Antigen Antibody Reaction

Antigen-Antibody Reaction

Question 1. Precipitation reaction.
Answer:

Precipitation Reaction Definition:

• When a soluble antigen reacts with its antibody in the presence of electrolytes at an optimal temperature and pH, the antigen-antibody complex forms an insoluble precipitate.
• This process is called precipitation.

Read And Learn More: Microbiology Question and Answers

Precipitation Reaction Mechanism

• Marrack in 1934 proposed the lattice hypothesis to explain the mechanism of precipitation.
• According to it, multivalent antigens combine with bivalent antibodies.
• Precipitation occurs only when a large lattice is formed.
• This is possible only in the zone of equivalence.
  • Zone Of Equivalence.
    • Antigen and antibodies are present in optimal proportion.
    • Thus, a large lattice is formed and precipitation occurs.
  • Zone Of Antigen Excess.
    • The valencies of the antibody are fully satisfied.
    • Thus lattice is not formed.
  • Zone Of Antibody Excess.
    • Valencies of the antigen are taken up by antibodies and a lattice is not formed.

Precipitation Reaction Types

Immunodiffusion Test

Immunodiffusion tests are precipitation tests that occur in gel media.

Immunodiffusion Test Types:

1. Single Diffusion In One Dimension.

Single Diffusion In One Dimension Steps:

• Mix antibodies in agar gel in a test tube
• Pour antigen over it.

Single Diffusion In One Dimension Result:

• Antigen diffuses downward.
• A line of precipitation is formed.

Double Diffusion In One Dimension

Double Diffusion In One Dimension Steps:

• Mix antibodies in agar gel in a test tube.
• Place a column of plain agar over it.
• Pour antigen over the plain agar.

Double Diffusion In One Dimension Result:

• Antigen and antibodies move towards each other
• A precipitation band is formed.

 Single Diffusion In One Dimension

Single Diffusion In One Dimension Steps:

• Mix antibodies in agar gel on a slide.
• Cut wells on the surface of the gel.
• Add antigens to these wells.

Single Diffusion In One Dimension Results:

• Antigen diffuses radially,
•  Ring-shaped bands of precipitation are formed.

Double Diffusion In Two Dimensions

Double Diffusion In Two Dimensions Steps:

• Place agar gel on a slide.
• Cut wells over it.
• Fill antibodies in the central well and antigens in other wells.

Double Diffusion In Two dimensions Results:

• Lines of precipitate formed between two identical adjacent antigens fuse.

 Immunoelectrophoresis

Immunoelectrophoresis Steps:

• Combines electrophoresis and immunodiffusion.
• Semisolid agar is layered on a slide,
• Cut wells over it and Fill it with antigen
• Electrophoresis of antigen is carried out for 1 hour,
• Cut a rectangular through in the agar and fill it with antibodies.
• Allow diffusion for 18 – 24 hours.

Immunoelectrophoresis Results:

• Precipitation lines develop with each separated antigen.

Electroimmunodiffusion

• Electroimmunodiffusion is a combination of electrophoresis and diffusion.
• Electroimmunodiffusion includes.
  • Counter immunoelectrophoresis.
  • Rocket electrophoresis.

Agglutination

Agglutination Definition:

• Agglutination is an antigen-antibody reaction, in which a particular antigen combines with its antibody in the presence of electrolytes at an optimal temperature and pH
• Agglutination results in clump formation.

Agglutination Properties

• Occurs with a particulate antigen.
• Agglutination is more sensitive.
• Agglutination takes place better with IgM antibodies.

Agglutination Principle

• When antigen and antibody are present in optimal proportion, lattice formation occurs.
• This results in agglutination.

Agglutination Types

Immunofluorescence

Immunofluorescence

The dyes used are:

ELISA test

ELISA is an abbreviated form of Enzyme-Linked ImmunoSorbent Assay.

• ELISA test is widely used.
• ELISA test is simple and sensitive.
• The test can be done in polystyrene tubes or polyvinyl microlitre plates.

ELISA test Types:

Antigen-Antibody Reaction

Question 1. Define precipitation and flocculation.
Answer:

Precipitation Definition

• When a soluble antigen reacts with its antibody in the presence of electrolytes at an optimal temperature and pH, the antigen-antibody complex forms an insoluble precipitate.
• This process is called precipitation.

Flocculation Definition

• When a particulate antigen reacts with its antibody in the presence of electrolytes at an optimal temperature and pH, the antigen-antibody reaction shows visible clumps of particles.
• This process is called flocculation.

Question 2. Zone of equivalence.
Answer:

Zone Of Equivalence

• When antigen and antibody are present in optimal or equivalent proportion, a large lattice is formed.
• This is results in precipitation.
• This zone where precipitation occurs in called the zone of equivalence.

Question 3. Types of electro immunodiffusion.
Answer:

Types Of Electro Immunodiffusion

Coombs Test

The Coombs test was devised by Coombs, Mourant, and Race in 1945.

Coombs Test Method:

Coombs Test Types

• Direct Coombs test – in-vivo test
• Indirect Coombs test – in-vitro test.

Coombs Test Uses

• Detect anti – Rh antibodies.
• Demonstrates incomplete antibody.

Question 5. Coaggiutination.
Answer:

Coaggiutination

• Coaggiutination is a type of passive agglutination test.
• Coaggiutination is based on the presence of protein A on Cown I strains of staphylococcus aureus.
• Specific IgG is coated on these bacteria.
• IgG has two portions.
  • Fc portion – Binds to protein A
  • Fab terminal – remains free.
    • When the corresponding antigen is mixed with it, the Fab terminal binds to it.
    • This results in agglutination.

Coaggiutination Uses

• Detects bacterial antigens in blood, urine, and CSF.
• Detects N.gonorrhoea, strep pyrogens, and H. influenzae antigens.

Complement fixation test

Complement Fixation Test Principle:

The antigen-antibody complexes are able to fix complement.

Complement Fixation Test Method:

An indicator system consisting of sheep erythrocytes coated with an amboceptor is used.

Complete fixation is detected by this system.

Complement Fixation Test Result

• Lysis of erythrocytes – indicates nagative reaction.
• No lysis of erythrocytes – indicates positive reaction.

Question 7. Define the Agglutination test with two examples.
Answer:

Agglutination Test Definition

• Agglutination Test is an antigen-antibody reaction in which a particulate antigen combines with its antibody in the presence of electrolytes at an optimal temperature and pH
• Agglutination Test results in clump formation

Agglutination Test Examples

• Weil – flex reaction – used for rickettsial infections
• Paul Bunnel test – used for diagnosis of infectious mononucleosis