Each one of us is born with one of four blood types – A, B, AB, and O – which are determined by sugars (the antigens) that we have on the surface of our red blood cells. If you have a type A blood and receives someone else’s blood that’s a type B, the molecules called blood antigens can cause your immune system to mark the red blood cells for destruction thinking they’re foreign objects. However, the type O blood doesn’t have any of these antigens, and hence, anyone can safely receive type O in transfusion.
Now, a team of researchers led by Stephen Withers, a chemical biologist at the University of British Columbia (UBC) in Vancouver, Canada, have discovered a way to convert type A blood into a universal donor type O. If the conversion process pans out, it could potentially incite radical changes in supply of universal blood as well as in blood transfusion.
“This is a first, and if these data can be replicated, it is certainly a major advance,” explains Harvey Klein, a blood transfusion expert at the Clinical Center in Bethesda, Maryland, in a news release.
Past study had researchers figured out certain enzymes that could doff the antigens right off A,B and AB blood cells, transforming them into type O. But when they zeroed in the safety and efficiency of those enzymes in doing the job properly, they had to be repudiated. So the search for the right enzymes drove them to the human gut.
So in this new study, the team settled on to look for an enzyme that could surmount any of those previous enzymes among the gut microbes. As they looked through the gut, they discovered that the microbes attached to the gut wall feed on the sugar-protein combo called mucins that line it. And these mucin’s sugars are basically the same sugars (the type-defining ones) found on red blood cells.
In the next step, the team then collected a human stool sample and isolated its DNA, which in principle would include genes that encode the bacterial enzyme that can strip mucins from the lining. Slicing the DNA up and loading each individual molecule into copies of Escherichia coli (E. coli) – bacteria that commonly found in intestines – the researchers checked if any of the microbes produced proteins that can remove A-defining sugars.
At first, the researchers were cynical. But when they examined two of the resulting enzymes at the same time, the sugars came off immediately. But how did they know when the sugars flaked off? Well they added the enzymes to substance that would glow when sugars are stripped away.
The enzymes originally stem from a gut bacterium called Flavonifractor plautii, and work wonders in human blood too. Just tiny amount added to a unit of type A blood could remove the sugar, converting them into a more universally accepted type – the type O.
“Around the United States and the rest of the world, there is a constant shortage,” says Mohandas Narla, a red blood cell physiologist at the New York Blood Center in New York City. “The findings are very promising in terms of their practical utility. In the United States, type A blood makes up just under one-third of the supply, meaning the availability of “universal” donor blood could almost double.”
For now, the researchers will principally work on converting type A, as it’s more common than type B blood. Although the new found enzymes could transform those blood types into type O 30 percent better than any enzymes discovered previously, more work – as in removing the offending A antigens completely, and ensuring the microbial enzymes do not inadvertently altered anything else on the red blood cells – is needed to make the enzymes and conversion process work to the full extent.
The study has been published in the journal Nature Microbiology, and it’s titled “An enzymatic pathway in the human gut microbiome that converts A to universal O type blood”