# why do different blood types "kill" each other when mixed?? **URL:** \ **Category:** Factual Questions\ **Created:** [July 5, 2007, 1:30pm UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589 "2007-07-05T13:30:37Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![meshosh](https://avatars.discourse-cdn.com/v4/letter/m/b77776/32.png) [@meshosh](https://boards.straightdope.com/u/meshosh)\ **Post date:** [July 5, 2007, 1:30pm UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/1 "2007-07-05T13:30:37Z")
Hi, there is one thing I always wondered, and no one could ever tell me… Why there are different blood types? And most important, why do they “kill” each other when mixed? I mean, our blood is not supposed to mix with other people´s blood anyway, so why does it carry something capable of destroying something else that is never supposed to be there in the first place? I mean, it´s like wearing a bullet-proof vest before guns were invented! what´s the logic in that?? ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [July 5, 2007, 1:48pm UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/2 "2007-07-05T13:48:26Z")
They don’t all cause adverse reactions. Wikipedia is a good place to start with these types of questions. [Blood types.](http://en.wikipedia.org/wiki/Blood_type) Note that type “O” individuals can donate to anyone and type “AB” can receive from anyone (that’s a slight oversimplification, but is a good rule of thumb). ---
**Author:** ![Strinka](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/strinka/32/512_2.png) [@Strinka](https://boards.straightdope.com/u/Strinka)\ **Post date:** [July 5, 2007, 2:00pm UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/3 "2007-07-05T14:00:25Z")
I don’t know for sure, but here’s my guess I imagine different blood types exist due to genetic drift. That is, if a mutation confers no benefit or disadvantage, whether it gets spread throughout the population is due to chance. And the immune system is designed to find and kill foreign bodies. All the immune system can distinguish between is “belongs to this body” or not. So someone else’s blood looks like a bacteria to it. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [July 5, 2007, 2:22pm UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/4 "2007-07-05T14:22:45Z")
Certain combo’s will cause the cells to clump together, due to the immune response. ---
**Author:** ![picunurse](https://avatars.discourse-cdn.com/v4/letter/p/7bcc69/32.png) [@picunurse](https://boards.straightdope.com/u/picunurse)\ **Post date:** [July 5, 2007, 2:24pm UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/5 "2007-07-05T14:24:02Z")
[QUOTE=John Mace] They don’t all cause adverse reactions. Wikipedia is a good place to start with these types of questions. [Blood types.](http://en.wikipedia.org/wiki/Blood_type) Note that type “O” individuals can donate to anyone and type “AB” can receive from anyone (that’s a slight oversimplification, but is a good rule of thumb). [/QUOTE] The universal donor is O-Rh negative. The universal recipient is AB-Rh negative. The Rh factor is a very important part of the compatability. ---
**Author:** ![WhyNot](https://avatars.discourse-cdn.com/v4/letter/w/c77e96/32.png) [@WhyNot](https://boards.straightdope.com/u/WhyNot)\ **Post date:** [July 5, 2007, 2:51pm UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/6 "2007-07-05T14:51:29Z")
[QUOTE=picunurse] The universal donor is O-Rh negative. The universal recipient is AB-Rh negative. The Rh factor is a very important part of the compatability. [/QUOTE] I think you mean AB+ is the universal recipient, no? An AB- person shouldn’t receive Rh positive blood of any type. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [July 5, 2007, 2:52pm UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/7 "2007-07-05T14:52:00Z")
Wow, one helpful answer out of [del]four[/del] five! ---
**Author:** ![Sattua](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sattua/32/11906_2.png) [@Sattua](https://boards.straightdope.com/u/Sattua)\ **Post date:** [July 5, 2007, 2:57pm UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/8 "2007-07-05T14:57:08Z")
The dummy answer: because they’re allergic to each other. ---
**Author:** ![picunurse](https://avatars.discourse-cdn.com/v4/letter/p/7bcc69/32.png) [@picunurse](https://boards.straightdope.com/u/picunurse)\ **Post date:** [July 5, 2007, 6:04pm UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/9 "2007-07-05T18:04:42Z")
[QUOTE=WhyNot] I think you mean AB+ is the universal recipient, no? An AB- person shouldn’t receive Rh positive blood of any type. [/QUOTE] I’m sorry, I mis-spoke (typed). However, an RH neg individual can recieve Rh pos [one time](http://byedr.com/medicine/2195-byedr.html). > [@](#): > > Men (and women beyond childbearing years) who are Rh negative can receive a first transfusion from Rh positive blood, but cannot receive any later transfusions, as they will then have an antibody against the Rh factor (known in blood banks as “D”). So in a dire emergency, if there is no Rh negative blood available, and the person has not been immunized to the D antigen, they can receive transfusions using Rh positive blood. It takes several weeks to form the antibody. Here’s a [chart](http://peoriabb.com/articles/Blood_Types.htm) for determining who can get what. ---
