Bhupesh Patel and Rajesh Kumar Mohapatra
Utkal University, Bhubaneswar, India
Immunohematology is the branch of science which deals with the study of the immune status in different blood groups.Blood is a liquid connective tissue which contains cells and the plasma.RBC contains H antigens in the cell surface which are carbohydrate in nature.Plasma contains antibodies which are IgM in nature.
ABO Blood Group System
A person doesn’t have antibody to his own antigen. A person has antibody to the antigen he lacks.
Discovery Of ABO Blood Group System: ABO Blood Group System contains four blood groups i.e. A, B, AB, O according to the presence or absence of two distinct antigens, A and B on the surface of erythrocytes.In 1900 Karl Landsteiner discovered the blood groups A, B, O by observing three distinct patterns of agglutination reactions of serum against different red blood cells. In 1902 his pupils von Decastallo and Sturli described the 4th blood group AB.
Distribution of ABO blood group
Characteristics of Antibodies: Anti-A and anti-B isoantibodies appear in the serum of the infants at the age of 6 months and persist thereafter which are called ‘natural’ antibodies. They are IgM in nature and react between 4oC to 18oC. Immune isoantibodies develop following the injection of substances containing blood group like antigens (horse serum or bacterial vaccine). They are IgG in nature and react at 37 oC.
ABO antigens:Its locus is located on chromosome 19.H antigen is a carbohydrate sequence. ABO locus is located in chromosome 9 which has three main allelic forms: A, B, and O. The A allele encodes a glycosyl transferase that bonds to the end of H antigen producing the A antigen. H antigen is an essential precursor to the ABO blood group antigens. The B allele encodes a glycosyl transferase that joins the end of H antigen creating the B antigen. In case of O allele it differs from the others slightly by deletion of a single nucleotide-Guanine at position 261.It lacks enzyme activity. So the H antigen remains unchanged.
Subgroups of ABO blood group system: A blood group contains about twenty subgroups. A1 and A2 are the most common, out of which 80% are A1 and 20% are A2. Agglutination reaction is faster in A1 than A2.A subgroups increase the no of ABO phenotypes from four to six: A1, A2, B, A1B, A2B, O. However these subgroups are interchangeable as far as transfusion is concerned, but sometimes complication can arise.
Rh Blood Group System
In 1940 Karl Landsteiner and Alexander Wiener discovered the Rh blood type. It is determined by three closely linked genes: Cc, Dd and Ee in chromosome. It is named so due to agglutination of rabbit antiserum with the erythrocyte of Rhesus monkey. In human being the presence of Rh positive and Rh negative depends on the presence and absence of antigen D on red cells.
Distribution Rh Blood Type: Distribution of Rh positive differs in different races.
Rh +ve 85% Rh +ve 93%
Rh -ve15% Rh -ve 7%
A variant of D is known as Du. Red cells of Du subtype react with some but not in all anti-D serum.
Inheritance of Rh blood type: Rh type mother-fetus incompatibility occurs when father is Rh positive and mother is Rh negative. Rh positive father can have either a DD or Dd genotype. So two mating combinations are possible. If father is homozygous, 100% children will be Rh positive. In case of heterozygous case, 50% children will be Rh positive & 50% will be Rh negative.
Other blood group system
Bombay or OH blood group where no antigen including H antigen are present, but anti-A, anti-B and anti-H antibodies are present. Their sera are incompatible with all red cells. In Lewis blood group, the antigens Lea and Leb are present in the plasma and the saliva. Red cells adsorb them from plasma. In MN system, using rabbit antiserum persons are classified into three groups: M, N, and MN.
Medical Application of Blood Groups
In routine blood transfusion practice, only the ABO and Rh antigens are relevant. Recipient’s plasma should not contain any antibody that will damage the donor’s erythrocytes. Donor’s plasma should not contain any antibody that will damage the recipient’s red cells. The donor’s red cells should not have any antigen that is lacking in the recipient.
Slide testing for ABO blood group: In a glass slide two samples of blood of a person are taken. To the 1st sample one drop of anti-A antibody is added and to the 2nd sample one drop of anti-B antibody is added. Agglutination reaction is observed in both the samples .If agglutination is present in 1st sample; the sample belongs to the “A” blood group. ”B” blood group is detected in sample if there is agglutination in the 2nd sample. In “O” blood group there will be no agglutination in both the sample whereas in “AB” blood group there will be agglutination in both the samples.
Slide testing for Rhesus blood group: In a slide a sample of blood of the person is taken. Agglutination is observed in the sample. If there is agglutination, the sample is Rh-positive; otherwise it is Rh- negative
.Rh Incompatibility: When an Rh negative mother caries an Rh positive fetus, she may be sensitized against the Rh antigen by the passage of some fetal red cells into the circulation of the mother during delivery. Mother is usually sensitized in the 1st delivery and the 1st child escapes from the damage. In subsequent pregnancy, the Rh antibodies which are IgG class pass from the mother to the fetus and damage its erythrocytes causing hemolytic disease of the newborn. Prevention of hemolytic disease (Erythroblastosis fetalis) in new born: Hemolytic disease in newborn can be prevented by injecting Rh antibodies to Rh negative mother around the 28th week of pregnancy and again with 72hrs after the delivery of Rh positive baby. This must be done in first and all subsequent pregnancies. Factors influencing the incidence of hemolytic disease due to Rh incompatibility: 1. Immunological unresponsiveness to the Rh antigen. 2. Fetomaternal ABO incompatibility. 3. No. of pregnancies. 4. Zygosity of the father.
In April 2007 an international team of researchers announced in the journal Nature Biotechnology an inexpensive and efficient way to converts types A,B and AB blood into type O. This is done by using glycosidase enzymes from specific bacteria to strip the blood group antigens from red blood cells. The removal of A and B antigens still does not address the problem of the Rhesus blood group antigen on the blood cells of Rhesus positive individuals, and so blood from Rhesus negative donors must be used. Patient trails will be conducted before the method can be relied on in live situations. Another approach to the blood antigen problem is the creation of artificial blood which could act as a substitute in emergencies.