Subscribe to our free daily newsletters
  Space Travel News  




Subscribe to our free daily newsletters



A Viral Cloaking Device

Human Cytomegalovirus
by Staff Writers
Pasadena CA (SPX) Jul 24, 2008
Viruses achieve their definition of success when they can thrive without killing their host. Now, biologists Pamela Bjorkman and Zhiru Yang of the California Institute of Technology have uncovered how one such virus, prevalent in humans, evolved over time to hide from the immune system.

The human immune system and the viruses hosted by our bodies are in a continual dance for survival--viruses ever seek new ways to evade detection, and our immune system devises new methods to hunt them down.

Human Cytomegalovirus (HCMV), says Bjorkman, Caltech's Delbruck Professor of Biology and a Howard Hughes Medical Institute (HHMI) Investigator, "is the definition of a successful virus--it thrives but it doesn't affect the host."

HCMV is carried by eight in 10 people. Although it generally harms only those who are immunocompromised, it has also been linked with brain tumors like the one for which Ted Kennedy recently had surgery. Understanding how HCMV survives may help in the development of a vaccine, as well as in the fight against other viruses with similar evasive tactics.

"We are interested in mechanisms taken by viruses to escape our immune system," says Caltech biology postdoc and HHMI associate Zhiru Yang. She and Bjorkman published their findings on HCMV survival mechanisms in the July 15 edition of Proceedings of the National Academy of Sciences. They describe the underpinnings of a viral cloaking device, partly made of stolen goods from healthy cells, that helps HCMV to move undetected through the body.

For 20 years, Bjorkman's lab has been dedicated to understanding class 1 major histocompatibility complex (MHC) proteins and the immune response, most recently related to AIDS research. MHC proteins carry peptides, small pieces that are chopped up from the cell's internal proteins, to the cell's surface. If a cell has been infected, MHC presents viral peptides to signal T cells to kill it. So some viruses evolved to evade T cells by keeping MHC from reaching the cell surface. In turn, the immune system recruited other hunters to search for cells that don't show MHC proteins.

Sometime along its treacherous evolutionary path, HCMV stole a class 1 MHC molecule from its host and modified it for supreme stealth. "This is a decoy," Bjorkman says. She and Yang analyzed the structure of the mimic, called UL18, to compare how similar it is to the real thing. They found that despite a mere 23 percent match in genetic sequences, UL18 looks almost exactly the same as a true class 1 MHC.

The same immune cells that search for missing MHC proteins are designed to bind to them when they find them, thereby inhibiting an immune response. Yang and Bjorkman found that UL18 happens to bind 1,000 times tighter to these inhibitory receptors than real MHC molecules do. "This is exactly what the virus wants--to avoid being recognized by T cells, but to engage inhibitory receptors to turn off immune cells," Yang notes. "Only a small number of UL18 molecules are required to have the same inhibitory effect as a large number of MHC class I molecules."

"What I find astounding is that the virus stole this gene and kept it almost identical but improved upon its binding," Bjorkman says.

UL18 didn't stop there. "It also binds peptides--that's unique to this MHC mimic. We don't know why," Bjorkman adds. The peptide is obscured from killer cells by yet another shield, Yang says. In a trait it shares with HIV proteins, HCMV's UL18 covers itself with carbohydrates, which are unrecognizable to the immune system. A real class 1 MHC molecule has one site for adding carbohydrates; the fake has 13, Bjorkman notes. The only place where it's not covered is where it binds to the inhibitory receptor.

All its efforts have made UL18 virtually undetectable. "It's a good example of a viral protein that evolved from its host ancestor to block unwanted interactions," Yang says. "The more we understand that, the more effectively we can fight viruses that hide out," Bjorkman adds.

Related Links
California Institute of Technology
Epidemics on Earth - Bird Flu, HIV/AIDS, Ebola



Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News


Dengue cases in Philippines rise by 43 percent: government
Manila (AFP) July 23, 2008
Global warming may have contributed to a 43 percent rise in the number of dengue cases in the Philippines for the first half of the year, the health secretary said Wednesday.







  • Russia unveils new spacecraft design
  • Russian Set To Install Soyuz Launch Systems At Kourou
  • NASA Conducts Full-Scale Test Firing Of Orion Jettison Motor
  • NASA in talks for Japanese spacecraft

  • South Korea's First Rocket Launch Might Be Put Off
  • Soyuz-ST To Be Launched From French Guiana In First Half Of 2009
  • AMC-21 Is Delivered To Spaceport
  • Sea Launch Delivers Echostar 11 To Orbit

  • External Tank ET-128 Sets New Standard During Recent Shuttle Mission
  • NASA Sets Launch Dates For Remaining Space Shuttle Missions
  • NASA shuttle to take last flight in May 2010
  • Disaster plan in place for Hubble mission

  • ISS Crew Inspired By Vision And Dreams Of Jules Verne
  • Space Station A Test-Bed For Future Space Exploration
  • Space chiefs ponder ISS transport problem, post-2015 future
  • Two Russian cosmonauts begin new space walk

  • UK Space Competition Unearths Young Talent
  • UCF Project Selected For NASA Explorer Mission
  • House Passes S And T Bills Commemorating NASA's 50th Anniversary, First Woman In Space
  • Magellan Aerospace Wins Lockheed Martin Orion Contract

  • China's Astronauts To Wear Domestic, Russian-Made Suits
  • Shenzhou's Unsuitable Dilemma
  • China's Long March 2F Rocket Ready For Trip To Launch Center
  • Shenzhou 7 Shipped To Launch Center For October Launch

  • NASA Robots Perform Well During Arctic Ice Deployment Testing
  • Eight Teams Taking Up ESA's Lunar Robotics Challenge
  • Three Engineers, Hundreds of Robots, One Warehouse
  • Tartalo The Robot Is Knocking On Your Door

  • Phoenix Completes Longest Work Shift
  • NASA's Phoenix Mars Lander Prepares For Next Sample Analysis
  • NASA's Phoenix Mars Lander Works Through the Night
  • Mars Sample Return: Bridging Robotic And Human Exploration

  • The content herein, unless otherwise known to be public domain, are Copyright Space.TV Corporation. AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space.TV Corp on any Web page published or hosted by Space.TV Corp. Privacy Statement