Antigen-antibody interactions

Antigen – Antibody reaction (goldberg’s theory)

What is Antigen antibody reaction?

Antigen antibody reaction was firstly descripted by Richard j goldberg.

Antigen antibody reaction is a process in which the chemical reaction between antibodies (which are produced by the B cells of immune system) and antigens.

Antigen-antibody interactions

The immune system of our body protects from the complex foreign molecules pathogens and some chemical toxins which are entered in our body.

The immune system treats these foreign particles which are entered in our body as foreign particles (antigens) and release the “antibodies “ which are highly affinity towards the antigens and forms “antigen – antibody complex”.

Thus by forming the complex the particular antigen which is entered in our body is transported to cellular system and deactivates finally it destroys.

There are several types of antibodies and antigens and each anti body is capable of binding once to a specific antigen, specificity of this binding is due to specific chemical constitution. The antigen is recognized as “epitop” by pacotop of the antibody which is present as a polypeptide chain.

Antigens are bound to antibodies through weak and non covalent interactions hydrogen bonds, vander wall forces and hydrophobic interactions.

Due to specific binding of antigen to particular antibody this causes the agglutination reactions when they are cross reactivated. The cross reactivity of the antigen-antibody interaction this is helpful for the clinical diagnostic purpose.

The basic laboratory purpose is determination of blood groups. It is also used as a molecular technique for infection with different pathogens such as HIV, microbes & helminth parasites.

Applications :

  • Antigen-antibody interactions is used for laboratory techniques like serological tests, blood compatibility & for various pathogenic diseases.
  • Determination of ABO blood group.
  • ELISA
  • Enzyme linked immunospot (Elispot).

What is agglutination reaction :-  In antigen – antibody reaction the agglutination is mainly caused by the antibodies cross link particular antigens, then it results in the formation of clumps of the particles, which are used in the diagnosis this reaction is known as the agglutination reaction.

Determination of ABO blood groups:-

The determination of ABO blood grouping system is based upon the antigen – antibody cross link reaction, it results in the formation of the agglutination reaction.

ABO Blood groups

  • In blood group determination we use the Antisera –A, Antisera-B & Antisera-O.
  • The two types of these determines the blood group & O determines the Rh+ve or – ve.
  • Here group-A agglutinates with a group B, but never with its own type.
  • Group – B agglutinates with a group-A but never with its own type.
  • Based on the cross link reaction of antigens with opposite antibodies forms agglutination, we can see clearly the visible clumps formed in a reaction.
  • This agglutination reaction decides whether the blood is either A or B or AB or O.
  • If agglutination forms in ‘A’ then the blood group type is A.
  • If agglutination forms in ‘B’ then the blood group B.
  • If agglutination forms in both ‘A & B’ then blood group is AB.
  • If agglutination doesn’t forms in both ‘A’ & ‘B’ then it is ‘O’.
  • The ‘O’ antisera decides the Rh +ve or – ve of the blood.
  • Hence the determination of the blood groups has been played an importance for blood transfusion, it made easy & safest way for blood transfusion.

Widal test :-

  • It was developed by goerges ferdinand widal in 1986. Widal test is used to detect the typhoid & paratyphoid fever, which is caused by the salmonella typhi bacterium.
  • Widal test is an agglutination test which detects the presence of serum agglutinins (H & O) in patients serum.

widal test

Principle :-

  • The main principle of widal test involves that if homologous antibody is present in patients serum, it will reacr with respective antigen in the reagent and gives visible clumping on the test slide or test card.
  • The antigens used in the widal test are H and O antigens of typhi.

Procedure of widal test :-

The procdure of widal test includes 3 types.

They are :-   1) slide test

                      2) semi quantitative method

                      3) stand tube test method

In any method the procedure is different but by the antigen-antibody reaction the agglutination was formed in all methods. Thus the formed agglutination decides the test either +ve or – ve.

Auto immune disease :-

  • Auto immune disease is regarded self-destruction of our own body cells in certain conditions the cells of our body or the immune system of our body triggers some cells as antigen and produce antibody’s for that specific cells and this forms antigen-antibody complex and destructs the own cells of our body by the own immune system.
  • The exact nature of antibody – antigen interaction is auto immune disease is not yet understood.

autoimmune disease

                                                                                                                                                                                  Prepared by

                                                                                                                                                                                        RAJESH

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