Human blood group systems- with best explanation

Human blood group systems

Human blood group system

Human  blood group systems the ABO blood group is represented by substances on the surface of Red Blood Cells (RBCs).  These substances are important because they contain specific sequence of amino acid and carbohydrates which are antigenic.  As well as being on the surface of RBCs, some of these antigens are also present on the cells of other tissues.  A complete blood type describes the set of 29 substances on the surface of RBCs, and an individual’s blood type is one of the many possible combinations of blood group antigens.  Usually only the ABO blood group system and the presence or absence of the Rhesus D antigen ( also known as the rhesus factor or Rh factor)  are determined and used to describe the blood type. Over 400 different blood group antigens  have been found, many  of these being very rare.  If an individual is exposed to a blood group antigen that is not recognised as self, the individual can become sensitized to that antigen;  the immune system makes specific antibodies which binds specifically to a particular blood group antigen and an immunological memory against that particular antigen is formed.  These antibodies can bind to antigens on the surface of transfused red blood cells (or other tissue cells) often leading to destruction of the cells by recruitment of other components of the immune system.  Knowledge of an individual’s blood type is important to identify appropriate blood for transfusion or tissue for organ transplantation.

Blood group

Human blood can be classified into four main  groups and several sub-groups  on the basis of the presence or absence of specific substances in the erythrocytes termed agglutination (antigens)(Agglutinogens are neutral, nitrogenous mucopolysaccharides (a type of heteropolysaccharide), containing amino acids or peptides as well as carbohydrate groups (N – acetyl D – glucosamine, N – acetyl-D galactosamine, L – fucose and D-galactose).  There are two major (viz. A and B) and several minor agglutinogens (viz. M,N, Pand Rh).  The A and B two major agglutinogens react specifically with alpha and Beta isoagglutinins (agglutinins), respectively).   
Erythrocytes containing agglutinogen are agglutinated (clumped) by plasma containing a – isoagglutinin.  Consequently, if a given agglutinogen occurs in the respective is agglutinin is never present in the plasma and thus the actual isoagglutinin present in the plasma is said to be an antibody of that agglutinogens, e.g.  alpha and beta-isoagglutinins are the antibodies of the agglutinogens B and A. respectively. 
 Thus on the basis of the presence or absence of agglutinogens A and / or B, blood groups may be of four types. 
  •  Group A  It contains agglutinogen A in red cells and hence the B – isoagglutinin (anti B) in plasma.  
  • Group B – It contains agglutinogen B in red cells and hence a – isoagglutinin (anti A) in plasma. 
  •  Group AB – It contains agglutinogens A as well as B in red cells and hence no isoagglutining in plasma.
  •  Group O –  It contains no agglutinogen in red cells and hence contains both (a and b) isoagglutinins in plasma.
Types of Blood group
Blood group

  A summary of the blood groups and the agglutinogen (antigen) and isoagglutinin (antibody) present in the respective group is tabulated here.  


ABO blood group system discovered

ABO blood group system is discovered by Karl Landsteiner (1900) . He recognized four types of blood groups in human beings commonly known as ABO blood groups . The ABO blood groups are determined by the gene I having three alleles (IA , IB and IO ) . In human alleles ,there are present two antigens A and B 
produced by  IA and IB alleles respectively . These antigens are always present on the surface of red blood cells . Also are present two antibodies in the plasma anti A and anti B . Accordingly , the four blood groups are :–
  1. Blood group A (having antigen A and antibody B ) .
  2. Blood group B (having antigen B and antibody A )  .                                  
  3.   Blood group AB (having both antigen A and B but no antibodies).
  4. Blood group O ( having no antigen but both the antibodies ).
According to Landsteiner Law , if an antigen is present on the red blood cells the corresponding antibody must be absent from the plasma . The second aspect of the law states that if the antigen is absent on the erythrocytes , the corresponding antibody must be present in the plasma .

