Highly Sensitive, Automated Immunoassay for Immunoglobulin Free Light Chains in Serum and Urine

Abstract

Background: Bence Jones proteins or monoclonal immunoglobulin κ and λ free light chains (FLCs) are important markers for identifying and monitoring many patients with B-cell tumors. Automated immunoassays that measure FLCs in urine and serum have considerable clinical potential. Methods: Sheep antibodies, specific for FLCs, were prepared by immunization with pure κ and λ molecules and then adsorbed extensively against whole immunoglobulins. The antibodies were conjugated onto latex particles and used to assay κ and λ FLCs on the Beckman IMMAGE^TM protein analyzer. Results: The unconjugated antibodies showed minimal cross-reactivity with intact immunoglobulins or other proteins. With latex-conjugated antibodies, κ and λ FLCs could be measured in normal sera and most normal urine samples. Patients with multiple myeloma had increased concentrations of the relevant serum FLC, whereas both FLCs were increased in the sera of patients with systemic lupus erythematosus. Conclusions: We developed sensitive, automated immunoassays for κ and λ FLC measurements in serum and urine that should facilitate the assessment of patients with light chain abnormalities.