Chemotherapy of a patient because of spuriously elevated alpha-fetoprotein levels. Identification of the responsible factor.

Because of spuriously elevated alpha-fetoprotein levels, a course of polychemotherapy was given to a patient. We purified and identified the serum factor responsible for falsely high AFP levels as an IgG directed against mouse IgG. On gel filtration it behaves differently from true AFP, exhibiting a molecular weight of around 150,000. Chromatography on 'Protein A-Sepharose' revealed properties indistinguishable from those of IgG. The patient had never been treated with mouse antibodies, neither for diagnostic nor therapeutic purposes and he had had no contact with animals professionally.