Monoclonal Antibodies in Hapten Immunoassays

This review deals with the potency of monoclonal antibodies (MAbs) to haptens in immunoassays. Specificity and affinity of MAbs to haptens are the major determinants to be considered. Specificity of MAbs depends on the selection of the hapten coupling site to the carrier protein and the antigen used for the screening of MAbs. Nevertheless, cross-reactivity can occur with compounds related to the hapten. This poly specificity may be circumvented with the use of many MAbs, as has been demonstrated for MAbs to cyclosporine. Affinity of MAbs to haptens is often lower than that of corresponding polyclonal antibodies (PAbs), thereby limiting assay sensitivity. Low affinity is more frequently observed with low molecular weight (100–300) haptens than with larger haptens, such as digoxin or cyclosporine. Affinity enhancement by increasing resemblance to the immunogen can be effective in resolving the lack of sensitivity. With suitable selection strategies, MAbs exhibit real advantages over classical PAbs to haptens because large amounts of worldwide standardized reagents can be prepared.