Changes

**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 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

*** 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 total amount of labelled antigen added (known amount)= 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