Biosynthesis and characterisation of IgMlambda in a case of chronic lymphocytic leukaemia with intracellular immunoglobulin inclusions.

Lymphocytes from a patient with chronic lymphocytic leukaemia were found to contain crystalline inclusions in the cytoplasm. These crystals were characterised as IgMlambda immunoglobulin. The cells did not have detectable surface immunoglobulin. No paraprotein was detected in the serum and no excess of immunoglobulin was detected in the urine. The cells incorporated radioactive leucine into mu and lambda chains during an 18-hour culture. Studies of labelled lysate immunoglobulin revealed a molar excess of heavy chain over light chain while in contrast free light chain was the only detectable secreted immunoglobulin product during the culture period. These findings are discussed in relation to immunoglobulin synthesis by normal and other neoplastic lymphocyte preparations.