Bacteria to the rescue.

A paper was published about a month ago about converting any blood type to type O. This caused quite a bit of commentary (e.g., here, and here) and so I thought I’d explain the science behind blood types and explain why this is such an important paper!

ABO Blood Groups

As you may know, there are four blood types: A, B, AB, and O. The difference between them is that the red blood cells in each blood type is covered in a different protein. These proteins are actually modified with some sugar attachments, and there are two types of them: the A-type proteins and the B-type proteins. If you have only A-type proteins, you are A-type blood type. If you have only B-type proteins, you are B-type blood. If you have both A- and B-type proteins, you are AB, and if you have neither, you are O-type.

Us versus Them

This system is a bit more complicated because of how the immune system works. You see, the immune system knows what’s really part of you and what’s not part of you. When it comes across something new, it assumes it’s an invader (like a virus) and raises an army that recognizes this foreign object to kill it. That’s all good - most of the time. In immunology lingo, anything the immune system recognizes (whether it’s part of you or foreign) is called an antigen. The tools the immune system uses to attack foreigners aree called antibodies.

In the ABO blood types, if you have an A-type, the immune system earlt in life recognizes that these A-type proteins as part of you, and so it leaves them alone. To rephrase, the A-type antigens are not attacked by the immune system. Likewise, if you have B-type blood, your immune system recognizes the B antigens as part of you and leaves them alone. In AB-type blood, both are recognized as friendly, and because there are no A- or B-type antigens in O-type blood, both are recognized as foreign.

In biological terms, a foreign chemical causes the creation of antibodies against it. So in A-type blood, there anti-B antibodies because the immune system recognizes B-type red blood cells as foreign. In B-type blood, there anti-A antibodies. In AB-type, there are no antibodies against either A- or B-type antigens. In O-type blood, there are antibodies against both A- and B-type antigens.

The presence of these antibodies is why in blood transfusions, O-type people cannot accept any other type of blood except O. Also, that’s why AB blood can accept from any blood group. The table below from Wikipedia sums it up nicely.

One Last Complication…

To make life that much more interesting, there is one other antigen: the Rhesus factor, which can be positive (you have the Rh factor) or negative (you don’t have the Rh factor). This is why blood type is given as A+ or AB- or the universal donor O-. The Rh factor is not relevant to our discussion today, so I’ll leave it up to you to find out more about it.

Converting Blood Types

This is where the new paper comes in. Over 20 years ago, scientists realized that if the can chop off the antigens from A-, B-, and AB-type blood, then you get O-type blood. Clever but no one has managed to do it - until now. The new paper describes a way to do exactly that.

To pull off this feat, a large international collaboration led in Denmark screened thousands of bacteria and fugi looking for enzymes that can remove the antigens. They found two bacterial strains (called Elizabethkingia meningosepticum and Bacterioides fragilis) that have the required activity. The conversion activity comes courtesy of enzymes belonging to the glycosidases family, a well known enzyme family. In short, the new process produces truly universal red blood cells from any bood type. However, as with all enzymes, they are quite specific, and so do nothing about the Rh factor.

So what next? This is very new and so extensive tests are needed. Part of the tests are clinical trials to affirm that the blood produced in this process is safe for human use. Watch this space - it will get very interesting.

References

Apart from the paper cited above, I found the patents that cover this process: EP1436387 in Europe and patent application number US2003157474 in the USA, both assigned to the company commercializing this technology, ZymeQuest Inc.

[tags]ZymeQuest, blood, blood groups[/tags]