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Monoclonal gammopathies of renal significance (MGRS) encompass a remarkable variety of kidney diseases that result from intrinsic nephrotoxic properties of certain monoclonal Igs or their subunits. Effective disease-modifying treatments rely on the targeting of a malignant B-cell clone that may be demonstrable but often is quite hypothetical. Hence, convincing arguments for the genuine monoclonal character of the causative mono-isotypic Ig tissue deposits is needed for design of appropriate treatment strategies. The purpose of this article was to critically analyze distinct situations of suspected MGRS that occur in the practice of pathologists, nephrologists, hematologists, and immunologists. A particular focus of interest is the group of conditions known as proliferative glomerulonephritis with mono-isotypic immunoglobulin deposits (PGNMIDs), which illustrates the difficulties and ambiguities surrounding a definitive assignment of MGRS status., (© 2021 International Society of Nephrology. Published by Elsevier Inc.)

Scleromyxedema is a rare skin and systemic mucinosis that is usually associated with monoclonal gammopathy (MG). In this French multicenter retrospective study of 33 patients, we investigated the clinical and therapeutic features of MG-associated scleromyxedema. Skin molecular signatures were analyzed using a transcriptomic approach. Skin symptoms included papular eruptions (100%), sclerodermoid features (91%), and leonine facies (39%). MG involved an immunoglobulin G isotype in all patients, with a predominant λ light chain (73%). Associated hematologic malignancies were diagnosed in 4 of 33 patients (12%) (smoldering myeloma, n = 2; chronic lymphoid leukemia, n = 1; and refractory cytopenia with multilineage dysplasia, n = 1). Carpal tunnel syndrome (33%), arthralgia (25%), and dermato-neuro syndrome (DNS) (18%) were the most common systemic complications. One patient with mucinous cardiopathy died of acute heart failure. High-dose IV immunoglobulin (HDIVig), alone or in combination with steroids, appeared to be quite effective in nonsevere cases (clinical complete response achieved in 13/31 patients). Plasma cell-directed therapies using lenalidomide and/or bortezomib with dexamethasone and HDIVig led to a significant improvement in severe cases (HDIVig refractory or cases with central nervous system or cardiac involvement). The emergency treatment of DNS with combined plasmapheresis, HDIVig, and high-dose corticosteroids induced the complete remission of neurological symptoms in 4 of 5 patients. Quantitative reverse-transcriptase polymerase chain reaction analysis of 6 scleromyxedema skin samples showed significantly higher profibrotic pathway levels (transforming growth factor β and collagen-1) than in healthy skin. Prospective studies targeting plasma cell clones and/or fibrotic pathways are warranted for long-term scleromyxedema management., (© 2020 by The American Society of Hematology.)

Randall-type heavy chain deposition disease (HCDD) is a rare disorder characterized by tissue deposition of a truncated monoclonal immunoglobulin heavy chain lacking the first constant domain. Pathophysiological mechanisms are unclear and management remains to be defined. Here we retrospectively studied 15 patients with biopsy-proven HCDD of whom 14 presented with stage 3 or higher chronic kidney disease, with nephrotic syndrome in 9. Renal lesions were characterized by nodular glomerulosclerosis, with linear peritubular and glomerular deposits of γ-heavy chain in 12 patients or α-heavy chain in 3 patients, without concurrent light chain staining. Only 2 patients had symptomatic myeloma. By serum protein electrophoresis/immunofixation, 13 patients had detectable monoclonal gammopathy. However, none of these techniques allowed detection of the nephrotoxic truncated heavy chain, which was achieved by immunoblot and/or bone marrow heavy chain sequencing in 14 of 15 patients. Serum-free kappa to lambda light chain ratio was abnormal in 11 of 11 patients so examined. Immunofluorescence studies of bone marrow plasma cells showed coexpression of the pathogenic heavy chain with light chain matching the abnormal serum-free light chain in all 3 tested patients. Heavy chain sequencing showed first constant domain deletion in 11 of 11 patients, with high isoelectric point values of the variable domain in 10 of 11 patients. All patients received chemotherapy, including bortezomib in 10 cases. Renal parameters improved in 11 patients who achieved a hematological response, as assessed by normalization of the free light chain ratio in 8 cases. Tissue deposition in HCDD relates to physicochemical peculiarities of both variable and constant heavy chain domains. Early diagnosis and treatment with bortezomib-based combinations appear important to preserve renal prognosis. Thus, monitoring of serum-free light chain is an indirect but useful method to evaluate the hematological response., (Copyright © 2016 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Results of Phase III studies involving a large number of Alzheimer's disease (AD) patients treated by passive immunotherapy with humanized anti-amyloid β monoclonal antibodies have recently been released. These approaches failed to show a significant clinical benefit in patients with mild to moderate AD. The most considered explanation is that the patients have been treated too late. Whereas targeting patients at asymptomatic stages of the disease is a critical step in the goal of improving the efficacy of such antibody-based strategies, several other important factors should be considered in the development and clinical evaluation of anti-amyloid β immunotherapies, including the as yet poorly understood relationship of AD with the immune system and the importance of cerebral amyloid angiopathy. Better understanding the role of immune responses in AD and their impact on immunotherapy appears essential in the design of alternative or combinatorial immunotherapy approaches in AD, which may imply effectors other than antibodies and even additional antigenic targets., (Copyright © 2013 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.)

