Aberrant immunoglobulin synthesis in light chain amyloidosis. Free light chain and light chain fragment production by human bone marrow cells in short-term tissue culture

Dissection of the amyloid formation pathway in AL amyloidosis

In antibody light chain (AL) amyloidosis, overproduced light chain (LC) fragments accumulate as fibrils in organs and tissues of patients. In vitro, AL fibril formation is a slow process, characterized by a pronounced lag phase. The events occurring during this lag phase are largely unknown. We have dissected the lag phase of a patient-derived LC truncation and identified structural transitions that precede fibril formation. The process starts with partial unfolding of the V_L domain and the formation of small amounts of dimers. This is a prerequisite for the formation of an ensemble of oligomers, which are the precursors of fibrils. During oligomerization, the hydrophobic core of the LC domain rearranges which leads to changes in solvent accessibility and rigidity. Structural transitions from an anti-parallel to a parallel β-sheet secondary structure occur in the oligomers prior to amyloid formation. Together, our results reveal a rate-limiting multi-step mechanism of structural transitions prior to fibril formation in AL amyloidosis, which offers, in the long run, opportunities for therapeutic intervention.

AL amyloidosis is caused by the accumulation of overproduced light chain (LC) fragments as fibrils in patient organs and it is the most prevalent systemic amyloidosis. Here, the authors combine biochemical and biophysical experiments to characterise the lag phase of a patient-derived truncated LC and they identify structural transitions that precede fibril formation.

Fatal amyloid formation in a patient's antibody light chain is caused by a single point mutation

In systemic light chain amyloidosis, an overexpressed antibody light chain (LC) forms fibrils which deposit in organs and cause their failure. While it is well-established that mutations in the LC’s V_L domain are important prerequisites, the mechanisms which render a patient LC amyloidogenic are ill-defined. In this study, we performed an in-depth analysis of the factors and mutations responsible for the pathogenic transformation of a patient-derived λ LC, by recombinantly expressing variants in E. coli. We show that proteolytic cleavage of the patient LC resulting in an isolated V_L domain is essential for fibril formation. Out of 11 mutations in the patient V_L, only one, a leucine to valine mutation, is responsible for fibril formation. It disrupts a hydrophobic network rendering the C-terminal segment of V_L more dynamic and decreasing domain stability. Thus, the combination of proteolytic cleavage and the destabilizing mutation trigger conformational changes that turn the LC pathogenic.

Amyloid light chain amyloidosis, shortened to AL amyloidosis, is a rare and often fatal disease. It is caused by a disorder of the bone marrow. Usually, cells in the bone marrow produce Y-shaped proteins called antibodies to fight infections. In AL amyloidosis, these cells release too much of the short arm of the antibody, known as its light chain, and the light chains also carry mutations. The antibodies are no longer able to assemble properly, and instead misfold and form structures, known as amyloid fibrils. The fibrils build up outside the cells, gradually causing damage to tissues and organs that can lead to life-threatening organ failure.

Due to the rareness of the disease, diagnosis is often overlooked and delayed. People experience widely varying symptoms, depending on the organs affected. Also, given the diversity of antibodies people make, every person with AL amyloidosis has a variety of mutations implicated in their disease. It is thought that mutations in the antibody light chain make it unstable and prone to misfolding, but it remains unclear which specific mutations trigger a cascade of amyloid fibril formation.

Now, Kazman et al. have pinpointed the exact mechanism in one case of the disease. First, tissue biopsies from a woman with advanced AL amyloidosis were analyzed, and the defunct antibody light chain was isolated. Eleven mutations were identified in the antibody light chain, only one of which was found to be responsible for the formation of the harmful fibrils. The next step was to determine how this one small change was so damaging. The experiments showed that after the antibody light chain was cut in two, a process that happens naturally in the body, this single mutation transforms it into a protein capable of causing disease.

In this ‘bedside to lab bench’ study, Kazman et al. have succeeded in determining the molecular origin of one case of AL amyloidosis. The results have also shown that the instability of antibodies due to mutation does not alone explain the formation of amyloid fibrils in this disease and that the cutting of this protein in two is also important. It is hoped that, in the long run, this work will lead to new diagnostics and treatment options for people with AL amyloidosis.

The Antibody Light-Chain Linker Regulates Domain Orientation and Amyloidogenicity

The antibody light chain (LC) consists of two domains and is essential for antigen binding in mature immunoglobulins. The two domains are connected by a highly conserved linker that comprises the structurally important Arg108 residue. In antibody light chain (AL) amyloidosis, a severe protein amyloid disease, the LC and its N-terminal variable domain (V_L) convert to fibrils deposited in the tissues causing organ failure. Understanding the factors shaping the architecture of the LC is important for basic science, biotechnology and for deciphering the principles that lead to fibril formation. In this study, we examined the structure and properties of LC variants with a mutated or extended linker. We show that under destabilizing conditions, the linker modulates the amyloidogenicity of the LC. The fibril formation propensity of LC linker variants and their susceptibility to proteolysis directly correlate implying an interplay between the two LC domains. Using NMR and residual dipolar coupling-based simulations, we found that the linker residue Arg108 is a key factor regulating the relative orientation of the V_L and C_L domains, keeping them in a bent and dense, but still flexible conformation. Thus, inter-domain contacts and the relative orientation of V_L and C_L to each other are of major importance for maintaining the structural integrity of the full-length LC.

