What blood group are you? It's a question most of us meet early in life, whether on a school form, at a hospital visit or in some other official enquiry. But here's a surprise: modern science only came to understand that humans have different blood groups in the nineteenth century.
The honour goes to Karl Landsteiner, who around the year nineteen hundred discovered the different blood types in humans. Working with his staff, he helped uncover why some blood transfusions work for some people yet prove deadly for others.
How the blood groups were found
When Karl and his team mixed one another's blood samples, they observed that some combinations produced different reactions. From that work came the discovery of the different types, which they named A, B and O.
You might wonder why, after A and B, there's no C. As it happens, the O group was initially called C. It was renamed to O for the German word "ohne", which conveys the idea of zero, or empty, or null.
What defines your blood type
To understand this better, consider that a type of protein, along with glycoproteins and glycolipids found on the surface of red blood cells, defines the blood type. These act as markers on the cells that flag which type they are. You may have come across the word antigen. For the four main blood types, A, B, AB and O, the key indicator is the presence or absence of the A and B antigens.
- Presence of only the A antigen — blood group A
- Presence of only the B antigen — blood group B
- Presence of both the A and B antigens — blood group AB
- Absence of both the A and B antigens — blood group O
Now you can see why it's called O. Since there's neither an A nor a B antigen, the group is essentially empty, or null, hence the name. There is no surface marker on the O blood cell. As an extra fact, the AB blood group was actually discovered a year later. And these aren't the only types around; in truth, it's said that more than twenty blood types have been discovered so far.
The Rh factor
What about the positive and negative attached to each blood type? That's down to the Rh factor, or Rhesus factor, so named because of the similarity observed with the Rhesus monkey. Whether a group is positive or negative depends on certain molecules being present or absent on the blood cells. The most important flag is the RhD protein: if it's present, the blood group is likely to be positive.
Donors, receivers and quirks
Based on the structure of each blood group, a person can act as a universal donor, a universal receiver, or only an individual donor or receiver. For example, someone with blood group A who receives blood group B, which carries the B antigen, sends their whole body into a defensive mode. But they can safely receive group O blood, because O carries no surface marker to provoke that resistance.
Each blood group also brings its own strengths and weaknesses. People with blood group A, for instance, are said to be more susceptible to malaria than those with group O. Meanwhile, group O types are more prone to stomach ulcers, possibly linked to the bacteria Helicobacter pylori, while group AB types are less prone.
Why so many groups?
Why we have different blood groups in the first place is a chapter all its own. What brought on these mutations, and which group came first, whether A or O, is still a matter of research. It's the kind of question a curious mind will always find to work on.
And speaking of recognition, Karl Landsteiner received the Nobel Prize for his contribution to medicine and physiology in nineteen thirty. So let that be a gentle reminder: keep that curious mind running. Who knows what you might end up discovering next?