The Rh blood group system is one of the most polymorphic and immunogenic systems known at this time in humans. It is controlled by two genes
, that encode two distinct Rh proteins
. One protein carries the C/c and E/e antigens
, and is therefore called the Rh CE or Rh ce (or Rh Ce or Rh cE) protein. The other carries the Rh D antigen, and is called Rh D protein. A fourth Rh antigen, Rh G, is located partly on the Rh CE and partly on the Rh D protein.
The genes encoding these two proteins have been cloned, end the molecular basis of the immunogenicity is being studied extensively world wide.
Rh D is a protein that sits in the plasma membrane of red blood cells. It crosses the membrane 12 times, creating 6 extracellular loops, and 5 intra cellular loops. Both the carboxy- and the amino-tail of the protein stick out into the interior of the cell.
The presence or absence of the Rh D protein from red blood cells determines if one is typed Rh+ (protein is present) or Rh- (protein is absent).
The Rh D blood group system is the second most immunogenic system known at this time. Only the ABO system has greater clinical importance.