now we've looked at the AO system and I'm just going to recap that very briefly now so here we have blood group a and the blood group is determined by the Red Cell so this has a antigens but if someone is blood group a they're going to have B antibodies or antibes in their plasma if someone's blood group B it's the red cells that to B but there's going to be anti-a antibodies in the plasma if someone's blood group AB they're blood group AB because it's the red cells that have the A and the B antigens so this is the way we've drawn an a antigen this is the way we've drawn a b antigen and as you can see there are no antibodies in the blood if someone is AB but if someone's blood group O that is blood group zero then there are no antigens on the red cells but there will be anti-a antibodies and antib antibodies in the plasma and these antibodies are described as being naturally occurring so you're going to have these type of IGM antibodies in the plasma to any of the groupings that you don't have so blood group a is going to have the antibody B in it because there's no B antigens and it's the same with blood group b there's going to be antia antibodies because there's no a antigen so for some reason you develop antibodies to any of the antigens you don't have and these are naturally occurring whoever you look in with a blood group a they are going to have antib antibodies in their plasma and these develop during the first few months to the first year of life so when a neonate is born they don't have these antibodies but they develop them in the first months and first year of life and the reason they develop them is probably because they're exposed to bacterial infections and different sorts of food that stimulate the development of the antibodies but we describe them as naturally occurring now the next blood group I want to introduce you to is the recess Factor now the recess factor is so called because it was discovered using Recess Monkeys and the recess factor is actually a complicated factor with many subgroupings like C D and E subgroupings but the one that is active that is immunologically active that can act as an antigen is the D Factor so when we're talking about the recess Factor really what we're talking about is the D Factor the letter D Factor now what the recess factor is it is an additional blood group and it's simply present or absent so if someone's blood group a as we see here we notice that there are a antigens on the surface of the Red Cell but we notice at the moment there are no other antigens on the surface of the Red Cell but if someone is a recess positive then they will have recess Factor antigens on the surface of their cells as well and this is another antigen it's protein based and it's present or absent and like the system it is genetically determined so what we've done now is we've added recess Factor antigens to someone who is blood group a and we've turned them from Recess negative into recess positive and in the same way if we look at blood group b here so we're looking at the outside of the B arthrite the outside of the red cell and we notice that there are B antigens but we also notice that there are no recess antigens on the surface of the Red Cell so at the moment this diagram is illustrating someone who is B recess Negative they don't have the recess Factor but if we add the recess Factor as an additional antigen we're making that a noong antigen today they are actually specific molecular shapes what we've done now is we've converted this into a b recess positive looking at the ab we see there are a antigens on the surface and B antigens on the surface but we notice there are no recess Factor antigens at the moment this person at the moment is recess Negative they are AB negative but if we add them they will become recess positive so we've now diagrammatically turn these people into recess positive as well and finally with the blood group O we notice there are no antigens on the surface of the arthrite so at the moment there are no recess Factor antigens so this is diagrammatically illustrating someone who is recess negative but if you want to diagrammatically represent someone whose recess positive now we see that there are the recess Factor antigens on the surface of the cell so this person is now o recess positive so the recess factor is mostly the D factor and it's simply present or absent so that means in addition to being a b a b or o someone can be either of those groups with or without the recess Factor so blood groups can be a positive or A negative B positive or B negative a positive or A negative and O positive or O Negative so that describes the blood groups simply using the resar system now blood groups are quite a bit more complicated than this and in fact there's a the last time I read anything about it there was 35 different types of blood groups which have been identified but the D or the Reis are the immunologically most significant ones to be taken into account first for blood transfusion but most transfusion Laboratories will take into account more factors than the recess Factor now we have noted that in the system there are naturally occurring antibodies in the plasma now with the recess Factor there are no naturally occurring antibodies so if someone is recess negative there will be no recess Factor antibodies no recess Factor immunoglobulins in the plasma and whether someone's recess positive or recess negative makes no difference there still will be no recess Factor antibodies in the plasma they are not naturally occurring but if someone is exposed to recess positive blood who is recess negative then that means they will be exposed to recess Factor antigens and of course an antigen is something that causes the body to produce an antibody an immunoglobulin so if someone's recess negative and they are exposed to recess positive blood even on one occasion only because this D recess factor is very antigenic and immunologically stimulating then after that person has been exposed to recess positive blood from then on they will have recess Factor antibodies in their plasma and that means if they're exposed to recess positive blood on a future occasion there can be an immunological reaction and we'll consider these in more detail when we consider the condition of hemolytic disease of the newborn