Polymeric Forms of Free Normal κ and λ Chains of Human Immunoglobulin

Clinical performance comparison of two medium cut-off dialyzers

INTRODUCTION

Medium-cut-off (MCO) dialyzers may beneficially impact outcomes in patients on hemodialysis.

METHODS

In a randomized, controlled trial in maintenance hemodialysis patients, the new Nipro ELISIO-17HX MCO dialyzer was compared to the Baxter Theranova 400 filter regarding middle molecule removal. Furthermore, the suitability of two assays for free lambda-light chain (λFLC) detection (Freelite vs. N-Latex) was verified.

RESULTS

ELISIO-HX achieved slightly lower reduction ratios for β₂ -microglobulin (71.8 ± 6.0 vs. 75.3 ± 5.8%; p = 0.001), myoglobin (54.7 ± 8.6 vs. 64.9 ± 8.7%; p < 0.001), and kappa-FLC (62.1 ± 8.8 vs. 56.3 ± 7.7%; p = 0.021). λFLC reduction ratios were more conclusive with the Freelite assay and not different between ELISIO-HX and Theranova (28.4 ± 3.9 vs. 38.7 ± 13.4%; p = 0.069). The albumin loss of Theranova was considerably higher (2.14 ± 0.45 vs. 0.77 ± 0.25 g; p = 0.001) and the Global Removal Score_{Loss alb} largely inferior (30.6 ± 7.4 vs. 82.4 ± 29.2%/g; p = 0.006) to ELISIO-HX.

CONCLUSIONS

The new ELISIO-HX expands the choice of dialyzers for MCO hemodialysis.

High-cutoff hemodialysis in multiple myeloma patients with acute kidney injury

Multiple myeloma (MM), an incurable hematological malignancy with clonal proliferation of plasma cells, is mainly characterized by excessive production of monoclonal immunoglobulins and free light chains (FLCs). Kidney injury is one of the main clinical manifestations and is also a significant predictor of the prognosis of symptomatic MM patients, especially those who require dialysis-supported treatment. Overproduction of FLCs is the trigger for kidney injury, as they can induce the transcription of inflammatory and profibrotic cytokines in the proximal tubule and bind to Tamm-Horsfall protein in the distal tubules to form casts that obstruct the tubules, leading to kidney injury and even renal fibrosis. In addition to traditional antimyeloma treatment, high-cutoff hemodialysis (HCO-HD), which can effectively remove FLCs in vitro, has attracted much attention in recent years. Due to its greater membrane pore size, it has significant advantages in removing larger molecules and can be applied in rhabdomyolysis, sepsis, and even myeloma cast nephropathy. However, mounting questions have recently been raised regarding whether HCO-HD can truly provide clinical benefits in MM patients with acute kidney injury (AKI). Therefore, in this study, we discussed the pathological causes of AKI secondary to MM and summarized the current situation of HCO-HD in MM patients compared with other available extracorporeal techniques. In addition, pivotal clinical trials that reflect the ability of the clearance of FLCs and the side effects of HCO-HD are highlighted, and the relevant protocol of HCO-HD is also provided to assist clinicians in decision-making.

Mono/polyclonal free light chains as challenging biomarkers for immunological abnormalities

Free light chain (FLC) kappa (k) and lambda (λ) consist of low molecular weight proteins produced in excess during immunoglobulin synthesis and secreted into the circulation. In patients with normal renal function, over 99% of FLCs are filtered and reabsorbed. Thus, the presence of FLCs in the serum is directly related to plasma cell activity and the balance between production and renal clearance. FLCs are bioactive molecules that may exist as monoclonal (m) and polyclonal (p) FLCs. These have been detected in several body fluids and may be key indicators of ongoing damage and/or illness. International guidelines now recommend mFLC for screening, diagnosis and monitoring multiple myeloma and other plasma cell dyscrasias. In current clinical practice, FLCs in urine indicate cast nephropathy and other renal injury, whereas their presence in cerebrospinal fluid is important for identifying central nervous system inflammatory diseases such as multiple sclerosis. Increased pFLCs have also been detected in various conditions characterized by B cell activation, i.e., chronic inflammation, autoimmune disease and HCV infection. Monitoring the coronavirus (COVID-19) pandemic by analysis of salivary FLCs presents a significant opportunity in clinical immunology worthy of scientific pursuit.

The Proximal Tubule Toxicity of Immunoglobulin Light Chains

Plasma and B cells dyscrasias that overproduce monoclonal immunoglobulin free light chains (FLCs) affect the kidney frequently in various ways. The hematologic dyscrasia responsible for the production of FLCs may or may not meet the criteria for cancer, such as multiple myeloma (MM) or lymphoma, or may remain subclinical. If there is overt malignancy, the accompanying kidney disorder is called myeloma- or lymphoma-associated. If the dyscrasia is subclinical, the associated kidney disorders are grouped as monoclonal gammopathy of renal significance. Glomeruli and tubules may both be involved. The proximal tubule disorders comprise a spectrum of interesting syndromes, which range in severity. This review focuses on the recent insights gained into the patterns and the mechanisms of proximal tubule toxicity of FLCs, including subtle transport disorders, such as proximal tubule acidosis, partial or complete Fanconi syndrome, or severe acute or chronic renal failure. Histologically, there may be crystal deposition in the proximal tubule cells, acute tubule injury, interstitial inflammation, fibrosis, and tubule atrophy. Specific structural alterations in the V domain of FLCs caused by somatic hypermutations are responsible for crystal formation as well as partial or complete Fanconi syndrome. Besides crystal formation, tubulointerstitial inflammation and proximal tubulopathy can be mediated by direct activation of inflammatory pathways through cytokines and Toll-like receptors due to cell stress responses induced by excessive FLC endocytosis into the proximal tubule cells. Therapy directed against the clonal source of the toxic light chain can prevent progression to more severe lesions and may help preserve kidney function.