Identification of two principal amyloid-driving segments in variable domains of Ig light chains in systemic light-chain amyloidosis

Systemic light-chain amyloidosis (AL) is a human disease caused by overexpression of monoclonal immunoglobulin light chains that form pathogenic amyloid fibrils. These amyloid fibrils deposit in tissues and cause organ failure. Proteins form amyloid fibrils when they partly or fully unfold and expose segments capable of stacking into β-sheets that pair and thereby form a tight, dehydrated interface. These structures, termed steric zippers, constitute the spines of amyloid fibrils. Here, using a combination of computational (with ZipperDB and Boston University ALBase), mutational, biochemical, and protein structural analyses, we identified segments within the variable domains of Ig light chains that drive the assembly of amyloid fibrils in AL. We demonstrate that there are at least two such segments and that each one can drive amyloid fibril assembly independently of the other. Our analysis revealed that peptides derived from these segments form steric zippers featuring a typical dry interface with high-surface complementarity and occupy the same spatial location of the Greek-key immunoglobulin fold in both λ and κ variable domains. Of note, some predicted steric-zipper segments did not form amyloid fibrils or assembled into fibrils only when removed from the whole protein. We conclude that steric-zipper propensity must be experimentally validated and that the two segments identified here may represent therapeutic targets. In addition to elucidating the molecular pathogenesis of AL, these findings also provide an experimental approach for identifying segments that drive fibril formation in other amyloid diseases.

Light chain amyloidosis: Where are the light chains from and how they play their pathogenic role?

Amyloid light-chain (AL) amyloidosis is a plasma-cell dyscrasia, as well as the most common type of systematic amyloidosis. Pathogenic plasma cells that have distinct cytogenetic and molecular properties secrete an excess amount of amyloidogenic light chains. Assisted by post-translational modifications, matrix components, and other environmental factors, these light chains undergo a conformational change that triggers the formation of amyloid fibrils that overrides the extracellular protein quality control system. Moreover, the amyloidogenic light-chain itself is cytotoxic. As a consequence, organ dysfunction is caused by both organ architecture disruption and the direct cytotoxic effect of amyloidogenic light chains. Here, we reviewed the molecular mechanisms underlying this sequence of events that ultimately leads to AL amyloidosis and also discuss current in vitro and in vivo models, as well as relevant novel therapeutic approaches.

Screening methods for identifying pharmacological chaperones

This review highlights recent screening methods for identifying pharmacological chaperones, which are small-molecules capable of rescuing misfolded proteins.

Amyloidosis and the lung

Amyloidosis is a disorder of protein folding in which normally soluble plasma proteins aggregate in an abnormal fibrillar form causing progressive disruption to tissue structure and organ function. This review covers systemic AA and AL amyloidosis which may arise as a consequence of chronic respiratory conditions; the manifestations of both systemic and of localised amyloid deposition within the respiratory tract and provides a summary of current approaches to diagnosis and management.

Inhibition by small-molecule ligands of formation of amyloid fibrils of an immunoglobulin light chain variable domain

Overproduction of immunoglobulin light chains leads to systemic amyloidosis, a lethal disease characterized by the formation of amyloid fibrils in patients' tissues. Excess light chains are in equilibrium between dimers and less stable monomers which can undergo irreversible aggregation to the amyloid state. The dimers therefore must disassociate into monomers prior to forming amyloid fibrils. Here we identify ligands that inhibit amyloid formation by stabilizing the Mcg light chain variable domain dimer and shifting the equilibrium away from the amyloid-prone monomer.

DOI:http://dx.doi.org/10.7554/eLife.10935.001

Systemic light chain amyloidosis is a disease that occurs when individuals produce too much of an immune protein. The excess protein chains normally exist in the body as individual molecules called “monomers” or in pairs called “dimers,” and they can readily switch between these two forms. However, the monomers are also prone to forming amyloid fibrils, which are difficult to break down. Amyloid fibrils are often deposited in the heart and kidneys and can lead to organ failure and death.

Finding molecules that prevent the formation of amyloid fibrils could help to develop treatments for amyloidosis. Now, Brumshtein, Esswein et al. have screened 27 compounds to identify those that stabilize the dimer form of the protein. This would reduce the number of monomers in the body, and so reduce the number of immune proteins that can form amyloid fibrils.

The experiments identified four compounds that could stabilize the dimers, including one called methylene blue. Comparing the chemical structures of these compounds with the structures of drugs approved for medical use identified thirteen drugs. However, follow-up tests showed that only one, called sulfasalazine, reduced the formation of amyloid fibrils. Neither methylene blue nor sulfasalazine is likely to have a strong enough effect to treat amyloidosis, but they may serve as templates for future drug designs.

DOI:http://dx.doi.org/10.7554/eLife.10935.002

Mechanisms of amyloid fibril formation

Amyloid and amyloid-like aggregates are elongated unbranched fibrils consisting of β-structures of separate monomers positioned perpendicular to the fibril axis and stacked strictly above each other. In their physicochemical properties, amyloid fibrils are reminiscent of synthetic polymers rather than usual proteins because they are stable to the action of denaturing agents and proteases. Their mechanical stability can be compared to a spider's web, that in spite of its ability to stretch, is stronger than steel. It is not surprising that a large number of diseases are accompanied with amyloid fibril depositing in different organs. Pathologies provoked by depositing of incorrectly folded proteins include Alzheimer's, Parkinson's, and Huntington's diseases. In addition, this group of diseases involves mucoviscidosis, some types of diabetes, and hereditary cataracts. Each type of amyloidosis is characterized by aggregation of a certain type of protein that is soluble in general, and thus leads to specific distortions of functions of the corresponding organs. Therefore, it is important to understand the process of transformation of "native" proteins to amyloid fibrils to clarify how these molecules acquire such strength and what key elements of this process determine the pathway of erroneous protein folding. This review presents our analysis of complied information on the mechanisms of formation and biochemical properties of amyloid fibrils.

