Same Idiotypc of B‐Lymphocyte Membrane IgD and IgM. Formal Evidence for Monoclonality of Chronic Lymphocytic Leukemia Cells

Idiotypic antisera were raised in rabbits against serum M‐cnmponents in two patients with chronic lymphocytic leukemia (CLL) In one of the patients the leukemic cells had membrane‐bound IgG. in the other IgM and IgD. The M‐components were IgG and IgM. respectively. By immunofluorescence technique the CLL cells were shown to be positive when stained with idiotypic antiserum prepared against the corresponding M component, whereas normal lymphocytes, as well as cells from other CLL patients, were negative. These findings represent strong evidence for the monoclonality of the malignant B cells in CLL The fact that the CLL cells had membrane‐bound Ig with the same idiotypic determinants as the corresponding serum M‐component indicated that the latter had been synthesized and secreted by the malignant clone of B cells. In further experiments redistribution of membrane‐bound Ig on CLL cells bearing both IgM and IgD was induced with idiotypic antiserum This indicated that IgM and IgD on the same cells share idiotypic specificity and therefore have the same variable region and. presumably, the same antibody specificity