A practical approach to the pathology of renal intratubular casts

The identification and proper characterization of pathologic renal intratubular casts can be an arduous task, especially since they often admixed with non-pathologic casts, obfuscating debris and inflammation. The list of pathologic intratubular casts is long, and they can be easily missed or misdiagnosed without a thorough understanding of their pathophysiology and morphologic variety. Correct characterization of tubular casts is important since each cast type has a unique pathogenic mechanism, with specific treatment and prognostic implications. This review discusses the clinicopathologic characteristics of the six most common pathologic casts: light chain, hemoglobin, myoglobin, red cell, neutrophilic and bile casts. We also discuss hyaline and uromodulin casts, the commonly encountered "benign" cast types that share certain histologic features with pathologic casts. We limit the discussion to proteinaceous and cellular intratubular casts, with crystalline casts discussed in a separate review within the same journal issue. While not exhaustive, this review covers pathogenesis, clinical and prognostic significance, and a practical discussion of the histomorphologic spectrum of each cast type, along with commonly encountered pitfalls.

κ and λ urine free light chains: a new method for quantification

BACKGROUND

Immunofixation electrophoresis of urinary proteins, coupled with densitometric analysis, is the gold standard method for determining urinary monoclonal free light chains (FLCs), i.e. Bence Jones protein. Recently, immunochemical methods have been developed for Bence Jones protein quantification, but no such method has been widely adopted. This study evaluated a new antibody-based immunoturbidimetry method for urinary FLC quantification, using immunofixation electrophoresis as reference.

METHODS

κ and λ FLCs were measured in urine specimens from 95 (training cohort) and 103 (testing cohort) patients by both immunofixation electrophoresis and immunoturbidimetry.

RESULTS

There was almost perfect concordance in the training cohort between the new immunoturbidimetry assay and immunofixation electrophoresis and substantial agreement, with Cohen kappa of 0.85 and 0.75, for κ and λ FLC determination, respectively. Results were confirmed in the testing cohort, where Cohen kappa was 0.86 for κ and 0.94 for λ FLCs. The κ FLC assay had 88% sensitivity and 98%-100% specificity; the λ FLC assay had 94% and 96% sensitivity and 91% and 99% specificity in the training and testing cohorts, respectively.

CONCLUSIONS

The new immunochemical method has a satisfactory performance and almost perfect agreement with immunofixation electrophoresis and gives the advantage of FLC quantification.

Inter-assay variability in automated serum free light chain assays and their use in the clinical laboratory

Serum κ and λ free light chain levels are markers of plasma cell proliferation, and their measurements have been included in recent guidelines by the International Myeloma Working Group for the management of patients with plasma cellular dyscrasias. Five in vitro diagnostic methods for the immunochemical quantification of serum free light chains (FLC) are available, three based on polyclonal antibodies (Freelite^®, The Binding Site; FLC ELISA κ and λ, Sebia; human κ and λ FLC, Diazyme Laboratories) and two on monoclonal antibodies (N Latex FLC, Siemens Healthineers; Seralite^®, Sebia). Several studies have shown that these methods cannot be used interchangeably for the follow-up of patients because measured κ and λ FLC concentrations may differ significantly, especially at high levels. Because no international reference material for the measurement of FLC is available, it is not possible to establish which method is the most accurate. For this reason, knowledge about the analytical and diagnostic performances of the assays used is important. The aim of this review is to describe the main analytical features of the κ and λ FLC assays and how they may influence the clinical use of these parameters.

Incomplete Refolding of Antibody Light Chains to Non-Native, Protease-Sensitive Conformations Leads to Aggregation: A Mechanism of Amyloidogenesis in Patients?

Genetic, biochemical, and pharmacologic evidence supports the hypothesis that conformationally altered or misfolded protein states enable aggregation and cytotoxicity in the systemic amyloid diseases. Reversible structural fluctuations of natively folded proteins are involved in the aggregation of many degenerative disease associated proteins. Herein, we use antibody light chains (LCs) that form amyloid fibrils in AL amyloidosis to consider an alternative hypothesis of amyloidogenesis: that transient unfolding and incomplete extracellular refolding of secreted proteins can lead to metastable, alternatively folded states that are more susceptible to aggregation or to endoproteolysis that can release aggregation-prone fragments. Refolding of full-length λ6a LC dimers comprising an interchain disulfide bond from heat- or chaotrope-denatured ensembles in buffers yields the native dimeric state as well as alternatively folded dimers and aggregates. LC variants lacking an interchain disulfide bond appear to refold fully reversibly to the native state. The conformation of a backbone peptidyl-proline amide in the LC constant domain, which is cis in the native state, may determine whether the LC refolds back to the native state. A proline to alanine (P147A) LC variant, which cannot form the native cis-amide conformation, forms amyloid fibrils from the alternatively folded ensemble, whereas all the full-length λ6a LCs we have studied to date do not form amyloid under analogous conditions. P147A LC variants are susceptible to endoproteolysis by thrombin, enabling amyloidogenesis of the fragments released. Thus, non-native LC structural ensembles containing a tyrosine 146-proline 147 trans-amide bond can initiate and propagate amyloid formation, either directly or after aberrant endoproteolysis.

Free light chains: Eclectic multipurpose biomarker

The production of antibodies is accompanied by a slight excess of synthesis of κ and λ immunoglobulin light chains; small amounts of them are released in the peripheral blood and can also be found in various body fluids, such as synovial fluid, cerebrospinal fluid, urine and saliva. They are rapidly filtered by the glomerulus and >99% are reabsorbed from the cells of the proximal convoluted tubule, making them present in the urine in only trace amounts. The production of an excess of protein without a reason or a specific function in a biological system is rare. Free light chains, considered for years a waste product of Ig synthesis, are currently known to be very active molecules, able to bind antigens as well as whole immunoglobulin and helping to develop specific antibody affinity. The ability of free light chains to activate mast cells and then become an active part of the pathogenic mechanisms of chronic inflammatory diseases has increased interest in their clinical use, both as an attractive therapeutic target or as a biochemical marker of disease evolution or remission. This is an overview of relevant scientific interest that immunoglobulin light chains κ and λ have attracted over the years, a report on the progress in knowledge about their structure and function, with a special focus on their biological meaning and potential clinical utility in different diseases.

