Antibodies : The Soldiers Who Never Sleep

Ever wondered why do we not get Chicken Pox twice ? Ever thought why are vaccines pathogens in themselves ? Ever wondered why should we not mix certain blood groups ?

The answer to all these and a lot more depend on one fundamental entity or rather a gift of nature to all organisms - Antibodies.

The response of immune system to external entities like virus, bacteria, fungi and other microbes that cause diseases in organisms is in creating complementary structures that either kill them or inhibits them from further action. Such structures are called antibodies.

[ FACT BOX ]

  • Average molecular weight of an antibody is 150 kDa.
  • They are usually large Y-shaped proteins which follow the lock & key mechanism of insertion, activation, tagging and neutralization of antigens.
  • Usually they belong to five different forms : IgM, IgG, IgA, IgD, IgE
by Nuruddin Bahar
1 year, 3 months ago
1

Primary Response : It is the first immunological response of the body against the initial entry phase of antigens. It involves a sudden urge in the immature IgM antibodies which prevent the propagation of infection by binding to the activated sites of antigens.

Secondary Response : Once the antigen is encountered , system confers protection to the body cells against future infections with the help of longer memory T & B cells. These cells commence a sudden increment in the levels of IgG antibodies , which happens approximately 10 days after the entry of antigens.

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Each lymphocyte produces antibodies that have receptors unique to a particular pathogen. Thus, it is a one-to-one response for the antibodies to act upon. This is quite a robust process which involves a selected antigen to bind to the cell surfaces receptors.

The surface receptors create a secondary response signal which triggers the cell division inside the nucleus. Once cell division starts, multiple copies of the same antibodies are produced, modified and dispatched to bind to more antigen of similar kind.

MECHANISM OF IMMUNE RESPONSE :

1. Antibody binds to the Antigen.

2. Around 20 interacting soluble proteins get activated within the cells.

3. C1 proteases on activation conduct proteolysis.

4. A cascade of proteolytic reactions begins.

5. C3 (Membrane Attack Complexes-MACs) are produced along with WBC's.

6. MACs punch holes in antigen plasma membrane and cause cell lysis.

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  • It consists of two basic parts : 1. Heavy Chain 2. Light Chain
  • Each chain in turn has two functionally different regions : 1. Constant 2.Variable
  • Heavy chain consists of 440 Amino Acid residues , while light chain has 110 residues.
  • The anterior region of every chain is the Variable region which binds to the specific antigens. The posterior region is the Constant region which acts as the antibody effector site. 
  • Each chain is bonded to the next chain via disulfide bonds (as shown in figure). IgG has 2 Antigen-Binding Sites (ABS) and 4 disulfide bonds. 
  • Every Variable region is further subdivided into Hypervariable Region and Framework Region which possess the unique properties of antigen binding and structural stability respectively.
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Here,

Fc = Crystallized Fragment  
>triggers complement system which kills pathogens and affects phagocytosis
Fab = Univalent Fragment of ABS    
>unable to cross-link antigens
F(a'b')2 = Divalent Fragment of ABS  
>capable of cross-linking antigens
Instead of the entire antibody, it is more desirable to work over fragments of antibodies, such as Fc, Fab and F(a'b')2. These make the antigen-binding more penetrable, increase its sensitivity and reduces unwanted fragment-associated effector functions, thereby making it suitable in vitro.The antibody fragmentation is conducted by certain antibody specific proteases like Papain and Pepsin, which help in proteolysis at specific positions, focusing on the rupture of disulfide bonds.
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1. Does Self-healing Take Time ?
2. The Soldier Factory
3. The Structure of an Antibody
4. Anti-soldiers
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