The Rh (not Rhesus) system is the
second most important blood group system in transfusion medicine because
antigen-positive RBCs frequently immunize antigen-negative individuals through
transfusion and pregnancy.
Inheritance of Rh antigens is
determined by a complex of two closely linked genes: one encodes the protein
carrying D antigen (RhD); the other encodes the protein carrying C or c and E
or e antigens (RhCE). RBCs from Rh-positive people have both RhD and RhCE,
whereas Rh-negative RBCs have only RHCE. In the Rh system, eight common antigen
combinations or haplotypes are possible: Dce (R0, Rh0),
DCe (R1, Rh1), DcE (R2, Rh2), DCE
(RZ, Rhz), ce (r, rh), Ce (r', hr'), cE (r″, hr″), and CE
(ry, rh″). The letter "d" is commonly used to designate the lack of
D, but there is no d antigen or anti-d.
