Comparison of Hevylite™ IgA and IgG assay with conventional techniques for the diagnosis and follow-up of plasma cell dyscrasia

Background: Heavy/light chain assay allows the characterization and quantification of immunoglobulin light chains bound to heavy chains for each Ig’k and Ig’ immunoglobulin class, discriminating between the involved/uninvolved isotypes in plasma cell dyscrasia. The Ig’k/Ig’ ratio (heavy/light chain ratio) enables to monitor the trend of monoclonal component during therapy and disease evolution. Objective: In this study, we evaluate the impact of the heavy/light chain assay in monitoring multiple myeloma patients in comparison with conventional techniques. Methods: Serum samples of 28 patients with IgG or IgA monoclonal component were collected for a mean of 109 days and analyzed. The heavy/light chain assay was compared with classical immunoglobulin quantification (Ig’Tot), serum immunofixation electrophoresis, serum protein electrophoresis, and serum-free light chains quantification. Serum samples from 30 healthy patients were used as control (polyclonal). Results: Heavy/light chain ratio and serum immunofixation electrophoresis were comparable in 86% of the cases, and free light chain ratio and heavy/light chain ratio in 71.8%. Heavy/light chain assay and Ig’Tot measurements showed a concentration-dependent agreement in monoclonal patients. The heavy/light chain assay was able to quantify the monoclonal component migrating in SPE b region: this occurred in 10% of our IgG and 50% of our IgA patients. Conclusions: The concordance scores indicate that heavy/light chain and Ig’Tot assays show differences at high monoclonal component values. The heavy/light chain ratio, serum immunofixation electrophoresis, and free light chain ratio showed partial concordance. Our study confirmed that, in the context of heavy/light chain assay, heavy/light chain Ig’k and Ig’ absolute values and heavy/light chain ratio are both important tools to monitor the presence of monoclonal component that are difficult to be identified in SPE

Biological role of immunoglobulin Free light chains interactomes

Background. Monoclonal Gammopathy of Undetermined Significance (MGUS) is a plasma cell disorder that could be diagnosed incidentally and behave like a benign, asymptomatic entity or progress (1% per year) to different haematologic malignancies such as multiple myeloma (MM). Monoclonal plasma cells often secrete high amounts of immunoglobulin free light chains (FLCs) that could induce tissue damage. Recently we showed (Di Noto et al., 2013) that FLCs are internalized in endothelial and myocardial cell lines and secreted in extracellular vesicles (EVs). Our data show that MM EVs internalization is FLCs and GAGs mediated and we could demonstrate that MM EVs induce NfkB nuclear translocation. Blocking FLCs with anti FLCs antibodies or masking the GAGs recognition with heparin altered the EVs intracellular uptake and NfkB nuclear translocation (Di Noto et al., 2014). EVs carry determinant information about the onset of MGUS-MM switching which can be exploited for early assessment of MM onset and progression. Objectives. We aim to identify binding partners that associate with the FLCs in the blood stream (FLCs interactome) and are involved in the EVs generation and cellular uptake. Methods. EVs, purified from serum of control, MGUS and MM patients, were analyzed by a blend of conventional analytical techniques, MALDI TOF analysis and surface plasmon resonance (SPR). Results and Conclusions. In a previous proteomic study immuno-purified FLCs isolated from patients with monoclonal gammopathies were characterised and some proteins such as clusterin and albumin associated with FLCs were identified. We then tracked the binding isotherms of EVs to a heparin-coated sensorchips. The results show a marked difference between the binding isotherms of EVs from healthy individuals and from MM and MGUS patients