From The School of Biomedical Sciences Wiki
The AB blood group is displayed in individuals whose red blood cells display both the A and B antigen. This is a rare blood group type, AB negative being the rarest.
The ABO gene encodes for the formation of glycosyltransferases that add N-acetylgalactosamine and galactose to the H antigen already present on the red blood cells, to form both A and B antigens.
The individual with the AB blood type does not contain any antibodies against A and B antigens. This is so the immune system does not attack the red blood cells.
- ↑ Dean L. Bethesda, blood groups and red cell antigens, 2005,5 
- ↑ Victor A. McKusick,ABO GLYCOSYLTRANSFERASE; ABO , 1986,OMIM entry description. 
- ↑ Marius Lixandru, What are blood types and what do they mean?, Natureworld, 2008