Rhesus system
[Ref: PK1:p241-242; WG21:p539-541; KB2:p202-203]
Genetic basis
RBC antigens of the Rhesus system are determined by 3 pair of alleles
- Main alleles
= D,d, C,c, and E,e
- On chromosome 1
Rhesus antigens
- Each antigen is defined by a specific antibody
* e.g. anti-C, anti-c
- d antigen does not exist
* d antigen is more the absence of D antigen
* Anti-d does not exist
- Rh positive means the presence of D antigen
Location of rhesus antigens
Rh antigen are present ONLY on RBC cells
* Unlike the ABO system
Rhesus antibodies
- Rh antibodies rarely occur naturally
* Development requires exposure to the antigen
- Most Rh antibodies are ??"immune warm" and IgG in origin
- 85% of Caucasian population possess the D antigen
* i.e. 85% are Rh positive, and 15% are Rh negative
- Over 99% of Asians are Rh positive
