Excellnet serological tests in identification of infectious agents
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Serological tests involved in identification of infectious agents
Prof M.I.N. Matee
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Precipitation Tests
Lattice Formation
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PRECIPITATION
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Precipitation reactions in fluids (p. 142)
Precipitation reaction can be seen
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Radial Immunodiffusion (Mancini)
• Interpretation– Diameter of ring is
proportional to the concentration
• Quantitative– Ig levels
• Method– Ab in gel– Ag in a well
Ag Concentration
Dia
met
er2
AgAgAgAg
Ab in gel
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Immunoelectrophoresis• Method
– Ags are separated by electrophoresis
• Interpretation– Precipitin arc represent individual antigens
Ag-+
Ag
Ab
Ag
Ab
– Ab is placed in trough cut in the agar
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Countercurrent electrophoresis• Method
– Ag and Ab migrate toward each other by electrophoresis
– Used only when Ag and Ab have opposite charges
• Qualitative–Rapid
Ag Ab- +
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Immunoelectrophoresis
• Method
• Interpretation
• Qualitative– Relative concentration
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Agglutination Tests
Lattice Formation
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Agglutination/Hemagglutination
• Definition - tests that have as their endpoint the agglutination of a particulate antigen– Agglutinin/hemagglutinin
+
• Qualitative agglutination test– Ag or Ab
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Agglutination/Hemagglutination• Quantitative agglutination test
– Titer– Prozone
1/2
1/4
1/8
1/16
1/32
1/64
1/12
8
1/25
6
1/51
2
1/10
24
Pos
.
Neg
.
Titer
64
8
512
<2
32
128
32
4
Patient
1
2
3
4
5
6
7
8
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Agglutination/Hemagglutination
• Definition
• Qualitative test
• Quantitative test• Applications
– Blood typing– Bacterial infections
–Fourfold rise in titer
• Practical considerations– Easy– Semi-quantitative
1/2
1/4
1/8
1/16
1/32
1/64
1/12
8
1/25
6
1/51
2
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Passive Agglutination/Hemagglutination
• Definition - agglutination test done with a soluble antigen coated onto a particle
+
• Applications– Measurement of antibodies to soluble antigens
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Hemagglutination
Used to identify blood group antigens or antibodies to them
Variations: Chemically couple haptens to RBC
Use other particles - bacteria, antigen-coated latex beads
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Agglutination Inhibition Assay for HCG
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Coombs (Antiglobulin)Tests
• Incomplete Ab• Direct Coombs Test
– Detects antibodies on erythrocytes
+
Patient’s RBCs Coombs Reagent(Antiglobulin)
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Coombs (Antiglobulin)Tests
• Indirect Coombs Test– Detects anti-erythrocyte antibodies in serum
Patient’s Serum
TargetRBCs
+ Step 1
+
Coombs Reagent(Antiglobulin)
Step 2
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Coombs (Antiglobulin)Tests
• Applications– Detection of anti-Rh Ab– Autoimmune hemolytic anemia
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Agglutination/Hemagglutination Inhibition
• Definition - test based on the inhibition of agglutination due to competition with a soluble Ag
+
Prior to Test
+ +
Test
Patient’s sample
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Agglutination/Hemagglutination Inhibition
• Applications– Measurement of soluble Ag
• Practical considerations– Same as agglutination test
• Definition
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Immunofluorescence
Antibodies can be labeled with fluorescent dye
Can localize binding sites on cells
Dyes: Fluorescein, rhodamine, phycoerythrincan be conjugated to Fc region of Ab
(so antigen binding is unaffected)
Absorb at one wavelength and emit at another
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Immunofluorescence
• Direct– Ab to tissue Ag is labeled with fluorochrome
Ag
FluorochromeLabeled Ab
Tissue Section
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Immunofluorescence
• Indirect– Ab to tissue Ag is
unlabeled– Fluorochrome-labeled
anti-Ig is used to detect binding of the first Ab.
Ag
FluorochromeLabeled Anti-Ig
Tissue Section
UnlabeledAb
• Qualitative to Semi-Quantitative
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ELISA- enzyme-linked immunosorbent assay
Based on RIA
Nearly as sensitiveCheaper and safer
Many detection systems have been developed
Many variations of the assay have been developed
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All ELISAs use an antibody conjugated with anenzyme that turns a colorless substrateinto a colored product
Direct- detects antigens using a single labeledantibody against that antigen
Relatively few applications and permutations
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ELI SA Enzyme-Linked Immunosorbent Assay (ELISA)
© 1998 Gold Standard Multimedia Inc.
1. Antigen HIV Protein2. Test antibody Human serum3. Developing Ab Enzyme-Goat anti-Human IgG4. Substrate Colorless > Blue
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Enzyme-Linked Immunosorbent Assay (ELISA)
HIV Ag HumanSerum
AP-Goat Anti-Human IgG
Colorless >Yellow
AP = alkaline phosphatase
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Western Blot for HIV Antibodies
+ - Patient sera
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Complement Fixation
– Ag mixed with test serum to be assayed for Ab– Standard amount of complement is added– Erythrocytes coated with Abs is added– Amount of erythrocyte lysis is determined
Ag
Patient’sserum
Ag No Ag
Ag
• Methodology
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Tests for Cell Associated Antigens
Lattice formation not required
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Immunofluorescence
• Direct– Ab to tissue Ag is labeled with fluorochrome
Ag
FluorochromeLabeled Ab
Tissue Section
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Immunofluorescence
• Indirect– Ab to tissue Ag is
unlabeled– Fluorochrome-labeled
anti-Ig is used to detect binding of the first Ab.
Ag
FluorochromeLabeled Anti-Ig
Tissue Section
UnlabeledAb
• Qualitative to Semi-Quantitative
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Radioimmuoassays (RIA)Enzyme-Linked Immunosorbent
Assays (ELISA)
Lattice formation not required
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Competitive RIA/ELISA for Ag
• Method– Determine amount
of Ab needed to bind to a known amount of labeled Ag
+
Prior to Test
Labeled Ag
+
Test
+Patient’ssample
LabeledAg
+
– Use predetermined amounts of labeled Ag and Ab and add a sample containing unlabeled Ag as a competitor
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Competitive RIA/ELISA for Ag • Method cont.
– Determine amount of labeled Ag bound to Ab NH4SO4
anti-Ig • Immobilize the Ab
• Quantitative– Most sensitive test
+ Test
+Patient’ssample
LabeledAg
+
– Concentration determined from a standard curve using known amounts of unlabeled Ag
SolidPhase
SolidPhase
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Solid Phase Non-Competitive RIA/ELISA
• Ag detection– Immobilize Ab– Incubate with sample– Add labeled antibody– Amount of labeled Ab
bound is proportional to the amount of Ag in the sample
• Quantitative
SolidPhase
Ag
Immobilized
Ag in Patient’s
sample
LabeledAb
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Tissue Immunofluorescence/Immunohistochemistry
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NEUTRALIZATION
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Immunofluorescence
• Flow Cytometry– Cells in suspension are labeld with fluorescent tag
• Direct or Indirect Fluorescence– Cells analyzed on a flow cytometer
FlowTip
Laser
FLDetector
LightScatter
Detector
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CD4
CD8
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Immunofluorescence
• Flow Cytometry cont.– Data displayed
Green Fluorescence Intensity
Nu
mb
er o
f C
ells
Unstained cells
FITC-labeled cells
One Parameter Histogram
Red Fluorescence Intensity
Gre
en F
luor
esce
nce
In
ten
sity
Two Parameter Histogram
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