First let me explain two basic terms-
Antigen- The tag that identifies something. These antigens exist, to help our body distinguish molecules as "self" or "non-self." Our immune system will recognize these antigens and react, or wont react. When there is an antigen-antibody reaction that is what causes the destruction of these cells and a massive clot forms.
Edited expansion- In my analogy. The antigens are the Locks. And the Antibodies are the keys. When your body encounters a Lock that doesnt belong to you, it tries to destroy it (open it) Once your body encounters this lock, it has now seen it and has now seen its design. After encountering a foreign lock, your body will now make keys to open and destroy these locks. Some of these locks are small (ABO blood group) and the keys can be made immediately and the reaction occurs immediately. However the locks of Blood type of +/- (explained more detailed below) are relatively big and can take a while for the appropriate keys to be made. So you constantly have these keys floating around in your blood constantly looking for a compatible lock. When a key matches a lock, that's what activates your immune response, destroys the lock and in turn causes all the negative effects of a transfusion reaction (explained more below)
Why are there different types of antigens? This boils down to their molecular structure. All blood types have the same "core" structure, but what differentiates the types is a Polysaccharide molecule that sticks out from the molecule. This polysaccharide (or Sugar in simpler terms) is what is the antigen and helps our body identify them as different blood types.
Antibodies- The main part of our immune system. Antigen-antibody interactions follow a lock (antigen) and key (antibody) When the key fits the lock that's what causes and immune reaction which ends up destroying the Red Blood Cell (RBC)
The locks are pre-determined due to the sugar "tag." Now one thing people dont realize is that certain blood types will have the specific antigen, but WILL HAVE THE OPPOSITE ANTIBODY.
What does that mean?
Blood Type A: Has A Antigen, and B Antibody
Blood Type B: Has B Antigen, and A Antibody
Blood Type AB: Has A and B antigens, No antibodies
Blood Type O: Doesn't have A and B, Has both A and B antibodies
edit- (as pointed out by nearquincy below, Blood Type O actually contains H antigen, which is the precursor antigen to both antigen A and antigen B. There are other antigens that is present on the surface of the blood type O itself although they are not significant in ABO system."
What does that translate into the real world?
Blood Type A: They only have 1 antibody-Type B, so if that antibody finds its partner antigen (found in Type B or type AB transfusion) then it will cause a reaction and essentially self-destruct.
Blood Type B: They only have 1 antibody-Type A, so if that antibody finds its partner antigen (found in Type A or type AB transfusion) then it will cause a reaction and essentially self-destruct.
Blood Type AB: Has both antigens, but no Antibodies. (Because if it had any antibodies to either A or B, the person wouldn't exist in the first place, because the Antibodies would keep finding their Locks, and self-destructing the RBC's) Because blood type AB has no Antibodies, they are known as Universal Recipients Meaning that because there are no keys, there will never be keys to correspond with the locks.
Blood type O: Has no antigens, but does have both types of antibodies. Because of the lack of antigens, they are known as universal donors meaning their blood can be transfused/mixed with any other blood type and there will not be a reaction.
Below an even simpler version of what this means
Type A blood- Can Receive type A or Type O Blood. Will react with type B or type AB.
Type B blood- Can receive Type B or Type O Blood. Will react with type A or type AB.
Type AB blood- Can receive all types of blood- Type A, B, AB, or O. Will not react with any.
Type O blood- Can only receive type O blood. But can be donated to any blood type person. Will react with types A, AB, and B (when type O is the type of the receipient)
edit- cheat sheet for blood types http://i.imgur.com/fTw8AIj.png
What is Positive and Negative Blood?
Well this refers to the presence or the lack of another type of antigen, known as the Rh Factor or also known as the D antigen.
Why is being positive or negative important?
Well, this is most important for pregnancies. Specifically a mother's second pregnancy. It occurs in a Rh(-) Mother and an Rh(+)Baby. What does being Rh (-) or (+) mean? Well like I said it depends on whether or not you have the Antigen or you don't. During the 1st pregnancy the fetal blood will mix with the mothers blood. Because the mother has no Rh factor, but the fetal blood does- the immune system will recognize these particles as foreign and will in turn start making antibodies to it. Anything your immune system recognizes as foreign, it assumes its an enemy and will start to attack it.
Why did you mention 2nd pregnancy and not first?
Well these antibodies belong to a different class than the ones that react with blood typing. These antibodies take MUCH longer to form. Hence it wont affect the first pregnancy, but can affect the second pregnancy.
Can you prevent this reaction?
Yes, quite easily.
there are drugs available (RhoGAM for example) that prevent this antibody reaction; nowadays they're routinely administered to Rh negative mothers during pregnancy. So it's theoretically bad, but it's easily managed with a little extra preventive care.
Another small point: the medication you're talking about for Rh type incompatibility is an antibody. It prevents the mothers immune system from becoming sensitized to the Rh antigen when blood mixes during birth. By binding to this spot, the mothers immune system never sees it, and so never makes antibodies to it, and her 2nd Rh(+) child will not be at increased risk.
