Colton blood group system

The Colton system is a blood group system of erythrocytes. It is determined by the aquaporin-1 protein (see also Aquaporins). The aquaporin-1 protein occurs on the cell surface of erythrocytes, is an erythrocytic blood group antigen and is called Colton antigen.

Colton antigens thus belong to the aquaporin protein family and are encoded by an allele of the gene AQP1, which is also located chromosome 7p14. Aquaporin-1 is a transmembrane protein that forms a water-specific channel that endows the plasma membranes of erythrocytes and proximal tubules of the kidney with high water permeability, thereby allowing the movement of water toward an osmotic gradient.

The AQP1- and AQP2-proteins are the only aquaporins found in the erythrocyte membrane. The AQP1 protein accounts for 2.4% of the total membrane proteins of the erythrocyte. The AQP1 protein is used to determine blood group characteristics (blood grouping). Colton antigen negative individuals (null phenotype) show no obvious clinical symptoms, but their red cells have a shorter half-life.

The Colton antigen is important in transfusion medicine. 99% of individuals carry the Co(a) allele. The phenotypic distribution in the population is Co(a+b-) 90%, Co(a+b+) 9.5%, and Co(a-b-) <0.01%. Individuals with Co(b) alleles or lacking Colton antigen are at risk for transfusion reactions such as hemolytic anemia or alloimmunization after contact with Co(a) antigen.

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