COURSE: Medical Microbiology, MBIM 650/720
TOPIC: Immunoglobulins: Ag-Ab Reactions and Selected Tests
Lecture # 8
FACULTY: Dr. Mayer
Office: Bldg. #2, Rm. B19
Phone: 733-3281
Email: MAYER@MED.SC.EDU
TEACHING OBJECTIVES:
1. To describe the nature of Ag-Ab reactions
2. To compare and contrast antibody affinity and avidity
3. To delineate the basis for antibody specificity and cross reactivity
4. To discuss the principles of commonly used tests for antigen/antibody
reactions
REQUIRED READING:
Roitt et al. Immunology, 6th Ed., pp 71-74, Chpt. 27
KEY WORDS:
Affinity, Avidity, Specificity, Cross reactivity, Agglutination, Hemagglutination,
Agglutinin, Titer, Prozone, Passive hemagglutination, Direct Coomb's test,
Indirect Coomb's test, Hemagglutination inhibition, Equivalence point, Antibody
excess, Antigen excess, Radial immunodiffusion, Immunoelectrophoresis,
Countercurrent immunoelectrophoresis, Radioimmunoassay,
Enzyme linked immunosorbent assay, Competitive RIA/ELISA, Noncompetitive
RIA/ELISA, Immunofluorescence, Flow cytometry, Complement fixation
IMMUNOGLOBULINS: AG-AB REACTIONS
I. NATURE OF AG-AB REACTIONS
A. Lock and Key Concept - The combining site of an antibody is located
in the Fab portion of the molecule and is constructed from the
hypervariable regions of the heavy and light chains. X-Ray
crystallography studies of antigens and antibodies interacting shows
that the antigenic determinant nestles in a cleft formed by the
combining site of the antibody as illustrated in Figure 1. Thus, our
concept of Ag-Ab reactions is one of a key (i.e. the Ag) which fits into a
lock (i.e. the Ab).
Figure 1
B. Non-covalent Bonds - The bonds that hold the Ag in the antibody
combining site are all non-covalent in nature. These include hydrogen
bonds, electrostatic bonds, Van der Waals forces and hydrophobic
bonds. Multiple bonding between the Ag and the Ab ensures that the
Ag will be bound tightly to the Ab.
C. Reversible - Since