Measurement of free light chains with assays based on monoclonal antibodies

Recently, serum free light chain (FLC) assays incorporating anti-kappa (κ) and anti-lambda (λ) FLC monoclonal antibodies have become available: N Latex FLC assay (Siemens) and Seralite

MCO Membranes: Enhanced Selectivity in High-Flux Class

Novel MCO high-flux membranes for hemodialysis have been developed with optimized permeability, allowing for filtration close to that of the natural kidney. A comprehensive in vitro characterization of the membrane properties by dextran filtration is presented. The sieving profile of pristine membranes, as well as that of membranes exposed to blood for 40 minutes, are described. The effective pore size (Stokes-Einstein radius) was estimated from filtration experiments before and after blood exposure, and results were compared to hydrodynamic radii of middle and large uremic toxins and essential proteins. The results indicate that the tailored pore sizes of the MCO membranes promote removal of large toxins while ensuring the retention of albumin.

Relationship between circulating syndecan-1 levels (CD138s) and serum free light chains in monoclonal gammopathies

Background

Monoclonal gammopathies encompass a wide range of diseases characterized by the monoclonal expansion of a B-cell clone. Despite emerging therapeutic strategies, chances of survival of patients who are affected are still scarce, which implies that new tools are necessary not only for the diagnosis but also for the follow-up of patients affected by such diseases. In this context, the use of free light chains (FLCs) has been incorporated into many guidelines.

Likewise, tumor microenvironment is consistently gaining importance as role player in tumor pathogenesis. Specifically, Syndecan-1 (CD138), a heparan-sulfate proteoglycan is attracting interests as it is highly expressed and shed by myeloma plasma-cells.

The aim of our study was to analyze CD138 levels in the serum of patients affected by multiple myeloma or light chain only disease, and to compare the values obtained with free light chain (FLC) kappa, lambda and FLC ratio in both groups of patients.

Methods

84 patients affected by Multiple Myeloma and Light Chain Myeloma were recruited for this study. Serum CD138 was assessed by ELISA (Diaclone Research, France) and FLC values were quantified by nephelometry (Freelite TM Human Kappa and Lambda Free Kits, The Binding Site, UK). Data was analyzed by GraphPad Prism software and Statgraph.

Results

We observed higher CD138 mean values in myeloma patients compared to the light chain only myeloma group. A positive linear regression of CD138 and FLC was observed in the light chain only cohort as opposed to myeloma patients which show an inverse trend.

Conclusions

The study highlighted an existing relationship between FLCs and CD138 and wishes to seek also a correlation in order to rapidly and efficiently perform diagnosis and different diagnostic schemes.

Mechanisms of light chain injury along the tubular nephron

The tubular nephron is responsible for reabsorption and catabolism of filtered low molecular weight proteins that include Ig free light chains. In the setting of a plasma cell dyscrasia, significant amounts of free light chains, now monoclonal proteins, present to the tubular nephron for disposal. The result may be clinical renal dysfunction in the form of AKI, progressive CKD, and end-stage kidney disease. Here, I review the mechanisms involved in these processes that result in tubular injury, including proximal tubulopathy and cast nephropathy.

Pivotal role of apoptosis signal-regulating kinase 1 in monoclonal free light chain-mediated apoptosis

Renal failure, a major complication associated with multiple myeloma, is usually related to deposition of monoclonal immunoglobulin free light chains (FLCs) and directly contributes to morbidity and mortality in this disease. The present study focused on the cytotoxic effects of monoclonal FLCs. Human proximal tubular epithelial cells (HK-2) were examined after incubation with two human monoclonal FLCs (termed κ2 and λ3). Incubation of HK-2 cells for 24 and 48 hours with either FLCs at 1 mg/mL promoted activation of caspase-9 and caspase-3 and increased the rate of apoptosis. Because prior studies demonstrated that FLCs generated intracellular oxidative stress, our studies focused on the redox-sensitive mitogen-activated protein kinase kinase kinase known as apoptosis signal-regulating kinase 1 (ASK1). A time-dependent increase in phosphorylation of ASK1 at T845, indicating activation of this enzyme, was observed. Small interfering RNA designed to reduce ASK1 expression in HK-2 cells successfully decreased ASK1, which was confirmed by Western blot analysis. Incubation of ASK1-depleted HK-2 cells with the two FLCs prevented the increase in apoptosis while pretreating HK-2 cell with nontargeting small interfering RNA did not prevent FLCs-mediated apoptosis. The combined data demonstrate that monoclonal FLCs activated the intrinsic apoptotic pathway in renal epithelial cells by activation of ASK1.

The pathogenesis and diagnosis of acute kidney injury in multiple myeloma

Renal failure remains a principal cause of morbidity for patients with multiple myeloma. Once reversible factors such as hypercalcemia have been corrected, the most common cause of severe renal failure in these patients is a tubulointerstitial pathology that results from the very high circulating concentrations of monoclonal immunoglobulin free light chains. These endogenous proteins can result in isolated proximal tubule cell cytotoxicity, tubulointerstitial nephritis and cast nephropathy (myeloma kidney). Less frequently, high levels of free light chains can lead to immunoglobulin light chain amyloidosis and light chain deposition disease, although these conditions are usually associated with insidious progression of renal failure rather than acute kidney injury. Unless there is rapid intervention, progressive and irreversible damage occurs, particularly interstitial fibrosis and tubular atrophy. Despite advances in our understanding of the pathogenesis of these processes there has been a gap in translating these achievements into improved patient outcomes. The International Kidney and Monoclonal Gammopathy Research Group was formed to address this need. In this Review, we discuss the mechanisms of disease and diagnostic approaches to patients with acute kidney injury complicating multiple myeloma.

