- All right when you're talking about disorders of the immune system you have to talk about what are called type two or cytotoxic reactions. So something happens that activates complement the complement system which is one of your non-specific defenses it basically can kind of drill holes in cell membranes and lyse them and tear them open. So either IgG or IgM antibodies are going to react to some antigen and activate this complement system. And the cell's gonna die it's gonna be broken down. This is where the transfusion reaction comes from so it's a good time to talk about the ABO blood typing system as well as the Rh blood grouping system. And we'll talk about hemolytic disease of the newborn. So starting with blood type. So it's been since that they've known about the blood typing system. And they knew that there were four basic blood types A B AB and O. There are tons of other blood types now. If you give plasma you might see some different things there's Lewis systems and different ones but these are the ones that matter the most. Actually there are dozens and dozens of different cell surface markers on red blood cells. These are the ones that are the most reactive though. If you were gonna get a bone marrow transplant or organ transplant they'd have to match your blood much more specifically. But for the average Joe Schmoe this is enough. All right so that means that basically your blood type is determined by the presence or absence of antigens on the surface of your cell membranes. So for example if you have type O blood cells that means you do not have A or B. So there isn't an O antigen O means the absence of A and B. So if you have a type O blood then that means that your blood cells do not have A or B antibodies or antigens sorry. If you have type A then you have the A antigens on your red blood cells. If you have type B you have the B antigens and if you have type AB you have both A and B. This is an example of a codominance like in genetics usually we have a dominant gene and a recessive gene here both A and B dominate O. So A can't dominate B B can't dominate A. So if you get type A gene from mom type B form dad you will be type AB. So the blood typing system and then so whatever antigens you have you have antibodies in your plasma for the opposite. So no one's quite sure where these come from 'cause where'd you get sensitized to it but it appears in either a microorganism or you ingested food or blood or something that looks awfully similar to these. So somewhere along the line very early in the process you develop these antibodies. So if you have type we'll start at the top this time. If you have type AB you don't have any of the anti-A or anti-B antibodies makes sense. Anti-A antibodies would attack A anti-B would attack B and you can't let that happen. So someone with type AB blood is considered the universal donor no matter who our recipients are no matter what kind of blood that you give them A B AB or O there are no antibodies in their bloodstream to attack them. Because they have both of the cell surface markers. Type B would have anti-A antibodies. So you can give them type B blood you can give them type O blood but you can't give them AB or A because their anti-A antibodies would attack the A antigen. A type A blood is the opposite they have the A antigen so they have anti-B antibodies. So you can give them type A blood which they have or type O which doesn't have any surface markers and they'll be fine. And then you see the last one is type O. Type O does not have any antigens so they have both antibodies. Which means that you can't give them any blood type but their own. If you give them type A they have anti-A antibodies. Give them type B they have anti-B antibodies. Give them AB obviously they have both. That makes them the universal donor. They can give their blood cells to anybody but they can only receive blood cells from their own kind their own type. Frequencies you can see that really they say that O negative we'll get to the negative and positive in a second O positive is actually gonna be the most common blood type in America there's about % of people have positive blood type. But you see O is the most common in all in whites blacks and Asian people. But then you see type A is also pretty common and type B is in some populations as well but type AB is pretty rare it takes a very specific genetic setup there. So where you're from genetically does certainly play a role here but so we're talking about the transfusion reaction. If you get the wrong type of blood then what's gonna happen is the complement system's gonna be activated by antibodies and it's gonna rip open your blood cells and destroy them. Really it starts right away but then you can have a problem for a few hours afterwards. So in some situations it'd be better to not get blood than to get the wrong type. That's why they're working on synthetic blood they're working on blood that they can just give people like on the battlefield and stuff. But in general if they don't know your blood type they can either cross match it specifically mixing your blood with a bag of blood or whatever and seeing if it reacts or just give you the universal donor which is O negative. So technically the universal donor is O negative because it wouldn't have the Rh antibody antigens either. The universal recipient is actually AB positive no matter what you give them they're fine. All right so that's the ABO blood typing system now let's talk about the Rh system and then we'll talk about hemolytic disease of the newborn. All right the Rh blood group system was developed found a little bit later. The Rh stands for rhesus monkey because they would use rabbit blood serum and it would react with monkeys. But about or % of the population is Rh positive which means that they have the Rh antigen on their cell surface so that would make you O positive A positive B positive whatever. The other % are gonna be negative. They're gonna be lacking the Rh antigen. Now here's the major difference though. If you have Rh negative blood if you're O negative you do not have anti-Rh antibodies until or unless you've been exposed to that blood. So secondly if you have O negative blood the first time you need a blood transfusion they can give you O positive and you'll be okay. But from there on out there's gonna be a problem. That leads us into this hemolytic disease of the newborn. So here we see a situation where an Rh positive father and Rh negative mother have a baby. And the mother's carrying an Rh positive fetus. So the fetus has Rh positive blood. Rh antigens from the developing fetus' blood during delivery when the placenta tears can actually enter her bloodstream. So now this first baby's fine mom is fine but now she's been sensitized. So now even though she has Rh negative blood she now has anti-Rh antibodies which you can see there. So the only issue would be with subsequent pregnancy. So when she gets pregnant again with the same situation Rh negative with an Rh positive child she now has anti-Rh antibodies that can cross the placenta and they can damage the fetal red blood cells. So you can survive but it's usually you're extremely sick and many of them don't survive anyways. So just remember that it's always mom's second pregnancy where this is a big problem and her immune system will attack and destroy fetal red blood cells basically. So this is obviously not as big of a deal now because of a drug called RhoGAM which is given to mom at very specific times. Now if they don't test the father 'cause oftentimes sadly they don't know who the father is. So basically if mom is a negative blood type they will treat her with RhoGAM. So what happens is when the baby is born their fetal blood is still being disintegrated and destroyed but the mom isn't helping clean it out so the kid can develop some pretty serious problems. So then you go that's what the RhoGAM who knows how many lives and how much disability and morbidity RhoGAM has prevented. So that's the issue with the hemolytic disease in newborn. Have to have an Rh positive father Rh negative mother second or later pregnancies. All right so that's an example of a group of immune reactions called type two or cytotoxic reactions.