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