Rh system

Rh is a blood group, which antigen /antigens occurs  only on erythrocytes. It is highly polymorphic- so far more than 40 serologically distinct Rh antigens have been identified.

Genetics
The region ,that controls the expresion of Rh antigens, lies on a short arm 1. chromosome. It consists of two closely related structural genes RHD and RHCE, which encode antigen-bearing membrane proteins D, d, C, c, E, e. Among the mention antigens is applied a very strong gene bond – a combination of alleles of both genes is transferred z  from generation to generation v bloku – tzv. haplotype. náhled|200px|Makak rhesus (Macaca mulatta) – this species is associated with the discovery of the Rh factor (Rhesus factor) The most important is antigen D – which determine the Rh positivity (Rh+). Rh negative individuals (Rh−) are recessive homozygous (genotype dd) – aproximatelly 17 % of the europe population.The presence of D antigen cannot be serologically demonstrated, which is due to the deletion of the D gene in the Rh region of DNA. Antigens C, c, E, e are not so strong and so significant as antigen D, despite this they can provoke a production of antibodies in case of incompatibility. Expresion of the antigens C, c, E, e is controled by one gene and is a result of an alternative splicing of the primary transcript RHCE gene. They appear as separate antigens on the plasma membrane of the erythrocyte. Amongs the alleles C/c a E/e is alelic interactions.

Antibodies
In the Rh system, 'antibodies do not occur naturally.''' (despite of AB0 system). This means that, Rh-negative individual does not have antibodies against antigen D. However antibodies can be produce in case of long-lasting (prolonged) contact with the RH-positive blood.

Rh incompability in blood transfusion
The formation of antibodies in the body may be conditioned by the incompatibility of Rh factor with Blood transfusions. In this case is Rh-positive blood administered to Rh negative recipient. Following such a transfusion, anti-Rh antibodies are formed in the body and upon the subsequent incompatible transfusion, the body's response is much greater.

Rh incompatibility of mother and fetus
náhled|300px|Formation of antibodies after trnasfer of incompatible blood through the placenta Another option for formation of the Rh antibodies is an incompatibility of the mother.a plodu. In this case the mother is Rh- and the fetus is Rh+ (after the father). When fetal erythrocytes enter the maternal cirulation D antigens stimulate the production of anti-D antibodies (classIgG). Mother's antibodies permeate through placenta a cause hemolysis of the fetal erythrocytes. Sensitization of the Rh-negative mother occurs usually Senzibilizace Rh-negativní matky nastává většinou after the delivery (during the delivery placenta is separated a and some amount of the fetal blood penetrates into the maternal blood circulation). The first child is by rule not handicapped,however the risk increase s with the higher amount of the next deliveries or abortions.

Another symptoms of fetal damage include:


 * hemolytic anaemia,
 * icterus (accumulation of bilirubin in the blood, damages the CNS when a certain limit is exceeded),
 * fetal erythroblastosis (in tough cases fetus die in utero).

Fetal damage can be prevented by administration of the anti-D antibodies to mother 72 hours after a sensitizing dose of Rh-positive erythrocytes (after delivery or invasive prenatal diagnosis)

Related articles

 * AB0 system • Blood groups • Heredity of blood group systems
 * Hemolytic disease of the newborn • Hyperbilirubinemie in newborns and infants • Exchange transfusion

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