Heterogeneity in primary structure, post-translational modifications, and germline gene usage of nine full-length amyloidogenic kappa1 immunoglobulin light chains

Immunoglobulin light chain amyloidosis is a protein misfolding disease in which a monoclonal immunoglobulin (Ig) light chain (LC) with a critically folded beta-conformation self-aggregates to form highly ordered, nonbranching amyloid fibrils. The insoluble nature of amyloid fibrils ultimately results in the extracellular deposition of the LC in tissues and organs throughout the body. Structural features that confer amyloidogenic properties on an Ig LC likely include amino acid sequence variations and post-translational modifications, but the specific natures of these changes remain to be defined. As part of an exploration of the effective range of amyloidogenic modifications, this study details the structural and genetic analyses of nine kappa1 LC proteins. Urinary LCs were purified by size exclusion chromatography using FPLC, and structural analyses were performed by electrospray ionization, matrix-assisted laser desorption/ionization, and tandem mass spectrometry. RT-PCR amplification, cloning, and sequencing of the monoclonal LC genes were accomplished using bone marrow-derived mRNA. Clinical data were reviewed retrospectively. Characterization of the urinary kappa1 LCs revealed extensive post-translational modification in all proteins, in addition to somatic mutations expected on the basis of results from genetic analyses. Post-translational modifications included disulfide-linked dimerization, S-cysteinylation, glycosylation, fragmentation, S-sulfonation, and 3-chlorotyrosine formation. Genetic analyses showed that several LC variable region germline gene donors were represented including O18/O8, O12/O2, L15, and L5. Clinical features included soft tissue, cardiac, renal, and hepatic involvement. This study demonstrated the extensive heterogeneity in primary structure, post-translational modifications, and germline gene usage that occurred in nine amyloidogenic kappa1 LC proteins.

Immunoglobulin Light Chains Generate Hydrogen Peroxide

As low molecular weight proteins, restriction from glomerular filtration is minimized, permitting significant amounts of Ig light chains to be endocytosed into the proximal tubule epithelium, particularly in plasma cell dyscrasias. Recent studies have shown that this effect of concentrating light chains within the proximal tubule alters cell function. This study demonstrated that light chains belonged to a class of proteins that are capable of catalyzing the formation of hydrogen peroxide. Sufficient amounts of hydrogen peroxide were produced in HK-2 cells to stimulate the production of monocyte chemoattractant protein-1 (MCP-1), a key chemokine involved in monocyte/macrophage migration and activation of the proximal tubule, and to increase lactate dehydrogenase release into the medium. The light chain-mediated effect on MCP-1 production was inhibited by co-incubation with 1,3-dimethyl-2-thiourea, which also inhibited lactate dehydrogenase release, and by pyrrolidine dithiocarbamate, an inhibitor of NF-kappaB. The amount of light chain that stimulated an intracellular redox-signaling pathway in the proximal tubule cells was well within levels that are seen in patients who have plasma cell dyscrasias. The conclusion is that light chains possess a unique property that permits the development of intracellular oxidative stress that in turn promotes activation of the proximal tubule and elaboration of MCP-1.

Consequences of receptor editing at the lambda locus: multireactivity and light chain secretion

To investigate the manner in which B cells with lambda light (L) chains undergo receptor editing, we have studied hybridoma panels from 56R/kappa-deleted (kdel) mice. 56R/kdel mice only produce four L chains (lambda1, lambda2, lambda3, and lambdaX). They also have a simplified heavy (H) chain repertoire: All B cells start out with a 56R anti-DNA H chain. A few frankly autoreactive 56R lambda1 cells appear to escape into the periphery, but the majority of the peripheral B cell repertoire in 56R/kdel is made up of B cells expressing the 56R H chain with the lambdaX L chain. Surprisingly, 56R lambdaX B cells are multireactive, binding to a variety of self and nonself antigens, including dsDNA (albeit at reduced affinity compared with the other lambda L chains). Another significant population in the 56R/kdel mouse consists of allelically included B cells that express lambdaX along with another L chain. The multireactivity of both 56R lambdaX and 56R lambdaX/lambda1 receptors could contribute to autoimmunity if these B cells were to become activated. Also found among 56R/kdel hybridomas are clones that have inactivated the H chain and secrete only L chains. These clones may represent products of exhaustive rearrangement. Multireactivity, allelic inclusion, and L chain secretion are three consequences of editing at the lambda locus that may predispose toward the development of autoimmunity.

Coelution of other proteins with albumin during size-exclusion HPLC: Implications for analysis of urinary albumin

BACKGROUND

Size-exclusion HPLC has been used as an alternative to immunoassays for quantifying urinary albumin (microalbumin). Systematically higher values for the HPLC method have been proposed to result from nonimmunoreactive albumin.

METHODS

We evaluated separation of purified proteins and urinary components by size-exclusion HPLC using a Zorbax Bio Series GF-250 column eluted with phosphate-buffered saline. Urinary components eluting in the "albumin" peak were analyzed by mass spectrometry and reversed-phase HPLC.

RESULTS

Several proteins, such as transferrin, alpha1-proteinase inhibitor, alpha1-acid glycoprotein, and alpha2-HS glycoprotein, analyzed as purified components, were not resolved from albumin by size-exclusion HPLC. Peaks for other proteins, such as IgG and urinary components identified as dimers of alpha1-microglobulin and immunoglobulin light chains, overlapped with the albumin peak. Profiles of urine specimens showed variable amounts of components overlapping with albumin. Furthermore, the albumin peak obtained by size-exclusion HPLC was found by mass spectrometry and reversed-phase HPLC to contain multiple components in addition to albumin.

CONCLUSIONS

Size-exclusion HPLC does not resolve albumin from several other proteins in urine. The albumin peak resolved by this technique, although predominantly composed of albumin, contains several coeluting globulins that would contribute to overestimation of albumin concentration by size-exclusion HPLC.

Management of paraproteinemic renal disease

PURPOSE OF REVIEW

Paraproteinemic renal diseases comprise a group of renal disorders that are difficult to manage, in part because of subtleties in the clinical presentation and confusion regarding diagnosis and appropriate therapy. Often, nephrologists make the diagnosis of the underlying plasma cell dyscrasia following renal biopsy. This review seeks to provide a greater understanding of the mechanism of disease and recent approaches to the management of patients who have AL-amyloidosis, monoclonal light-chain and light and heavy-chain deposition disease [termed ML(H)CDD], and cast nephropathy. All three renal lesions are caused by deposition of immunoglobulin light chains. This review seeks to provide a greater understanding of the mechanism of disease and recent approaches to the management of these patients.

