[Study for the nature of interfering substances responsible for non-specific reactive phenomena occurred occasionally in EIA determination of CA125].

We studied the nature of IgM-like protein responsible for non-specific reactive phenomena occurred occasionally in EIA determination of CA125. We isolated highly purified IgM-like protein from two patients with non-specifically high CA125 serum values in affinity high performance liquid chromatography (HPLC) using anti-human IgM antibody-TSKgel Tresy15PW column. The isolated IgM-like protein possessed CA125 activity determined in EIA method. SDS-PAGE profiles of this isolated IgM-like protein were compatible with that of normal human IgM, and were distinct from those of CA125 antigen. Moreover, we ruled out the possibility that the Fc region of anti-CA125 monoclonal antibody might be responsible for the non-specific reactive phenomena. Thus, the data obtained from the present study indicate that the IgM-like protein is an anti-idiotypic antibody against the anti-CA125 monoclonal antibody (OC125).