Free light chains of immunoglobulins in serum from patients with leukaemias and multiple myeloma.

The serum concentration of free kappa and lambda light chains of immunoglobulins were measured in 114 patients with myelo- and lymphoproliferative disorders including multiple myeloma. Increased concentrations of a single light chain type, suggesting monoclonal origin, were found with high frequency in B-cell diseases only. Thus 6 out of 9 patients with chronic lymphatic leukaemia and 24 of 28 patients with multiple myeloma had increased concentrations of a single chain type. The highest values reported in chronic lymphatic leukaemia were approximately 10 and in multiple myeloma 1000 times normal mean. Cytostatic treatment of chronic lymphatic leukaemia was followed by a decrease in the light chain levels. The levels were, however, not correlated to the number of circulating lymphocytes, the lymphatic infiltration of tissue or clinical activity. Increased concentrations of both chain types, suggesting a polyclonal origin, were found in both of 2 patients with acute monocytic leukaemia, 6 of 7 with acute myelomonocytic leukaemia, 2 of 23 with acute myeloid leukaemia and 1 of 7 with acute lymphoblastic leukaemia. The highest levels of light chains in these groups were 5 times normal mean. All patients with myeloproliferative disorders revealed normal values of both light chain types.