Transcript Immunology
Immunology Chapter 4 • • • • • • Richard L. Myers, Ph.D. Department of Biology Southwest Missouri State Temple Hall 227 Telephone: 417-836-5307 Email: [email protected] Properties of antigens • Antigens are: – immunogenic - induce a humoral or cellmediated immune response – antigenic - combine specifically with antigen – allerogenic - induce an allergic response – tolerogenic - induce specific immunologic nonresponsiveness Membrane 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 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 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 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 Mosaic antigens 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 Karl Landsteiner Hapten reacting with ab 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 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) 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 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 Assignment • Review question 2 (pg 105) • Read Chapter 5, Immunoglobulin • Review question 2 (pg 141)