In this article I want to talk about a mechanism that, when I read about it, completely fascinated me. Yes, bacteria can still amaze me with their countless abilities to affect almost everything within our body!
A new study just found that bacteria are even able to change our blood type!
But as always, let’s start with the basics.
We have four different blood types based on the sugars that are on the surface of our blood cells (I am not going to talk about rhesus factors here). These sugar blocks are generally called antigens, because they are recognised by their cognate antibodies.
Specifically, if someone has blood type 0, the person has the H antigen on their blood cells. These are depicted as the three sugars (purple-yellow-red) in the picture below. Someone with blood type A has the A antigen, which is basically the H antigen with the additional sugar GalNac (yellow square). Similarly, someone with blood type B has the B antigen, which is the H antigen with the additional sugar Gal (yellow circle).
As you might be aware of, individuals with blood type A can produce antibodies against the antigen B and the other way around. When an antibody binds its cognate antigen within the body, it activates a whole regulatory cascade that can be lethal for us.
This is why blood type 0 is always a safe bet when it comes to blood transfusions since no antibodies would bind to these blood cells. However, blood banks are always in need for blood of type 0.
In the wall of the human gut, these antigens are also present. So, bacteria, that live in our gut, would be in contact with these antigens. And whenever bacteria encounter something in their environment, they somehow develop a way to use it. This is why scientists were looking for bacteria within our human gut microbiota that would be able to change blood types.
And indeed, scientists found that the almost unknown bacterium Flavonifractor plautii can change the blood types A and B to blood type 0.
This bacterium produces two proteins that can work in a consecutive way, which I show in the picture below.
First, one protein (blue scissors) cuts the ac off the GalNac sugar (yellow square) at the end of the A antigen. This leaves the GalN sugar (yellow pentagon). Then, the second protein (grey scissors) cuts the GalN off the antigen, so that the H antigen remains and thus blood type 0.
Also, the GalN sugar after the first cleavage is very similar to the Gal sugar (yellow circle) at the end of the B antigen. The same grey scissors-protein can cut off the Gal sugar from antigen B, again leaving antigen H. With this, the same two proteins can change the blood type A or B to type 0.
So why did bacteria develop to cleave off the sugars from the antigens I hear you ask? My guess is they can then use the cleaved sugar as food for themselves. They do not have in mind to change our blood type, they – as always – just want to survive.
Also, this mechanism of blood type change was already described 50 years ago, but scientists did not know what to make of it. Some patients, that were infected with some nasty pathogenic bacteria, showed a sudden change in blood type, which completely puzzled scientists back in the days.
Now, researchers are trying to optimise this process and make it available for use in bigger scales. This would certainly help to produce sufficient amounts of blood of type 0 to stockpile blood supplies.