Modulation of the IL-6 Receptor α Underlies GLI2-Mediated Regulation of Ig Secretion in Waldenström Macroglobulinemia Cells

Ig secretion by terminally differentiated B cells is an important component of the immune response to foreign pathogens. Its overproduction is a defining characteristic of several B cell malignancies, including Waldenström macroglobulinemia (WM), where elevated IgM is associated with significant morbidity and poor prognosis. Therefore, the identification and characterization of the mechanisms controlling Ig secretion are of great importance for the development of future therapeutic approaches for this disease. In this study, we define a novel pathway involving the oncogenic transcription factor GLI2 modulating IgM secretion by WM malignant cells. Pharmacological and genetic inhibition of GLI2 in WM malignant cells resulted in a reduction in IgM secretion. Screening for a mechanism identified the IL-6Rα (gp80) subunit as a downstream target of GLI2 mediating the regulation of IgM secretion. Using a combination of expression, luciferase, and chromatin immunoprecipitation assays we demonstrate that GLI2 binds to the IL-6Rα promoter and regulates its activity as well as the expression of this receptor. Additionally, we were able to rescue the reduction in IgM secretion in the GLI2 knockdown group by overexpressing IL-6Rα, thus defining the functional significance of this receptor in GLI2-mediated regulation of IgM secretion. Interestingly, this occurred independent of Hedgehog signaling, a known regulator of GLI2, as manipulation of Hedgehog had no effect on IgM secretion. Given the poor prognosis associated with elevated IgM in WM patients, components of this new signaling axis could be important therapeutic targets.

Formation of amyloid fibers by monomeric light chain variable domains

Systemic light chain amyloidosis is a lethal disease characterized by excess immunoglobulin light chains and light chain fragments composed of variable domains, which aggregate into amyloid fibers. These fibers accumulate and damage organs. Some light chains induce formation of amyloid fibers, whereas others do not, making it unclear what distinguishes amyloid formers from non-formers. One mechanism by which sequence variation may reduce propensity to form amyloid fibers is by shifting the equilibrium toward an amyloid-resistant quaternary structure. Here we identify the monomeric form of the Mcg immunoglobulin light chain variable domain as the quaternary unit required for amyloid fiber assembly. Dimers of Mcg variable domains remain stable and soluble, yet become prone to assemble into amyloid fibers upon disassociation into monomers.

Systemic amyloidoses

The amyloidoses are a group of protein misfolding diseases in which the precursor protein undergoes a conformational change that triggers the formation of amyloid fibrils in different tissues and organs, causing cell death and organ failure. Amyloidoses can be either localized or systemic. In localized amyloidosis, amyloid deposits form at the site of precursor protein synthesis, whereas in systemic amyloidosis, amyloid deposition occurs distant from the site of precursor protein secretion. We review the type of proteins and cells involved and what is known about the complex pathophysiology of these diseases. We focus on light chain amyloidosis to illustrate how biochemical and biophysical studies have led to a deeper understanding of the pathogenesis of this devastating disease. We also review current cellular, tissue, and animal models and discuss the challenges and opportunities for future studies of the systemic amyloidoses.

A molecular history of the amyloidoses

The molecular investigation of the amyloidoses began in the mid-19th century with the observation of areas in human tissues obtained at autopsy that were homogeneous and eosinophilic with conventional stains but became blue when exposed to mixtures of iodine and sulfuric acid. The foci corresponded to regions formerly identified as "waxy" or lardaceous. Subsequent identification of the characteristic staining of the same tissues with metachromatic dyes such as crystal violet or with the cotton dye Congo red (particularly under polarized light) and thioflavins allowed the pathological classification of those tissues as belonging to a set of disorders known as the amyloidoses. Not unexpectedly, progress has reflected evolving technology and parallel advances in all fields of biological science. Investigation using contemporary methods has expanded our notions of amyloid proteins from being simply agents or manifestations of systemic, largely extracellular diseases to include "protein-only infection," the concept that "normal" functional amyloids might exist in eukaryotes and prokaryotes and that aggregatability may be an intrinsic structural price to be paid for some functional protein domains. We now distinguish between the amyloidoses, that is, diseases caused by the deposition of amyloid fibrils and amyloid proteins (i.e., purified or recombinant proteins that form amyloid fibrils in vitro), which may or may not be associated with disease in vivo.

Treatment of immunoglobulin light chain amyloidosis

No therapy is uniformly effective in the management of immunoglobulin light chain amyloidosis (AL amyloidosis). Despite the common generalization, therapy is highly effective. Options available to patients with AL amyloidosis include high-dose therapy, but this is applicable to only about one fourth of patients. Therapies shown to be effective are based on alkylators, dexamethasone, or combinations of an alkylator and steroids. In the past 5 years, novel agents previously shown to be effective in multiple myeloma (eg, thalidomide, lenalidomide, and bortezomib) have been shown to have efficacy in the management of AL amyloidosis. Predictors of outcome include the serum brain natriuretic peptide, the number of organs involved, and the severity of cardiac involvement detected by echocardiography. Virtually all patients are candidates for a trial of therapy, and it is possible to find a nontoxic regimen that can be administered to virtually any patient.

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

BACKGROUND

Organ dysfunction in AL amyloidosis is related to the production and deposition of amyloidogenic monoclonal light chains. These pathological light chains can now be quantified using the recently developed serum free light chain assay.

METHODS

We retrospectively reviewed 31 patients with AL amyloidosis to determine the frequency of abnormal free light chain assay results at diagnosis and whether changes in the serum free light chain assay predict outcome after therapy.

RESULTS

An abnormal free light chain assay was found in 30 of 31 patients (97%) at the time of diagnosis. In the subset of our patients who received treatment for AL amyloidosis, a >50% reduction of the pathological free light chain following treatment was shown to predict improved overall survival. In our series of analyses, achievement of greater magnitudes of reduction of the free light chain result did not appear to provide additional prognostic information, nor did the baseline free light chain result predict outcome.

CONCLUSION

Our findings support the use of the free light chain assay in the diagnostic work-up of patients with suspected AL amyloidosis, and also as a sensitive biomarker of response to therapy.

