BLOOD GROUP ANTIGENS 101 



receptors as well, contains a sugar of group 4, it may surprise some 

 people, for sugars of this group have not previously been found in 

 human tissues. We may still expect many surprises regarding the 

 natural occurrence of sugars. In the field of protein chemistry it is 

 commonly assumed that only one enantiomer of each amino acid occurs 

 in nature, and yet Oncley (1959) has pointed out reasons for doubting 

 this. The finding of a derivative of L-glucose in streptomycin has 

 already shown that some of these "unnatural" sugars occur in nature. 

 In the next chapter it will be seen that such sugars play a role in 

 the antigens of Salmonella and certain parasites. 



Since the above was written, Dodd, Bigley, and Geyer (1960), 

 starting from the observation that the receptor-destroying mumps 

 virus liberates from human erythrocytes a specific anti-D inhibitor, 

 found that A^-acetyl-neuraminic acid and other compounds related 

 to sialic acid inhibited anti-D but not anti-C or anti-E, thus pro- 

 viding a cltie to the chemical differences between D and the other 

 Rh antigens. In my laboratory we found that colominic acid, thought 

 to be a polymer of A^-acetyl neuraminic acid, also inhibits anti-D 

 specifically, and suggested it might even have clinical application 

 in preventing erythroblastosis fetalis (Boyd and Reeves, 1961). 



We have also found other substances, including some amino acids, 

 not closely related to any of the substances discussed above, to have 



