Precipitation and Agglutination Reactions

Question 1

Antigen–Antibody Binding: Affinity

Answer 1

Is the initial attraction force between a Fab site on an antibody molecule and an epitope or determinant site on an antigen
strength of attraction depends on the specificity of the antibody for a particular antigen

Question 2

Antigen–Antibody Binding: Avidity

Answer 2

the sum of the attractive forces between an antigen and an antibody that keeps the molecules together
Is a measure of the overall stability of an antigen–antibody complex

Question 3

Precipitation Reactions

Answer 3

Involve combining soluble antigen with soluble antibody to produce insoluble complexes that are visible

Question 4

What is required for antigen and antibody in Precipitation reactions?

Answer 4

Multiple binding sites for one another
Equal relative concentration of each

Question 5

Zone of Equivalence

Answer 5

Number of multi-valent sites of antigen and antibody are approximately equal

Question 6

Prozone

Answer 6

antibody excess
Antigen combines with only one or two antibody molecules
False-negative reactions may occur as a result of high antibody concentration

Question 7

Postzone

Answer 7

antigen excess
The presence of a small amount of antibody may be obscured, causing false-negative results

Question 8

Nephelometry

Answer 8

Light that is scattered at an angle is measured, indicating the amount of antigen or antibody present

Question 9

Radial immunodiffusion

Answer 9

Antigen diffuses out into gel that is infused with antibody. Measurement of the radius indicates concentration of antigen

Question 10

Ouchterlony double diffusion

Answer 10

Both antigen and antibody diffuse out from wells in a gel. The lines of precipitate formed indicate the relationship of antigens

Question 11

Immuno-electrophoresis

Answer 11

Electrophoresis of serum is followed by diffusion of antibody from the wells

Question 12

Immunofixation electrophoresis

Answer 12

Electrophoresis of serum is followed by direct application of antibody to the gel

Question 13

Difference b/n Ouchterlony and Radial immunodiffusion

Answer 13

Radial immunodiffusion: single diffusion
Ouchterlony: Double diffusion

Question 14

Ouchterlony result interpretation

Answer 14

Arch: Identity
X shape: non identity
A line with a spur: Partial Identity

Question 15

Agglutination

Answer 15

Is the visible aggregation of particles resulting from combination with specific antibody

Question 16

How many steps are in agglutiation?

Answer 16

2 Steps
Sensitization: Antigen and antibody unite through antigenic determinant sites
Lattice formation: Rearrangement of antigen and antibody bonds to form a stable lattice

Question 17

Direct agglutination

Answer 17

Uses known bacterial antigens to test for the presence of unknown antibodies in the patient

Question 18

Passive agglutination

Answer 18

Employs particles that are coated with antigens not normally found on their surfaces

Question 19

Reverse passive agglutination

Answer 19

Used to detect microbial antibodies
Antibody is attached to the carrier particle
Agglutination occurs if antigen is present in patient sample

Question 20

Agglutination inhibition

Answer 20

Is based on competition between particulate and soluble antigens for limited antibody-combining sites
Lack of agglutination = positive reaction