title: Polyclonal versus monoclonal immunoglobulin-free light chains quantification.
abstract: BACKGROUND
  The clinical usefulness of the serum-free light chain assays has expanded since their first description, and further applications other than plasma cell dyscrasia are emerging. Currently, we have the ability to perform the measurements with two certified methods: the Freelite™ assay (The Binding Site Ltd, Birmingham, UK) and the new N Latex free-light chain assay (Siemens, Germany). In the present study, we investigated the impact of free light chain concentrations and structures on their quantification, performed with both tests.
  
  
  METHODS
  A total of 524 serum samples from 497 patients from our routine laboratory were analysed with the Freelite™ and the N Latex free light chain assay. The results were compared in two subgroups: with or without monoclonal component. Twenty-four samples were subsequently investigated for the presence of dimeric and monomeric free light chain with sodium dodecyl sulphate polyacrylamide gel electrophoresis and densitometric quantification.
  
  
  RESULTS
  Methods comparison showed that the Pearson rank correlation coefficients were 0.90 for polyclonal k and 0.91 for polyclonal λ free light chain. Conversely for monoclonal immunoglobulins, the Pearson rank correlation coefficient was lower with 0.82 for kM >500 mg/L and 0.56 for λM >500 mg/L. Furthermore, densitometric quantification of the involved monoclonal free light chains showed that both assays do not reflect the Coomassie-stained protein mass.
  
  
  CONCLUSIONS
  Samples containing high amounts of a single pathologic free light chain may not be considered like a sample containing a sum of different polyclonal free light chains. Indeed, free light chain dimerization leads to different scatter efficiency of macromolecular complexes.
authors.affiliation: Department of Molecular and Translational Medicine, Faculty of Medicine, University of Brescia, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Di Noto
authors.affiliation: Department of Molecular and Translational Medicine, Faculty of Medicine, University of Brescia, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Cimpoies
authors.affiliation: Department of Molecular and Translational Medicine, Faculty of Medicine, University of Brescia, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Dossi
authors.affiliation: Department of Molecular and Translational Medicine, Faculty of Medicine, University of Brescia, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Paolini
authors.affiliation: Department of Molecular and Translational Medicine, Faculty of Medicine, University of Brescia, Italy.
authors.forename: Annalisa
authors.initials: A
authors.lastname: Radeghieri
authors.affiliation: Department of Molecular and Translational Medicine, Faculty of Medicine, University of Brescia, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Caimi
authors.affiliation: Department of Molecular and Translational Medicine, Faculty of Medicine, University of Brescia, Italy doris.ricotta@unibs.it.
authors.forename: Doris
authors.initials: D
authors.lastname: Ricotta
mesh_terms: D000911:Antibodies, Monoclonal / Q000097:blood*; D006801:Humans; D007118:Immunoassay / Q000592:standards*; D007147:Immunoglobulin Light Chains / Q000097:blood*
chemical_list: D000911:Antibodies, Monoclonal; D007147:Immunoglobulin Light Chains
keywords: Monoclonal component; dimers; monomers; plasma cell dyscrasia; serum-free light chain