Human immune system uses chlorine bleach active ingredient to kill bacteria

Hypochlorous acid, the active ingredient in chlorine bleach is the main ingredient in a toxic cocktail produced by the human immune system to destroy bacteria, according to a new study (Eurekalert.org, March 6). The study, by researchers from two German universities, was published in eLife journal.

When bacteria enter the bloodstream, a group of immune system cells – neutrophil granulocytes, which are the most common white blood cells – are the first line of defense against infections. These defend the body by wrapping themselves around bacteria, and effectively ‘eating’ them, notes the journal. During this process, called phagocytosis, the cell also drenches the bacteria with a deadly cocktail of chemicals, including hypochlorous acid and the antiseptic, hydrogen peroxide. This mixture chemically burns, and then kills, the invaders.

Phagocytosis is still poorly understood, and difficult to study, notes the journal. It is not clear when the toxic mix is released, and which of its components are the most effective. Eurekalert.org quotes senior author Lars Leichert, of Ruhr-Universität Bochum, Germany, as saying that once these questions are answered, “we will understand how some bacteria outwit our immune system and how the immune system is impaired by certain genetic defects.”

To examine this process, the team genetically engineered E. coli bacteria and gave them a built-in chemical burn tracker. These bacteria carry fluorescent proteins that normally glow under blue light, but also begin to react to violet light if exposed to a chemical burn. Under the microscope, when these bacteria encounter immune cells, they start glowing under violet light after only a few seconds. This shows that, during phagocytosis, the toxic chemical mix is used almost immediately. The new technique also reveals that cells without a working NOX2 enzyme – which cannot produce hydrogen peroxide – could not burn the bacteria.

Hydrogen peroxide is used by a second enzyme, MPO, to create bleach. If just MPO is deactivated, the immune cells can burn the bacteria, but much less efficiently. This, and the speed with which these fluorescent proteins were burnt, shows that the hypochlorous acid is the main component of the toxic mix used during phagocytosis, according to eLife.

Patients with the rare, inherited immune system disorder, chronic granulomatous disease, can have a faulty version of the NOX2 enzyme, which makes it harder for them to fight infection. This disorder occurs in around one in 250,000 births, and those affected can become very sick from infections that would be mild in healthy individuals. Understanding the mechanisms and the enzymes associated with phagocytosis could lead to improved treatment in the future, concludes eLife.