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IgG kappa and IgG lambda concentrations were quantified in 96 paired CSF and sera using Hevylite™ antibodies in an in-house developed sandwich ELISA method. In 56 of these samples, the results were compared with a qualitative isoelectric focusing/affinity-mediated immunoblotting assay for oligoclonal IgG kappa and IgG lambda. Normal IgG kappa/lambda ratio in the CSF was the same as in serum. In 19/33 patients with intrathecal oligoclonal IgG synthesis, skewed IgG kappa/lambda ratio was observed (increased in 16 and decreased in 3 cases). The analysis of light chain composition of intrathecally synthesised immunoglobulins could contribute to our understanding of intrathecal humoral immune response, although its diagnostic utility is limited.

Objectives: We aimed to compare various methods for free light chain (fLC) quantitation in cerebrospinal fluid (CSF) and serum and to determine whether quantitative CSF measurements could reliably predict intrathecal fLC synthesis. In addition, we wished to determine the relationship between free kappa and free lambda light chain concentrations in CSF and serum in various disease groups., Methods: We analysed 166 paired CSF and serum samples by at least one of the following methods: turbidimetry (Freelite™, SPAPLUS), nephelometry (N Latex FLC™, BN ProSpec), and two different (commercially available and in-house developed) sandwich ELISAs. The results were compared with oligoclonal fLC detected by affinity-mediated immunoblotting after isoelectric focusing., Results: Although the correlations between quantitative methods were good, both proportional and systematic differences were discerned. However, no major differences were observed in the prediction of positive oligoclonal fLC test. Surprisingly, CSF free kappa/free lambda light chain ratios were lower than those in serum in about 75% of samples with negative oligoclonal fLC test. In about a half of patients with multiple sclerosis and clinically isolated syndrome, profoundly increased free kappa/free lambda light chain ratios were found in the CSF., Conclusions: Our results show that using appropriate method-specific cut-offs, different methods of CSF fLC quantitation can be used for the prediction of intrathecal fLC synthesis. The reason for unexpectedly low free kappa/free lambda light chain ratios in normal CSFs remains to be elucidated. Whereas CSF free kappa light chain concentration is increased in most patients with multiple sclerosis and clinically isolated syndrome, CSF free lambda light chain values show large interindividual variability in these patients and should be investigated further for possible immunopathological and prognostic significance., Competing Interests: Competing Interests: I have read the journal´s policy and the authors of this manuscript have the following competing interests: The Binding Site Company provided Hevylite antibodies and Hevylite diagnostic kits free of charge to the University Hospital Ostrava for research use. These reagents, however, were not used in this study and the provision of these antibodies has no impact on the study design, data collection and analysis, decision to publish, or preparation of the manuscript. All reagents used in this study were purchased under standard pricing conditions. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Background: The results of free light chains quantitation in the cerebrospinal fluid were recently compared with the presence of cerebrospinal fluid-restricted oligoclonal IgG, but not oligoclonal free kappa light chains and oligoclonal free lambda light chains. We therefore aimed to compare the performance of the quantitative tests with the qualitative one for the same molecule., Methods: Seventy-five paired cerebrospinal fluid and serum samples were analysed for oligoclonal IgG, oligoclonal free kappa light chains and oligoclonal free lambda light chains. Cerebrospinal fluid and serum free kappa and lambda light chains were quantified using Freelite™ kits on SPA Plus analyzer. ROC curves were analysed for the prediction of intrathecal synthesis and compared for cerebrospinal fluid concentration, cerebrospinal fluid/serum quotient (QfLC) and index (QfLC/QAlbumin). The presence of cerebrospinal fluid-restricted oligoclonal free kappa light chains and oligoclonal free lambda light chains bands was used as reference., Results: No statistically significant differences were observed among cerebrospinal fluid concentration, QfLC and index for the prediction of free light chain intrathecal synthesis. Each parameter was able to predict the occurrence of cerebrospinal fluid-restricted oligoclonal free light chain bands (AUCs 0.932-0.999). However, we noted elevated cerebrospinal fluid free light chain concentrations in the absence of cerebrospinal fluid-restricted oligoclonal free light chain bands in two patients with very high serum free light chain values., Conclusions: Quantitation of cerebrospinal fluid free light chains reliably predicts their intrathecal synthesis. Yet, cerebrospinal fluid/serum quotient may still be preferred to correct for high serum free light chain concentrations. An appropriate formula should be sought to correct for blood-cerebrospinal fluid barrier status., (© The Author(s) 2015.)