Proposed reference material for human free immunoglobulin light chain measurement

Human free immunoglobulin light chain (FLC) kappa and lambda are useful clinical markers for light chain myeloma and AL amyloidosis. With the recent development of specific and reliable FLC immunoassays, the quantitative measurement of FLCs will be widely used in clinical practice. However, researchers have used various calibrators, mainly monoclonal FLCs; thus, no standardization has been performed among the assay methods. This prompted us to purify intact FLCs from the pooled urine specimens of healthy volunteers as the first reference materials for FLC assays. After precipitation with ammonium sulfate, FLCs were purified by the following steps of chromatography; cation exchange, gel filtration, and antibody-assisted immunoaffinity. SDS-PAGE and Western blotting analyses showed that the purity of FLC kappa and FLC lambda was more than 98%. These purified FLCs did not contain the other immunological types of light chains. These intact and purified FLCs are suitable as the first reference materials to standardize FLC assays.