BLOOD GROUP

 INTRODUCTION

  When blood from two individuals, sometimes agglutination (clumping) of RBCs occurs. Agglutination is because of the immunological reactions. But why it occurs in some cases and not in other cases remained a mystery until the discovery of blood groups by the Austrian Scientist Karl Landsteiner, in 1901. He was honored with Nobel Prize in 1930 for this discovery.

ABO BLOOD GROUPS

Determination of ABO blood groups depends upon the immunological reaction between antigen and antibody. Landsteiner found two antigens on the surface of RBCs and named them as A antigen and B antigen. These antigens are also called agglutinogens because of their capacity to cause agglutination of RBCs. He noticed the corresponding antibodies or agglutinins in the plasma and named them anti-A or a-antibody and anti-3 or B-antibody. However, a particular agglutinogen and the corresponding agglutinin cannot be present together. If present, it causes clumping of the blood. Based on this, Karl Landsteiner classified the blood groups. Later it became the 'Landsteiner's Law' for grouping the blood.

LANDSTEINER'S LAW

Landsteiner's law states that:

  1. If a particular agglutinogen (antigen) is present in the RBCs of a person, corresponding agglutinin (antibody) must be absent in the serum.

2. If a particular agglutinogen is absent in the FBC the corresponding agglutinin must be present in s serum.

Though the second part of Landsteiner's law is a fact, it is not applicable to Rh factor.

BLOOD GROUP SYSTEMS

More than 20 genetically determined blood group systems are known today. But Landsteiner discovered two blood group systems called the ABO system and the Rh system. These two blood group systems are the most important ones that are determined before blood transfusions.

ABO SYSTEM

Based on the presence or absence of antigen A and antigen B, blood is divided into four groups:

1. 'A' group.

2. B' group.

3. 'AB' group.

4. 'O' group.

 Blood having antigen A belongs to 'A' group. This blood has B-antibody in the serum. Blood with antigen B and a-antibody belongs to 'B' group. If both the antigens are present, blood group is called 'AB' group and serum of this group does not contain any antibody. If both anti gens are absent, the blood group is called 'O' group and both and B antibodies are present in the serum.

 Antigens and antibodies present in different groups of ABO system are given in Table a Percentage of people among Asian and European population belonging to different blood group is given in Table b. 

Table a. Antigen and antibody present in ABO blood groups. 

Table b. Percentage of people having different blood groups. 

DETERMINATION OF ABO GROUP

Determination of the ABO group is also called bl grouping, blood typing or blood matching

Principle of Blood Typing: Agglutination

 Blood typing is done on the basis of apgulinssion: Agglutination means the collection of separate particles like RBCs into clumps or masses Agglutination occurs if an antigen is mixed with its corresponding and body which is called isoagglutinin. Agglutination occurs. when A antigen is mixed with anti-A or when B antigen is mixed with anti-B.

Requisites for Blood Typing

 To determine the blood group of a person, a suspension of his/her RBC and testing antisera are required. Suspension of RBC is prepared by mixing blood drops with isotonic saline (0.9%)

Test sera are:

 1. Antiserum A, containing anti-A or a-antibody 2. Antiserum B. containing anti-B or B-antibody

Procedure

 1. One drop of antiserum A is placed on one end of a glass slide (or a tile) and one drop of antiserum B on the other end.

 2. One drop of RBC suspension is mixed with each antiserum. The slide is slightly rocked for 2 minutes.The presence or absence of agglutination is observed by naked eyes and if necessary, it is confirmed by using microscope.

 3. Presence of agglutination is confirmed by the presence of thick masses (clumping) of RBCs, 4. Absence of agglutination is confirmed by clear mixture with dispersed RBCs.       

Results

 1. If agglutination occurs with antiserum A

 The antiserum A contains a-antibody. The agglutination occurs if the RBC contains A antigen.So, the blood group is A. 

 2.If agglutination occurs with antiserum B The antiserum B contains B-antibody. The agglutination occurs if the RBC contains B antigen So, the blood group is B

 3. If agglutination occurs with both antisera A and B The RBC contains both A and B antigens to cause agglutination And, the blood group is AB.

Determination of blood group. 

