Blood Drug Testing

Why do we produce antibodies related to blood type before exposure?

I know blood types have to do with antigens on the blood cells and clotting with exposure to a different antibody. Normally you don't make antibodies to an antigen unless you have been exposed to the antigen before. Are blood typing antigens different somehow? Otherwise the blood typing test wouldn't work unless the person had been exposed before...

Public Comments

1. yes u r absolutely right. during foetal development the B cells come into contact with the microorgaisms present in the gut. these microorganisms possess the same antigens on their cell surface that are the blood group antigens viz antigen A and antigen B and antigen H that are found on the surface of the red blood cells. so antivodies are made against A , B and H. now if u r blood group A, it means u have both antigens A and H on ur RBCs thus these antigens are recognized as self and antibodies against them are eliminated so u have anibodies only against B. therefore even though blood of other blood group hasnt ever come in contact with ur blood u still possess ready made antibodies against them. similarly for antigen B. for AB blood individuals all three antigens are counted as self and hence they do not have antibodies against any of the antigens and hence they can receive blood from any blood group. note: antigen A and antigen B are slightly different (by the terminal galactose and glucose units) and they both arise from antigen H (which does not stand for Rh factor) individuals with blood group O have only antigen H on their cell surface and hence have antibodies against both antigens A & B.