principles of immunodetection 2
TRANSCRIPT
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Principles of
immunodetection
by
Martin Loignon Ph.D.
Lady Davis Institute for Cancer Research
Jewish General Hospital
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• Antibody-based methods allowing the
specific:
– Detection
– Quantification
– Localisation
• Of antigens by means of antibody binding
Immunodetection
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Aims and Objectives
• Basis of antibody production and antigen
interaction
• Conceptualise the different analyticaltechniques based on this interaction
• Examples of clinical application
• Research problems requiringimmunoanalyses
• Troubleshooting of some common problems
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Discovery of antibodies
• 1899 *Jules Bordet, Complement and antibody activity in bacteriolysis
• 1900 *Paul Erlich, Antibody formation theory
• 1926 Lloyd Felton & GH Bailey, Isolation of pure antibody preparation
• 1934-8 John Marrack, Antigen-antibody binding hypothesis
• 1941 Albert Coons, Immunofluorescence technique
• 1948 Astrid Fagraeus, Demonstration of antibody production in plasma B cells
• 1959-62 *Rodney Porter et al., Discovery of antibody structure
• 1963 Jaques Oudin et al., antibody idiotypes
• 1964-8 Anthony Davis et al., T and B cell cooperation in immune response
• 1965 Thomas Tomasi et al., Secretory immunoglobulin antibodies
• 1975 *Kohler and Milstein, Monoclonal antibodies used in genetic analysis
• 1985 *Tonegawa, Hood et al., Identification of immunoglobulin genes
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Generation of an antibody:
antigen processing
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B cell activation
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Structure of an antibody
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Antibody and VDJ recombination
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Classes of antibodies
Isotype Structure Placenta
transfert
Activatescomplement
Additional features
IgMNo Yes First Ab in development and response
IgDNo No B-cell receptor
IgGYes Yes Involved in opsonization and ADCC.
Four subclasses; IgG1, IgG2, IgG3,
IgG4
IgENo No Involved in allergic responses
IgANo No Two subclasses; IgA1, IgA2. Also found
as dimer (sIgA) in secretions.
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Commercial production of antibodies:
polyclonal vs monoclonal• Host animals ca be used to raise antibodies
against a given antigen
• Slected clones from a polyclonal each recognizing
a single epitope can be fused to a tumor cell
(hybridoma) to proliferate indefinitely
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Antigen-antibody interaction
• Antigen: foreign molecules that generate antibodies or any
substance that can be bound specifically by an antibody
molecule
– Proteins, sugars, lipids or nucleic acids
– Natural or synthetic
• Antibody: molecules (protein) responsible for specific
recognition and elimination (neutralization) of antigens
– Different structures (7-8 classes in mammals)
– Powefull research tools for basic research, clinical applications and
drug design
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Antigenic determinants
• An antibody will recognize
– Epitope: defined segment of an antigen
– Immunoreactivity of epitopes may depend on primary,
secondary, tertiary or quaternary structure of an antigen
– Define the possible applications
– Variability of epitopes depends on the species
• Antibodies are antigen themselves
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Nature of binding forces
• Hydrogen bonding
– Results from the formation of hydrogen bridges between appropriate atoms
•Electrostatic forces – Are due to the attraction of oppositely charged groups located on two protein side
chains
• Van der Waals bonds
– Are generated by the interaction between electron clouds (oscillating dipoles) • Hydrophobic bonds
– Rely upon the association of non-polar, hydrophobic groups so that contact with water
molecules is minimized (may contribute up to half the total strength of the antigen-antibody
bond)
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Antigen-antibody binding
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Antigen-antibody affinity
The affinity with which antibody binds antigen results from a balance
between the attractive and repulsive forces. A high affinity antibody implies
a good fit and conversely, a low affinity antibody implies a poor fit and a
lower affinity constant
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Antigen-antibody interaction:
concentration dependence
Concentration of unknown samples are determined from a standard curve
STD concentration values are obtained when the interaction between
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Non specific binding
Saturation radioligand binding experiments measure specific radioligand binding at equilibrium at various concentrations of the radioligand.
These experiments are performed to determine receptor number and affinity on cells but also between radiolabeled antigen and Ab.
This can take anywhere from a few minutes to many hours, depending on the ligand, receptor, To, and other experimental conditions.
The lowest concentration of radioligand will take the longest to equilibrate.
When testing equilibration time, therefore, use a low concentration of radioligand (perhaps 10-20% of the KD).
Nonspecific binding is almost always a linear function of ligand concentration.
The analyses depend on the assumption that you have allowed the incubation to proceed to equilibrium.
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Dissociation ‘off rate’ experiments
Each ligand-receptor complex dissociates at a random time, so the amount of specific binding follows an exponential dissociation.
Variable Meaning Comment
X Time Usually expressed in
units of sec. or min.
Y Total binding Usually expressed in
units of cpm, mol/mg,
sites/cellSpan Difference
between binding
at time zero and
plateau
Specific binding
(same units as Y)
Plateau Binding that
doesn't dissociate
Nonspecific binding
(same units as Y).
K Dissociation rateconstant
Expressed In units of inverse time (inverse
of units of X-axis)
T1/2 Half-life 0.69302/k
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• General equation for a dose
response curve
• It shows response as a
function of the logarithm of concentration
• X is the logarithm of agonist
concentration and Y is the
response
• Log EC50 is the logarithmof the EC50 (effective
concentration, 50% of
maximal response)
• IC50 (inhibitory conc.)