RECENT FINDINGS

The immunoglobulin light chain takes the center stage in the pathogenesis of AL-amyloidosis, ML(H)CDD and cast nephropathy. Modifications in the variable domain are responsible for the affinity of the light chain for a given segment of the nephron and the subsequent toxic manifestations. Therapy aimed at eradicating the offending clone of plasma cells that secrete the monoclonal light chain should be beneficial, but this hypothesis lacks confirmation. Four nonrandomized studies have now demonstrated clinical benefit, including return of renal function, of high-dose chemotherapy with autologous stem cell transplantation (HDT/SCT) in the treatment of patients who have AL-amyloidosis or ML(H)CDD.

SUMMARY

While randomized trials are lacking, the data support the clinical efficacy of more aggressive treatments designed to reduce the plasma cell clone responsible for these renal disorders.

Trimolecular Complexes of λ Light Chain Dimers in Serum of a Patient with Multiple Myeloma

Background: Patients with multiple myeloma often have Bence Jones proteins composed of free monoclonal light chains of the κ or λ type in their urine. Usually, these light chains exist as monomeric or dimeric forms, but rarely, larger molecules, such as tetramers, have been reported in the serum.

Methods and Results: We report the presence of trimeric complexes of λ light chain dimers in a patient who was diagnosed with a free λ light chain multiple myeloma 2 years earlier and subsequently underwent a stem cell transplant. Recently, the patient presented with a large serum M-spike (23 g/L) by protein electrophoresis. The spike consisted of monoclonal λ light chains without a heavy chain. The urine contained only 8 mg of λ light chain in a 24-h specimen. Quantitative analysis of the serum and urinary free light chains (FLCs) indicated the probability of larger aggregates of FLCs. Size-exclusion chromatography, electrophoresis, analytical ultracentrifugation, and mass spectrometric studies of the serum revealed almost exclusively the presence of trimolecular aggregates of λ light chain dimers without other multimeric species.

Conclusion: Monoclonal λ light chains may present as hexameric aggregates that cannot be cleared by renal excretion.

Identification and location of a cysteinyl posttranslational modification in an amyloidogenic kappa1 light chain protein by electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry

Amyloid-deposited light chain (AL) amyloidosis is correlated with the overproduction of a monoclonal immunoglobulin light chain protein by a B-lymphocyte clone. Since the amyloid fibril deposits in AL amyloidosis most often consist of the N-terminal fragments of the light chain, the majority of studies have focused on the determination of the primary structure of the protein, and reducing agents have been used routinely in the initial purification process. In this study, two light chain proteins were isolated and purified, without reduction, from the urine of a patient diagnosed with kappa 1 (kappa1) AL amyloidosis. One protein had a relative molecular mass of 12,000 and the other 24,000. Electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry, in combination with enzymatic digestions, were used to verify the amino acid sequences and identify and locate posttranslational modifications in these proteins. The 12-kDa protein was confirmed to be the N-terminal kappa1 light chain fragment (variable region) consisting of residues 1-108 or 1-109 and having one disulfide bond. The 24-kDa protein was determined to be the intact kappa1 light chain containing a cysteinyl posttranslational modification at Cys214 and disulfide bonds located at Cys23-Cys88, Cys134-Cys194, and Cys214-Cys. The methods used in this report enable high-sensitivity determination of amino acid sequence and variation in intact and truncated light chains as well as posttranslational modifications. This approach facilitates consideration of the effect of cysteinylation on the native protein structure and the potential involvement of this modification in AL amyloidosis.

Efficient vasoactive intestinal polypeptide hydrolyzing autoantibody light chains selected by phage display

An immunoglobulin light chain (L chain) library derived from the peripheral blood lymphocytes of a patient with asthma was cloned into a phagemid vector. Phage particles displaying L chains capable of binding vasoactive intestinal polypeptide (VIP) were isolated by affinity chromatography. Two VIP binding L chains were expressed in Escherichia coli in soluble form and purified to electrophoretic homogeneity by metal chelating and protein L affinity chromatography. Both L chains catalyzed the hydrolysis of [tyr10-125I]VIP substrate. The catalytic activity eluted at the molecular mass of the monomer form of the L chain (28 kDa) from a gel filtration column. The activity was bound by immobilized anti-kappa-chain antibody. A control recombinant L chain displayed no catalytic activity. Hydrolysis of VIP by the catalytic L chains was saturable and consistent with Michaelis-Menten kinetics. The turnover of the L chains was moderate (0.22 and 2.21/min) and their Km values indicated comparatively high affinity recognition of VIP[111 and 202 nM), producing catalytic efficiencies comparable to or greater than trypsin. Unlike trypsin, the L chains did not display detectable cleavage of casein, suggesting a catalytic activity specialized for VIP. Comparisons of the nucleotide sequences of the L chain cDNA with their putative germ-line counterparts suggested the presence of several replacement mutations in the complementarity determining regions (CDRs). These observations suggest: (a) Retention or acquisition of catalytic activity by the L chains is compatible with affinity maturation of antibodies; and (b) The autoimmune L chain repertoire can serve as a source of substrate-specific and efficient catalysts.

Patient-specific microheterogeneity patterns of monoclonal immunoglobulin light chains as revealed by high resolution, two-dimensional electrophoresis

Preliminary observations have indicated that both heavy and light chains of monoclonal immunoglobulin exhibit diagnostically useful microheterogeneity patterns when examined with high resolution two-dimensional electrophoresis (2DE) and silver staining (Clin Chem 1990; 36: 993). The present study is a survey of the distribution and types of monoclonal light chain isoforms as observed with 2DE in a group of 68 sera and urine specimens from a cohort of 41 patients with monoclonal gammopathy. The light chain patterns were patient-specific and varied in both the type (kappa, lambda, charge or mass or both) and the number of isoforms present (one to six). A large proportion (31 of 41 cases, 75.6%) exhibited significant microheterogeneity, i.e., distribution of light-chains among two or more isoforms. Charge-based microheterogeneity alone occurred in 17 cases and both charge and mass isoforms were observed in 14 cases. The distribution of charge isoforms of the light chains corresponded qualitatively to the densitometric profiles of agarose gel and immunofixation electrophoresis studies. There was no correlation between heavy chain type and light chain pattern. A carbamylation assay was used to demonstrate that the chemical charge differences between the isoforms were unitary. Ascertainment of this light-chain microheterogeneity has not only proved useful in resolving some diagnostic immunoglobulin typing dilemmas but also is germane to understanding the molecular basis of neoplastic B-cell paraprotein metabolism.

