K12 IS LOCATED ON THE KELL BLOOD-GROUP PROTEIN IN PROXIMITY TO K K AND JS(A)/JS(B)/

K12 is a high-prevalence antigen, with no known antithetical partner, that is associated with the Kell blood group system. We report studies on the 5th propositus (MS) with the K:-12 phenotype and the second ca se to show that the K12 is inherited. The anti-K12 in his serum did no t destroy antigen-positive incompatible red cells transfused on at lea st 3 occasions over 6 years. Red cell membranes from MS possessed the Kell protein that was indistinguishable from control membranes. K12 an tigen was shown by immunoprecipitation to be on a protein with an appa rent molecular mass of 93,000 and by monoclonal antibody immobilizatio n of erythrocyte antigens (MAIEA) assay to be on the Kell protein in p roximity to Wk and Js(a)/Js(b) antigens. These data remove the K:-12 p henotype from its current Kell-related (or para Kell) status and eleva tes the K12 antigen to a bona fide member of the Kell blood group syst em.