Kell and Kx Blood Group Systems

Kell consists of 35 antigens, including six sets of antigens with antithetical relationships. Anti-K (KEL1) can cause severe haemolytic transfusion reactions and haemolytic disease of the fetus and newborn. Other Kell-system antibodies may also be clinically significant. The Kell glycoprotein (CD238), encoded by KEL, is a metalloendopeptidase that processes endothelin-3. It spans the red cell membrane once, has a large, folded extracellular C-terminal domain, and is linked through a disulphide bond to the Xk protein of the Kx system. Absence of Xk resulting from mutations or deletion of XK, an X-linked gene, causes weakened expression of Kell antigens and McLeod syndrome, a form of neuroancanthocytosis.