February 22, 2010

Bacteria-killing proteins cover blood blind spot

A set of proteins found in our intestines called galectins can recognize and kill bacteria that have human blood type molecules on their surfaces, Emory scientists have discovered.

The results were published online Feb. 14 in the journal Nature Medicine.

Many immune cells have receptors that respond to molecules on the surfaces of bacteria — but these proteins are different because they recognize structures found on our own cells, says biochemist Richard Cummings.

“It’s like having a platoon in an army whose sole purpose is to track down enemy soldiers that are wearing the home country’s uniforms,” he says.

Blood type comes from differences in sugar molecules attached to proteins on red blood cells. If incompatible blood types are mixed, the antibodies from one person will make red blood cells from the other person clump together. But someone’s immune system usually doesn’t make antibodies to the sugar molecules on his or her own red blood cells. That creates a potential blind spot that bacteria could exploit.

The Cummings laboratory’s discovery explains why bacteria can’t sneak past our immune systems by camouflaging themselves with blood type sugar molecules.

It may also explain why the human population has a diversity of blood types; the galectins create a “protected space” for the diversity to flourish.

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