Immunofixation Electrophoresis (IFE)
Type I Immunoassay, single site, Heterogenous, Noncompetitive
Methodology: Identification procedure that combines electrophoresis and an Ab-Ag reaction.
Enzyme-Linked Immunosorbant Assay (ELISA)
Type II, Two-site, Noncompetitive
Methodology: An enzyme/label is conjugated with an Ab that reacts with a colorless substrate to generate a colored reaction product. The "Sandwich" Assay.
Heterogenous, non-isotropic assay that utilizes an enzyme-labeled ligand and an Ab immobilized onto a solid support.
Typical Enzyme Labels:
Horseradish Peroxidase (used to enhance the reaction)
Methodology: Technique in which proteins are separated by gel electrophoresis, transferred to a membrane, and identified through the use of labeled Abs specific for the protein of interest.
Current standard test for the confirmation of human immunodeficiency virus HIV
Enzyme-Multiplied Immunoassay Technique EMIT
Type III Immunoassay
Methodology: Limited Ab is mixed with patient Ag and enzyme labeled Ag. The Ags complete for Ab binding sites and Ab-Ag bindig inactivates enzyme label. Substrate is then added to the assay and only free, unbound Ag* -enzyme can react with substrate. Enzyme product is quantified.
Fluorescence Polarization Immunoassay FPIA
Generally Type III Immunoassay
Methodology: Based on the amount of polarized fluorescent light detected when the fluorescent label is excited with polarized light. Fluorescent label can be attached to Ag or Ab.
Interpretation: Amount of polarized fluorescent light resulting from a competitive binding reaction is inversely proportional to the concentration of unlabeled ligand.
Methodology: Technique based on quantitation of an analyte based on emission of light resulting from a chemical reaction. Label is not inactivated by binding to Ab.
Often measured with a luminometer. The amount of light emitted is inversely proportional to the amount of analyte present in sample.
Indirect Immunofluorescence Analysis
Methodology: Based on the fact that Abs not only react with specific Ags, but can themselves be Ags. Typically second Abs recognizes an entire class of Igs. i.e. anti-immunoglobulins
Used extensively in the detection of auto-antibodies, antibodies on or in tissue and to identify cellular Ags.
Often used in the cytotechnology and histotechnology
Methodology: A measurement of light transitted through a suspension of particles which can be measured by a spectrophotometer.
Absorbance measurements are made at 180 degrees to the incoming light source beam, unscattered light.
Methodology: A direct measurement of light scattered by particles suspended in solution. Detects scattered light at a 90 degree angle from the incoming light source.
Common Analyte: Albumin
Can detect analytes at 1-10 mg/dL
What is an immunoassay?
Procedure that relies on the use of antibodies as "specific" binding Reagents.
Refers to the thermodynamic quantity defining the energy of interaction of a single antibody-binding site and it's corresponding epitope on the antigen "Random Attraction"
Refers to the overall strength of the binding of antibody and antigen includes the sum of the binding affinities of all the individual combining sites on the antibody
How many chains does an antibody have?
4. Two identical heavy chains and two identical light chains.