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Immune System Passports

Immune System Passports Phagocytes, like this neutrophil, "eats" invading cells.
Photo Credit: Volker Brinkmann [CC-BY-2.5], via Wikimedia Commons

Researchers have successfully copied a molecule that protects our bodies from our own immune systems.


Transcript

An immune system passport. I’m Bob Hirshon and this is Science Update.

Our immune systems are designed to attack invaders, but spare our own cells. Now, researchers have copied the molecule that gives our cells that protection.

University of Pennsylvania biomolecular engineer Pia Rodriguez and her colleagues created a synthetic version of a peptide called CD47, which protects cells from being eaten by immune cells called phagocytes. Doctors could use the synthetic version like a passport, to safely deliver drugs and other medical devices into the body.

Rodriguez:
We found a way to fool our immune system, in order to send the right drugs to the right place.

The molecules could also help treat autoimmune diseases like arthritis, in which the immune system mistakenly attacks the host body. Rodriguez says that a lack of these CD47 peptides is part of the problem, and flooding healthy tissue with the artificial version may protect it. I’m Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

Our immune systems have a tricky job: attack foreign invaders, including harmful bacteria, viruses, parasites, and even non-living particles, without attacking our own bodies or other organisms that belong there (like gut bacteria). Most of the time, the immune system does the job well. But sometimes, it overreacts to harmless substances, like peanut proteins, or mistakenly attacks the host's own cells. 

Diseases caused by this sort of immune malfunction include type I diabetes, celiac disease, rheumatoid arthritis, lupus, and dozens more. Moreover, the immune system makes it difficult to create artificial implants like pacemakers, since these, too, are recognized as foreign. In order to create effective new treatments for allergies and autoimmune disorders, and to improve organ transplants and medical implants, researchers need to understand exactly how the body identifies its own cells. 

In 2008, the same research group found that a peptide, or section of a protein, called CD47 protects native cells from immune cells called macrophages (the name translates to “big eaters”). Macrophages patrol the body, looking for foreign particles to gobble up. But if they touch a cell with CD47 on its surface, the CD47 peptide binds to a receptor on the macrophage that signals it to leave the cell alone. In other words, CD47 acts as a “don't eat me” sign.

Now, Rodriguez and her colleagues have taken this a step further: they've determined the minimum portion of a CD47 peptide—a sequence of amino acids—that it takes to protect cells from macrophages. They then artificially copied this amino acid sequence, and attached it to nanoparticles that can be designed to seek out particular cells in the body and deliver the “passport” to them. 

In the future, this technology could be used to coat artificial implants, to prevent the body from becoming dangerously inflamed at the implant site. It could also be delivered to tissues that are under attack in an autoimmune crisis—for example, joint tissues in a patient with arthritis. It's been shown that not having enough CD47 surface peptide can make tissues more vulnerable to autoimmune attacks. This technique may make it possible to replenish the CD47 and turn away misguided macrophages.

Now try and answer these questions:

  1. What are some situations in which our immune systems might work against us?
  2. What is CD47? What role does it play in protecting our own cells?
  3. Why is it important that the researchers were able to artificially copy CD47?
  4. How might the artificial peptides be used in future medical treatments? 
You may want to check out these related resources:


For more about the immune system, the Science Update Instant Immunity describes an experimental technique that creates all-purpose antibodies that can be activated at a moment's notice.

In Transplant Tolerance, learn why researchers are also studying the human eye to better control immune reactions to medical treatments.

In the online game Immune Attack, created by the Federation of American Scientists (FAS), players navigate through a 3-D representation of the human body, fighting germs and restoring a healthy immune system to a sick patient. 


Going Further


For Educators

For more about the immune system, the Science Update lesson Instant Immunity describes an experimental technique that creates all-purpose antibodies that can be activated at a moment's notice.

In Transplant Tolerance, learn why researchers are also studying the human eye to better control immune reactions to medical treatments.

In the online game Immune Attack, created by the Federation of American Scientists (FAS), players navigate through a 3-D representation of the human body, fighting germs and restoring a healthy immune system to a sick patient. 


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