Free immunoglobulin light chains in connective tissue diseases.

The basic immunoglobulin subunit consists of two heavy and two light chains held together by covalent disulphide bonds. In most cases of myeloma and Waldenstrom's disease there is an excess synthesis of light over heavy chains, resulting in Bence Jones proteinaemia and proteinuria. Furthermore, in some cases ("light chain disease"), there is absence of detectable heavy chain synthesis, and the only abnormal proteins detected are Bence Jones light chains (Williams, Brunning, and Wollheim, 1966). Free light chains, believed to be qualitatively similar to Bence Jones light chains, have been detected in very small amounts in normal serum and urine (BerggArd, 1961; Stevenson, 1960). Recently, Epstein and Tan (1966) have identified increased amounts of free light chains in the sera, urine, and synovial fluids of some patients with systemic lupus erythematosus and rheumatoid arthritis. We have studied the incidence of free light chains in a large group of patients with connective tissue and allied disorders and have quantitated the light chains in some of these cases using the radial immunodiffusion method. In addition, we have purified the free light chains from the urine of one of the patients with systemic lupus and have shown by starch gel electrophoresis that they are very heterogeneous.