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Monday, March 12, 2012

What’s your blood type?

You may know whether you’re A, B, O or AB, and even whether you’re Rhesus (Rh) positive or negative.  But do you know where you fall amongst the other 30 categories of blood types?  Hold on, make that 32.  An international team of scientists, led by Lionel Arnaud of the National Institute of Blood Transfusion and Bryan Ballif of the University of Vermont, has added two new proteins to the rolls of molecules that determine blood type compatibility.

Our red blood cells (RBCs) can have any of a wide variety of different molecules on their surfaces.  For example, if you have type A blood, you have type A antigen on your RBCs.  People with type B blood have B antigens, people with AB blood have both, and people with type O blood have neither.  Why is this important?  Under normal circumstances, it isn’t.  One blood type is just as good as another for serving all the purposes that RBCs have, namely carrying around oxygen and nutrients.  It only becomes an issue when someone else’s RBCs get deposited into your body.  There are two main ways in which this can occur, by transfusion and during pregnancy.

If a person receives a blood transfusion of RBCs with the same or fewer antigens (O or A blood going into a person with AB blood), there’s no problem.  If, however, a person receives blood containing alien antigens (A blood going into a person with O or B blood), the recipient’s immune system will attack the new blood, leading to a devastating cascade of symptoms and possibly even death. Pregnant women may not be able to carry babies to term if those babies inherit incompatible blood groups from their fathers.

Diagram showing blood group compatibility for transfusion purposes.

As you can see, the more tightly doctors can type blood groups, the less chance of rejection for transfusion patients.  Thanks to the efforts of researchers like Arnaud and Ballif, we now have thirty-two separate antigen groups to screen for.  Interestingly, the new ones, Langereis (Lan) and Junior (Jr), also happen to be associated with resistance to anti-cancer drugs.

Both Lan and Jr are molecular transporters, responsible for moving specific molecules across membranes.  They are encoded by ABCB6 and ABCG2, respectively.  The ABCG2 protein is also known as the Breast Cancer Resistance Protein because it actively transports many anticancer drugs out of cells.  Getting rid of toxins would normally be a good thing, but not when you’re trying to kill tumor cells. Until recently, it had not been known that Lan and Jr were also blood type systems.  The significance of this is that there are perfectly healthy people (particularly many Japanese in the case of Jr) who are negative for these transporter proteins.  If the genes can be knocked out in cancer patients, that might make treatment easier.

If you like, you can peruse the list of blood types here.  

Helias, V., Saison, C., Ballif, B., Peyrard, T., Takahashi, J., Takahashi, H., Tanaka, M., Deybach, J., Puy, H., Le Gall, M., Sureau, C., Pham, B., Le Pennec, P., Tani, Y., Cartron, J., & Arnaud, L. (2012). ABCB6 is dispensable for erythropoiesis and specifies the new blood group system Langereis Nature Genetics, 44 (2), 170-173 DOI: 10.1038/ng.1069.

Saison, C., Helias, V., Ballif, B., Peyrard, T., Puy, H., Miyazaki, T., Perrot, S., Vayssier-Taussat, M., Waldner, M., Le Pennec, P., Cartron, J., & Arnaud, L. (2012). Null alleles of ABCG2 encoding the breast cancer resistance protein define the new blood group system Junior Nature Genetics, 44 (2), 174-177 DOI: 10.1038/ng.1070.

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