Monoclonal serum protein with anti-microsome antibody activity in the patient with multiple myeloma and Hashimoto's thyroiditis

A 57-year-old female suffered from Hashimoto's thyroiditis since 1959. When she was hospitalized in Nov. 1979 for acute bronchitis, her home doctor pointed out her sera showed marked hypergammaglobulinemia. She was referred to our hospital for further examination. Her case was diagnosed as multiple myeloma according to the findings; increasement of IgG1, k monoclonal gammaglobulin, increasement of immature plasmacytes in bone marrow and multiple osteolytic lesions in the skull. Her sera also showed anti-microsome antibody activity at a dilution of 1: 25, 600.The monoclonal protein was purified from her sera to testify the presence of anti-microsome antibody activity. The results were as follows.1) Patient's purified IgG, F (ab')2 and light chain kappa F (ab')2 showed anti-microsome antibody activity at a dilution of 1: 102, 400, 1: 102, 400 and 1: 25, 600 respectively. However, light chain lambda F (ab')2 did not show this antibody activity.2) Anti-idiotypic antybody was prepared by immunizing rabbit with F (ab')2 fragment of patient's IgG followed by absorption with IgG of Cohn's fraction II. This anti-idiotypic antibody binded only F (ab')2 of patient's IgG but not IgG of Cohn's fraction II. This anti-idiotypic antibody inhibited the binding between the monoclonal protein and microsome antigen.These results suggested that patient's monoclonal protein was the antibody to microsome.This is the first case reported in the literature whose serum monoclonal protein has been proved to be anti-microsome antibody.