Immunoassays for IgG subclasses: quantitative and methodologic considerations

In summary I have tried to provide my own statement of the status quo in current efforts to develop quantitative and reliable immunoassays for IgG subclass proteins and antibodies. Some of the trends I have commented upon are summarized in Table III. First, monoclonal antibodies have clearly won the day for almost all IgG subclass work. Second, solid phase immunoassays are almost indispensable for most IgG subclass antibody assays in order to circumvent the problem of subclass antibody competitions for soluble antigen. Third, the "captured" antigen or antibody by insolubilized antisera has a number of demonstrated advantages over passive adsorption or covalent linkage, in terms of assay parallelism, sensitivity, and specificity. Fourth, subclass immune responses can only be compared directly if serum dilution curves are parallel. More attention is needed for further technical refinements to achieve this important goal. Finally, the value of absolute quantitation, that is specification of nominal value in terms of weight/volume units, is an important ultimate goal. Among the feasible approaches to this problem are solid phase elution techniques, myeloma protein based quantitation, and by comparison to a single allergen system where nominal values can be established by conventional techniques. We have come a long way since IgG subclasses were first recognized more than 25 years ago. We are not in a phase of rapid expansion of techniques which seek to quantify IgG subclass immune responses. Much work remains to be done, but the tools for ultimate success are, I believe, within our grasp.