c. There is a numerical system for designating the Kell antigens similar to that
used for the Rh-Hr system. Table 2-19 presents this nomenclature and includes some
additional antigens that currently are thought to be part of the Kell system.
d. As with most of the other group systems, there are rare individuals whose red
blood cells react very weakly or not at all with the antibodies of the Kell system. Red
blood cells of the Ko (or Knull) phenotype seem to lack all antigens that are produced by
the Kell genes. An antigen Kx (K15) is present in large amounts on Ko cells but very
little is detected on other phenotypes. Kx appears to be a precursor in the Kell
biosynthetic pathway and its synthesis controlled by an X-linked gene, independent to
the Kell locus. Anti-Kx can be found together with anti-KL (K9) in the serum of some
rare individuals who have such weak Kell antigens that adsorption and elution
techniques may be needed to demonstrate them; such weakly reactive cells are said to
have the McLeod phenotype. Individuals with the Ko phenotype can produce an
antibody, anti-Ku (K5), that will react with all cells except those of the Ko phenotype.
Table 2-19. Antigen frequencies in the Kell system.