What’s the difference between blood in people that means we have different “types” and why are some incompatible?
In: Biology
Immune system explanation time.
Basically, the way your immune system works is that certain proteins are present on your defense cells that will attach to certain other proteins, called antigens, on other cells. It’s how they attach to bacteria. Due to genetics, your blood cells have a certain antigen on them that should be different than one your white blood cells will bond to. If that’s not the case, that’s something entirely different and bad.
The types of blood cells, roughly, are A, B, AB, and O. A means their genetics code for either AA or AO, as you have two sets of genes. B means their genetics code for either BB or BO. AB means their genes code for AB, and O means they have the code of OO. Now, O has no antigens, AB has A and B antigens, A has only A, and B only B. Basically, they have to determine what blood tyoe they have, and then select one that won’t be attacked by the immune system. An A needs A or O, a B needs B or O, a AB needs A, B, AB, or O, and an O needs O, because, respectively, an antigen that is present in the new blood an that wasn’t in the old will be attacked by the receivers immune system. This is also why organ transplants are difficult, as there’s even more complexoty and variety of antigens.
Your immune system is constantly patrolling your body, like a police force, looking for things that don’t belong. To do this they have a long list of “markers”, things that “look suspicious”. If your immune system finds something that fits a marker on the list, it attacks the thing. THESE LISTS CAN BE DIFFERENT FOR DIFFERENT PEOPLE.
Now, blood cells often have some of the markers that appear on the lists… your own blood cells shouldn’t appear on your own immune system’s list, of course. Then your immune system would attack them. But your blood cells might have some markers that appear on other people’s lists, so if you donated blood to them, their immune system would attack the blood they got from you… and that would be very bad for them.
To keep track of these markers and lists, blood types are used. There are three markers that matter here: A, B, and rhesus (+). If your blood type is A+, for instance, your blood has the A and rhesus markers, but not the B marker. That means your immune system will *not* attack blood with the A and/or rhesus markers, but it *will* attack blood with the B marker. Which means you could receive blood from anyone who does not have a B in their blood type, and you could give blood to anyone with A and + in their blood type (so A+ and AB+ only).
Hope this wasn’t too complicated!
[removed]
Our blood contains antibodies and antigens. Different people have different antibodies/antigens. Antibodies attack antigens of the same type. Blood type O has no antigens and both A and B types of antibodies. Blood type A has antigen A and antibody B. Blood type B has antigen B and antibody A. Blood type AB has both antigens and neither antibodies. There is a final important antigen, known as D, which people are either positive for (they have it) or negative for (they don’t have it). This means that someone whose blood type is A+ has antigens A and D, as well as antibody B.
In the strictest sense, a blood type refers to the presence of certain types of *antigens* on the surface of blood cells.
Antigens are molecules such as proteins or carbohydrates that can trigger a response by the immune system, such as those found on the surface of certain viruses and bacteria, or proteins on the surface of pollen grains.
In general antigens produced by your body’s own cells will not produce an immune response by your respective immune cells. There are mechanisms to prevent this from happening. In rare cases where this does occur, it can produce diseases like rheumatoid arthritis or lupus.
However, different people may produce different antigens on their blood cells, because they inherited a given set of genes from their parents that produces that antigen, but not another one.
This means that if blood from one type is transfused to someone with a conflicting one, it may cause proteins called antibodies to attach to the antigens on the surface of blood cells. This causes blood cells to clump together, which can result in lethal blood clots.
There are in fact 49 different Blood Group Systems known at present, but in most of those, variation is very rare and nearly everybody has one type and only a few thousand differ. This makes adverse reactions unlikely with those types.
The most important types are the “ABO” system and the “Rh” system.
These are the types of antigens where there is the greatest degree of variation in the human population.
In the ABO there is a set of two genes that produce a kind of carbohydrate on the surface of cells. One called A, one called B.
Depending on your parent’s blood types you may get the gene for A, B, both A and B. You may also receive a non-functional gene that doesn’t produce an antigen. If you get two copies if this gene, neither is produced and your blood type is O, which is the rarest.
Unfortunately, because either of these antigens is common in other people, if you only have B for example, your body is likely to develop an immune response to A due to being around other people in the same way that exposure to a virus causes an immune response. This is how vaccines work. So, just interacting with other people essentially vaccinates you against A as a young child.
Because of this the immune system produces antibody proteins that bind strongly to the A antigen.
This will result in a life threatening reaction if you receive A type blood, but not if you receive O.
In the case of having O, you cannot be given other blood types because it’s likely your body produces antibodies that react with both A and B.
The Rh system is more complex, but works by the same basic kind of mechanism.
In general, people will only be given the exact same blood type except in an emergency because adverse effects can still occur otherwise.
Latest Answers