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**Precipitate complexes using secondary isotype-specific antiimmunoglobulin
**Precipitate complexes using secondary isotype-specific antiimmunoglobulin
**If complex contains IgG, it can be removed by mixing with formalin-killed ''Staphylococcus aureus''- protein A of ''S. aureus'' has a high affinity for IgG
**If complex contains IgG, it can be removed by mixing with formalin-killed ''Staphylococcus aureus''- protein A of ''S. aureus'' has a high affinity for IgG
*** Removal of the complex by either of these methods leaves an amount of free labelled antigen in the supernate (liquid section from precipitation)- the radioactivity of this can be measured and the value taken away from the amount of labelled antigen= amount of bound labelled antigen
*** Removal of the complex by either of these methods leaves an amount of free labelled antigen in the supernatant (liquid section from precipitation)- the radioactivity of this can be measured and the value taken away from the amount of labelled antigen= amount of bound labelled antigen
**A number of solid-phase RIAs have been developed
**A number of solid-phase RIAs have been developed
***Sometimes the antibody can be absorbed onto the surface- the amount of radiolabelled antigen bound to the beads can be measured after washing
***Sometimes the antibody can be absorbed onto the surface- the amount of radiolabelled antigen bound to the beads can be measured after washing
***Antibody can be immobilised on PVC or polystyrene
***Antibody can be immobilised on PVC or polystyrene
==Applications==
==Applications==
*As the technique requires small amounts of sample it can be conducted on 96-well microtiter plates and large numbers of samples can be tested
*As the technique requires small amounts of sample it can be conducted on 96-well microtiter plates and large numbers of samples can be tested