Our body's immune system can be thought of as a nifty little defense mechanism designed to answer one question: is a given molecule part of us, or part of something else? For example, if I inject a *foreign* protein into an individual, that person's immune system will quickly recognize that protein as being 'non-self' and act to destroy it. On the other hand, the immune system is able to recognize the multitude of proteins that are native to that person's body as being 'self', and do not attack those.For a simple model of how a typical immune response might work, think back to the last nasty bacterial infection you had. The little invading bugaboo that made you so ill had proteins all over its cell surface. The proper term for these foreign proteins is *antigens*. Your immune system, upon recognizing that these antigens were 'non- self' then attacked the little bugaboo with (among other things) another type of protein called an *antibody*. These antibodies are able to recognize the specific foreign antigen. They (the antibodies) attach to the foreign antigen, which eventually leads to the destruction of the little bugaboo that made you sick.
In terms of blood types, first note that our red blood cells have quite an array of proteins on their surface. The proteins we are concerned with here (and the ones by which we classify the most well- known of several blood group systems) are called the 'A, B, O' group of antigens. An individual who has the 'A' antigen on the surface of his/her blood cells is termed 'Type A'; likewise, an individual with the 'B' antigen on the surface of their blood cells is 'Type B'. If you should have inherited *both* the A and the B antigens from your parents, you are 'Type AB'. And if you have *neither* the A or B antigens on your blood cells, you are 'Type O'. A funny thing about blood. . .within a few months of birth we automatically get antibodies in our blood plasma against whatever blood antigens we don't naturally have. That is, someone who is 'Type A' will automatically have antibodies against the B antigen. Individuals who are 'Type B' have antibodies against the A antigen. Someone who is 'Type O' (remember, Type O has neither the A or B antigens on their blood cells) really hits the jackpot--they have antibodies that can attack both the A and the B antigens.
Blood transfusions are an excellent way to illustrate this system (though discussing this topic causes my fangs to descend--I'll try to stay calm). Let us say that you are Type A (you have the A antigen on your red blood cells, and the B antibody in your plasma). Oops! You scored in the danger zone on the vamp vulnerability test, and some list-member has snacked upon you! You need a transfusion, quick! Not thinking terribly clearly from your loss of Type A blood, you stumble into the evil Dr. Nightingale's laboratory and beg for help. Unfortunately for you, Dr. Nightingale has terrible organizational skills, and has mislabeled a bag of Type B blood as Type A. . .and promptly infuses all of this Type B blood into your poor Type A body. The B antibodies in your plasma promptly start destroying all of the B blood cells that just got pumped into you (resulting in nasty things like blood clots going up to your already-befuddled brains). Worse still, since Dr. Nightingale gave you *whole blood* you have an additional problem: that bag of type B blood has A antibodies in the plasma, and those antibodies start attacking your native Type A red blood cells (more nastiness). Let us hope that your vampyric attacker transformed you, because at this point if you are not undead you are just plain dead.
Researched by . . .
Roel
