Blood Types Can Be Converted; May End Shortages

Amitabh Avasthi
for National Geographic News

April 4, 2007

Blood types A, B, and AB can be efficiently converted to type O, which is safe to give to anyone, says an international team of researchers.

The scientists identified bacterial proteins that can quickly convert one blood type to another by clipping away sugar molecules on red blood cells.

The find may create a universally safe supply of blood and may help end shortages, since mismatched blood transfusions can quickly cause death.

Deadly Mismatches

Under the ABO system discovered in 1900, blood is classified into four groups based on the presence or absence of complex sugar molecules on the surfaces of red blood cells.

"Group A has an enzyme that puts a sugar molecule on the end," explained Geoffrey Daniels, a transfusion scientist at the University of Bristol in England.

"Group B also has an extra sugar molecule, different from that on group A, at the end of its structure," he added. "But group O has neither kind of sugar molecule."

People naturally create antibodies to the sugars they lack. So people with blood type A naturally have antibodies to the blood plasma from type B, and vice versa.

If people get blood transfusions of the wrong type, their antibodies attack the foreign sugars, mounting a vigorous and oftentimes deadly immune response.

"The blood cells clump together as a consequence of the antibodies acting like a glue between cells, and thus blood gets very thick," said Steve Withers, a bioorganic chemist at the University of British Columbia, Canada.

"The red blood cells can explode."

People with blood type O, however, are considered universal donors, since their blood cells contain no sugars to attack. (Related: "Umbilical Cord Blood: The Future of Stem Cell Research?" [April 6, 2006].)

But this causes some problems, as demand for type O blood often outstrips supply.

Protein Clippers

One way to solve the supply crunch is to snip away the sugar molecule in the A and B groups, giving antibodies no targets, said Henrik Clausen, a sugar biologist at the University of Copenhagen in Denmark.

Researchers elsewhere had demonstrated this could be done. But Clausen and his colleagues looked at hundreds of different bacteria for enzymes that could do the task much more efficiently.

"Think of the sugar molecules attached to a blood cell as a string of pearls," Clausen said.

"We carefully clipped away one pearl that was the 'A' and 'B' in the blood groups A, B, and AB, making the blood acceptable to all recipients," he added.

"The process may help address the current blood shortage."

Clausen's findings are outlined in this week's issue of the journal Nature Biotechnology.

Blood Supply

The method is useful in generating the type of blood from groups A and B that will help all recipients when there is a shortage in blood supply, said the University of Bristol's Daniels.

"On a more immediate level, it will help patients who need regular transfusions, and specifically require blood from group O."

According to study leader Clausen, "accidental transfusion of the wrong type of blood has a higher risk of death than infectious disease.

"This method makes blood transfusion more safe."

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