Immunology Chapter 6, Lecture 1

1. ImmunologyChapter 6, Lecture 1 • Richard L. Myers, Ph.D. • Department of Biology • Southwest Missouri State • Temple Hall 227 • Telephone: 417-836-5307 • Email: rlm967f@mail.smsu.edu • Homepage: http://creative.smsu.edu/biology/myersr/index.html • TopClass: http://creative.smsu.edu

2. Antigen-Antibody interactions • Similar to enzyme-substrate reactions • Involves noncovalent interactions • between epitope and CDRs of antibody • the reaction is very specific • used in diagnosing disease • monitoring level of the humoral response • identifying certain molecules • Ag-Ab reactions differ and speed and sensitivity

3. Strength of Ag-Ab reactions • Involves noncovalent interactions • hydrogen bonds • ionic bonds • hydrophobic interactions • van der Waals interactions • Requires many of these interactions • operating over a small distance (1 angstrom) • Therefore, depends upon a very close fit

5. Antibody affinity • Defined as the strength of the sum total of noncovalent interactions • Low-affinity antibodies bind antigen weakly • High-affinity bind more tightly • Ag-Ab association can be determined by equilibrium dialysis

8. Antibody avidity • Defined as the strength of multiple interactions between multivalent antibody and antigen • IgM has a low affinity compared to IgG, but has a high avidity

9. Cross-reactivity • Ag-Ab reactions are highly specific, but • Ab may cross-react with an unrelated Ag • affinity is usually less • An example of a cross-reacting Ab is the ABO blood-group antigens • originally elicited by microbial antigens • will cross-react with similar antigens on RBCs

10. Precipitin reactions • Results when antigen and antibody interact • Forms a lattice that becomes visible • antibody must be bivalent • called precipitins • Reaction may take place in fluids • dilute the antibody, hold antigen constant • used as a rapid test for presence of Ag or Ab • the interfacial or ring test is very useful

13. Precipitin reactions (cont) • Reactions may occur in gels • produces a visible line of precipitation • called immunodiffusion • used to determine relative concentration of Ag or Ab • used to compare antigens • or determine relative purity of an antigen • Mancini method (radial diffusion) • antigen placed in a well • diluted antibody placed into agar

16. Precipitin reactions (cont) • Ouchterlony method • double diffusion in agar • antigen and antibody diffuse toward each other • form visible precipitation line where they meet • show relationships between different systems • identity • nonidentity • partial identity

19. Precipitin reactions (cont) • Immunoelectrophoresis • seperation of proteins with electrophoresis • followed by double diffusion in gel • can detect concentrations of 3 - 20 mg/ml • rocket electrophoresis is similar but can detect level of protein as low as 0.2 mg/ml • 2-D immunoelectrophoresis • electrophoresis followed by overlay with gel with antiserum

21. Assignment • Read Chapter 6, Antigen-Antibody Interactions • Review question 6 (pg 163)