Two unusual but similar cases of very high serum iron, extremely high transferrin concentrations (5.4 to 6.5 g/L), and increased transferrin saturation are reported. No anemia or microcytosis was observed. The ferritin concentration remained within the normal range, and no iron overload was observed. In one case, the in vivo half-life of 59Fe-labeled transferrin was shown to be prolonged (206 minutes versus 75 minutes for controls). In both patients, a monoclonal IgG was observed in the serum. The association between serum transferrin and monoclonal IgG was demonstrated by Western blot analysis and affinity chromatography. We suggest that the transferrin bound to the monoclonal IgG molecule has a prolonged half-life in the circulation, leading to high transferrin concentrations, and that the increased serum iron values prevent the onset of anemia. The antitransferrin activity of monoclonal antibody should be added to the list of situations accounting for elevated serum iron with elevated transferrin saturation.

Background: Renal disease related to the deposition of monoclonal immunoglobulins containing both heavy and light chains can occur in type 1 cryoglobulinemia, Randall type light and heavy chain deposition disease (LHCDD), and immunotactoid glomerulonephritis. We report a novel phenotype of glomerular injury that does not conform to any of the previously described patterns of glomerular involvement by monoclonal gammopathy., Methods: Ten cases of unclassifiable proliferative glomerulonephritis manifesting glomerular monoclonal immunoglobulin G (IgG) deposits were identified retrospectively from the archives of the Renal Pathology Laboratory of Columbia University over the past 3 years (biopsy incidence 0.21%)., Results: The monoclonal immunoglobulins formed granular electron dense deposits in mesangial, subendothelial, and subepithelial sites, mimicking ordinary immune complex-mediated glomerulonephritis and producing a diffuse endocapillary proliferative or membranoproliferative glomerulonephritis. However, by immunofluorescence, the deposits were monoclonal, staining for a single light chain isotype and a single gamma subclass (including two IgG1kappa, one IgG1lambda, one IgG2lambda, four IgG3kappa, and one IgG3lambda). All cases stained for the three constant domains of the gamma heavy chain (CH1, CH2, and CH3), suggesting deposition of a nondeleted immunoglobulin molecule. Tissue fixation of complement was observed in 90% of cases, and 40% of patients had hypocomplementemia. Clinical presentations included renal insufficiency in 80% (mean serum creatinine 2.8 mg/dL, range 0.9 to 8.0), proteinuria in 100% (mean urine protein 5.8 g/day; range 1.9 to 13.0), nephrotic syndrome in 44%, and microhematuria in 60%. A monoclonal serum protein with the same heavy and light chain isotype as that of the glomerular deposits was identified in 50% of cases (including three IgGkappa and two IgGlambda); however, no patient had clinical or laboratory features of type 1 cryoglobulinemia. No patient had overt myeloma or lymphoma at presentation or over the course of follow-up (mean 12 months)., Conclusion: Glomerular deposition of monoclonal IgG can produce a proliferative glomerulonephritis that mimics immune-complex glomerulonephritis by light and electron microscopy. Proper recognition of this entity requires confirmation of monoclonality by staining for the gamma heavy chain subclasses.

