An ordinary parasite pulls a face out of your cages to wear it as a mask

New research has shown how the parasitic amoeba Entamoeba histolytica takes bites from your cells to use as a mask, hiding them from the immune system.

Getting into the body through contaminated food or water, most infections from the parasite cause diarrhea, if there are any symptoms at all. In particularly bad cases, amoeba can spread through the bloodstream to other vital organs, where it can cause serious problems.

For example, if the infection reaches the liver, the amoebic abscesses it creates can be fatal, causing complications that take the lives of almost 70,000 people every year.

Exactly how this tiny monster sows such chaos in its host was largely unknown until microbiologist Catherine Ralston - currently at the University of California at Davis, but then published at the University of Virginia - researched the amoeba more thoroughly in 2011.

The theory was that E. histolytica injected poison into the cells of its victim. But Ralston saw something completely different, going through her microscope. E. histolytica removed what looked like real bites from human cells.

To develop new treatments or vaccines, you really need to know how E. histolytica damages tissues," Ralston says. "You could see how small parts of the human cell break off."

Even more strange, the amoeba seemed to be satisfied with just a few pieces from the membrane of each cell before moving on to its next victim, leaving behind many half-chewed cells with cytoplasms oozing from their pierced wounds.

"He can kill anything you throw at him, any human cell," says Ralston. He can even walk white blood cells, which are designed to swallow such intruders.

Now Ralston and her colleagues Maura Ryuechan and Wesley Juan discovered that this seemingly wasteful habit actually allows E. histolytica to collect proteins of the outer membrane from human cells, which she continues to place on the surface of her own body to protect against blood.

Surprisingly, this disguise protects it not only from human immune "guards": it also acts on immune reactions present in the blood of other species.

"It became clear that amoebas kill human cells by performing cellular gnawing known as trogocytosis," the authors write. "After trogocytosis, amoebas show human proteins on their own surface and are resistant to lysis [rupture] by human serum [blood component]".

This molecular camouflage prevents our immune system from attacking the amoeba by presenting chemical labels that identify it as safe, a bit like stealing an identity card from a security guard. When E. histolytica delivers human proteins CD46 and CD55, it can safely pass by "complementary proteins" that are tasked with tracking and destroying foreign cells.

This allows him to continue gnawing, forming abscesses full of liquefied cells in the organs it inhabits.

It is intriguing that the team conducted an experiment in which they allowed the amoeba to collect material from human cells before exposing "disguised" parasites to mouse blood serum.

"Althous mice are not the natural host of E. histolytica, experimental infection of mice with amoebae mimics many aspects of human infection, ranging from immune reactions to genetic determinants of the host's susceptibility to infection," the authors write.

Its camouflage was effective, despite the fact that it came from a completely different species, reflecting the similarity between the human and mouse supplement protein safety systems. This knowledge will allow researchers to further explore treatments and amoeba vaccines using mouse models before starting human trials.

"Science is the process of construction," says Ralston. "You have to build one tool on top of another until you are finally ready to discover new methods of treatment."