Rh(Rhesus) blood group system history

Human blood possesses another factor i.e Rh factor . Accordingly, human blood can be categorized into two groups: Rh – positive and Rh – negative .
              During blood transfusion, Rh factor is also taken into account.  The Rh symbol signifies rhesus.  With the discovery of Rh factor, the terms universal donor and universal recipient are no longer applicable in toto.  
Rh factor was discovered in the year 1940 by Landsteiner and Wiener after immunizing the rabbits with the blood of a monkey (Macaca rhesus).  It was also found that when guinea pigs were injected blood from a rhesus monkey, the guinea pigs also produced antibodies which could agglutinate the red blood cells of the rhesus monkey.  Evidently, it was concluded that red blood cells of rhesus monkeys contain a peculiar antigen on their surface known as Rh antigen.  Similar types of experiments were done in man .Here, human blood was tested by inoculating serum from the above mentioned guinea pig.  It was observed that the red blood cells of some individuals showed clumping, whereas, those of the others did not.  Based on these results, it was seen that Rh antigen was present in some human beings and not in all.
  • Rh – positive –  Those human beings who had present antigen were termed as Rh – positive (Rh+).  
  • Rh- negative–The persons in whom Rh antigen was absent, were designated as Rh – negative (Rh-). 


      Note – Rh+ is a dominant character over Rh- which are is recessive .

Rh factor

Many people have the Rh factor on the the red blood cell . Rh carriers do not have the antibodies for the Rh factor ,but can make them if exposed to Rh . Most commonly Rh is seen when anti-Rh antibodies cross from the mother’s placenta into the child’s before birth.
                                    Rh factor plays a critical role in child’s birth born out of a marriage between Rh-  woman and Rh+ man .In such case, the mother becomes sensitive while  carrying a first Rh + child within her womb.  The reason for such sensitivity is that some of the RBCs from the developing embryo to get into the blood stream of the mother during development, causing her to produce anti-Rh antibodies .  In fact, the first child of such parents is nearly normal and is delivered safely.  However, if such a mother gets pregnant again, the subsequent Rh + faetuses will be exposed to anti – Rh antibodies produced by the mother . As a result serious damage to the red blood cells of the developing embryo will occur causing  Hemolytic disease of the newborn .

Blood group system Antigens

Rh Antigen ( Rh+ and Rh- group )

  • What does Rh antigen mean ? 
Rh antigen are found on the surface of red blood cellsAbout 85 percent of all white people are Rh+ and 15 percent Rh-  . In American blacks, the percentage of Rh+ is about 95 , whereas in African blacks, it is virtually 100 percent.  
  •    How many Rh antigen are there ?   

   There are six common types of Rh antigens , each of which is called an Rh factor . These types are designated C, D, E ,c, d and e. 

A person who has a  C antigen does not have the c antigen , but the person missing the C antigen always has the c antigen . The same is true for the D-d  and E-e antigens . Also because of the manner of inheritance of these factors , each person has of each of the three pairs of antigens . The type D antigen is widely prevalent in the population and considerably more antigenic than the other Rh antigens . Anyone who has this type of antigen is said to the Rh+ , whereas a person who does not have type D antigen is said to be Rh – .

Surface Antigens

Several different Rh surface antigens stemming from one allele ( or very closely linked gene ) are collectively labelled as a blood group system or blood group .

Blood donation

Blood transfusion from one person to another is said to be blood donation . Blood transfusion was observed that in some cases the attempt of transfusion was successful while in other situations immediate or delay agglutination and haemolysis  of red blood cells occurred . While doing blood transfusion , care should be taken to match the blood groups of the donor and the recipient . If a transfusion is made between an incompatible donor and the recipient , reaction of antigen and antibodies ( agglutination ) will produce clots that will block circulation of blood through capillaries .

Blood group system of donor and receiver

  • If the blood sample is agglutination by anti A and not by anti B , then the blood group is A .
  • If a given blood sample shows reaction ( agglutination) with anti B and not with anti A , then the sample has blood group B .
  • If the blood sample agglutination with anti A and anti B , then the blood group of the sample is AB.
  • Finally , if the blood sample does not show any reaction with both the anti A and anti B , then the blood sample belongs to blood group O .
  • Persons having blood group AB can receive blood  from person having A,B, AB,O group as they possess no antibodies in the plasma . This is the reason why persons with AB blood groups are called univesal recipients . Person with blood group O have no antigens on the surface of RBCs but have both the antibodies in the plasma . Hence , these can donate blood to anyone ( universal donors ) . However, such person can receive blood only from those persons who have blood group O. 
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