The ABO blood groups were discovered over one hundred years ago. In the early 1900’s, an Austrian scientist, Karl Landsteiner, found through experimentation that red blood cells of some people clumped or agglutinated when mixed with serum (here difference between serum and plasma) from other people. Through his experiments he noted that this was a common phenomenon, and that blood could be separated into groups. Much later, in fact in 1930, Landsteiner received the Nobel Prize for his work and discovery.
There are four principal blood groups, A, B, AB and O. The presence of specific antigens on the red blood cells determines which blood type a person is. If your red blood cells have the “A” antigen, you are blood type A, and you have antibody “B” in your plasma. If you have the “B” antigen, you are type B and you have antibody “A” in your plasma. It you have both A and B antigens, than you are blood type AB, and you have no circulating antibodies in your plasma. Finally, if you are blood type O, you have no antigens on your red blood cells, and you have both antibodies A and B in your plasma.These discoveries were crucial because knowing this information is vital when a person is receiving a blood transfusion.
Because of the presence of antibodies, people with type A blood, can’t receive blood from people of type B blood due to the presence of the antibodies to type A found in type B people. The reverse is also true. Type O blood, since it has no antigens found on its red blood cells, can be used as a universal donor for people of all blood types, and type AB red blood cells because they produce no antibodies can be used as universal recipient blood. This however, is a simplistic version of red blood cell antigen and antibodies. There are many other factors involved and they all have to be tested for to make sure that blood is suitable for transfusion. One of these factors is Rh factor.
Rh factor was discovered by Landsteiner and Alexander Weiner. Rh factor is very complex and may involve a total of forty five different antigens. To put it simply, if your red blood cells react to antiserum by agglutinating, you are Rh+; if they do not you are Rh-. Fetal incompatibility is a major problem with Rh factor. If a pregnant woman is Rh- and the baby’s father is Rh+, it’s possible that the mother may pass antibodies through the placenta and into the baby’s circulation, destroying the baby’s red blood cells, if the baby is Rh+.
Type O blood is the most common blood type found, accounting for about forty four percent. This is followed closely by type A which makes up around forty three percent, type B which makes up around nine percent, and finally type AB, at around four percent. The majority of people are Rh positive (around 85 % depending on race) and the rest, around 15 % are Rh negative.
Blood groups are very complex and involve many antigens and alleles. People who are blood type A, may be AA or AO for their genotype, but the A antigen will mask the O and their blood type will be A. The same can be said for blood type B. A person can be BB or BO and the B antigen will be expressed. For type AB, you can only be AB, and for type O, you can only be OO. So as you can see, blood group types can be complex and need to be studied thoroughly in order to make accurate decisions.
Sources: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=rbcantigen&part=ch05ABO
http://anthro.palomar.edu/blood/ABO_system.htm