Drug Insight: emerging therapies for amyloidosis

Amyloidosis is a clinical disorder caused by extracellular deposition of proteins that are normally soluble as insoluble, abnormal fibrils that impair organ function. More than 20 unrelated proteins can form amyloid fibrils in vivo. All fibrils share cross-beta core structure and pathognomonic red-green birefringence when viewed under cross-polarized light after staining with Congo red. Amyloidosis can be acquired or hereditary, localized or systemic, and is classified according to the fibril precursor protein. Local amyloid deposition occurs in the brain in Alzheimer's disease and in the pancreas in maturity-onset diabetes, but a direct role in the pathogenesis of these diseases remains unproven. Systemic amyloidosis, with amyloid deposits in the viscera, blood vessel walls and connective tissues, is usually fatal and is the cause of about one death per thousand in developed countries. Recent elucidation of fundamental aspects of the pathogenesis of amyloidosis, and developments in diagnosis and monitoring of this disorder have greatly improved outcome for patients. Several exciting novel therapeutic strategies, reviewed in this article, are in development. These include interference with different stages of fibrillogenesis and enhancement of clearance of amyloid deposits.

A patient with severe renal amyloidosis associated with an immunoglobulin γ-heavy chain fragment

The authors report a patient with progressive renal dysfunction caused by severe renal amyloidosis associated with a gamma-heavy chain variable region (V(H)) fragment. The patient was a 71-year-old woman who had renal insufficiency without nephrotic syndrome. Laboratory data showed a monoclonal IgG lambda component in her serum and urine. Renal biopsy results showed massive amyloid deposition in the mesangial region, but the glomerular basement membranes and epithelial cells were preserved. Because immunohistochemical studies using antibodies against a number of known amyloid fibril proteins failed to detect the amyloid protein, the amyloid protein extracted from a small piece of the biopsied renal tissue was subjected to biochemical analysis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the extracted amyloid protein showed a prominent band at 11-kDa, and this protein was identified by amino acid sequence analysis as a gamma-heavy chain variable region fragment (V(H)3 subgroup) without the first N-terminal residue. Our results indicate that the patient's renal amyloidosis was associated with a gamma-heavy chain variable region fragment. Microextraction and biochemical characterization of amyloid fibrils was of great use for reaching a definitive diagnosis.

Outcome in systemic AL amyloidosis in relation to changes in concentration of circulating free immunoglobulin light chains following chemotherapy

Monoclonal immunoglobulin light chains are deposited as amyloid fibrils in systemic AL (primary) amyloidosis, but the underlying plasma cell dyscrasias are often difficult to detect or unquantifiable. The relationships between circulating monoclonal light chains, amyloid load and clinical outcome, and the relative efficacies of chemotherapy regimens aimed at suppressing monoclonal immunoglobulin production, have not been determined. Circulating free immunoglobulin light chain (FLC) concentration was measured with a sensitive nephelometric immunoassay in 262 patients with AL amyloidosis, and followed serially in 137 patients who received either high-dose chemotherapy or one of two intermediate-dose cytotoxic regimens. Amyloid load was quantified by serum amyloid P component scintigraphy. A monoclonal excess of FLC was identified at diagnosis in 98% of patients. Among 86 patients whose abnormal FLC concentration fell by more than 50% following chemotherapy, 5-year survival was 88% compared with only 39% among those whose FLC did not fall by half (P < 0.0001). Amyloid deposits regressed in 58 patients. The magnitude and duration of the FLC responses to intermediate- and high-dose chemotherapy regimens were similar. The FLC assay enabled the circulating fibril precursor protein in AL amyloidosis to be quantified and monitored in most patients. Reduction of the amyloidogenic FLC by more than 50% was associated with substantial survival benefit, regardless of the type of chemotherapy used. Clinical improvement following chemotherapy in AL amyloidosis is delayed, but treatment strategies can be guided by their early effect on serum FLC concentration.

Coexistence of beta2 microglobulin and lambda light chain in amyloid fibrils of dialysis-unrelated plasma cell dyscrasia-associated systemic amyloidosis

BACKGROUND

Systemic amyloidosis occurs as a result of amyloid deposition in various tissues. The amyloid fibrils in systemic amyloidosis have been reported to originate from immunoglobulin light chains.

OBJECTIVE

We studied the composition of amyloid fibrils from two patients with plasma cell-associated systemic amyloidosis (PASA).

METHODS

A double immunofluorescence study of the lesional skin of PASA was undertaken. Amyloid proteins were extracted with distilled water from one case of PASA.

RESULTS

The double immunofluorescence study showed that anti-lambda light chain and anti-beta2 microglobulin antibodies mostly reacted with the same area of amyloid deposit. Amyloid deposits from two patients with PASA who had never undergone haemodialysis showed a positive reaction with the antibodies for beta2 microglobulin as well as immunoglobulin lambda light chain. By the use of immunoblot assay of amyloid fibril proteins, polypeptides immunoreactive with antigamma light chain antibody (29 kDa) and with anti-beta2 microglobulin antibody (12 kDa) were detected.

CONCLUSIONS

These results indicate that beta2 microglobulin is a component of amyloid fibrils in PASA.

Abnormal immunoglobulin synthesis in monoclonal immunoglobulin light chain and light and heavy chain deposition disease

The Congo red-binding fibrils of AL amyloidosis are the most common form of monoclonal immunoglobulin tissue deposition (MIDD). Nonetheless, the less structured deposits found in light chain deposition disease (LCDD) and the similar, but distinct, deposits of light and heavy chain deposition disease (LHCDD) and heavy chain deposition disease (HCDD) can produce significant clinical pathology. Analyses of immunoglobulin synthesis by bone marrow cells obtained from 7 patients with LCDD and LHCDD demonstrated the production of excess light chains in all and the presence of incomplete light chains or heavy chain fragments in 5, regardless of the presence of an intact monoclonal protein or related subunit in the serum or urine. Our data indicate that, as is the case with the fibrillar deposits of AL amyloid, the non-fibrillar forms of monoclonal Ig deposition (LCDD and LHCDD) can be associated with the presence of immunoglobulin fragments in bone marrow cells. In some instances these appeared to be synthetic in origin, although rapid intracellular proteolysis or a combination of both could not be excluded. In either case the fragments may be more susceptible to tissue deposition, with subsequent organ compromise, than intact Ig chains.

