Chapter 6 Ag-Ab Interactions

Nature of the Ag-Ab interaction Immunological assays

4 types of noncovalent forces

Affinity The 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. Avidity The strength of multiple interactions between a multivalent 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 fluids Precipitation in gels - radial immunodiffusion (Mancini method) - double immunodiffusion (Ouchterlony method) Immunoelectrophoresis

Precipitation Reactions

Lattice Formation ( 格子 )

Double Immunodiffusion (Ouchterlony method)

Immunoelectrophoresis

Agglutination Reactions: Hemagglutination Bacterial Agglutination Passive Agglutination Agglutination 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-activated Cell sorter

Immunoelectron microscopy