The estimation of free light chains of immunoglobulins in biological fluids

Methods for the estimation of the free light chains of immunoglobulins in serum, urine and cerebrospinal fluid are divided into two groups, electrophoretic and immunological, and the analytical performance of each method described. The problems associated with the accurate and precise determination of free light chains by the different methods are discussed and their complementary clinical roles emphasized. It is proposed that an International Reference Preparation for free light chains is established.

The effect of exercise on urinary excretion of different size proteins in patients with insulin-dependent diabetes mellitus

To examine whether exercise-induced proteinuria in diabetes is dependent upon the size of the excreted protein, we measured urinary excretion of beta 2-microglobulin, kappa light chains, albumin and IgG before and after 20 min of moderate ergometer exercise in 34 patients with insulin dependent diabetes mellitus (IDDM) and in eight healthy control subjects. Seventeen patients with newly diagnosed IDDM and 17 patients (seven of which had elevated albumin excretion rate) with longstanding IDDM were studied. Exercise did not significantly influence protein excretion in control and newly diagnosed IDDM subjects. In contrast, exercise enhanced excretion of beta 2-microglobulin (p less than 0.05-0.01), kappa light chains (p less than 0.001), albumin (p less than 0.005-0.001) and IgG (p less than 0.01-0.001) in patients with long-standing IDDM independently of whether the patient had proteinuria in the resting state or not. In conclusion, proteinuria induced by moderate exercise is not observed in the early stages of IDDM, and is independent of the size of the excreted protein. Therefore, moderate exercise does not appear to influence the size selectivity of the glomerular capillary wall in patients with longstanding IDDM.

Morphologic alterations of the proximal tubules in light chain-related renal disease

Previous studies from our laboratory have shown that human immunoglobulin light chains (LC) can be toxic to the epithelium of the rat proximal tubule. To examine the toxicity of monoclonal LC's in man, 11 kidney specimens (EXP group) obtained from patients with monotypical LC-related renal disease (7 lambda, 4 kappa), documented by the presence of monoclonal LC's in the serum or urine and in the tissue, were examined by light, immunofluorescence, electron, and immunoelectron microscopy. This EXP group had monotypical LC deposition in the tubules and/or the glomeruli and did not have evidence of intraluminal LC precipitation and cast formation, which alters tubule morphology. A control group (CON; N = 12) of kidney specimens was obtained from patients who had proteinuria greater than 2.5 g/24 hr and mean age (49 +/- 4 vs. 59 +/- 3 years; P = NS), serum creatinine concentration (2.4 +/- 0.5 vs. 3.2 +/- 1.5 mg/dl; P = NS) and creatinine clearance (65 +/- 13 vs. 63 +/- 12 ml/min; P = NS) similar to the EXP group. All of the EXP specimens demonstrated varying degrees of proximal tubule damage, manifested by cell vacuolation, desquamation, loss of the luminal brush border, and, often, coagulation necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Human Bence Jones protein toxicity in rat proximal tubule epithelium in vivo

To investigate the direct toxicity of human Bence Jones protein (BJP), individual nephrons of male Sprague-Dawley rats were perfused in vivo at 20 nl/min with an artificial tubule fluid (ATF) that contained no protein, a human kappa BJP (5 g/dl), or bovine serum albumin (5 g/dl), and proximal convoluted tubule function and morphology were examined. Perfusion with BJP perfusate for less than or equal to 5 minutes produced no changes (P = NS) in absorption of water, Jv, (1.09 +/- 0.20 vs. 1.50 +/- 0.25 nl/min/mm), chloride, JCl, (95 +/- 47 vs. 123 +/- 41 pEq/min/mm), and glucose, JG, (39 +/- 3 vs. 40 +/- 5 pmol/min/mm) compared to perfusions with only ATF. However, perfusion for at least 20 minutes with the same BJP perfusate produced decreased (P less than 0.025) in Jv (0.58 +/- 0.12 vs. 1.15 +/- 0.14 nl/min/mm) and JG (27 +/- 3 vs. 38 +/- 3 pmol/min/mm) compared to perfusions with ATF alone; the decrease in JCl (64 +/- 47 vs. 119 +/- 27 pEq/min/mm) did not reach statistical significance. Perfusion for 20 minutes with ATF containing albumin resulted in no changes in Jv (1.22 +/- 0.21 vs. 1.15 +/- 0.14 nl/min/mm), JCl (207 +/- 29 vs. 119 +/- 27 pEq/min/mm), and JG (31 +/- 1 vs. 38 +/- 3 pmol/min/mm), when compared to the ATF perfusions. Immunocytochemistry, immunofluorescence and immunoelectron microscopy of the BJP-perfused tubules demonstrated the kappa light-chain protein in endosomes and activated lysosomes. In addition, cellular desquamation and fragmentation, prominent cytoplasmic vacuolation, and focal loss of the microvillus border were found in the BJP-perfused tubules, but not in the albumin-perfused tubules. In conclusion, these functional and morphologic data show that a human kappa light-chain is toxic to the proximal convoluted tubule of the rat. This toxicity occurred in a time-dependent fashion when the lysosomal system was markedly activated. Direct damage of the tubule epithelium by BJP's may be involved in the development of the tubulointerstitial nephropathy associated with multiple myeloma.

