Learning Biology : Rh Blood Group System

Rh Blood Group System

The Rh Blood group system is one of the clinically most important blood group systems. The term Rh in the name of this system refers to the Rhesus monkey. This blood group is determined by the Rh antigen present on the surface of the RBC.

The antigen was first discovered in Rhesus monkeys by Landsteiner in the 1930s.

Basis of Rh blood group system

The Rh Blood group system is determined by up to 50 known antigens among which D, C, E, c, and e are the most significant. Rh blood group system is mainly controlled by the D gene.

The dominant gene D expresses D-antigen/Rh factor, while its alternative allele d inhibits the formation of Rh factor. The allele D is completely dominant over the allele d.

Rh Blood group types

There are two types of blood groups in this system.

1. Rh-positive: The person having a “D” antigen on the RBC membrane will have the Rh-positive blood group.

2. Rh negative: The person without “D” antigen on the RBC membrane will have the Rh negative blood group

Table 22.4 Rh-Blood group system
Blood group	Rh antigen	Genotypes	Anti-Rh-Antibody	Can receive blood from	Can donate blood to
Rh Positive	Present	DD or Dd	Not Produced	Rh Positive and Rh-Negative	Rh Positive
Rh-Negative	Absent	dd	Produced (if stimulated)	Rh-negative	Rh Positive and Rh-Negative

Maternal-Foetal Rh incompatibility – Erythroblastosis Foetalis

Erythroblastosis fetalis is a hemolytic disease of the newborn. In this disease, the red blood cells (erythrocytes) of the fetus are destroyed due to blood group incompatibility between the fetus and its mother. This incompatibility arises when the fetus inherits the Rh factor from the father that is absent in the mother.

Causes

Rh factor inherits as a dominant trait. When a male with Rh-positive blood (having Rh antigen) marries a female with Rh-negative blood (without Rh antigen), the fetus will have the Rh-positive blood group. When fetal red blood cells with the Rh factor enter the mother’s bloodstream, the production of Rh antibodies occurs. These antibodies pass across the placenta into fetal blood and cause the destruction of the red blood cells of the fetus. The anemic fetus then starts to produce many immature erythroblasts. This is called erythroblastosis fetalis. This may lead to abortion or stillbirth