Chapter 6 Antigen-Antibody Interactions Dr. Capers immunology

Kindt • Goldsby • Osborne Kuby IMMUNOLOGY Sixth Edition Chapter 6 Antigen-Antibody Interactions: Principles and Applications Copyright © 2007 by W. H. Freeman and Company

Antigen-Antibody (Ag-Ab) Interaction Similar to enzyme-substrate interaction However, does not lead to irreversible chemical alteration in either the antibody or antigen

Noncovalent Interactions Hydrogen bonds Ionic bonds Hydrophobic reactions Van der Waals All weak so need combination of all of them to make strong interaction

Cross-reactivity Mechanisms of tolerance prevent formation of Abs against one’s own blood group antigens However, exposure to microbial antigens on intestinal bacteria induce formation of Abs, these antigens share similarity to blood group antigens

Immunoassays – measuring Ag-Ab interactions Vital roles: Diagnosing disease Monitoring level of humoral response Identifying molecules of biological or medical interest

Precipitation Reactions Ag-Ab interactions can form visible precipitate Examples: Radial immunodiffusion Double immunodiffusion immunoelectrophoresis

In this example, Anti-dog IgG is Mixed in agar so only what is Placed in wells (Ag) diffuses out

In this example, both antibody and antigen diffuse Out of wells

Immunoelectrophoresis – Antigen is 1st put into wells, charge is applied to separate components of antigen mixture, then troughs are cut and antibody is allowed to diffuse through gel

Agglutination Reactions Visible clumping – agglutination Examples: Hemagglutination Bacterial Agglutination Important in all tests for Antibody to be in right concentation Too much antibody will cause univalent binding, need multivalent for preciptitate or agglutination to occur

ELISA Enzyme-Linked Immunosorbent Assay Examples: Indirect ELISA Sandwich ELISA Competitive ELISA

Indirect ELISA Used to determine if a particular antibody is present

Immunoprecipitation Using microscopic magnetic beads Below is cell with magnetic beads attached

Immunofluorescence

Using Immunofluorescence to see the effect of cancer treatments E. decrease beta-tubulin III (found in developing neurons, if found in other tissue it can be used as cancer marker) F. decrease thymidilate kinase (needed by tumor cell to repair DNA)

Flow Cytometry Can provide quantitative data