Renal manifestations of plasma cell dyscrasias: an appraisal from the patients' bedside to the research laboratory

One of the most prominent features of plasma cell dyscrasias is the frequent occurrence of renal dysfunction. Renal insufficiency is a common finding with elevated serum creatinine in more than 50% of patients with multiple myeloma at the time of diagnosis. Renal failure is the second most common cause of death in myeloma surpassed only by infections. The reasons for renal failure are multifactorial and early accurate diagnosis of the renal alterations may significantly impact morbidity and survival. Renal failure may result from selective glomerular, tubular interstitial, or vascular pathology or from a combination of pathologic events. The disorders associated with plasma cell dyscrasias include those characterized by monoclonal light chain deposition, encompassing AL-amyloidosis, in addition to the less well-characterized entities, such as heavy chain deposition disease and heavy chain amyloidosis. Therefore, it is more accurate to refer to them as monoclonal immunoglobulin deposition diseases. Staining of renal biopsy specimens for kappa and lambda light chains using immunofluorescence techniques and more sophisticated advanced diagnostic techniques such as immunoelectron microscopy permit detailed characterization of the various renal pathologic manifestations. Renal biopsies can identify monoclonal immunoglobulin deposition, and nephrologists have an opportunity to detect an underlying plasma cell dyscrasia early in its clinical course before overt hematologic alterations become manifest and irreversible renal damage has occurred. The overall spectrum of clinical and pathologic manifestations of monoclonal immunoglobulin deposition renal diseases has expanded considerably in recent years. Recent developments in the research arena promise new therapeutic interventions aimed at avoiding or ameliorating renal damage and even promoting reversal of some of the pathologic alterations. Currently, the 5-year survival rate in myeloma is 29% in white patients and 30% in African-American patients, a rather modest improvement from 24% in the 1970s. Bone marrow ablation followed by transplantation is available as an alternative mode of therapy that may be extraordinarily helpful in a subset of patients with early myeloma.

Urine free light chains in SLE: clonal markers of B-cell activity and potential link to in vivo secreted Ig

As a marker of in vivo B-cell activity, urine levels of free light chain (FLC) were measured twice weekly by radioimmunoassay (RIA) and correlated with disease activity over periods of 5-10 months in seven patients with systemic lupus erythematosus (SLE). In addition, RIA-measured urine albumin was used to track glomerular injury, and alpha1-microglobulin (alpha1-M) levels, 28- to 32-kDa protein, provided control measurements on excretion of low-molecular-weight proteins. As controls, urine FLC levels were obtained from healthy normals and in subjects with acute pharyngitis, sickle-cell anemia, and acute sepsis or pneumonia. The control results showed that with acute sepsis/pneumonia had marked increases in urine FLC, while pharyngitis and sickle-cell controls had normal FLC levels. In SLE, active patients receiving intravenous cyclophosphamide and high-dose steroids exhibited highly increased urine FLC that fluctuated widely during therapy and fell to normal range levels with disease remission. During active SLE, urine albumin often was increased, while alpha1-M levels remained in normal range. In contrast to the increased FLC of active disease, inactive patients on low-dose maintenance therapy had predominantly normal FLC levels throughout the collection period. These results support our hypothesis that longitudinal levels of urine FLC can be used to track disease-related B-cell activity in SLE. Furthermore, we suggest that the urine FLC of active SLE would share LC idiotype with the clonal associated in vivo secreted Ig, and thus permit the identification of these antibodies that are targeted to the culprit immunogen(s) responsible for the pathogenesis of SLE.

Light chain-associated amyloid deposits comprised of a novel kappa constant domain

Light chain-associated amyloidosis is characterized by the deposition as fibrils of monoclonal light chain-related components consisting predominately of the variable domain (VL) or the VL plus up to approximately 60 residues of the constant domain (CL). Here, we describe a patient (designated BIF) with light chain-associated amyloidosis and kappa Bence Jones proteinuria in whom, notably, >80% of the amyloid deposits were comprised of CL-related material. The extracted amyloid protein consisted of 99 aa residues identical in sequence to the main portion of the Ckappa region (positions 109-207) of the precursor Bence Jones protein. Remarkably, the CLs from both molecules contained a Ser-->Asn substitution at position 177. This heretofore undescribed Ckappa alteration did not result from somatic mutation but rather was germline encoded. When tested in our in vitro fibrillogenic kinetic assay, Bence Jones protein BIF was highly amyloidogenic. Notably, endopeptidase treatment of amyloid fibrils prepared from the native light chain revealed the VL to be markedly susceptible to enzymatic digestion, whereas the CL was protease-resistant. Our findings provide evidence that the fragmented light chains typically present in this disease result from proteolytic degradation and suggest that, in this case, conformational differences in VL/CL packing within the fibrils may account for the unusual composition of the amyloid deposits. Additionally, we posit that the previously unrecognized Asn177 substitution represents yet another Ckappa allotype, provisionally designated Km4.

Lymphadenopathy due to amyloid deposition in non-Hodgkin's lymphoma

BACKGROUND

Amyloidosis is a rare complication of non-Hodgkin's lymphoma. Most of the reported patients have had systemic amyloidosis and have died as a result of complications of this disease.

MATERIALS AND METHODS

The clinical cases of two patients with lymphoplasmacytic non-Hodgkin's lymphoma who presented with lymphadenopathy due to localised amyloid deposition are reviewed. Immunohistochemical studies were performed on the amyloid deposits and adjacent lymphoma.

