Each human is born with one out of the four blood types viz. A, B, AB, and O and this determines the type of blood they can receive in a transfusion. For a successful blood transfusion, the patient and donor blood types must be compatible. Using the “wrong” type could cause a reaction that can be fatal. Now, researchers analyzing bacteria in the human gut have reported that microbes there produce two enzymes that can change the common type A into a more universally accepted type. If this process is proved, blood specialists believe it could revolutionize blood donation and transfusion.
Harvey Klein, a blood transfusion expert at the National Institutes of Health’s Clinical Center in Bethesda, Maryland, who was not involved with the work, “This is a first, and if these data can be replicated, it is certainly a major advance,”
Blood types in humans are defined by unusual sugar molecules called blood antigens on the surfaces of their red blood cells. If a person receives a mismatched blood type, these antigens trigger the immune system to mount a deadly attack on the red blood cells. But type O cells do not possess such antigens, making it possible to transfuse this blood type into anyone making it the “universal” blood. This proves useful especially in emergency rooms, where there may not be enough time to determine an accident victim’s blood type.
Mohandas Narla, a red blood cell physiologist at the New York Blood Center in New York City, said, “Around the United States and the rest of the world, there is a constant shortage”.
To increase the supply of universal blood, scientists have attempted transforming the second most common blood, type A, by taking away its “A-defining” antigens. Till now they’ve had limited success because the known enzymes that can remove the antigens from red blood cell aren’t efficient enough to be used economically.
A team led by Stephen Withers, a chemical biologist at the University of British Columbia (UBC) in Vancouver, Canada, decided to look for a better enzyme among human gut bacteria, after 4 years of trying to improve on known enzymes. Here, some microbes can latch onto the gut wall to “eat” the sugar-protein mucins that line it. Mucins’ sugars are comparable to the type-defining ones on red blood cells.
Therefore, UBC postdoc Peter Rahfeld took a human stool sample to isolate its DNA, which in theory covered genes that encode the bacterial enzymes that digest mucins. By slicing this DNA and filling different pieces into copies of the commonly used lab bacterium Escherichia coli, the researchers observed whether any of the microbes later produced proteins with the ability to remove A-defining sugars.
Initially, they didn’t see anything promising. But after testing two of the resulting enzymes at once by adding them to substances that could glow if the sugars were removed, they found that the sugars came right off. The enzymes proved effective in human blood. Withers, Rahfeld and their colleagues reported in Nature Microbiology, that these enzymes originally come from Flavonifractor plautii, a gut bacterium. They found that adding tiny amounts to a unit of type A blood could get rid of the offending sugars.
Narla says, “The findings are very promising in terms of their practical utility”.
In the United States, type A blood constitutes just under one-third of the supply, implying that the availability of “universal” donor blood could almost double.
But Narla concedes that more work is needed to ensure that all the offending A antigens have been cleanly removed, a problem in previous attempts. According to Withers, researchers need to ensure the microbial enzymes have not unintentionally altered anything else on the red blood cell that could produce effects. The researchers are presently focusing on only converting type A, as it’s more common than type B blood.
Withers says, “ Having the ability to transform type A to type O would broaden our supply of blood and ease these shortages.”