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 IMMAGETM 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.

Free light chains in plasma of patients with light chain amyloidosis and non‐amyloid light chain deposition disease. High proportion and heterogeneity of disulfide‐linked monoclonal free light chains as pathogenic features of amyloid disease

“…Patients with a biopsy-proven diagnosis of AL (n = 13) and NALCDD (n = 5) were randomly chosen for this study (Table I). Plasma samples collected from these patients were analyzed by the FLC assay (FREELITE TM , The Binding Site Ltd., Birmingham, UK) (Bradwell et al, 2001) on a Dade Behring BNII automated nephelometer. Diagnoses were obtained from the Dysproteinemia database and the patient medical history by following a protocol approved by the Mayo Institutional Review Board.…”

Diagnostic and prognostic utility of the serum free light chain assay in patients with AL amyloidosis

“…The assay thus detects only free circulating light chain monomers and dimers with minimal cross-reactivity with whole immunoglobulin. 3 Advantages of this investigation include technical simplicity and very high sensitivity of up to 100 times greater than serum or urine electrophoresis (EPP) with a limit of detection below that of the normal serum light chain level. The sFLC assay provides a readily obtainable and quantitative result that rapidly reflects changes in production of light chains by the aberrant plasma cell population due to the short half-life of free light chains in serum (2-6 h compared with 20-25 days for intact immunglobulin G when renal function is normal).…”

Guidelines on the diagnosis and management of AL amyloidosis

“…Serum free light chain (FLC) estimation. A new immunoassay can detect and quantify FLCs in serum with remarkable specificity and sensitivity (Bradwell et al, 2001). The assay gives a positive result (raised level of either kappa or lambda together with an altered ratio of free kappa to free lambda light chain) in 98% of patients with systemic AL amyloidosis (Lachmann et al, 2003), including those in whom a monoclonal immunoglobulin cannot be demonstrated by conventional means.…”

“…The objective of chemotherapy in AL amyloidosis is to suppress production of amyloidogenic monoclonal immunoglobulin light chains as quickly and safely as possible, but the relative efficacies of different chemotherapy regimens have not been determined. Recent experience at the NAC suggests that treatment strategies in individual patients are presently best guided by their early effect on quantifiable measurements of circulating free immunoglobulin light chains (Bradwell et al, 2001;Lachmann et al, 2003). Although these patients were selected and had not been randomized to receive particular therapies, it is notable that neither the magnitude nor durability of the clonal disease responses differed significantly among patients who were treated with VAD, monthly intravenous IDM or stem cell transplantation.…”