Everyone who gets a blood transfusion is exposed to foreign red cell antigens (unless they receive their own blood, or blood from an identical twin). Yet not everyone makes red cell antibodies. Only 1 - 2% of hospitalized patients have irregular alloantibodies (5% or more if multitransfused or multiparous). Factors which affect whether or not antibodies will be made include these:
Immunogenicity: Only a few red cell antigens are very immunogenic (e.g., ABH in the ABO system, D in the Rh system, and Kk in the Kell system). Other Rh antigens (CcEe) and antigens in the Kidd and Duffy systems are not nearly as immunogenic. The strong immunogenicity for the D antigen is shown by the fact that approximately 70% of Rh(D) negative persons produce anti-D upon exposure to the D antigen. After the D antigen, the K antigen appears to be the most immunogenic.
Antigen Volume: Exposure to a very small volume of antigen may result in immune tolerance. Similarly, exposure to a large volume of foreign antigens simultaneously may produce immune paralysis. In general, the greater the volume of foreign antigen, the more likely it is that antibody will be produced.
Immune response genes: Antibody production seems partially to be under the genetic control of immune response (IR) genes that are closely linked to the HLA-D region on chromosome #6. IR genes can control whether or not someone is a good or a poor antibody responder. They can also be specific in their control of antibody production. For example, approximately 30% of Rh(D) negative people fail to produce anti-D no matter how much Rh(D) positive blood they receive. Perhaps these people have IR genes that make them incapable of producing anti-D.
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| Antigen - Antibody Reactions |
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