Four Types of Adaptive Immunity
(few years - life long)
(weeks - months)
(few years - life long)
(~3 weeks)
Natural = normal environmental exposure or delivery
Artificial = medical intervention
Active = immune response: antibody production and T cell activation
Passive = delivery of preformed antibodies, limited, not long term immunity, no
development of an immune response
Amy Warenda Czura, Ph.D.
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SCCC BIO244 Chapter 17 Handout
Monomer or Bivalent Antibody molecule / Immunoglobulin
Disulfide linkage
Antigen-binding site:
bind epitope here
2 Heavy Chains
2 Light Chains
V = variable region, different
for each different antibody,
specific for one kind of
epitope
The Fc region can bind complement
to trigger complement fixation
when the antigen binding sites are
bound to their epitopes
Amy Warenda Czura, Ph.D.
C = constant region, same for all
antibodies in the same class, 5 classes
of antibodies total: IgG, IgM, IgA,
IgD, IgE
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SCCC BIO244 Chapter 17 Handout
Classes of Antibodies/Immunoglobulins
IgG antibodies
•
•
•
•
•
•
Monomer
80% of serum antibodies
Produced on second+ exposure
In blood, lymph
Can enter tissues, cross placenta
Fix complement, enhance phagocytosis,
neutralize toxins & viruses, protects fetus
& newborn, antiserum
IgG
IgM antibodies
•
•
•
•
•
Pentamer
5-10% of serum antibodies
Produced only on first exposure
In blood, lymph, on B cells
Fix complement, agglutinates antigens
IgM
IgA
IgA antibodies
•
•
•
•
Dimer
10-15% of serum antibodies
In secretions
Mucosal protection
IgD
IgD antibodies
•
•
•
•
Monomer
0.2% of serum antibodies
Surface receptor on B cells
Initiate humoral immune response by B cells
IgE antibodies
•
•
•
•
Monomer
0.002% of serum antibodies
Surface receptor on mast cells and basophils
Inflammation, allergic reactions;
lysis of parasitic worms
Amy Warenda Czura, Ph.D.
IgE
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SCCC BIO244 Chapter 17 Handout
Activation and Clonal Selection of B cells
T-independent Antigen
(Epitope tends to be polysaccharide, produces
weaker immune response than T-dependent Antigen)
1. IgD antibody receptor on B cell binds its specific antigen/epitope
2. B cell is activated and undergoes clonal selection: the B cell proliferates and differentiates
into two types of cell populations: Memory B cells and Plasma Cells
3. Plasma cells secrete antibodies specific for the original epitope (2000 antibody molecules
per second) for 3-5 days [Time from initial antigen binding to antibodies appearing in the
blood is 7-10 days] Antibodies bind to free antigens.
4. Upon second exposure to the same antigen/epitope, memory cells bind antigen and are
triggered to differentiate into plasma cells and secrete antibodies. [Time from initial
antigen binding to antibodies appearing in the blood is 2-5 days]
Memory cells = long term immunity
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SCCC BIO244 Chapter 17 Handout
Results of Antigen-Antibody Binding:
1.
6.
MAC
5.
2.
Antigen bound to IgE on Mast cells
triggers histamine release and
3.
4.
Macrophages
Eosinophils
NK cells
Amy Warenda Czura, Ph.D.
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SCCC BIO244 Chapter 17 Handout
Class I MHC
Infected cell
Class I MHC is found on
all cell types and
displays all antigens that
are present in a cell, both
self and non-self.
Class II MHC is found
only on APCs and only
displays antigens that
have been endocytosed
Class II MHC
Antigen
Presenting Cell
(e.g. Macrophage, Dendritic Cell)
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SCCC BIO244 Chapter 17 Handout
Activation of Helper T Cells
Class II
TH1
TH2
Defense against free pathogens
Defense against intracellular pathogens
Amy Warenda Czura, Ph.D.
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SCCC BIO244 Chapter 17 Handout
Activation of Cytotoxic T Cells
T cell
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SCCC BIO244 Chapter 17 Handout
Activation and Clonal Selection of B cells
T-dependent Antigen
(Epitope tends to be protein, produces stronger
immune response than T-independent Antigen)
1. B cell binds specific antigen in the
IgD receptor and internalizes it.
2. B cell transfers antigen to a Class
II MHC receptor and returns antigen
now bound to MHC back to the
surface of the cell. B cell is now
sensitized.
3. A TH2 cell specific for the antigen
recognizes and binds to the antigen
in the Class II MHC and becomes
activated.
4. The activated TH2 cell secretes
cytokines on the B cell.
5. Cytokines activate the B cell.
6. The activated B cell undergoes
clonal selection producing Memory
B and Plasma cells.
7. Plasma cells secrete antibodies
that are specific for the original
antigen
*Most B cell activation is by the T-dependent mechanism (and most antigens/epitopes are
protein type molecules). This produces a much stronger immune response than the Tindependent mechanism.
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SCCC BIO244 Chapter 17 Handout
Body Defense Summary
Non-specific defenses and the immune response are integrated:
both function together for overall defense
Defense against free
pathogens
Defense against
intracellular pathogens
Amy Warenda Czura, Ph.D.
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SCCC BIO244 Chapter 17 Handout