Background: Transmissible spongiform encephalopathies are associated with a structural transition in the prion protein that results in the conversion of the physiological PrPc to pathological PrP(Sc). We investigated whether this conformational transition can be inhibited and reversed by peptides homologous to the PrP fragments implicated in the abnormal folding, which contain specific residues acting as beta-sheet blockers (beta-sheet breaker peptides)., Methods: We studied the effect of a 13-residue beta-sheet breaker peptide (iPrP13) on the reversion of the abnormal structure and properties of PrP(Sc) purified from the brains of mice with experimental scrapie and from human beings affected by sporadic and variant Creutzfeldt-Jakob disease. In a cellular model of familial prion disease, we studied the effect of the peptide in the production of the abnormal form of PrP in intact cells. The influence of the peptide on prion infectivity was studied in vivo by incubation time assays in mice with experimental scrapie., Findings: The beta-sheet breaker peptide partly reversed in-vitro PrP(Sc) to a biochemical and structural state similar to that of PrPc. The effect of the peptide was also detected in intact cells. Treatment of prion infectious material with iPrP13 delayed the appearance of clinical symptoms and decreased infectivity by 90-95% in mice with experimental scrapie., Interpretation: Beta-sheet breaker peptides reverse PrP conformational changes implicated in the pathogenesis of spongiform encephalopathies. These peptides or their derivatives provide a useful tool to study the role of PrP conformation and might represent a novel therapeutic approach for prion-related disorders.

Light chain deposition disease (LCDD) and light chain amyloidosis (AL) are disorders of monoclonal immunoglobulin deposition in which normally soluble serum precursors form insoluble deposits in tissues. A common feature in both is the clonal proliferation of B-cells that produce pathogenic light chains. However, the deposits in LCDD differ from those in AL in that they are ultrastructurally granular rather than fibrillar and do not bind Congo red or colocalize with amyloid P component or apolipoprotein E. The reason(s) for their differences are unknown but are likely multifactorial and related to their protein conformation and their interaction with other molecules and tissue factors in the microenvironment. Knowledge of the primary structure of the light chains in LCDD is very limited. In the present study two new kappa(1) light chains from patients with LCDD are described and compared to seven other reported kappa-LCDD proteins. The N-terminal amino acid sequences of light chain GLA extracted from the renal biopsy and light chain CHO from myocardial tissue were each identical to the respective light chains isolated from the urines and to the V-region amino acid sequences translated from the cloned cDNAs obtained from bone marrow cells. The germline V-region sequences, determined from the genomic DNA in both and in MCM, a previously reported kappa(1) LCDD light chain, were identical and related to the L12a germline gene. The expressed light chains in all three exhibit amino acid substitutions that arise from somatic mutation and result in increased hydrophobicity with the potential for protein destabilization and disordered conformation.

We retrospectively analyzed the B-cell function and leukocyte chimerism of 22 patients with severe combined immunodeficiency with B cells (B(+) SCID) who survived more than 2 years after bone marrow transplantation (BMT) to determine the possible consequences of BMT procedures, leukocyte chimerism, and SCID molecular deficit on B-cell function outcome. Circulating T cells were of donor origin in all patients. In recipients of HLA-identical BMT (n = 5), monocytes were of host origin in 5 and B cells were of host origin in 4 and of mixed origin in 1. In recipients of HLA haploidentical T-cell-depleted BMT (n = 17), B cells and monocytes were of host origin in 14 and of donor origin in 3. Engraftment of B cells was found to be associated with normal B-cell function. In contrast, 10 of 18 patients with host B cells still require Ig substitution. Conditioning regimen (ie, 8 mg/kg busulfan and 200 mg/kg cyclophosphamide) was shown neither to promote B-cell and monocyte engraftment nor to affect B-cell function. Eight patients with B cells of host origin had normal B-cell function. Evidence for functional host B cells was further provided in 3 informative cases by Ig allotype determination and by the detection, in 5 studied cases, of host CD27(+) memory B cells as in age-matched controls. These results strongly suggest that, in some transplanted patients, host B cells can cooperate with donor T cells to fully mature in Ig-producing cells.

