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. Senzibilizace Rh-negativní matky nastává většinou po porodu (při porodu dochází k odlučování placenty a určité množství fetální krve proniká do oběhu matky). První dítě zpravidla nebývá postižené, riziko stoupá s počtem dalších inkompatibilních těhotenství nebo potratech.

Mezi příznaky poškození plodu patří:


 * hemolytická anémie,
 * ikterus (hromadění bilirubinu v krvi, při překročení určité hranice poškozuje CNS),
 * fetální erytroblastóza (v těžkých případech umírá plod in utero).

Poškození plodu lze předejít podáváním anti-D protilátek matce 72 hodin po senzitizační dávce Rh-pozitivních erytrocytů (po porodu či invazivní prenatální diagnostice)

Související články

 * AB0 systém • Krevní skupiny • Dědičnost krevních skupin
 * Hemolytická nemoc novorozence • Hyperbilirubinemie novorozenců a kojenců • Výměnná transfuze

Zdroj