Antigen-Antibody Reaction Short Essays
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.
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.
- Zone of equivalence.
Precipitation reaction Types:
Question 2. Immunodiffusion test.
Answer:
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.
2. 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.
Read And Learn More: Microbiology Question and Answers
Double diffusion in one dimension Result:
- Antigen and antibodies move towards each other
- A precipitation band is formed.
3. 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.
4. 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.
5. 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.
6. Electroimmunodiffusion
- It is combination of electrophoresis and diffusion.
- It includes.
- Counter immunoelectrophoresis.
- Rocket electrophoresis.
Question 3. Agglutination
Answer:
Agglutination Definition:
- It 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
- It results in clumps formation.
Agglutination Properties:
- Occurs with a particulate antigen.
- It is more sensitive.
- It 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:
Question 4. Immunofluorescence.
Answer:
Immunofluorescence
The dyes used are:
Question 5. ELISA test.
Answer:
ELISA test
ELISA is an abbreviated form of Enzyme-Linked ImmunoSorbent Assay.
- It is widely used.
- It is simple and sensitive.
- The test can be done in polystyrene tubes or polyvinyl microlitre plates.
ELISA test Types:
Antigen-Antibody Reaction Short Answers
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
Question 4. Coombs test.
Answer:
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
- It is type of passive agglutination test.
- It 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 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.
Question 6. Complement fixation test.
Answer:
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:
- It 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
- It results in clump formation
Agglutination test Examples:
- Weil – flex reaction – used for rickettsial infections
- Paul Bunnel test – used for diagnosis of infectious mononucleosis