Affinity bonus

The strategy of the immune system to produce polyclonal antibodies yields two important bonus effects, i.e. the affinity bonus (or avidity) and the specificity bonus , both of which are eliminated by cloning (Sections 8.4 to 8.6). The specificity of monoclonal antibodies may sometimes prove to be not as high as expected. Some may cross-react, and this cross-reactivity cannot, in contrast to polyclonal antisera, be removed with immunosorbents (Brodsky et al., 1979). A monoclonal antibody is unable to distinguish different antigens if they bear the same epitope. For example, Bundesen et al. (1980) encountered this problem with a peptide sequence common to several hormones. Kurstak et al. (1983) emphasized problems with monoclonal reagents in virus diagnosis. 

The use of lectins in EIA largely depends on the avidity bonus (Section 8.5), since their intrinsic affinities are often significantly lower than those of antibodies and insufficient for EIA. 

A general comparison of monoclonal antibodies and polyclonal antisera is given in Table 5.2. The lower avidity bonus (Section 8.5) of monoclonal antibodies and the small fraction of high-affinity... 

In general, IgM constitutes about 10% of the antibodies. Monomeric forms are occasionally found in low concentrations in serum. IgM is produced early in the immune response and reacts quite strongly with an antigen, despite its frequent low affinity, due to the avidity bonus (Section 8.5). The pentameric IgM is particularly sensitive to mild reduction by thiol reagents at neutral pH (splitting into monomers), thus loosing its high avidity. Such treatment can... 

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