52 INTRODUCTION TO IMMUNOCHEMICAL SPECIFICITY 



If a donor of the same blood group as the recipient is chosen, it 

 is ol)vious that the chances of a successful transfusion are good, 

 unless other blood factors yet to be discussed come into operation, 

 or unless the technique is faulty. Transfusion consists in introducing 

 a relatively small amount of the donor's blood, 500 ml. or less, into 

 the circulation of the recipient. This means that the donor's cells are 

 exposed to a large amount of whatever agglutinins the recipient 

 possesses, in full concentration. If the donor's cells contain an ag- 

 glutinogen capable of reacting with the recipient's agglutinin or 

 agglutinins, the donor's cells may be agglutinated, and a serious or 

 even fatal transfusion reaction may result. 



It is not, however, always necessary to use a donor of exactly the 

 same blood group as the recipient. Introduction of a donor's ag- 

 glutinin which could react with the recipient's cells is often not 

 serious, for the agglutinin gets diluted by the recipient's plasma and 

 is also partly neutralized by soluble blood group substance in the re- 

 cipient's plasma and in his tissues. This means that, in general, trans- 

 fusions in the directions shown in Fig. 4-1 are possible, although 

 it is always preferable to use a donor of the same group as the 

 patient. 







I 







/ 



AB 



t 

 AB 



Fig. 4-1. Theoretical possibilities of transfusion, based on blood groups of 



donor and recipient. 



Blood groups are inherited. Parents with any given combination 

 of blood groups may produce children of certain blood groups but 

 not of others, except that the mating of A X B may produce children 

 of any of the four groups. Inheritance is based on three allelomorphic 

 genes. A, B, and O, which can occur in any combination of two : 

 OO, AA, AO, BB, BO, or AB. The blood groups of individuals 

 of genotype AO are the same, so far as we can tell in the laboratory, 



