TurbidimetricAssay of lgG With Use of Single MonoclonalAntibodies

We describea turbidimetric assay forquantifyingtotal immunoglobulinG (IgG) in serum with use of a singlemonoclonal antibody. The reaction,monitoredby a centrifugalanalyzer, is technicallysimple, rapid, and precise. Bufferof low ionic strengthand polyethyleneglycolare requiredfor formationof detectableantibody-antigencomplexes.We measured lgG concentrationsin 49 polyclonalsera (Group 1) and 84 sera containingmonoclonalIgG (Group 2) in assays in whichwe used either of two anti-lgG monoclonalantibodies(HG6 or HG8). Results compared well with those obtained with a nephelometricassay involvingpolyclonalantiserum,except for sera from four personsof Group 2 whose immunoglobulins were not detected by antibody HG6. HG6 bound lgG fromthese foursera ina solid-phasebindingassay. HG6 and HG8 recognize epitopes on the Fab and Fc regions of lgG, respectively,and they do not compete for binding to the whole molecule. However, use of the two monoclonalantibodiescombinedfailed to improvethe sensitivityor rangeof the assay. We conclude that light-scatteringassays of lgG can be validlyperformed with a singlemonoclonalantibody.