The immune system is the body's primary defense against disease-causing pathogens. In a new study, scientists filmed how the immune system kill bacteria in the blood.

The study, conducted by a team from the University College London, can lead to a better understanding of the processes that take place within the body during bacterial infection. It can also be used to develop new treatment options that will take advantage of the immune system to attack rogue cells.

They published their findings in the journal Nature Communications on Monday, May 6.

The Immune System Against Bacteria

The immune system is a collection of structures and processes that guards the human body against foreign invaders such as bacteria, viruses, and parasites. It can distinguish between the self (the human body) against the nonself (the foreign invader).

To kill bacteria, the immune system makes use of nanomachines, which can open holes into the pathogen and kill it without harming the self. To further understand the process, the researchers mimic the creation of these deadly holes formed by the membrane attack complex, or MAC, using a model bacterial surface.

They filmed the immune system's response to bacteria using atomic force microscopy at nanometer resolution and at a few seconds per frame. The microscopy functions like Braille: the instrument feels rather than see the molecules on a surface.

The needle repeatedly scans the surface and produce an image. It refreshes rapidly in order to track every step of the processes that take place when the immune system attacks a foreign invader.

How The Immune System Avoids Damaging Human Cell

The researchers found that after each hole forms, the attack briefly pauses in order to allow the human cells to react if it is affected.

"It appears as if these nanomachines wait a moment, allowing their potential victim to intervene in case it is one of the body's own cells instead of an invading bug, before they deal the killer blow," explained Edward Parsons of the University College London Center for Nanotechnology.

The researchers said that, initially, one copy of the protein is inserted into the bacterial surface. Then, the attack pauses of a bit, after which the other copies are added more rapidly. The process needs 18 copies of the same protein to complete a hole.

"It is the insertion of the first protein of the membrane attack complex which causes the bottleneck in the killing process," shared Bart Hoogenboom, a professor at the University College London Physics & Astronomy. "Curiously, it coincides with the point where hole formation is prevented on our own healthy cells, thus leaving them undamaged."