2. INTRODUCTION
ELISA is a qualitative or quantitative immunological
procedures in which the Ag-Ab reaction is monitored by
enzyme measurements.
The term ELISA was first used by Engvall & Perlma in
1971.
The ELISA test was the first screening test commonly
employed for HIV. It has a high sensitivity.
3. Principle
Its principle is similar to RIA but depends on an enzyme
rather than a radioactive label.
An enzyme conjugated with an antibody reacts with a
colorless substrate to generate a colored reaction
product. Such a substrate is called a chromogenic
substrate.
A number of enzymes have been employed for ELISA
including alkaline phosphatase, horseradish peroxidase
and β-galactosidase.
8. General Procedure of ELISA
The wells are coated with antibodies.
Sample is added which may contain antigen.
Removal of unbound antigens by washing.
Addition of another antibody which is linked with enzyme.
Interaction of enzyme with particular substrate.
This interaction produces color through which we can observe
a particular antigen (disease).
The antigen-antibody interaction took place.
13. Advantages of ELISA
Equipment's are inexpensive and widely
available. ELISA can be used to detect variety of
infections.
Reagents are relatively cheap and have a long shelf life.
No radiation hazards occur during labelling or disposal of
waste.
ELISA is highly specific and
sensitive.
Easy to perform and quick procedures.
14. Disadvantages of ELISA
Measurement of enzyme can be more complex.
Kits are commercially available, but not cheap.
Very specific to a particular antigen. Won’t recognize any
other antigen.
False positives/negatives possible, especially with
mutated/ altered antigen.
Enzyme activity may be affected by plasma constituents.