The statement about RhoGaM is wrong. It IS an antibody. By covering up the Rh antigen on any Rh-positive cells from the baby that may have gotten into mom's circulation, it prevents mom from recognizing the antigen and making new antibodies.
How come Blood type mismatch reactions are immediate? *And how come a different blood type mother and fetus can exist? Wouldn't two different blood types cause a reaction and kill the mother or the fetus?*
Well, No. Blood type Antibodies form fast, but cant cross the placenta. This is what allows a different blood type fetus and mother to exist in the same body. Because if these antibodies could cross the placenta, you could only have a baby of your same blood type (or type O) otherwise there would be a reaction.
The Rh Antibody belongs to a different class of antibodies. It CAN cross the placenta
So back to my example. Rh(+) child with Rh (-) mother. After the first prengacy, after the fetal blood has mixed with the maternal blood. The mothers immune system now starts to produce Rh Antibodies. So now when a mother has a second child who is Rh antigen (+) her immune system has already recognized these foreign molecules, and assume its an enemy invading, so it will immediately attack them. These antibodies will flow through the placenta, and will go to the fetal blood stream and recognize the Rh Antigens and subsequently attack and destroy them all. This reaction is known as erythroblastosis fetalis, which can result in jaundice, anemia, and as the name itself implies- fetal death.
memorableZebra asks "If the problem is X-antigen binding with and X-antibody (A with A, B with B), then why can O donate to anyone if they have both antigens? Wouldn't O donor blood to, say A-type, be giving A-antibodies that will react with A's A-antigens? If you're not getting a lot of blood, I guess it might not be life threatening, but it seems like some people have received a majority of a body's worth a blood. In that case, if half the volume of a person's blood has antibodies that will bind with antigens on their red blood cells, wouldn't that trigger the immune response? Why doesn't it?"
mo_bio_guy responds "When blood is processed after donations, it is centrifuged and the plasma is expressed off of the bag. This removed the majority of any donor antibodies. Whole blood transfusion is almost never done in modern transfusion medicine. One exception to this is when Mass Transfusion Protocol is inititated. In this case, the recipient is losing so much blood that they are unlikely to have the immune system factors (Abs, WBCs) present to attack donor cells, at least immediately. TL;DR Antibodies are not necessarily degraded through storage, as when you donate blood there are preservatives in the bag to preserve the blood components. Rather, it's that the antibodies are removed and what is transfused is Packed Red Blood Cells."
skepitcalstag responds **"As a Transfusion and Transplant specialist I would differ in this regard. 1.Transfusion reactions not only occur if the patient's(host) antibodies react with the donor cells but also when donor antibodies react with the patients cells (seen commonly in immunocompromised or malignant states). "Graft-versus-host disease"
When blood is stored the antibodies are (I believe) destroyed, so they would die and not even be present in the donor. not true. antibodies are not destroyed at all during storage. Although, they can be removed from the blood unit by removing its plasma. 3. Both antigens and antibodies are transferable. The transferred antibodies are fully capable of using patients factors (complement system) to cause hemolysis on their own. With these things being said, i refer to the original question if half the volume of a person's blood has antibodies that will bind with antigens on their red blood cells wouldn't that trigger the immune response? Why doesn't it? Answer is: It Does. You will be amazed that massively transfused individuals actually show two parallel blood groups for some time until the 'foreign' Blood group is washed out/ excluded from the system. The foreign blood antibodies recognize the patient's own cells and can lyse them. but we have found a very simple way to prevent or let’s modestly say - reduce the incidence of such foreign vs. native reaction by A. simply removing the plasma from donor unit B. using just RBC concentrates for transfusion"**
Also, can a A- receive A+ blood?
A+ can receive blood from a A- Negative donor, or A+ donor.
A- can only receive blood from A-.
Its the antigens that make up the difference. Negative means you have no antigen, so even if - donor blood present inside of a + person's body, the body doesn't recognize it as foreign, so its okay.
The problem exists when - person receives + blood. + Blood does contain the antigen, so when - Persons body sees the + blood, it sees the antigen, recognizes it as foreign and attacks it. So this blood transfusion is incompatible
edit- If the patient is in a stable condition, and is not of child bearing age. A mismatch of a + and - person can be done. They will simply be given the same RhoGAM drug to stop the immune response that would occur. The +/- antibodies take weeks to form, so even if there would be a reaction it would take quite a while, and hopefully by then the patient is stable to be treated appropriately. The times when you would want to absolutely be sure about matching the +/- is if the person is in an immune deficiency/compromised state (IE- AIDS, Leukemia, etc) or if they are the subject of an organ or bone marrow transplant
What happens when you have an incompatible blood type?
