Immunology Chapter 4

1. ImmunologyChapter 4 • Richard L. Myers, Ph.D. • Department of Biology • Southwest Missouri State • Temple Hall 227 • Telephone: 417-836-5307 • Email: rlm967f@mail.smsu.edu

2. Properties of antigens • Antigens are: • immunogenic - induce a humoral or cell-mediated immune response • antigenic - combine specifically with antigen • allerogenic - induce an allergic response • tolerogenic - induce specific immunologic nonresponsiveness

3. Membrane

4. Immunogenicity • Proteins make the best antigens, and polysaccharides are next • proteins and polysaccharides evoke humoral • for cell-mediated use only proteins • Lipids and nucleic acids must be complexed with proteins or polysaccharides to work • Must be foreign to the host • Must be degraded and presented with an MHC molecule

5. Immunogenicity (cont) • Foreignness - the greater the phylogenetic distance, the greater the immunogenicity • Molecular size - best immunogens have molecular weights greater than 100,000 • Chemical composition - organization of the molecule contributes • Degradability - must be phagocytized and degraded and presented with MHC

6. Contributions to immunity • Factors influencing the immune response: • genetic constitution • immune responsiveness maps to the MHC • MHC haplotye is inherited MHC alleles • dosage of immunogen • route of administration • adjuvants • Adjuvants • Freund’s (complete and incomplete) • Role of activated macrophages

7. Epitopes • Epitopes - discrete sites on macromolecules • Also are immunologically active regions • Sometimes called “antigenic determinants” • Epitopes recognized by B cells are most accessible sites • Epitopes recognized by T cells are on the surface of APCs in association with MHC

8. Mosaic antigens

9. Haptens • Haptens are small organic molecules attached to larger proteins called carriers • The hapten functions as an epitope • Hapten alone will not stimulate a response • Many sustances (drugs and hormones) may serve as haptens • Landsteiner demonstrated the importance of haptens

10. Karl Landsteiner

12. Hapten reacting with ab

13. Viral/Bacterial antigens • A response to a virus will form to envelope proteins, core proteins and proteins associated with the viral genome • Usually a cell-mediated response will occur in response to a virus • may be presented with class I molecule and stimulate a cytotoxic T cell or • presented with class II molecule and stimulate a helper T cell

14. Viral/Bacterial antigens (cont) • Several bacterial structures (capsule, flagella, fimbriae or pili) are antigenic • It is possible to identify microbes based on antigenic properties (i.e., Streptococcus) • Surface antigens must be accessible and repeated (i.e., O antigens)

15. Mitogens • Mitogens are agents that induce cell division, particularly in T and B cells • Induction of T or B cells by mitogens is irrespective of their antigen specificity • Many mitogens are lectins derived from plants and bind sugars • Some activate T cells, others B cells

16. Mitogens (cont) • T cell mitogens: • Concanavalin A (Con A) • Phytohemagglutinin (PHA) • B cell mitogen: • Lipopolysaccharide • T and B cell mitogen: • Pokeweek mitogen • Superantigens are very potent mitogens

19. Assignment • Review question 2 (pg 105) • Read Chapter 5, Immunoglobulin • Review question 2 (pg 141)