Chapter 6 Ag-Ab Interactions

Nature of the Ag-Ab interaction

Immunological assays

4 types of noncovalent forces

AffinityThe strength of the total noncovalent interactions between a single Ag-binding site on an Ab and a single epitope is the affinity of the Ab for that epitope.

AvidityThe strength of multiple interactions between amultivalent Ab and Ag is called the avidity.

Example: secreted pentameric IgM often has a lower affinity than IgG, but the high avidity of IgM, resulting from its higher valence, enables it to bind Ag effectively.

Immunological Assays

1. Precipitation

2. Agglutination

3. Radioimmunoassay

4. Enzyme-linked Immunosorbent Assay

5. Western Blotting

6. Immunofluorescence

7. Flow Cytometry and Fluorescence

8. Immunoelectron Microscopy

Precipitation Reactions:

Precipitation in fluidsPrecipitation in gels - radial immunodiffusion (Mancini method) - double immunodiffusion (Ouchterlony method)Immunoelectrophoresis

Precipitation Reactions

Lattice Formation(格子 )

Double Immunodiffusion (Ouchterlony method)

Immunoelectrophoresis

Agglutination Reactions:

HemagglutinationBacterial AgglutinationPassive AgglutinationAgglutination Inhibition

Hemagglutination

Agglutination No Agglutination No Ab

Agglutination Inhibition

Solid-phase Radioimmunoassay (RIA)

Enzyme-linked Immunosorbent Assay (ELISA):

- Indirect ELISA

- Sandwich ELISA

- Competitive ELISA

- Chemiluminescence

Elispot Assay

Western Blotting

Immunofluorescence

Flow Cytometry

FACS:

Fluoresence-activatedCell sorter

Immunoelectron microscopy