Policing cells demand ID to tell friend from foe

Mar 11, 2008

University of Pennsylvania scientists studying macrophages, the biological cells that spring from white blood cells to eat and destroy foreign or dying cells, have discovered how these “policemen” differentiate between friend and foe. The paper appears as the cover article in the March 10 edition of the Journal of Cell Biology.

The knowledge suggests new ways science may be able to turn off rogue macrophages that are the root cause of the many inflammatory diseases ranging from atherosclerosis to arthritis and that provide the mechanism for tissue and organ rejection after transplant.

There is also evidence that some types of cancer cells over-express the molecular protein that macrophages recognize as friendly — like a fake ID — which allows the cancer to avoid being perceived as foreign. In addition, the molecules involved in the recognition mechanism appear somewhat variable from person to person, with possible links to success or failure in transplantation of stem cells.

Researchers studied these main “policing cells” in the body, macrophages, from the Greek for “eating cells,” and how they choose to attack and engulf foreign cells and particles but recognize and refuse to eat their own kind.

“Like a police dog, a macrophage responds to a signal that means ‘let go,’ Dennis Discher, professor of chemical and biomolecular engineering at Penn, said. “It’s what makes your body more of a 'dog eat cat' kind of world rather than a 'dog eat dog' world.”

Discher and his team observed macrophages in culture using “friendly” human blood cells and “foreign” sheep blood cells as well as plastic particles. In all cases, the macrophage binds to a target, often identified by a cloak of common IgG antibodies (the community watch), and “frisks” the target with a cell extension. This protein extension becomes a muscle-like headlock with foreign targets, wrapping around the target and pulling it in. Self-cells have a molecular protein on their surface that is specifically recognized by the macrophage to switch off the headlock, thus stopping engulfment and allowing self cells to coexist and move on.

The team found that both actin and non-muscle myosin were involved in the attack of foreign sheep cells due to recognition of the foreign protein CD47. Human red blood cells activated only actin, in a meet-and-greet maneuver. Macrophages, therefore, use a form of identification, much like police ask for a driver’s license at a traffic stop; however, not every cell tailed by antibodies is a danger to the body, so macrophages check for that marker, the protein CD47. If the latter is missing or even of the wrong species, the target is devoured.

Additional experiments also showed that protein CD47 affects its receptor, SIRP-alpha, which in turn inactivates the myosin by preventing the addition of a phosphate group to the brawny molecule. By shutting down a pulling protein needed to complete phagocytosis, CD47 prevents cells that belong from being eaten.

Source: University of Pennsylvania

Explore further: Study to use Google data search analytics to understand marine networks

add to favorites email to friend print save as pdf

Related Stories

Rare new species of plant: Stachys caroliniana

37 minutes ago

The exclusive club of explorers who have discovered a rare new species of life isn't restricted to globetrotters traveling to remote locations like the Amazon rainforests, Madagascar or the woodlands of the ...

New terahertz device could strengthen security

41 minutes ago

We are all familiar with the hassles that accompany air travel. We shuffle through long lines, remove our shoes, and carry liquids in regulation-sized tubes. And even after all the effort, we still wonder if these procedures ...

European space plane set for February launch

50 minutes ago

Europe's first-ever "space plane" will be launched on February 11 next year, rocket firm Arianespace said Friday after a three-month delay to fine-tune the mission flight plan.

Space station rarity: Two women on long-term crew

51 minutes ago

For the 21st-century spacewoman, gender is a subject often best ignored. After years of training for their first space mission, the last thing Samantha Cristoforetti and Elana Serova want to dwell on is the ...

Recommended for you

Genomes of malaria-carrying mosquitoes sequenced

9 hours ago

Nora Besansky, O'Hara Professor of Biological Sciences at the University of Notre Dame and a member of the University's Eck Institute for Global Health, has led an international team of scientists in sequencing ...

Bitter food but good medicine from cucumber genetics

9 hours ago

High-tech genomics and traditional Chinese medicine come together as researchers identify the genes responsible for the intense bitter taste of wild cucumbers. Taming this bitterness made cucumber, pumpkin ...

New button mushroom varieties need better protection

14 hours ago

A working group has recently been formed to work on a better protection of button mushroom varieties. It's activities are firstly directed to generate consensus among the spawn/breeding companies to consider ...

User comments : 0

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.