The RH System and the RH Immunization during Pregnany

The RH System and the RH Immunization during Pregnany

  Autor Daniela Chirila Data: 21.07.2005

The RH System and the RH Immunization during Pregnany

The human body contains a very large number of antigens which conditions the existence as species, group or individual. The erythrocytes antigens are the most important categories of antigens. These may be divided into three groups, according to their specificity:

- Heterophile antigens, which are found in other animal species besides humans;
- species antigens, which are common to all people;
- group antigens, specific to certain groups of people.

Among the most important erythrocytes antigens, we mention the ones f ABO, Rh, MN, Kell-Cellano and Lewis system.

The RH system.

K. Landsteiner and A.S. Wiener reported in 1940, the fact that the serum of immunizing rabbits with red blood cells from Rhesus Macaque monkey, agglutinated with about 85% of the humans. First, there was discovered the existence of an antigen which was common to the monkeys and to people, called the D factor, but later, the existence of other antigens was discovered too (Cc, D, Ee), controlled by six genes organized in three pairs of alleles: Cc, Dd and Ee. The D antigen is the most powerful among these, and corresponds to the classic factor RH. In the medical field, the presence or absence of this antigen is determining and important for transfusions or for the evolution of a pregnancy. The other types which are inexact from an immunological point of view, identify the individual differences helpful for the genetic investigations or the paternity tests.

The detection of D antigen (RH blood group) is useful because there might occur transfusion accidents in this system in case of incompatible transfusions, which lead to acute intravascular hemolytic disease.

The RH-immunization during pregnancy

The RH-immunization is similar with the immunization in RH system nd is caused by the incompatibility between mother and child in the RH blood group.

If a RH D woman is fertilized by a RH D+ man, her serum will contain anti-D antibodies which may cause the hemolytic disease and severe RHD+ fetus disorders, phenomena which could lead even to his death. In case of RH system, the organism doesn't produce natural antibodies, thus the immune sensitivity develops after repeated exposures to the system's antigens. That is the reason why the first pregnancy is usually without problems.

As we mentioned above, the human body does not normally produce anti-D antibodies, but when these ones exist, they are very cytotoxic as they act against only one target cell (the erythrocyte RH+).

The pregnancy immunization is determined by the tapping of a small quantity of fetal erythrocytes RH D+ into the maternal blood flow during the labor. The existent antibodies resist for a long time and, if their concentration is high, at the next pregnancy they pass through the placenta, get into the fetal blood where they destroy the fetal erythrocytes. As a result, the fetal body will develop a severe anemia, known as the hemolytic disease of the newborn.

In such conditions, the prevention consists in the administration of anti RhD antibodies which will break down the RhD+ cells, thus avoiding mother's sensitizing.

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