors of the study, Professor Bart Hogenboom.
To photograph the immune system in action with nanometer resolution, scientists used atomic force microscopy. This type of microscopy uses a needle, the end of which is several nanometers wide, to feel the molecules on the surface. It's like a blind person reading Braille. The needle repeatedly scans the surface to produce an image that updates quickly enough to track how immune proteins come together and cut through the bacterial wall.
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