Different efficacy of various blocking reagents to eliminate interferences by human antimouse antibodies with a two-site immunoassay.
OBJECTIVE
The efficacy of three reagents to eliminate interferences with the cancer antigen 125 (CA-125) assay Enzymun CA-125 II by human antimouse antibodies (HAMA) formed by patients after injection of the murine anti-CA-125 antibody OC125 is compared.


METHODS
Apparent CA-125 concentrations of 14 serum samples obtained from 6 patients after multiple injections of 1 mg radiolabeled OC125 F(ab')2 fragments were measured with the Enzymun CA-125 II before and after preincubation, either with nonspecific mouse IgG, with the polymerized mouse IgG MAK-33, or with the commercially available HAMA-blocking reagent IIR.


RESULTS
In all samples with HAMA concentrations ranging from 341 to 46900 microg/L, false-positive CA-125 values were measured with the Enzymun CA-125 II, which could be reduced by preincubation with the HAMA-blocking reagents. However, although after preincubation with 2 g/L IIR for all samples the CA-125 concentrations measured were reduced to values within the normal range, after preincubation with 0.7 g/L of polyclonal mouse IgG for five samples and after preincubation with 0.7 g/L of MAK-33 for all samples also the reduced values were considerably elevated. Larger amounts of mouse IgG or MAK-33 led only to a slight reduction of the remaining false-positive CA-125 values.


CONCLUSIONS
The present results demonstrate that the polymerized mouse IgG MAK-33 and also the normal murine IgG are not suitable for completely eliminating interferences by HAMAs formed after OC125 treatment. Only the HAMA-blocking reagent IIR seems to be an effective agent to eliminate these interferences. Thus, further studies of this material as a blocking reagent seem to be warranted.
Reinsberg
J
J
Zentrum für Frauenheilkunde und Geburtshilfe, Universität Bonn, Germany.
D000818:Animals; D019138:Antibodies, Blocking; D000910:Antibodies, Heterophile / Q000097:blood*; D001774:Blood Chemical Analysis / Q000379:methods*; D018394:CA-125 Antigen / Q000097:blood*; D005069:Evaluation Studies as Topic; D005189:False Positive Reactions; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007202:Indicators and Reagents; D051379:Mice
D019138:Antibodies, Blocking; D000910:Antibodies, Heterophile; D018394:CA-125 Antigen; D007202:Indicators and Reagents