RESULTS

The amyloid deposits in both patients were derived from monoclonal light chains of the same isotype as those expressed by the lymphoma cells and were localised to areas adjacent to the lymphoma despite the presence of circulating light chains. Both patients had an indolent clinical course and treatment appeared to have little influence on the amyloid deposition.

CONCLUSIONS

Non-Hodgkin's lymphoma may be associated with localised amyloidosis secondary to local production and deposition of amyloid from monoclonal light chains synthesised by the lymphoma cells. This is a rare cause of lymphadenopathy which does not respond to treatment of the underlying lymphoma.

Biology and therapy of immunoglobulin deposition diseases

All forms of MIDD represent pathologic deposition of immunoglobulin as amorphous casts, crystals, congophilic fibrils (in AL amyloid), or punctate noncongophilic deposits (in LCDD/HCDD/LHCDD). Diagnosis is based on identification and immunohistochemical characterization of deposits and Congo red staining. Current information including development of novel in vitro and in vivo models suggests a contributory role of both protein and host factors in the pathogenesis of these disorders. In particular, primary structural features of the VL portions of the light chain molecule may affect not only the extent but also the morphologic type of protein deposits. Thus, certain types of light chains may be particularly pathogenic, although the nature or extent of proteolysis/processing involved in the pathogenesis of these deposits is yet unclear. Recent data also point to the importance of accessory molecules, cytokines, and host factors in this process. Newer therapeutic approaches using high-dose therapy with cytotoxic agents or dexamethasone appear promising, although these data need to be confirmed in a larger number of patients. The serendipitous discovery of I-DOX as an agent capable of promoting amyloid resorption provides another novel approach in patients with AL amyloidosis. Continued research on the mechanisms of deposition and resorption of these immunoglobulin deposits should provide important information that can be used to design strategies for more effective therapy and, ultimately, prevention of MIDD.

Monoclonal immunoglobulin deposition disease: a review of immunoglobulin chain alterations

Monoclonal immunoglobulin deposition disease, a complication of overtly malignant or apparently benign immunoproliferative disorders, is a severe disease featuring tissue deposition of monoclonal light, light and heavy, or heavy chains. A number of converging arguments strongly suggest a direct pathogenetic role of structural abnormalities or peculiarities of variables regions of light and/or heavy chains (associated with deletions in the constant region for the heavy chains). Recent structural data on these abnormal immunoglobulin chains are reviewed.

Pattern variations of polyclonal and monoclonal immunoglobulins of different isotypes analyzed by high-resolution two-dimensional electrophoresis

High-resolution two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was used to analyze serum samples and purified immunoglobulins (Ig) obtained from "normal" individuals and from patients diagnosed with monoclonal gammopathies (MG) (n = 47; 5 IgA, 15 IgM, 15 IgG, 4 biclonal IgG, 1 IgD, 7 Bence Jones proteins). Polyclonal and monoclonal heavy (H) chains were located at different restricted gel positions according to their isotype. Monoclonal H chains appeared as sets of spots characterized by charge (pI) and size (M(r)) microheterogeneity. Most of the monoclonal gamma chains were not seen on the gels (12/15). Supplementary polypeptides of 45-48 kDa were detected in serum samples containing monoclonal IgM, but were not seen in MG of other isotypes. However, these polypeptides were not specifically associated with monoclonal IgM because they were also found on protein maps of purified polyclonal IgM. Polyclonal light (L) chains appeared as cloudy bands containing several zones of higher density, whereas monoclonal L chains were usually resolved as single sharp spots. In 6 samples, monoclonal L chains were not seen, and in 9 samples, they appeared as two or more spots, characterized by different pI and/or M(r). In one sample obtained from a patient with a biclonal gammopathy, the L chains were resolved as 4 different spots. Our results confirm that 2-D PAGE is an excellent tool to study Ig. Analysis of the L chain region of the gels was particularly informative. Several monoclonal L chains exhibited heterogeneous two-dimensional spot patterns, suggesting that "subtile" clonal mutations of B-cell lineage and/or posttranslational modifications were involved in their production.

Application of monoclonal anti-idiotypes in the study of AL amyloidosis: therapeutic implications

A monoclonal anti-idiotyped antibody (IgG1k MAb 3B11D4) has been raised against the lambda-chain dimers isolated from the urine of a patient (DEP) with AL amyloidosis. This antibody binds a conformational idiotope present on the monoclonal DEP IgA, but does not recognize the reduced and alkylated lambda-chain monomers, nor the 15- to 17-kDa light chain fragments obtained from the amyloid fibrils, which have the same N-terminal sequence as the urinary light chains. The nonreactivity of this MAb with amyloid fibrils was confirmed by immunohistochemical examination of cryostatic sections of an amyloidoma surgically removed from the patient's subcutaneous tissue. Our data demonstrate that the deletion of about 70 amino acid residues of the C-terminus of the lambda chain prevents the formation of the self-limiting dimer and may facilitate the deposition of fragments into amyloid fibrils. With regard to the amyloidogenic clone, MAb 3B11D4 recognizes the plasma cell clone in bone marrow and 9% of circulating B lymphocytes. Panning and cytotoxicity experiments demonstrate that this antibody has the capability of selectively eliminating the idiotype-positive cells from peripheral blood. Antibodies with these properties could find application in a new therapeutic strategy which provides high-dose chemotherapy, total body irradiation, and rescue with circulating stem cells. These antibodies could be used in two distinct phases: first, in the purging of the stem cells to be infused from the amyloidogenic clone and, secondly, in an attempt to eliminate residual disease by intravenous infusion.

Use of an anti-idiotypic monoclonal antibody in studying amyloidogenic light chains in cells, urine and fibrils: pathophysiology and clinical implications

A monoclonal anti-idiotype antibody (IgG1k MoAb 3B11D4) raised against the amyloidogenic DEP lambda chain dimer binds a conformational idiotope also present on the monoclonal DEP IgA immunoglobulin. MoAb 3B11D4 does not recognize the reduced and alkylated lambda chain monomers, nor the 15-17-kDa fibrillar light chain fragments which have the same N-terminal sequence of the urinary light chains. The lack of about 70 amino acid residues of the C terminal of the protein prevents the formation of the self-limiting dimer and may facilitate the deposition of the fragments into amyloid fibrils. MoAb 3B11D4 recognizes the plasma cell clone in bone marrow and 9% of circulating B lymphocytes. Panning experiments demonstrate that this antibody has the capability to selectively eliminate the idiotype positive cells from peripheral blood. Antibodies with these characteristics could become a useful tool for better understanding the pathogenesis of the disease and for new therapeutic options.

Complementary DNA sequence of human amyloidogenic immunoglobulin light-chain precursors

The primary structure of three amyloid precursor light chains was deduced from the sequence of complementary DNA (cDNA) from bone marrow cells from patients affected with classical lambda (patient Air) or kappa (patient Arn) amyloidosis and from a patient (Aub) in whom lambda amyloid deposits were unusual by their perimembranous location in the kidney glomerulus. All three RNAs were of normal size, as estimated by Northern blotting, and encoded normal-sized light chains. The deduced light-chain sequence from patient Arn was related to the V kappa 1 subgroup, and included ten residues that had not been previously reported at these positions, only one of which (Leu-21) was located in a beta-sheet (4-2). The unusual presence of Asn-70 determined a potential N-glycosylation site. The sequence of the light chain from patient Air belonged to the V lambda 1 subgroup, and included three unusually located amino acid residues, one of which had already been reported in an amyloidogenic lambda-chain. The sequence of the light chain from patient Aub was related to the V lambda 3 subgroup, and contained five amino acid residues that had not previously been described at the corresponding positions; two of them (His-36 and Ser-77) were located in beta-sheets (3-1 and 4-3 respectively). This sequence was also peculiar because of the presence of numerous acidic residues in the complementarity-determining regions. Such unusual primary structures might be responsible for the amyloidogenic properties of these light-chain precursors.

Induction in mice of human light-chain-associated amyloidosis

Primary (idiopathic) or multiple myeloma-associated amyloidosis is characterized by the deposition in tissue of monoclonal light chains or light-chain fragments (AL amyloidosis). In contrast to other types of amyloidosis, information regarding the pathogenesis of light-chain-related amyloid has heretofore been limited due to the lack of a suitable in vivo model. The authors report the successful experimental induction of human AL amyloid deposits. The repeated injection into mice of Bence Jones proteins obtained from two patients with AL amyloidosis produced the histopathologic lesions characteristic of this disease. Partial dehydration of animals before protein injection resulted in the acceleration of amyloid formation. The human proteins were deposited as amyloid within the mouse renal blood vessel walls and parenchymal tissue, as well as in other organs. The deposits were Congo red-positive, exhibited green birefringence, and had a fibrillar ultrastructure. As evidenced immunohistochemically, the experimentally induced amyloid deposits consisted of the injected human light chains, and in addition, contained mouse amyloid P component (AP); mouse immunoglobulin (Ig) or inflammatory-associated amyloid A protein was not detected. Extraction and characterization of the amyloid deposits found within the mouse kidney revealed the presence of a predominantly intact human light polypeptide chain. Mice injected in identical manner with a non-amyloid-associated Bence Jones protein had no or only rare amyloid deposits. The experimental mouse model provides a means to ascertain the amyloidogenic potential of human monoclonal light chains and to study further the pathogenesis of AL amyloidosis.

Frequency and genetic background of the position 122 (Val----Ile) variant transthyretin gene in the black population

Transthyretin (TTR) (122 Val----Ile), caused by a point mutation which destroys a MaeIII restriction site, is associated with cardiac amyloidosis in black individuals. To estimate the frequency of the MaeIII(-) gene in the black population without overt cardiac disease, DNA from 177 black individuals without amyloidosis was amplified by the PCR around TTR codon 122 and was digested with MaeIII. The MaeIII(-) gene frequency was 4/354 (1.1%; 95% confidence interval 0.32%2.7%), suggesting that the variant is relatively common in blacks. HLA genotype testing did not suggest that the TTR (122 Val----Ile) heterozygotes were of a closely related genetic background.

Nephrotoxic potential of Bence Jones proteins

BACKGROUND

The renal manifestations of diseases associated with the production of monoclonal light chains--myeloma (cast) nephropathy, light-chain deposition disease, and amyloidosis AL--result from the deposition of certain Bence Jones proteins as tubular casts, basement-membrane precipitates, or fibrils, respectively. For unknown reasons, the severity of the renal manifestations of these diseases varies greatly from patient to patient. We employed an experimental in vivo model to determine the pathologic importance of various Bence Jones proteins.

METHODS

Mice were injected intraperitoneally with 300 mg of Bence Jones protein from 40 patients with multiple myeloma or amyloidosis AL and killed 48 hours later. The mouse kidneys were examined by light and electron microscopy, and light-chain deposits were identified immunohistochemically with highly specific antihuman light-chain antiserum.

RESULTS

Of the 40 different human Bence Jones proteins studied, 26 were deposited in the mouse kidneys predominantly as tubular casts, basement-membrane precipitates, or crystals; no light-chain deposits were detected in the kidneys of the mice that received the other 14 Bence Jones proteins. Of the 18 patients for whom renal tissue was available for study, the findings in 14 were comparable to those in the mice. Furthermore, the proteins obtained from 22 of the 27 patients whose serum creatinine concentrations equaled or exceeded 168 mumol per liter (1.9 mg per deciliter) were deposited in the mouse kidneys, whereas protein deposition occurred after the injection of proteins from only 4 of the 13 patients with serum creatinine concentrations below 168 mumol per liter. The repeated injection of Bence Jones proteins from two patients who had amyloidosis AL resulted in deposition of the protein in the mouse kidneys as amyloid.

CONCLUSIONS

Particular Bence Jones proteins are primarily responsible for producing the distinctive types of protein deposition in renal tissue and the clinical manifestations that occur in patients with light-chain-associated diseases. This experimental model has potential value for the identification of nephrotoxic or amyloidogenic light chains.

Structure of a monoclonal kappa chain of the V kappa IV subgroup in the kidney and plasma cells in light chain deposition disease

That structural abnormalities may be responsible for nonamyloid immunoglobulin (Ig) light chain deposition disease (LCDD) is suggested by previous results of Ig biosynthesis studies, but this hypothesis was not documented at the molecular level. We report on the first complete primary sequence deduced from cDNA analysis of a kappa light chain responsible for LCDD associated with an apparently nonsecretory myeloma. Bone marrow myeloma cells contained intracellular kappa chains and no heavy chains by immunofluorescence. Kidney biopsy showed typical nonamyloid PAS-positive kappa chain deposits. SDS-PAGE analysis of material extracted from a kidney biopsy specimen and of Ig produced by the myeloma cells revealed kappa chains of abnormally high apparent molecular mass (30,000). Comparison of the NH2-terminal aminoacid sequence of the kappa chain deposited in the kidney and of the complete sequence of several identical kappa cDNA clones from bone marrow cells showed the identity of the tissue deposited and plasma cell kappa chain. The kappa mRNA had an overall normal structure and corresponded to the V kappa IV gene rearranged to J kappa 1 and followed by a normal constant exon of the Km(3) allotype. The variable sequence differed from the V kappa IV germline gene by nine point mutations, including an Asp----Asn substitution at position +70 resulting in a potential N-glycosylation site. In vitro biosynthesis experiments and treatment with N-glycosidase provided evidence for the intracellular glycosylation of the monoclonal kappa chain. The peculiar sequence and the glycosylation of a kappa chain of the rare V kappa IV subgroup might be responsible for structural abnormalities leading to tissue deposition.

Relevance of class, molecular weight and isoelectric point in predicting human light chain amyloidogenicity

The ability to predict the amyloidogenicity of certain light chains may facilitate an earlier diagnosis of AL amyloidosis and, possibly, lead to more effective treatment. Using current methods, available in clinical chemistry laboratories, we assessed the class, the relative molecular mass (Mr) and the isoelectric point of urinary monoclonal light chains from 35 patients with AL amyloidosis (A+) and 51 without amyloidosis (A-). The light chain class (LCC) was lambda in 77% and 45% of A+ and A- patients, respectively. Light chain fragments (LCF) with low Mr (12-18 x 10(3) were detected in the urine of 30/35 A+ patients and in 15/51 A- ones. The mean (SD) isoelectric point (pI) of A+ light chains was 4.8 (1.1) while in A- patients it was 6.2 (1.6). Univariate analysis showed significant differences between the two groups for the three parameters. Discriminant analysis gave a function which allowed a correct allocation of 81% of the cases between the two groups.

Restriction of blood and marrow CLL-B cells to free L-chain Ig secretion: implication for normal B-cell function and control

The culture supernatant immunoglobulin (CSIg) of blood mononuclear cells (MNCs) from 14 patients with chronic lymphocytic leukemia (CLL) was determined using a panel of nanogram-sensitive radioimmunoassays that measured IgM, IgG, IgA, total kappa-Ig, and total lambda-Ig. Bone marrow cells from three patients were also cultured and the blood and marrow CSIg results were compared. The CSIg of 1-day cultures was employed as a measure of shed surface membrane Ig (SmIg) for the 7- and 14-day cultures. Adjusting for shed SmIg, it was found that in resting unstimulated conditions, monotypic free light (L) chain was virtually the only identifiable secreted Ig product in 12 of 14 blood MNC cultures and in three of three marrow cell cultures. In pokeweed mitogen (PWM)-stimulated cultures, monotypic free L chain also dominated, except for significant polyclonal Ig secretion found in three cultures from residual normal blood MNCs. The secretion by CLL-B cells of significant amounts of free L chain with a virtual absence of whole Ig raises important questions about the presence and function of phenotypically equivalent normal B cells in blood and bone marrow, and also the immunological role of secreted free L chain. Noting recent evidence that PWM-stimulated normal blood MNCs secrete significant amounts of polyclonal free L chain, the argument is advanced that normal blood and bone marrow contain B cells of CLL-B phenotype and that secreted free L-chain-bearing clonal idiotypic markers interact with autologous cells of the idiotypic regulatory network and possess a key role in the regulation of clonal growth and Ig synthesis.

Immunoglobulin synthesis in primary and myeloma amyloidosis

Bone marrow cells from 14 patients with primary amyloidosis and two patients with myeloma amyloidosis were studied by immunofluorescence and biosynthesis experiments after incorporation of radioactive amino acids. Cells from four patients affected with non-myeloma secondary amyloidosis were also studied as controls. In primary amyloidosis, monoclonal plasma cell populations were demonstrated by immunofluorescence in virtually every case, even in patients without serum and urine monoclonal immunoglobulin and with a normal percentage of bone marrow plasma cells. Biosynthesis experiments showed the secretion of large amounts of free light chains, most often of the lambda type, in every primary or myeloma amyloidosis case and the presence of light chain fragments in almost all cases. Special features in certain patients were the synthesis of short gamma chains (two cases), assembly block at the HL half molecule level of a monoclonal IgA (one case) and secretion of decameric abnormally large kappa chains (one case). This is in contrast with non-myelomatous secondary amyloidosis where the distribution of bone marrow plasma cells was normal by immunofluorescence and where normal sized immunoglobulins were synthesized, without free light chain secretion and fragments. These data confirm that primary amyloidosis belongs to plasma cell dyscrasias and emphasize the role of free light chains and light chain fragments in the pathogenesis of amyloid deposition.