Amoebic dysentery is a type of diarrheal disease that affects millions
around the globe annually. Passed around by contaminated water,
amoebas get into people's intestines, causing bloody diarrhea. If left
untreated, these single-cell organisms can eventually perforate the
intestines, spread throughout the body and kill the host. As Rose Hoban
reports, researchers are learning more about the amoeba's ability to
outwit the body's immune system.
When a foreign material, like an amoeba, enters the body, immune cells don't recognize the proteins on the surface of the cell... that's because they're foreign. So immune antibodies attack these foreign proteins, and are able to neutralize the invading cell. But amoebas can evade the human immune system.
Johns Hopkins biochemist Sin Urban says these simple organisms have evolved a sophisticated method to escape this immune attack. "What the amoeba does, [is] it takes all these proteins once they become attacked by antibodies, and it shuttles all of them to the back of the cell and jettisons them in a little ball," Urban explains. "So essentially, it's taking all of the things that our immune system is attacking, and jettisons it, and essentially gets away scot free." The antibodies continue to attack the protein, while leaving the amoeba alone.
The key to creating this immune decoy is the rhomboid enzymes produced by the amoeba. Enzymes are present in almost every living thing. Urban explains that they facilitate chemical reactions in – and on – cells. "We found out that the rhomboid enzyme is usually on the surface, but during this jettisoning process, it actually forms a tight seal around the base of this little ball that's being released. Being an enzyme, and being in that part of the cell during this release process, we think it might actually be involved in release of this little ball of surface proteins."
Urban is trying to learn more about the role of rhomboid enzymes in this decoy process. He says in the future, rhomboids could end up being a good target for new medications to treat amoebic dysentery.
Urban's research is in a recent issue of Genes and Development.