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

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Multiple Alleles

ABO Blood group system

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ABO BLOOD GROUP

 ABO BLOOD GROUP

    ABO blood group system was discovered in 1901 by Karl Landsteiner of the University of Vienna. Later he was awarded a Nobel Prize. ABO blood groups are found in all humans and in many primates such as apes, chimpanzees, baboons and gorillas.

Genetic Basis

    The ABO blood groups are controlled by Gene I located on the chromosome 9. Gene I has three allelic forms i.e. I^A , I^B and i. The I^A and I^B alleles each encode a glycosyltransferase that catalyzes the A and B antigen synthesis, respectively. The O or i allele encodes an inactive glycosyltransferase that leaves the ABO antigen precursor (the H antigen) unmodified. 

Blood type	Antigen on RBC	Allele for Antigen	Possible Genotypes	Dominance relation
A	A	IA	IA IA ,  IAi	IA Dominant to i
B	B	IB	IB IB , IBi	IB Dominant to i
AB	A & B	IA and IB	IA IB	IA and IB  Co-Dominant
O	None	I	ii	i is recessive

Blood group types

    A person’s blood group may be one of four types: A, B, AB, or O. These blood group types are due to the presence of antigen A and antigen B on the surface of RBC. A person having antigen a on the surface of RBC will have blood group A, having antigen B on the surface of RBC will have blood group B, and having both A and B antigens will have blood group AB. When no antigen is expressed (nor A or B), then the blood group is said to be the O blood group. 

Ability to produce Antibodies against antigen A and Antigen B

    The blood group is determined by antigens present on the surface of RBCs. The immune system can produce antibodies against the foreign antigens. In normal conditions, the body does not produce antibodies against the body's cells but can produce against any foreign agent that enters into the body.

Blood group A:     An individual with blood group A has antigen A on the RBC surface, therefore, it only produces Antibodies against antigen B. 

Blood group B:     A person having blood group B produces antibodies against the antigen A.

Blood group O:    A person having no antigen A or B on the surface of RBC (Blood group O) produces anti-A and anti-B antibodies.

Blood group AB:     Those who have AB blood group do not produce antibodies. 

Universal donor:

    Blood type O has no antigen therefore; a person with blood group O can donate the blood to all blood types.

Universal recipient: 

    A person with blood type AB does not produce anti-A and anti-B antibodies and, therefore can transfuse blood from all blood types.

Other blood group systems:  Besides the ABO blood group system there are also some other blood group systems i.e. Rh, MNS, P, Lutheran, Kell, Lewis, secretor, Duffy, Kidd, Diago, etc.

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Multiple Alleles

Rh blood group system

Rh Blood Group system

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 Multiple Allele

    An allele is the alternative form of a gene. When more than two forms of a gene exist on a single chromosome locus, the alleles are called multiple alleles.

Production of multiple alleles

    Multiple alleles are produced by gene mutation. A slight change in the nucleotide sequence of a gene results in the formation of alleles.

Number of multiple alleles

    The number of alleles controlling a character varies. The ABO blood group system is controlled by three alleles of gene I. Some genes may have as many as 300 alleles for a character. Multiple alleles exist in the individual of a population but individuals have only two of those alleles. This is because most organisms are diploid with two homologs of each chromosome. 

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ABO Blood group system

Rh blood group system

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