Sigmoidal dose response curve
10%
90%
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• Ligand receptor interaction
– Growth factors
– Hormones
• Antibody antigen interaction
– RIA, ELISA
• Activity of chemotherapeutics • Enzymatic activators/inhibitors
Doses response curves
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Cross reactivity
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One and two sites competition
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Laboratory use of antibodies
• Quantitation of an antigen
– RIA, Elisa
• Identification and characterization of protein antigens
– Immunoprecipitation
– Western blotting
• Cell surface labelling and separation
• Localisation of antigens within tissues or cells
• Expression librairies
• Phage display
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Detection principles
• Radiolabelled isotopes (antigen)
– 125I, 32P, 35S• Enzymes (Ab)
– Peroxydase
• Chromophores (Ab) – Fluorogenic probes (UV, visible or IR)
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Peroxydase reaction
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RIA: radio immuno assay
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Typical RIA standard curve
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RIA interference
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Elisa: Enzyme-linked immunosorbent assay
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Sandwich Elisa
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Western blotting
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Two dimensional electrophoresis
pH
M o l e c u l a r w e i g h t k D a
1st dimension 2nd dimension
Stable
pH gradient
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Immunoprecipitation
Proteomics
Western Blotting
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Immunohistochemistry
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• Phosphorylation and dephosphorylation affect
the structure and activity of proteins
• Cellular signalling is characterized by cascades
of phosphorylation
• Kinases and phosphatases maintain
phosphorylated/dephosphorylated state of proteins
• Phospho/Tyrosine/Threonine/ Serine
Phosphospecific antibodies to study
cellular signaling
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DNA damage inducible cascades
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Phosphospecific detections
• Phospho Ser, Thr, Tyr
• Sequence specific ( -Ser18 p53)
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Antibodies against other post-
translational modifications
• Ubiquitination
• Sumoylation• Acetylation
• Methylation
• Geranylation
• Etc...
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• Specific DNA damage (CPD, 6-4PP)
• Sugars• Lipids
• Vitamins (vit D)
• Iodine
Antibodies against non-protein
antigens
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• Identification of signaling pathways
– Protein modifications
– Signaling partners
• Activity of drugs (lead compounds)
•Lack of specific molecules – Specific ligands (side effects)
– New antibodies
Research requiring
immunoanalyses
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Phage display
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Bacteriophage structure
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Production of recombinant phages
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cDNA librairies
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Phage display: Ab production
Originally developped to produce monoclonal
antibodies, phage display is a simple yetpowerful technology that is used to rapidly
characterize protein-protein interactions from
amongst billions of candidates. This widely
practiced technique is used to map antibody
epitopes, create vaccines and to engineer
peptides, antibodies and other proteins as both
diagnostic tools and as human therapeutics
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Alternatives to specific antibodies
Gene of interest
Fluoresent
proteins
CFP
GFP
YFP
RFP
a-FP Ab Direct visualisation
TAGS
His
Myc
Flag
Strep
GST
Affinity a-Tag Ab
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FRET:Fluorescence resonance energy transfer
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Localization of BFP- and RFP-C/EBP protein expressed in mouse 3T3 cells using
2p-FRET microscopy. The doubly expressed cells (BFP-RFP-C/EBP) were excited
by 740 nm and the donor (A) and acceptor (B) images of proteins localized in the
nucleus of a single living cell were acquired by single scan
Localization of CEBP by FRET
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Therapeutic applications
• Neutralizing antibodies – Antidotes and antivenin (snake & spider bites)
– Tumor antigens ErbB-2, melanoma and T-cell leukemia,antibodies coupled to toxins
– Autoimmune antibodies, cytokines TNF-a – Antisera aigainst virus, bateria and toxins (vaccine)
– Anti IgE and IgM for allegies (experimental)
– Quantitation of blood peptides (hormones metabolites)
• Activating antibodies – Complement activating for uncontrolled bleeding (hemophilia)
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Concentration of serum peptides
• Blood levels of:
– Hormones – Antibodies
– Enzymes
– Metabolites
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Detection of HIV proteins by WB
gp160 viral envelope precursor (env)
gp120 viral envelope protein (env) binds to CD4
p31 Reverse Transcriptase (pol)
p24 viral core protein (gag)
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Immunodiffusion
Zone of equivalence:
formation of large complexes
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The problems of chemotherapy
Chemotherapy/radiotherapy
Sensors
Transducers
Cytoplasmic/Nuclear effectors
ChromatinStructureTranscription
DNA repairCell cyclecheckpoints
Apoptosis
Drug resistance arisingfrom sensor/transducer
defects
Drug resistance arisingfrom effector defects
DNA Damage
Drug resistance arisingfrom altered drugdelivery to target
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Physiological roles of antibodies
• Protect against – Viral infections
– Bacterial infections
– Foreign bodies
• Antigens
• Deleterious in – Autoimmune diseases
• Reumathoid arthritis Lupus
• Type 1 diabetes Croh’n disease
– Graft rejection and hypersensitivity
responses
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Health care perspectives
• Ab against antigens could lead to diagnostic
test or vaccine for several diseases
– BSE (mad cow disease) or human variant Creutzfeldt Jakob.Paramithiotis et al. A prion protein epitope selective for the pathologically misfolded conformation.
Nat Med. 2003 Jul;9(7):893-9
Caprion Pharmaceuticals Inc., St-Laurent, Quebec, Canada.
– Vaccine against HIV Crystal structure of a neutralizing human IGG against HIV-1: a template for vaccine design.
Science. 2001 Aug 10;293(5532):1155-9. – SARS
– Nil virus
– Antidotes
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Lacking an antibody for your
protein or antigen of interest islimiting the progression of your
research!
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Expression librairies