**Author:** ![aruvqan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aruvqan/32/2891_2.png) [@aruvqan](https://boards.straightdope.com/u/aruvqan)\ **Post date:** [July 6, 2007, 1:32am UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/10 "2007-07-06T01:32:38Z")
[QUOTE=picunurse] I’m sorry, I mis-spoke (typed). However, an RH neg individual can recieve Rh pos [one time](http://byedr.com/medicine/2195-byedr.html). Here’s a [chart](http://peoriabb.com/articles/Blood_Types.htm) for determining who can get what. [/QUOTE] AB- and sensitized, I used up my one shot :rolleyes: ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [July 6, 2007, 3:21am UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/11 "2007-07-06T03:21:29Z")
Correct me if I’m wrong. I’ve heard that if you’re A you’re born with antibodies to the B factor. If you’re B you have them for A. And if you’re O, you have them for both. But you have to be exposed to the Rh factor to develop the antibodies. Why you’d be born with the antibodies, I don’t know. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [July 6, 2007, 3:22am UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/12 "2007-07-06T03:22:33Z")
I’m type O-, btw. The blood bank has been calling again this week. They know where I live. ---
**Author:** ![Sattua](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sattua/32/11906_2.png) [@Sattua](https://boards.straightdope.com/u/Sattua)\ **Post date:** [July 6, 2007, 3:38am UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/13 "2007-07-06T03:38:39Z")
[QUOTE=Yllaria] Correct me if I’m wrong. I’ve heard that if you’re A you’re born with antibodies to the B factor. If you’re B you have them for A. And if you’re O, you have them for both. But you have to be exposed to the Rh factor to develop the antibodies. Why you’d be born with the antibodies, I don’t know. [/QUOTE] It’s more like, whatever letters are in your blood type are the proteins that you _have_ and that therefore \*don’t bother \* you. Type A and AB both have the A proteins, so they can tolerate them. Type B and AB both have the B proteins, so they can tolerate the B proteins. Type O doesn’t have either and can’t tolerate either–it’s the universal donor because it doesn’t contain any offensive proteins. Type AB is the universal recipient because it can tolerate whatever proteins are present. Giving AB blood to any other blood type, however, causes problems. ---
**Author:** ![Sattua](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sattua/32/11906_2.png) [@Sattua](https://boards.straightdope.com/u/Sattua)\ **Post date:** [July 6, 2007, 3:40am UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/14 "2007-07-06T03:40:57Z")
By the way, blood type is a matter of really simple Mendelian genetics. There are three alleles for the blood type gene: A, B, and O. To have type O blood, you have to inherit two O alleles. To have AB blood, you inherit one A allele and one B allele. Type A blood can be either A+A or A+O. Type B is either B+B or B+O. See? I was awake in the biology weed-out course. ---
**Author:** ![Antigen](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Antigen](https://boards.straightdope.com/u/Antigen)\ **Post date:** [July 6, 2007, 4:28am UTC](https://boards.straightdope.com/t/why-do-different-blood-types-kill-each-other-when-mixed/410589/15 "2007-07-06T04:28:27Z")
[QUOTE=Yllaria] Correct me if I’m wrong. I’ve heard that if you’re A you’re born with antibodies to the B factor. If you’re B you have them for A. And if you’re O, you have them for both. But you have to be exposed to the Rh factor to develop the antibodies. Why you’d be born with the antibodies, I don’t know. [/QUOTE] You’re partly right. The ABO antibodies are naturally occurring and very strong, but you’re NOT born with them. They develop very early in life, though, and there are still a few theories about how and why they develop. The important thing to remember is that they’re not triggered by a transfusion, they’re there pretty much from the start and there’s not much you can do about it. If you’re type A, you’ll make Anti-B antibodies, and that’s just the way it is. The Rh antibodies, on the other hand, will only develop on exposure to a foreign Rh type, either through a transfusion or pregnancy. Just to add to the fun, there are several other blood group antigens, so even if you’re B neg and you’re getting B neg blood, there’s still a chance you’ll develop an antibody to some other antigen the donor has on his cells that you don’t. Once that happens, it’s a little harder to find compatible blood for the next transfusion, since the blood bank not only has to match the type and Rh, but they also have to make sure the donor doesn’t have whatever your antibody is against, because you’d likely have a reaction. I’ve seen some sickle cell patients with up to 11 different antibodies formed, because they get transfused so often. It’s very difficult to find blood that’s safe for them, and sometimes it ends up being a case of giving them the least incompatible blood we can find.