Technique	ELISA ,(/,)/,(
Principle	Immunoglobulins and some antigens can be coupled to enzymes so that the antigen/antibody reactions can be visualized by colourmetric or histochemical examination. Histochemical staining with enzyme conjugated antibodies enables the resulting tissue to be examined with routine light microscopes. Changing the enzyme/ substrate system allows the tissue to be examined by electron- microscopy. EIA is also known as enzyme linked immunosorbant assay (ELISA) because either the antigen or antibody can be fixed to a solid- phase surface. The enzyme is co-valently bound to the antibody. The reaction between the antigen and antibody stays bound to the surface and is made visible by the enzyme/substrate reaction. EIA is an extremely sensitive assay technique because of the amplification of the ag/ab reaction by the enzyme. A small number of enzyme molecules bound can convert a large number of substrate molecules to a measurable level. ELISA can be used to detect bacterial antigens in body fluids, but has not been highly utilized for this type of assay as latex agglutination is more rapid and as sensitive. ELISA is widely used for the detection and quantitation of antibodies to bacterial antigens and has largely replaced complement fixations procedures. Cautions: All unreacted sites on the solid-phase medium must be blocked or non-specific reactions will occur. Washing between reagent additions is critical. The reactivity of the reagents must be assured. EIA is affected by the problems in immunoassays and also by enzyme kinetics, but careful design and monitoring of the test system will ensure accurate results.
Cautions
Method
Results
Positive control
Negative control
Reagents
Reference