last updated 20-11-2024

A/B/O system

The A/B/O system in transplant

Donors and recipients of organs must be matched for the A,B,O system of blood group antigens normally present at the surface of erythrocytes. The O-antigens consist of a core oligosaccharide (5 sugar groups), the A-antigens have an extra N-acetyl galactosamine (red hat) added to the O-antigen and the B-antigens an extra galactose group (blue molecule on top).

Type O recipients who lack A and B antigens, have both anti-A and anti-B antibodies, whereas type AB recipients have neither. The combinations of donor and recipient that allow organ transplant are indicated by green figures, the combinations that should be avoided are represented by red figures.

As A, B, O antigens are also present on the endothelial cells of blood vessels, this is an important factor for successful transplantation of solid organs such as kidneys. The antibodies produced would lead to a very rapid rejection of the graft, called hyperacute reaction by fixing complement throughout the vasculature of the graft that can occur within minutes or hours.

HLA class I molecules are expressed on the vascular endothelium and can also cause hyperacute reaction. HLA class II are normally not expressed on endothelium.

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Which blood group is universal donors’ blood?

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