Serum-free light chain analysis by crossed immunoelectrophoresis: correlation with plasmapheresis in light chain...

The technique of crossed immunoelectrophoresis (X-IEP) has been used to quantify free monoclonal light chains (LC) directly in the serum of patients with light chain disease, without preliminary gel or membrane filtration of serum to separate whole immunoglobulin. LC concentration is proportional to the area under an immunoprecipitin peak formed by LC in the patient's serum and an anti-LC antibody of appropriate specificity. Light chains of beta electrophoretic mobility can be processed in the standard X-IEP technique at pH 8.6. Light chains of gamma mobility must be processed in a modified technique using a pH of 5.0 and a carbamylated antiserum in the second dimension gel. Dose response curves obtained from the method in serial dilution experiments with sera from 18 patients gave correlation coefficients greater than or equal to 0.99. Replicate measurements of absolute LC concentration on the same specimens were within +/- 10%. The method can also detect polymerized light chains. Serum light chain levels were measured during the course of plasmapheresis therapy in three patients with light chain disease and renal failure. Light chain levels were shown to fall after plasmapheresis and to rise rather rapidly in the interval between treatments.