Immunoelectron microscopy of Kell and Cellano antigens on red cell ghosts

The ultrastructural arrangement of Kell (K1) and Cellano (K2) antigens on red cells was studied using ferritin-conjugated rabbit antihuman IgG to stain ghosts derived from antibody-sensitized intact red cells. Estimates of the number of sites under equilibrium binding were obtained by counting both ferritin grains and ferritin clusters on electron micrographs. Values for Kell sites on heterozygous red cells ranged from 2300 to 5900 and for Cellano sites from 2000 to 5000 with no discernible dosage effects. Both the Kell and Cellano antigens were clustered, which was due to conjugate staining of the ghost membranes and does not reflect the topological arrangement of these antigens on the native membrane. The ferritin grain patterns found with the Kell and Cellano antigens was similar to those observed with the Rh antigens except for the markedly reduced antigen site density.