CHAPTER 6 – IMMUNOASSAYS Flashcards
Designed for antigens and antibodies that may be small in size or present in very low concentrations.
INDICATOR LABELLED IMMUNOASSAYS
The presence of such antigens or antibodies is determined indirectly by using a [?] to detect whether or not specific binding has taken place.
labeled reactant
Labels:
Fluorescent
Radionuclide (Radioisotopes)
Enzymes
Free radical
Ferritin
Utilzes fluor or fluorochrome
FLUORESCENCE IMMUNOASSAYS
Have the ability to absorb light at shorter wavelenghts (infrared light) and emit lgiht waves at a visible spectrum/longer wavelengths (UV light)
FLUORESCENCE IMMUNOASSAYS
Covalently linked to Ig or to antiglobin to detect the presence of Ag or Ab.
FLUORESCENCE IMMUNOASSAYS
Examples:
Fluoroscein Isothiocyanate (FITC) with fluorescence of color
Tetramethyl rhodamine(TRITC) with fluorescence of color
green
red
(direct = Ag+Ab)
Ig
(indirect = Ag+Ab+carrier)
antiglobin
RADIOIMMUNOASSAYS (RIA) General Uses
- Monitoring levels of hormone
- Detection of vitamins
- Detection of viral antigens
- Detection of therapeutic and abused drugs such as digoxin, opiates, barbiturates and amphetamine.
RIA DISADVANTAGE
- Exposure to radiation
- Use of sophisticated machine
- Disposal of radioisotope waste (burial underground)
RIA ADVANTAGE
- Extremely sensitive
- Relative ease of development
- Relatively low cost (FALSE: it is expensive)
most sensitive of all immunoassays
RIA
oldest immunoassay (discovered by Rosalyn Yalow)
RIA
Radioactive Labels
– more automated tests
Immunoassays
Emit gamma radiation
Emit beta radiation
Beta Emitters
Iodine25I and Iodine 311
Gamma Emitters
3H (Tritium)
Beta Emitters
Uses solid/crystal scintillation counter for measurement
Gamma Emitters
Measured with liquid scintillation counter
Beta Emitters
Most commonly used
Gamma Emitters
• Naturally occurring molecules
ENZYME
Catalyze certain biochemical reactions; React with suitable substrates to produce products
ENZYME
ENZYME EXAMPLES
Chromogenic (change in color), fluorogenic or luminescent
More on measurement of absorbance of the color emitted
Chromogenic
• Cheap, readily available and has long shelf life
ENZYME LABELS
• Can be used quantitatively (can detect the actual concentration of the analyte) and qualitatively (detect the presence or absence of antibody)
ENZYME LABELS
TYPICAL ENZYMES USED
• Horseradish peroxidase
• Glusoce-6-Phosphate-Dehydrogenase
• Alkaline phosphatase
• Beta-D-Galactosidase
- Has the highest turnover rate
Horseradish peroxidase
Alkaline phosphatase
Easy to detect
Horseradish peroxidase
Often used in EIA together w/ ALP
Horseradish peroxidase
Horseradish peroxidase AKA
Malunggay
Enzyme Assays
Requires steps to physically separate free from bound analyte (washing required)
HETEROGENOUS ENZYME IMMUNOASSAY
No separation step is necessary (no washing required)
HOMOGENOUS ENZYME IMMUNOASSAY
Enzyme activity diminishes when binding of an antibody and antigen occurs
HOMOGENOUS ENZYME IMMUNOASSAY
TYPES OF FIA
TYPES OF RIA
TYPES OF EIA
Procedure:
1. Ag from patient sample fixed to a microscopic slide
2. Fluorescent labelled Ab added
3. Ab binds to Ag and becomes fixed to slide
4. Washing to remove unattached Ab
5. Positive test: Fluorescence
- Direct Immunofluorescent Assays
Examples: Fluorescent Ab Dark Field Technique for Treponema pallidum
- Direct Immunofluorescent Assays
Antihuman globulin is combined with patient cells that have become coated with antibody in vivo.
- Direct Immunofluorescent Assays