Decreased blood pressure
Increased heart rate
Increased breathing rate
Acute kidney failure (if severe enough)
Blood in urine (after it reaches the kidney failure stage)
Shock ( if severe, and untreated)
Death ( if severe and untreated due to the sudden loss of blood pressure and the shock)
Basically I described it as self destruct, because the host antibodies attack the foreign antigens and cause these red blood cells to be destroyed. When your red blood cells are destroyed they release a molecule know as hemoglobin. Hemoglobin is normally a good molecule which is responsible for oxygen transport, but that is only of its attached to/inside of the Red blood cell. When there is too much free floating hemoglobin in the blood- that is what causes all of the above symptoms.
Can transfusion reactions be treated? And is it symptomatic treatment or does it require another full transfusion? Yeah it's basically sympomatic treatment.
But remember, that symptoms that appear are really variable and dependent on how severe the reaction is. But for a complete overall treatment of the above symptoms you would require-
Treating and anticipating the Shock (Which would also treat the low blood pressure and fast heart rate
Treating the kidney failure (Dialysis to filter out the hemoglobin) (If the reaction is severe enough, it may require a complete re-transfusion)
Treat the subsequent clot that will form. (When there is a transfusion reaction there will also be a massive blood clot that forms due to all of the now destroyed Red Blood cells)
Certain blood types have shown greater incidence with certain diseases/infections. But there is no increased susceptibility
Blood Type A: Hepatitis, Small Pox
Blood Type O: Black Plague, other digestive system infections, Autoimmune disorders(when your body attacks itself)
Blood Types A, B, AB: Clots in your veins
edit- to quote user hammurarbisan "A and B types routinely have elevated platelet counts versus the other blood types - most especially female A types"
read my comment below if you want to understand the difference between incidence, and susceptibility Because there is one, and its important. But as someone else replied, the simplest way to explain it- Correlation does not mean causality
Also some other interesting things to note is that-
ABO (+/-) Blood typing will fit and categorize about 99.97% of the worlds population. But there is still that 0.03% who's blood has neither A/B Antigens nor the A/B Antibodies.
For these special people we have to to EXTREMELY careful when transfusing any type of blood, also we have to use other systems to type/categorize their blood
When a Blood Type O patient, receives blood from a blood type A patient. This causes the most severe of the transfusion reactions.
About 40% of the population is Type O. Type AB is the rarest.
About 80% of the population is +. So being AB- is the rarest of blood types
Edit- The really SOL people are O-, because they can ONLY receive blood from other O- people. The rarest of blood types is AB- (if we are talking about the ABO system) (Even rarer than those, are the abnormal categories that cant follow our standard system, such as the Rhesus Blood type) (This blood type was the subject of a House episode I believe)
Edit- There are also blood types known as the Bombay blood type. Basically Blood type O has no A or B antigens, but it does contain the H antigen (which is a precursor to both the A and B antigens) Bombay blood type lacks this special H antigen and as such is its own unique blood type.
Edit - ABO Blood typing is the most commonly used blood typing system. But its not always the best, especially when you are talking about people who are very very seriously ill (immuno compromised and immunodeficient as in Leukemias, and AIDS) along with pregancies, bone marrow and organ transplant recipients. Some examples of the other blood group systems are the Kell System, Lewis system, Duffy system, Bombay system, and the list goes on. I however wont be going into the details of them in this post
Are there any benefits to having either A, B, AB, or O blood types?
Type O can donate to all types of blood.
Type AB can receive all types of blood.
Types- A, AB, B dont have a distinct advantage over the other. edit- as pointed out by /u/hammurarbisan " both A and B types routinely have elevated platelet counts versus the other blood types - most especially female A types - and thus more frequently tested for platelet counts and targeted for apheresis collection. Platelets are commonly used for transfusion during surgery."
Being + however is an advantage over being negative. + Can receive from + or - people. Negative people however can only receive from Negative people.
edit- Type AB can donate PLASMA to all people, since they dont have any antibodies (the donation rules for plasma and whole blood are opposite in terms of antigens and antibodies)
EDIT- just fixed some formatting issues.
2nd EDIT- Some other relevant questions were asked in the thread, so I'm copying the questions and my response/ explanations here to keep one big response that explains everything.
3rd EDIT- Changed up some more formatting. Moved some questions and responses around. Expanded a bit more on questions previously answered
4th EDIT- Made an error stating that AB- are the most SOL people. They are the rarest blood type, but the most SOL people are O- because they can ONLY receive that exact bloodtype.
5th and (hopefully) final EDIT Changed up even more!!!! Made a lot of corrections as pointed out by others below. Also added some more info. Copy pasted some of the corrections into my responses.
PLEASE GO OUT AND DONATE BLOOD TODAY! SAVE A LIFE Blood and plasma are always short hand in stock at hospitals and blood banks. Rumors you may have heard about there being wharehouses of blood is simply not true. Blood usually only has a shelf life of about 45 days, after which it is not usable. So it is always important to keep a stock for those emergency situations. Donating is especially important if you are blood type O- and also AB- Blood type O- can only receive blood of that same type, so save your fellow blood groupers life! Blood type AB- lacks Antibodies so it is considered the universal plasma donor