There are 6 main antigens Rh. Two nomenclatures are used to designate this system of antigens: the Wiener nomenclature and the Fischer-Reis nomenclature.
According to Wiener nomenclature, symbols denote Rh antigens Rh0, rh I, rh II, Nr0, hr I, hr II.
The classification of Fisher-Reis is based on the assumption that there are 3 sites in the Rh chromosome for 3 genes that determine the Rh factor. Currently, the designation of Fischer-Reus antigens is recommended by the WHO Expert Committee on Biological Standards. Each gene complex consists of 3 antigenic determinants: D or absence of D, C or c, E or e in various combinations. The existence of antigen d has not been confirmed to date, since there is no gene responsible for the synthesis of this antigen. Despite this, the symbol d is used in immunohematology to indicate the absence of D antigen on erythrocytes when describing phenotypes.
Often two nomenclatures are used simultaneously. In this case, the symbols of one of the notations are placed in parentheses, for example Rh0 (D).
Thus, there are 6 genes that control the synthesis of the Rh factor, and there are at least 36 possible genotypes of the Rh system. However, fewer antigens can be detected phenotypically (5, 4, 3), depending on the number of homozygous loci in the individual. Antigen Rh0 (D) - the main antigen of the rhesus system, which has the greatest practical significance. It is found on the red blood cells of 85% of people living in Europe. It is on the basis of the presence of the antigen Rh0 (D) on the erythrocyte, the Rh-positive blood type is isolated. The blood of people whose erythrocytes are devoid of this antigen is referred to as a Rh-negative type. Antigen Rh0 (D) in 1.5% of cases occurs in a weakly expressed genetically determined variant - variety Du.
Persons with Rh-positive blood can be homozygous (DD) and heterozygous (Dd), which has the following practical significance :
- If the father is homozygous (DD), which is observed in 40-45% of all Rh-positive men, then the dominant gene D is always transferred to the fetus. Therefore, in Rh-negative women (dd), the fetus will be Rh-positive in 100% of cases.
- If the father is heterozygous (Dd), which is noted in 55-60% of all Rh-positive men, the fetus can be Rh-positive in 50% of cases, since it is possible to inherit both a dominant and a recessive gene.
Thus, in a woman with Rh-negative blood during pregnancy from a man with Rh-positive blood in 55-60% of cases, the fetus will have Rh-positive blood. Determining the heterozygosity of the father presents certain difficulties and can not be introduced into routine practice. Therefore, pregnancy in a woman with Rh-negative blood from a man with Rh-positive blood should be conducted as a pregnancy with a fetus with Rh-positive blood.
Approximately 1-1.5% of all pregnancies in women with Rhesus-negative blood the first pregnancy is complicated by erythrocyte sensitization in the course of gestation, after birth this percentage increases to 10%. This frequency is significantly reduced when using anti-Rh0 (D) -immunoglobulin.
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