Re: Blood group names in Canada vs. US?

Greetings -

I'm not fully certain why you use I^A, I^B, and ii to represent the ABO system - I do not recognize the it as part of the standard nomenclature, and came across no similar usage in a MEDLINE search, or current texts on blood banking. However, I'll give you my best guess as to what it might mean..

I and i represent a particular set of blood group antigens (the Ii system), distinct from the ABO system. In fact, there are more than 250 characterized "antigens" on red blood cells; 195 of these have been placed into 23 distinct systems. The antigens represent parts of proteins associated with the cell membrane, or in the case of ABO and Ii, carbohydrate chains (=sugars) attached to proteins (glycoproteins) or to lipids (glycolipids).

I and i represent internal portions of the carbohydrate chain that ultimately forms the ABO antigens. Enzymes called glycosyltransferases add I or i-specific sugars before subsequent glycosyltransferases add sugars defining A, B or H (H = O group). I and i are believed to be preliminary sequential steps, with the i gene catalyzing a reaction before the I gene. The product of the I-gene creates a branching sugar; its presence is not required to create target sites for the action of the A, B or H genes. At birth I is largely undetectable; i-chains predominate. By 1-2 years of age, however, I-chains become the predominant chain, except in rare individuals who remain i-positive. Levels of ABO antigens in neonates are ~1/3 those of adults.

The above could explain why you use I^A, and I^B to represent the A and B blood groups? The designation indicates that the person "added" A or B-type sugars to an underlying I chain (the predominant form in most adults). However, i^A and i^B should also be possible in individuals produceing only i-chains. I am less certain about the use of ii to represent type-O. O individuals have the "H-gene" glycosyltransferase, but lack the A or B-specific glycosyltransferases. H comes after i and I in the biosynthetic pathway, as follows:

      Pathway (greatly abbreviated!):
                     -> A
                   /
    	i -> I -> H 
                   \
                     -> B 

     Type-O:
    	i -> I -> H -> Type-O

     Type A:
    	i -> I -> H -> A -> Type-A

     Type B:
        i -> I -> H -> B -> Type-B

     Type AB: (both A and B genes present)
    	i -> I -> H -> A + B -> Type-AB

Hope this helps..

-L. Bry, MD/PhD
Resident in Clinical Pathology
Brigham & Womens' Hospital
Harvard Medical School
Boston, MA 02115

References:
1. Zdebska E. Krauze R. Koscielak J. Structure and blood-group I activity of poly(glycosyl)-ceramides. Carbohydrate Research. 120:113-30, 1983.
2. McCullough, J. Ch. 9 - Blood Groups, in Transfusion Medicine, © 1998 McGraw Hill.
3. American Association of Blood Banks