The incidence, clonal origin and secretory nature of serum paraproteins in chronic lymphocytic leukaemia.

Immuno-isoelectric focusing (IIEF) showed a 61% incidence of serum paraproteinaemia in 56 patients with chronic lymphocytic leukaemia (CLL). A strong correlation between the serum paraprotein heavy chain isotypes and those of the cytoplasmic heavy chain immunoglobulins was observed with no discrepancy noted in light chain expression. Density gradient ultracentrifugation analysis of selected sera containing monoclonal IgM showed that the IgM paraproteins were mostly 19S, secretory IgM but one patient was found to have both 19S and 8S monoclonal IgM. When the cellular origin of the IgM and IgD paraproteins found in one patient was investigated, both paraproteins were found to share the same idiotype and originate from the neoplastic clone. These findings confirm the view that there is an incomplete maturation block in chronic lymphocytic leukaemia and that in vivo secretion of paraproteins by the neoplastic cells is a relatively common occurrence.