Blood group antigens defined by the amino acid sequences of red cell surface proteins.

The antigens of 18 blood group systems are expressed on proteins that are intrinsic to the red cell. The proteins which carry the antigens of these systems have been identified and primary sequence information is available for all but two (SC, DO). Several different functional groups are evident. Antigens of the DI, CO, RH, XK and JK systems are located on proteins which have the structure of membrane transport proteins. The FY antigens mark a cytokine receptor. The IN, LW, XG antigens are associated with molecules which have adhesion functions and the LU glycoprotein also has a structure which suggests a role in adhesion. YT and KEL antigens are located on cell surface enzymes and the CR and KN antigen on molecules involved in complement regulation. Finally, the MN and GE antigens are located on sialic acid-rich glycoproteins (glycophorins A, B and C/D respectively), a group of molecules which do not, as yet, have a clearly defined function. The molecular basis of antigens in several blood group systems have been defined and shown to depend upon the amino acid sequence.