Determination of the N-terminal sequence of human red cell Rh(D) polypeptide and demonstration that the Rh(D), (c), and (E) antigens are carried by distinct polypeptide chains

Human monoclonal antibodies (MoAbs) directed against the blood group Rh(D), (c), and (E) antigens produced by Epstein-Barr virus (EBV)- transformed lymphoblastoid cell lines have been used to characterize the Rh components of human red cell membranes and to determine whether the Rh(D), (c), and (E) epitopes are carried by distinct polypeptides. After immunoprecipitation with the anti-Rh(D) antibody and preparative gel electrophoresis, a homogenous preparation of the Rh(D) protein was obtained from two different erythrocyte samples (Blo and D--/D--), which have an increased density of Rh(D) antigen. Both preparations exhibited the same N-terminal sequence (S)-(S)-K-Y-P-R-S-V-R-R-(L)-L-P- L-X-A, indicating that different Rh(D)-positive red cells are carrying a similar Rh(D) protein. Comparative immunoprecipitation studies with the human monoclonal anti-Rh(D), (c), and (E) antibodies have also shown that Rh components from intact and papain-treated erythrocytes have similar apparent mol wt of 30 to 32 Kd and are buried in the lipid bilayer and are not readily available to the proteolytic enzyme. Further investigations by indirect affinity chromatography and one- dimensional peptide mapping of the Rh(D), (c), and (E) molecules immunopurified from a single red cell sample demonstrate that a common Rh haplotype encodes three distinct polypeptide chains carrying the Rh(D), (c), and (E) epitopes, respectively.