Researchers discover how human body fights off African parasite

September 7, 2007

Trypanosoma are a nasty class of single-celled parasites that cause serious, even fatal, diseases in human and animals. Two species cause sleeping sickness, a disease that threatens all of sub–Saharan Africa. There’s a catch though: one parasite, Trypanosoma brucei brucei (T. b. brucei), infects animals but seems to spare humans, and scientists haven’t quite understood why.

Now, a team of researchers led by biochemists at the University of Georgia propose that T. b. brucei actually does infect humans but that the infection triggers release of hemoglobin from red blood cells. Hemoglobin appears to “arm” the human innate immune system by binding to a small fraction of high density lipoprotein (HDL), or “good cholesterol.” The hemoglobin-HDL complex then becomes a super toxin and clears the body of trypanosomes.

“This is a real paradigm shift in understanding what T. b. brucei does in humans,” said Stephen Hajduk, professor and head of the department of biochemistry and molecular biology at the University of Georgia. “It had always been assumed that it didn’t infect humans at all, but it now appears that it does and that the release of free hemoglobin leads to clearance of the infection. It was incredibly surprising to us.”

Lead author on the research is Justin Widener, a graduate student in Hajduk’s lab. The research was published today in the Public Library of Science Pathogens. Widener is also a student at Brown University, where he began his work with Hajduk, who joined the UGA faculty in 2006. Other authors on the paper include April Shiflett of UGA and Marianne Jensby Nielsen and Søren Krag Moestrup of University of Aarhus in Denmark.

Hajduk and his group are interested in a parasite that does not harm humans because they asked a simple question: why can’t T. b. brucei infect humans although it is nearly identical to the African sleeping sickness-causing parasite" After all, two cousins of T. b. brucei, known as T. b. gambiense and T. b. rhodensiense, cause, respectively, chronic and acute sleeping sickness in humans. The parasites, which are carried by the tsetse fly and injected into humans and animals with its bite, have been a major health issue since the first recorded outbreak of sleeping sickness beginning in 1906.

“We know that humans are protected against T. b. brucei by the action of a high-density lipoprotein called Trypanosome Lytic Factor [TLF],” said Widener. “We investigated the mechanism of how TLF kills the parasite by using a purification technique that allowed us to show that a protein associated with TLF strongly binds hemoglobin and that hemoglobin stimulates TLF to kill the parasite.”

Because all three strains are closely related—T. rhodensiense is different from T. b. brucei by a single gene—what is true for one species could be useful in understanding the others.

While human sleeping sickness has been an important human disease in Africa for more than a century, recent epidemics of the disease in five African nations underscore the potential threat of this disease to travelers and aid workers.

One interesting aspect of trypanosomes is their ability to infect a wide range of mammals, from humans to wild game. The severity of disease caused by T. b. brucei varies depending on the host; infections in humans are cleared while a fatal disease develops in infected cattle. The application of the discovery by Widener on the mechanism of human protection may lead to better treatment of cattle infections by these parasites.

The value of the new research may lie as much in its potential as a model system for studying all trypanosomes as it does in specifically understanding why T. b. brucei doesn’t infect humans.

Source: University of Georgia

Explore further: To survive, a parasite mixes and matches its disguises, study suggests

Related Stories

Blocking African sleeping sickness' tiny culprit

October 6, 2014

A tsetse fly bites a girl. She becomes itchy, feverish, and her joints ache. Weeks later, she loses coordination and some sensation in her limbs. It becomes difficult to think, to sleep.

Parasite helps itself to sugar

July 8, 2013

Trypanosoma brucei, the parasite that causes sleeping sickness, is transmitted to mammals by the tsetse fly, and must adapt to the divergent metabolisms of its hosts. A new study shows how it copes with the frugal diet offered ...

Researchers unravel secrets of parasites' replication

July 10, 2012

A group of diseases that kill millions of people each year can't be touched by antibiotics, and some treatment is so harsh the patient can't survive it. They're caused by parasites, and for decades researchers have searched ...

Recommended for you

ATLAS and CMS experiments shed light on Higgs properties

September 1, 2015

Three years after the announcement of the discovery of a new particle, the so-called Higgs boson, the ATLAS and CMS Collaborations present for the first time combined measurements of many of its properties, at the third annual ...

Fossil specimen reveals a new species of ancient river dolphin

September 1, 2015

The careful examination of fossil fragments from Panama has led Smithsonian scientists and colleagues to the discovery of a new genus and species of river dolphin that has been long extinct. The team named it Isthminia panamensis. ...

Distant planet's interior chemistry may differ from our own

September 1, 2015

As astronomers continue finding new rocky planets around distant stars, high-pressure physicists are considering what the interiors of those planets might be like and how their chemistry could differ from that found on Earth. ...

Magnetic fields provide a new way to communicate wirelessly

September 1, 2015

Electrical engineers at the University of California, San Diego demonstrated a new wireless communication technique that works by sending magnetic signals through the human body. The new technology could offer a lower power ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.