Allergy to rabbits. I. Specificity and non-specificity of RAST and crossed-radioimmunoelectrophoresis due to the presence of light chains in rabbit allergenic extracts

Investigations have been carried out into the presence of antibody light chains in rabbit allergenic extracts and the interference in RAST and crossed-radioimmunoelectrophoresis (XRIE) caused by antibodies directed against them. A "non-specific" uptake of radioactivity in XRIE has been demonstrated to be caused by direct cross-linking of the 125I rabbit anti-human IgE by the sheep antibodies in the immunoprecipitate of rabbit light chains. Preincubation with normal rabbit serum blocked this direct uptake of the labelled antibody and enabled specific IgE uptake on the light chains to be demonstrated for rabbit allergic sera. Verification of the allergenicity of the light chains was obtained from a specific light chain RAST. Elution from a Sephacryl S-200 gel filtration column indicated a MW of approx. 50 Kd and confirmation of the component as light chain dimers, not Fab fragments, was obtained by allotyping for loci present on heavy chains and light chains in the Fab region. Light chains were detected in urine from rabbits of all ages and in an extract of dust collected in a rabbit housing area. No background staining was observed in XRIE using rabbit antisera, either with rabbit allergic sera with specific IgE or with a human serum containing specific IgG antibodies to rabbit IgG. This latter serum also showed no evidence of uptake on all immunoprecipitates in systems using rabbit antisera, and did not give false positive RAST results when the labelled rabbit anti-human IgE contained unlabelled rabbit IgG. Those sera with specific IgE to light chains showed no uptake in XRIE using rabbit antisera, indicating that the IgE was possibly specific for epitopes revealed by the dissociation of the whole IgG molecule.

Detection of Bence-Jones protein by isoelectric focussing of unconcentrated urine followed by nitrocellulose blotting and immunoperoxidase staining

Urine specimens from 164 patients sent to the laboratory for testing for Bence-Jones proteinuria were investigated using a new procedure. The protein in the untreated urine was subjected to isoelectric focussing in an agarose gel, transferred to a nitrocellulose membrane by blotting, and then stained by an immunoperoxidase technique for either immunoglobulin kappa or lambda chains. This technique was compared with a routine procedure for the detection of immunoglobulin light chains involving concentration by ultrafiltration, electrophoresis and then immunofixation. The new technique achieved a much increased rate of detection of Bence-Jones proteinuria. Among 51 patients known to have myeloma or macroglobulinaemia, Bence-Jones proteinuria was detected in 35 cases with the new procedure and in only 27 by the conventional method. In 28 patients with paraproteinaemia without other evidence of myeloma, macroglobulinaemia, leukaemia or lymphoma, 12 instances of Bence-Jones proteinuria were discovered with the new procedure, 10 of which were missed by the conventional method. The improved efficiency of detection is attributed to the high resolution of isoelectric focussing and the avoidance of protein loss from adsorption on to ultrafiltration membranes.

Turbidimetric measurement of Bence-Jones proteins using antibodies against free light chains of immunoglobulins. An artifact caused by different polymeric forms of light chains

The different polymeric forms of free kappa and lambda light chains from urines of two myeloma patients were separated by gel filtration. When samples containing kappa chains in equal protein concentration were quantified by turbidimetry with anti-free kappa chain antibodies, two out of three samples reacted much less sensitively than the third sample. When analysed with SDS-polyacrylamide gel electrophoresis in conditions dissociating non-covalent but not covalent linkages, these two samples contained monomeric light chains, whereas the third sample contained dimers.

Alpha-1-microglobulin: an indicator protein for renal tubular function

A comparison of urinary alpha 1-microglobulin concentrations to the behaviour of other indicators of renal tubular disorders, beta 2-microglobulin, retinol-binding protein and N-acetyl-beta-D-glucosaminidase (NAG) has been made. In acute tubular disorders the concentrations of urinary beta 2M and RBP are highly correlated (r = 0.89) but this is less marked for alpha 1M and beta 2M (r = 0.55) and alpha 1M and RBP r = 0.48. NAG tends to run a parallel course to alpha 1M concentrations but lags behind the recovery of low molecular weight protein reabsorption following injury of the tubular cells. The concentrations of alpha 1M, and in particular its stability at low pH suggest that this protein may be useful in screening for tubular abnormalities and detecting chronic asymptomatic renal tubular dysfunction. Urinary alpha 1M greater than 15 mg/g creatinine is strongly suspicious of a proximal tubular dysfunction. The distinction between pure tubular proteinuria and mixed glomerular and tubular proteinuria requires further analysis.

Renal lesions in multiple myeloma: their relationship to associated protein abnormalities

Renal biopsy and autopsy specimens were studied in 43 patients with renal complications of multiple myeloma and correlated with immunoelectrophoresis (IEP) and other clinical data at the time of biopsy. Lesions specifically related to multiple myeloma fell into two categories, with different patterns of protein excretion. (1) Myeloma Cast Formation: When other lesions which might contribute to renal insufficiency (RI) were excluded, there was a good correlation between the extent of myeloma cast formation and severity of RI. Sixteen of 19 patients excreted free light chains (LCs) in the urine, in seven as the predominant or sole urinary protein. (2) Tissue Deposition of Paraproteins: Nine cases had generalized glomerular, tubular basement membrane and vascular deposits of presumed kappa-chains (one with associated alpha-heavy chains). Four patients, all with myelomas secreting lambda LCs, had diffuse amyloid deposits in similar distribution. All patients (save two who were anuric) had diffuse, nonselective proteinuria by IEP, most within the nephrotic range. Four patients had free LCs in the urine, but in none was this the predominant component. Cast nephropathy and LC tissue deposition tended to occur in mutually exclusive fashion. Cases with diffuse tissue deposits of LCs showed few or no myeloma casts. Cases with cast nephropathy had only occasional mild mesangial lesions and focal interstitial and vascular deposits of amyloid. Evidence indicates that these lesions represent incidental LC deposition in cases whose basic lesion is longstanding and/or severe cast nephropathy, and that their contribution to RI is minor in comparison to that of the myeloma casts.

Simple method for the screening of polymeric Bence Jones proteins

The author tested the electropherograms of previously identified, concentrated urine samples in agarose gel. Before electrophoresis, the gel plate containing the samples was covered with a cellulose-acetate membrane soaked with 0.1 M 2-mercaptoethanol, and it was incubated for 10 min in a moist chamber, at room temperature. If the polymeric Bence Jones protein is present, the electropherogram of the sample changes. In the following, a quick and easy method of recognizing this rare structural anomaly is recommended.

