Non-competitive, solid-phase enzyme immunoassays

A general approach for the detection of antigens is to create a so-called antibody sandwich (immobilized antibody, antigen, antibodies Fig. 2.2c). If the indirect method is used to detect the captured antigen, the second antibody should be from a different species, to prevent the reaction of the labeled anti-Ig with the first, immobi- 

A recently developed variant of this method is the class-capture technique useful in the diagnosis of infectious diseases. This method is based on the observation that after the first infection primarily IgM antibodies (Section 5.1.1) are produced which are gradually replaced by IgG antibodies in chronic or recurrent infections. Vari jus laborious methods have been developed to separate IgG from IjM and to establish the relative proportion of antibodies in the two classes. In the very simple but powerful class-capture method, the presence of IgM can be detected by immobilizing an anti-IgM antibody which will capture the IgM from the serum. If the IgM contains antibodies, they will, in turn, be able to capture the antigen, which can be revealed by the methods shown in Figs. 2.2c or 2.2d. The titres of IgM and IgG antibodies can be established in parallel experiments. 

Proximal linkage systems for enzyme immunoassays (adapted from Sevier et al., 1981)  

GOase/POase glucose/H-donor peroxide/oxidized H-donor 

Depending on the system, both activation or inhibition may occur. It will be seen later (Section 10.2.2) that the same antiserum may contain a fraction of antibodies which activates the enzyme and a fraction which inhibits the enzyme. 

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Direct non-competitive solid-phase enzyme immunoassays This approach is little used for quantitative investigations, but often in qualitative tests, e.g. for the detection of antigens on protein blots (Chapter 16) or in EIH (Chapter 17). For each epitope a corresponding labeled antibody is needed. The immobilized antigen (] = Ag) reacts directly with the conjugate (Ab E) ... 

Non-competitive solid-phase enzyme immunoassays based on the avidin-biotin system for the determination of antibody activity in sera ... 

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