ABO blood grouping is critically linked to several important determinants, which are considered precursors to the formation of detectable, testable antigen. The main precursor is the H antigen. Creation of specific A and B antigens is determined by the addition of specific glycosyltransferases (enzymes) that add specific sugars to the H antigen.
These added sugars result in the precursor conversion to a detectable RBC antigen.
H Gene (Hh or HH)
The antigenic precursor on which A and B antigens are made. Without the H antigen, individuals cannot demonstrate the expression of A or B antigenic determinants on the RBC membrane surface.
| Gene | Glycosyltransferase | Immunodominant Sugar
| Resulting Antigen
|
| H | α-2-L-fucosyltransferase | L-fucose
| H |
| A | α-3-N-acetylgalactosaminyltransferase | N-acetyl-D-galactosamine | A |
| B | α-3-D-galactosyltransferase
| D-galactose
| B
|
