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3. Old stuff 3.2.3. Physiology 3.2.3.6. Haematology 3.2.3.6.2. Transfusion medicine 3.2.3.6.2.1. RBC antigens and antibodies
3.2.3.6.2.1.2. Rhesus system 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