Basics of Immunology
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Basics of Immunology
What is the immune system?
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Biological mechanism for identifying and
destroying pathogens within a larger
organism.
– Pathogens: agents that cause disease
Bacteria, viruses, fungi, worms, etc.
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Types:
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• Innate Immunity
• Adaptive Immunity
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Immunity - Definition & Types
Innate Immunity
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Definition:
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Adaptive Immunity
Resistance to infectious diseases and is
mediated by immune system
Types:
• Innate or Non Specific
• Anatomic barriers: Skin, mucous
membrane
• Physiologic barriers: Temperature, pH
• Phagocytic Barriers:
• Inflammatory barriers: redness, swelling,
heat and pain
• Adaptive or Specific
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Antigen specificity
Diversity
Immunological Memory
Self or non self recognition
Innate immunity
Adaptive Immunity - Types
• Naturally acquired Immunity
Arises as a result of accidental interaction
of a disease causing agent
• Artificially acquired Immunity
Immunity due to deliberate interaction of a
disease causing agent. e.g.., vaccination
The colors of the receptors indicate specificity: each can
bind to one specific antigen. Adaptive immunity can only
attack targets that it has prepared for
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Adaptive Immunity
Adaptive Immunity
Naturally acquired
Active
Antigens enter the
body naturally;
body induces
antibodies and
specialized
lymphocytes
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Artificially acquired
Passive
Active
Passive
Antibodies pass
from mother to
fetus via placenta
or to infant via the
mother’s milk
Antigens are
introduced by
vaccination; body
produces
antibodies and
specialized
lymphocytes
Preformed
antibodies in
immune serum
are introduced by
injection
Components of Immune System
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Cells
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Proteins
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Cytokines
Antibodies
Acute phase Reactants
Antibodies
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Antigen presenting cells
Polymorphic mono nuclear Leukocytes
Cytotoxic leukocytes
Natural Killer (NK) Cells
Lymphokine activated Killers (LAK)
Lymphocytes, B cells and T Cells
Each B cell produces a specific type of antibody
Antigen: Antibody Generator
Any substance that can elicit an immune response
when administered parenterally
Reacts with the antibody thus produced
Structure of Antibody
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Composed of 2 heavy and 2 light chains –
encoded by different genes
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Single disulfide bond between heavy and
light, two disulfide bonds between 2 heavy
chains.
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Light chain is either ƙ (kappa) or λ
(lambda); 98% of mouse antibodies are ƙ.
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Heavy chain constant region varies
depending on isotype.
Epitope – Paratope Interaction
Variable and constant regions are
encoded by different gene segments
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variable region binds antigen
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constant region binds receptors,
bacterial products, complement, etc.
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Types of Antibodies - IgG
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Induced by protein antigens
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Constitutes about 80% of antibody in
serum
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Composed of two light chains (κ or λ)
and one type of heavy chain (γ)
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Coats Ag for its speedy uptake
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Four isotypes
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IgG1, IgG2, IgG3, IgG4
Most of BioGenex Antibodies are IgG Type
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Types of Antibodies - IgA
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Constitutes 13% of total antibodies
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Predominant class of Ab in
extravascular secretions
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Present in saliva, tears, nasal secretions,
bronchial and digestive tract mucus and
mammary gland secretions
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Exists either as monomer or dimer
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Dimer is formed by two IgA monomers,
a J chain and secretory component
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Has two isotypes IgA1 and IgA2
Types of Antibodies - IgM
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Largest antibody
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Constitutes upto 8% of total Abs
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It is a pentamer formed by five
monomers of IgM Abs joined by
disulphide bridges
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First Ab that appears during immune
response
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Activates complement system
Types of Antibodies - IgD
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Membrane bound
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Constitutes less than 1% of total Abs
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Membrane bound and one of the main
receptors on mature B cells
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May play an important role in
regulation of immune responses.
Types of Antibodies - IgE
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Constitutes less than 0.003% of
total Abs
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Triggers allergies
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Binds to Mast cells and Basophils
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Subsequent exposure to the same
antigen triggers allergic reaction
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Responsible for release of factors
that attracts Eisonophils
Polyclonal vs. Monoclonal Antibodies
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Polyclonal Abs are produced from different
clones of B cells for a given Ag
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Recognizes the different epitopes on an Ag
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Monoclonal Ab are produced against a
single epitope
Polyclonal vs. Monoclonal Antibodies
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Polyclonal Abs is produced from different
clones of B Lymphocytes and hence different
antibodies with distinct specificity for given
antigen (i.e same antigen different
epitopes).It’s robust, exhibit cross reactivity
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Monoclonal Abs is produced from a single
clone and directed against a single epitope.
It show lot to lot consistency and is specific
Polyclonal vs. Monoclonal Antibodies
Monoclonal
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Polyclonal
Single plasma cell population /
single epitope
Multiple epitopes
Higher Specificity
Higher Sensitivity
Hybridoma technology
Produced in lab animals like Rabbit,
Goat, etc.
Lot to lot stability
Lot to lot variations
Longer time to generate
Cross Reactivity
Applications of Antibodies
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Western blotting: Detection of protein of interest in a mixture
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Flow cytometry: Detection of proteins in live cells
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ELISA: Binding characteristics of proteins and quantitation
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IHC: localization of proteins of interest with in a cell
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In situ Hybridization: detect modification and abnormalities at genetic level
Western
IHC
Direct Bind
ELISA
Denatyred/linear epitope
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IP/ChIP
Sandwich
IF/Flow
Cytometry
Functional
Modulation
folded/discontinuous epitope
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