Featured Research

from universities, journals, and other organizations

On the trail of a stealthy parasite Biologist shows why some strains of Toxoplasma are more dangerous than others

Date:
January 5, 2011
Source:
Massachusetts Institute of Technology
Summary:
About one-third of the human population is infected with a parasite called Toxoplasma gondii, but most of them don't know it. Though Toxoplasma causes no symptoms in most people, it can be harmful to individuals with suppressed immune systems, and to fetuses whose mothers become infected during pregnancy. Toxoplasma spores are found in dirt and easily infect farm animals such as cows, sheep, pigs and chickens. Humans can be infected by eating undercooked meat or unwashed vegetables.

This image shows two human skin cells. The cell at left is infected with the Toxoplasma gondii parasite expressing type II GRA15, which can be seen in green. The cell on the right (with a blue nucleus) is not infected. The nucleus of the infected cell contains many copies of the NF-kB transcription factor (shown in pink).
Credit: Image courtesy of the Saeij Laboratory

About one-third of the human population is infected with a parasite called Toxoplasma gondii, but most of them don't know it. Though Toxoplasma causes no symptoms in most people, it can be harmful to individuals with suppressed immune systems, and to fetuses whose mothers become infected during pregnancy. Toxoplasma spores are found in dirt and easily infect farm animals such as cows, sheep, pigs and chickens. Humans can be infected by eating undercooked meat or unwashed vegetables.

Jeroen Saeij, an assistant professor of biology at MIT is investigating a key question: why certain strains of the Toxoplasma parasite (there are at least a dozen) are more dangerous to humans than others. He and his colleagues have focused their attention on the type II strain, which is the most common in the United States and Europe, and is also the most likely to produce symptoms. In a paper appearing in the Jan. 3 online edition of the Journal of Experimental Medicine, the researchers report the discovery of a new Toxoplasma protein that may help explain why type II is more virulent than others.

Toxoplasma infection rates vary around the world. In the United States, it's about 10 to 15 percent, while rates in Europe and Brazil are much higher, around 50 to 80 percent. However, these are only estimates -- it is difficult to calculate precise rates because most infected people don't have any symptoms.

After an infection is established, the parasite forms cysts, which contain many slowly reproducing parasites, in muscle tissue and the brain. If the cysts rupture, immune cells called T cells will usually kill the parasites before they spread further. However, people with suppressed immune systems, such as AIDS patients or people undergoing chemotherapy, can't mount an effective defense.

"In AIDS patients, T cells are essentially gone, so once a cyst ruptures, it can infect more brain cells, which eventually causes real damage to the brain," says Saeij.

The infection can also cause birth defects, if the mother is infected for the first time while pregnant. (If she is already infected before becoming pregnant, there is usually no danger to the fetus.)

There are drugs that can kill the parasite when it first infects someone, but once cysts are formed, it is very difficult to eradicate them.

A few years ago, Saeij and colleagues showed that the Toxoplasma parasite secretes two proteins called rhoptry18 and rhoptry16 into the host cell. Those proteins allow the parasite to take over many host-cell functions.

In the new study, the MIT team showed that the parasite also secretes a protein called GRA15, which triggers inflammation in the host. All Toxoplasma strains have this protein, but only the version found in type II causes inflammation, an immune reaction that is meant to destroy invaders but can also damage the host's own tissues if unchecked. In the brain, inflammation can lead to encephalitis. This ability to cause inflammation likely explains why the type II strain is so much more hazardous for humans, says Saeij.

Saeij and his team, which included MIT Department of Biology graduate students Emily Rosowski and Diana Lu, showed that type II GRA15 leads to the activation of the transcription factor known as NF-kB, which eventually stimulates production of proteins that cause inflammation. The team is now trying to figure out how that interaction between GRA15 and NF-kB occurs, and why it is advantageous to the parasite.

Ultimately, Saeij hopes to figure out how the parasite is able to evade the immune system and establish a chronic infection. Such work could eventually lead to new drugs that block the parasite from establishing such an infection, or a vaccine that consists of a de-activated form of the parasite.

MIT Department of Biology graduate students Emily Rosowski and Diana Lu are the paper's two first authors and contributed equally to the research. Other authors include MIT postdoc Kirk Jensen, lab technician Lindsay Julien, MIT undergraduate student Lauren Rodda, and Rogier Gaiser, a graduate student at Wageningen University in the Netherlands.

Source: "Strain-specific activation of the NF-kB pathway by GRA15, a novel Toxoplasma gondii dense granule protein," by Emily E. Rosowski, Diana Lu, Lindsay Julien, Lauren Rodda, Rogier A. Gaiser, Kirk D.C. Jensen, Jeroen P.J. Saeij. Journal of Experimental Medicine, 3 January 2011.

Funding: American Heart Association, Massachusetts Life Sciences Center, Singapore-MIT Alliance for Research and Technology (SMART), National Institutes of Health, Cleo and Paul Schimmel Fund, Cancer Research Institute, MIT UROP office and the John Reed Fund.


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by Anne Trafton, MIT News Office. Note: Materials may be edited for content and length.


Journal Reference:

  1. Emily E. Rosowski, Diana Lu, Lindsay Julien, Lauren Rodda, Rogier A. Gaiser, Kirk D.C. Jensen, Jeroen P.J. Saeij. Strain-specific activation of the NF-kB pathway by GRA15, a novel Toxoplasma gondii dense granule protein. Journal of Experimental Medicine, 2011; DOI: 10.1084/jem.20100717

Cite This Page:

Massachusetts Institute of Technology. "On the trail of a stealthy parasite Biologist shows why some strains of Toxoplasma are more dangerous than others." ScienceDaily. ScienceDaily, 5 January 2011. <www.sciencedaily.com/releases/2011/01/110104114311.htm>.
Massachusetts Institute of Technology. (2011, January 5). On the trail of a stealthy parasite Biologist shows why some strains of Toxoplasma are more dangerous than others. ScienceDaily. Retrieved July 30, 2014 from www.sciencedaily.com/releases/2011/01/110104114311.htm
Massachusetts Institute of Technology. "On the trail of a stealthy parasite Biologist shows why some strains of Toxoplasma are more dangerous than others." ScienceDaily. www.sciencedaily.com/releases/2011/01/110104114311.htm (accessed July 30, 2014).

Share This




More Health & Medicine News

Wednesday, July 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Health Insurers' Profits Slide

Health Insurers' Profits Slide

Reuters - Business Video Online (July 30, 2014) Obamacare-related costs were said to be behind the profit plunge at Wellpoint and Humana, but Wellpoint sees the new exchanges boosting its earnings for the full year. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Concern Grows Over Worsening Ebola Crisis

Concern Grows Over Worsening Ebola Crisis

AFP (July 30, 2014) Pan-African airline ASKY has suspended all flights to and from the capitals of Liberia and Sierra Leone amid the worsening Ebola health crisis, which has so far caused 672 deaths in Guinea, Liberia and Sierra Leone. Duration: 00:43 Video provided by AFP
Powered by NewsLook.com
At Least 20 Chikungunya Cases in New Jersey

At Least 20 Chikungunya Cases in New Jersey

AP (July 30, 2014) At least 20 New Jersey residents have tested positive for chikungunya, a mosquito-borne virus that has spread through the Caribbean. (July 30) Video provided by AP
Powered by NewsLook.com
Generics Eat Into Pfizer's Sales

Generics Eat Into Pfizer's Sales

Reuters - Business Video Online (July 29, 2014) Pfizer, the world's largest drug maker, cut full-year revenue forecasts because generics could cut into sales of its anti-arthritis drug, Celebrex. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins