The idiotypic specificities of lymphocytes in human monoclonal gammopathies: analysis with the fluorescence activated cell sorter.

Four monoclonal IgG kappa gammopathies were studied with anti-idiotypic sera and the percentage of lymphocytes bearing such idiotypes was evaluated with a fluorescence activated cell sorter (FACS). A large percentage (10-15%) of peripheral lymphocytes bearing receptors with the same idiotypic specificities as the M component was observed in multiple myeloma (MM) and in monoclonal gammopathy of undetermined significance (MGUS), suggesting a malignant origin for both these diseases. Capping-endocytosis and resynthesis experiments showed that these idiotypic receptors were not simply adsorbed on the cell membrane, but actually synthesized by the cells bearing them. Experiments performed after effective conventional chemotherapy showed a strong reduction of the idiotypic compartment in only one MM patient.