Properties of isolated human alpha1-antitrypsins of Pi types M, S and Z

1. alpha1-Antitrypsin contains a single thiol group partly blocked in native plasma and reactive after mild reduction. 2. Human alpha1-antitrypsins of Pi types F, M, S and Z have been isolated with native microheterogeneity using thiol-disulfide (SH-SS) interchange reactions utilizing the reactive thiol group. 3. The pI of the various microheterogeneous fractions are given for protein M. Stepwise desialylation of alpha1-antitrypsin indicates that the charge difference between the major fractions is one sialic acid residue between each. This is further supported by the pI changes obtained on substitution of the single thiol with positively or negatively charged compounds. 4. Desialyation of purified proteins from each Pi type converts the individual microheterogeneous fractions to one major fraction. The pI shift for the variants studied indicate a difference of plus or minus one or two charge units between protein M and the variants. 5. A difference of one sialic acid residue was obtained for proteins M and Z by the thiobarbituric assay, but stepwise removal of sialic acid with neuraminidase revealed almost identical stepwise change of pattern of both proteins indicating the same number of sialic acid residues. 6. Electrofocusing has been used to identify CNBr fragments from proteins M, S and Z. 7. An amino acid substitution has been found to be located in one of the eight CNBr fragments, glutamic acid in protein M is substituted by lysine in protein Z. 8. The average concentration of alpha1-antityprsin in plasma from healthy males was found to be 1.32 g/1.

Polymeric forms of free light chains in serum from normal individuals and from patients with renal diseases

The polymeric forms of free light chains from the immunoglobulins have been estimated in serum from 10 healthy individuals and from 10 anephric patients. Light chains were also estimated in serum and urine from 29 patients with various degrees of renal insufficiency. The measurements were carried out by a radioimmunoassay. The mean concentrations of light chains in normal serum were found to be 4.9 mg/l for dimeric forms of kappa chains, 5.6 mg/l for monomeric forms of kappa chains, 5.1 mg/l for dimeric forms of lambda chains, and 2.7 mg/l for monomeric forms of lambda chains. The concentration of light chains in anephric man was increased to 5 times the normal level. The concentration of the different forms was 26.7 mg/l for dimeric forms of kappa chains, 29.6 mg/l for monomeric forms of kappa chains, 32.6 mg/l for dimeric forms of lambda chains, and 5.8 mg/l for monomeric forms of lambda chains. A minor amount of tetrameric forms of kappa chains was found. Gel filtration showed that a majority of the kappa chains in normal and anephric serum existed as monomers and non-covalently linked dimers, whereas the lambda chains mainly existed as stable, covalently linked dimers. In renal disease the serum concentration of light chains was found closely correlated to creatinine clearance. The 24-h urinary excretion of light chains was generally increased when the GFR was diminished regardless of the type of renal disease.

The subunit structure of thymus leukemia antigens

EDTA-containing buffer solubilizes thymus leukemia antigens (TLa) from crude thymocyte membrane fractions. The TL antigens consist mainly of molecules of a size similar to immunoglobulin G when gel chromatography analyses were performed under physiological conditions. A single component of TLa was apparent on sucrose density gradient ultracentrifugation of solubilized thymocyte membrane macromolecules as monitored by indirect immunoprecipitation. The sedimentation constant for the TL antigens (5.8 S) was considerably less than that for immunoglobulin G. The gel chromatography and ultracentrifugation data suggest an apparent molecular weight for TLa of about 120000. TLa isolated by indirect immunoprecipitation is composed of two types of polypeptide chains. The smaller subunit was identified as beta2-microglobulin. The larger polypeptide chain carried the alloantigenic determinants and displayed a molecular weight of about 50000 after reduction and alkylation. TLa subjected to molecular weight determination under denaturing conditions was composed of two components. The smaller component was beta2-microglobulin which evidently is linked to the larger polypeptide chain by noncovalent interactions only. The larger component had a size greater than reduced and alkylated immunoglobulin G heavy chains. Upon reduction and alkylation of the latter component its size was reduced and it appeared to have a molecular weight of about 50000. Consequently, TLa is composed of two disulfide linked heavy polypeptide chains and two beta2-microglobulin molecules. TLa solubilized by papain digestion comprises two polypeptide chains, one of which is beta2-microglobulin. The larger 37000-dalton subunit is a fragment of the heavy polypeptide chain. This was demonstrated by digesting solubilized 120000-dalton TLa with papain. The proteolytic fragments obtained were indistinguishable from those directly released from the cell surface by proteolysis. The papain-derived TLa fragment exhibited most if not all the alloantigenic determinants.

Purification of alpha1-antitrypsin from plasma through thiol-disulfide interchange

1. Monomeric nu-chains were conjugated with CNBr-activated Sepharose 4B. The C-terminal cysteine of the conjugated nu-chain was converted to a mixed disulfide with 3-carboxy-4-nitro-benzenethiol (Nbs) and used to separate plasma proteins with reactive thiol groups. The plasma proteins, alpha1-antitrypsin and prealbumin have the greatest affinity for the interchange reaction with mixed disulfides. The disulfide link between alpha1-antitrypsin and nu-chain is sensitive to excess Nbs, and is selectively cleaved in the presence of 5,5'-dithiobis(2-nitrobenzoate) (Nbs2) which accepts the sulfhydryl group of alpha1-antitrypsin. 2. A Simple method developed for the isolation of human alpha1-antitrypsin was equally effective for the various inherited phenotypes and for alpha1-antitrypsin from the dog, baboon, and monkey, Glutathione-Sepharose was also used successfully, but the nu-chain conjugate yielded alpha1-antitrypsin less contaminated with mercaptalbumin and prealbumin. 3. The alpha1-antitrypsin is harvested from this procedure as a mixed disulfide with Nbs. The negative charge of Nbs at pH 8.1 causes an increased electrophoretic mobility of the alpha1-antitrypsin derivative. Mild reduction liberates Nbs and electrophoretic mobility of alpha1-antitrypsin returns to normal. The method described can increase the alpha1-antitrypsin content of a plasma fraction from 5% of the total protein to 95% within one day with a yield of about 50%. This purification procedure does not exert any detectable effect on microheterogeneity.