4.if agglutination does not occur either with antiserum A Or antiserum B:

The agglutination does not occur because RBC does not contain any antigen. 

                                                                     IMPORTANCE OF ABO GROUPS IN BIOOD TRANSFUSION

During blood transfusion, only compa lood must be used. The one who gives blood is called 'donor' and the one who receives the blood is called 'recipient'.

  While transfusing the blood, antigen of the donor and the antibody of the recipient are considered. The antibody of the donor and antigen of the recipient are ignored mostly.

  Thus, RBC of 'O' group has no antigen and so agglutination does not occur with any other group of blood. So, 'O' group blood can be given to any blood group persons and the people with this blood group are called 'universal donors'.

  Plasma of AB group blood has no antibody. This does not cause agglutination of RBC from any other group of blood. People with AB group can receive blood from any blood group persons. So, people with this blood group are called 'universal recipients'.

MATCHING AND CROSSMATCHING

Blood matching (typing) is a laboratory test done to determine the blood group of a person. When the person needs blood transfusion, another test called crossmatching is done after the blootd is typed. It is done to find out whether the person's body will accept the donor's blood or not.

For blood matching, RBC of the individual (recipient) and test sera are used. Crossmatching is done by mising the serum of the recipient and the RBCs of don Crossmatching is always done before blood transfun If agglutination of RBCs from a donor occurs d crossmatching, the blood from that person is not for transfusion. 9 d

Matching= Recipient's RBC Crossmatching = Recipient's serum + Donor's RC+ Test sera

INHERITANCE OF ABO AGGLUTINOGENS AND AGGLUTININS

  Blood group of a person depends upon the two ge es inherited from each parent. Gene A and gene Bre dominant by themselves and gene O is recessive. Inheritance of blood group is represented schematically as given in Table c. 

   Agglutinogens appear during the 6th month of fetal life. Concentration at birth is 1/5 of the adult concentra tion. It rises to the adult level at puberty. Agglutinogens are present not only in RBCs but also present in many organs like salivary glands, pancreas, kidney, liver, lungs, etc. The A and B agglutinogens are inherited from the parents as Mendelian phenotypes.

  Agglutinin a or B is not produced during fetal life. It starts appearing only 2 or 3 months after birth. Agglutinin is produced in response to A or B agglutinogens which enter the body through respiratory system or digestive system along with bacteria. Agglutinins are the gamma globulins which are mainly IgG and IgM immunoglobu lins.

Inheritance of ABO blood group. 

Rh FACTOR

  Rh factor is an antigen present in RBC. This antigen was discovered by Landsteiner and Wiener. It was first discovered in Rhesus monkey and hence the name 'Rh factor'. There are many Rh antigens but only the D antigen is more antigenic in human.

  The persons having D antigen are called 'Rh positive' and those without D antigen are called 'Rh negative". Among Indian pop ation, 85% of people are Rh positive and 15% are Rh negative. Percentage of Rh positive people is more among black people.

  Rh group system is different from ABO group system because, the antigen D does not have corresponding natural antibody (anti-D). However, if Rh positive blood is transfused to a Rh negative person anti-D is developed in that person. On the other hand, there is no risk of complications if the Rh positive person receives Rh negative blood.

INHERITANCE OF Rh ANTIGEN

 Rhesus factor is an inherited dominant factor. It may be homozygous Rhesus positive with DD or heterozygous Rhesus positive with Dd  Rhesus negative occurs only with complete absence of D (i.e. with homozygous dd).

APPLIED PHYSIOLOGY

  TRANSFUSION REACTIONS DUE TO ABO INCOMPATIBILITY

  Transfusion reactions are the adverse reactions in the body, which occur due to transfusion error that involves transfusion of incompatible (mismatched) blood. The reactions may be mild causing only fever and hives (skin disorder characterized by itching) or may be severe lead ing to renal failure, shock and death.

   In mismatched transfusion, the transfusion reactions occur between donor's RBC and recipient's plasma. So, if the donor's plasma contains agglutinins against recipient's RBC, agglutination does not occur because these antibodies are diluted in the recipient's blood.

   But, if recipient's plasma contains agglutinins against donor's RBCs, the immune system launches a response against the new blood cells. Donor RBCs are agglutinated resulting in transfusion reactions.