1. Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding specifically with antigen detected by B cells

2. Copyright © 2010 Pearson Education, Inc. Basic Antibody Structure T-or Y-shaped monomer of four looping linked polypeptide chains Two identical heavy (H) chains and two identical light (L) chains Variable (V) regions of each arm combine to form two identical antigen-binding sites

3. Copyright © 2010 Pearson Education, Inc. Basic Antibody Structure Constant (C) region of stem determines The antibody class (IgM, IgA, IgD, IgG, or IgE) The cells and chemicals that the antibody can bind to How the antibody class functions in antigen elimination

4. Copyright © 2010 Pearson Education, Inc. Figure 21.14a Antigen-binding site Stem region Hinge region Light chain constant region Disulfide bond Light chain variable region Heavy chain constant region Heavy chain variable region (a)

5. Copyright © 2010 Pearson Education, Inc. Classes of Antibodies IgM A pentamer; first antibody released Potent agglutinating agent Readily fixes and activates complement IgA (secretory IgA) Monomer or dimer; in mucus and other secretions Helps prevent entry of pathogens

6. Copyright © 2010 Pearson Education, Inc. Table 21.3

7. Copyright © 2010 Pearson Education, Inc. Classes of Antibodies IgD Monomer attached to the surface of B cells Functions as a B cell receptor IgG Monomer; 75–85% of antibodies in plasma From secondary and late primary responses Crosses the placental barrier

8. Copyright © 2010 Pearson Education, Inc. Classes of Antibodies IgE Monomer active in some allergies and parasitic infections Causes mast cells and basophils to release histamine

9. Copyright © 2010 Pearson Education, Inc. Table 21.3

10. Copyright © 2010 Pearson Education, Inc. Generating Antibody Diversity Billions of antibodies result from somatic recombination of gene segments Hypervariable regions of some genes increase antibody variation through somatic mutations Each plasma cell can switch the type of H chain produced, making an antibody of a different class

11. Copyright © 2010 Pearson Education, Inc. Antibody Targets Antibodies inactivate and tag antigens Form antigen-antibody (immune) complexes Defensive mechanisms used by antibodies Neutralization and agglutination (the two most important) Precipitation and complement fixation

12. Copyright © 2010 Pearson Education, Inc. Neutralization Simplest mechanism Antibodies block specific sites on viruses or bacterial exotoxins Prevent these antigens from binding to receptors on tissue cells Antigen-antibody complexes undergo phagocytosis

13. Copyright © 2010 Pearson Education, Inc. Agglutination Antibodies bind the same determinant on more than one cell-bound antigen Cross-linked antigen-antibody complexes agglutinate Example: clumping of mismatched blood cells

14. Copyright © 2010 Pearson Education, Inc. Precipitation Soluble molecules are cross-linked Complexes precipitate and are subject to phagocytosis

15. Copyright © 2010 Pearson Education, Inc. Complement Fixation and Activation Main antibody defense against cellular antigens Several antibodies bind close together on a cellular antigen Their complement-binding sites trigger complement fixation into the cell’s surface Complement triggers cell lysis

16. Copyright © 2010 Pearson Education, Inc. Complement Fixation and Activation Activated complement functions Amplifies the inflammatory response Opsonization Enlists more and more defensive elements

17. Copyright © 2010 Pearson Education, Inc. Figure 21.15 Inactivates by AntigenAntibody Fixes and activates Enhances Leads to Phagocytosis Chemotaxis Histamine release Inflammation Cell lysis Agglutination (cell-bound antigens) Precipitation (soluble antigens) Neutralization (masks dangerous parts of bacterial exotoxins; viruses) Complement Antigen-antibody complex Adaptive defensesHumoral immunity

18. Copyright © 2010 Pearson Education, Inc. Polyclonal antibodies generally an immune response activates a number of different plasma cells which can produce only one type of antibody. Each individual antibody will have its own affinity for antigen and specificity for the antigen. The sum of these antibodies that recognize a particular antigen is called Polyclonal antibodies because they arise from many different B cells (plasma cells).

19. Copyright © 2010 Pearson Education, Inc. Monoclonal Antibodies Commercially prepared pure antibody Produced by hybridomas Cell hybrids: fusion of a tumor cell and a B cell Proliferate indefinitely and have the ability to produce a single type of antibody. With a homogenous affinity and specificity. Used in research, clinical testing, and cancer treatment. mAb

20. Copyright © 2010 Pearson Education, Inc. Anti-antibodies An immune response can be directed Against a part of a particular animals Antibody common chain. As a consequence, we can detect when such A antibody is present. Example anti-human IgG antibody (made in rabbits or mice)

21. Copyright © 2010 Pearson Education, Inc. Possibilities with conjugates are limitless.