Megalin is an endocytic receptor expressed on the luminal surface of the renal proximal tubules. The receptor is believed to play an important role in the tubular uptake of macromolecules filtered through the glomerulus. To elucidate the role of megalin in vivo and to identify its endogenous ligands, we analyzed the proximal tubular function in mice genetically deficient for the receptor. We demonstrate that megalin-deficient mice exhibit a tubular resorption deficiency and excrete low molecular weight plasma proteins in the urine (low molecular weight proteinuria). Proteins excreted include small plasma proteins that carry lipophilic compounds including vitamin D-binding protein, retinol-binding protein, alpha(1)-microglobulin and odorant-binding protein. Megalin binds these proteins and mediates their cellular uptake. Urinary loss of carrier proteins in megalin-deficient mice results in concomitant loss of lipophilic vitamins bound to the carriers. Similar to megalin knockout mice, patients with low molecular weight proteinuria as in Fanconi syndrome are also shown to excrete vitamin/carrier complexes. Thus, these results identify a crucial role of the proximal tubule in retrieval of filtered vitamin/carrier complexes and the central role played by megalin in this process.

51 monoclonal antibodies (McAb) with putative specificity for human IgA, the IgA subclasses, Am allotypes or secretory component (SC) were evaluated for immunoreactivity and specificity by nine laboratories employing immunodiffusion, agglutination, immunohistological assays, immunoblotting and direct binding and competitive inhibition enzyme immunoassays. McAbs specific for IgA PAN (n = 24), IgA1 (n = 7), IgA2 (n = 3), IgA2m(2) (n = 2), non-IgA2m(2) (n = 4) and SC or secretory IgA (n = 5) were identified that were immunoreactive and specific in the assays employed. The McAbs identified as IgA- or SC-reactive were shown to be non-reactive to human IgG, IgM, IgD, IgE, kappa and lambda by direct binding and competitive inhibition immunoassays. Interestingly, no McAbs with restricted specificity for IgA2m(1) were identified. Some McAbs displayed higher affinity and/or better performance in one or several of the assay groups. The IgA- and SC-specific McAbs identified in this international collaborative study have potential as immunochemical reference reagents to identify and quantitate monomeric and polymeric IgA in human serum and secretions.

Light chain deposition disease (LCDD) results from a propensity of some human monoclonal L chains to form tissue deposits. We designed an experimental model for in vivo expression of human kappa L chain sequences in mice and compared a somatically mutated LCDD chain with a closely related control kappa chain, both encoded by the unique V kappa IV gene. Mice secreting the LCDD chain but not those producing the control chain showed deposits with a distribution similar to that observed in patients. These data show that discrete changes in V region sequences can play a major role in tissue deposition of human L chains.

Kidney tubule dysfunction and lesions are frequent complications of myeloma, related to unknown properties of the monoclonal light chain. We have analyzed protease sensitivity and binding properties of urinary light chains from four patients with Fanconi's syndrome, 12 with cast nephropathy, and four control patients without myeloma-associated tubulopathy. All light chains were normal-sized, monomeric and/or dimeric, and none was N-glycosylated. Kinetic studies of light chain digestion by pepsin and the lysosomal enzyme cathepsin B showed the generation of a protease-resistant 12 kDa fragment, corresponding to the V domain of the kappa chain in the four Fanconi's syndrome patients; in two out of four the V domain was also completely resistant to trypsin. Western and dot blots revealed similar patterns of reactivity of light chains from patients with the Fanconi's syndrome towards other light chains. Properties of cast-nephropathy light chains were more heterogeneous but clearly differed from those of Fanconi's syndrome: (i) 9 out of 12 were of the lambda-type; (ii) only four yielded a transient 12 kDa fragment after cathepsin B digestion, but all showed some resistance to proteolysis of the entire molecule or a fragment thereof to at least one protease, at variance with control light chains; (iii) they displayed various patterns of reactivity with other light chains; (iv) 7 out of 12 reacted specifically with Tamm-Horsfall protein (THP) by ELISA, in contrast with those of Fanconi's syndrome. In one patient who presented with cast nephropathy and the Fanconi's syndrome, the light chain exhibited both partial resistance of the V kappa domain to cathepsin B and the highest reactivity with THP.(ABSTRACT TRUNCATED AT 250 WORDS)

To study the subclass distribution of autoantibodies and their complement-fixing capacity in cicatricial pemphigoid (CP) and epidermolysis bullosa acquisita (EBA) we studied the sera from 23 patients by both indirect immunofluorescence (IIF) on 4-microns cryostat sections of normal human skin and immunoblotting of epidermal or dermal extracts. Monoclonal antibodies of strict specificity for human IgG subclasses were used. Sera from 20 patients with BP served as controls. In addition, total IgG subclass levels were determined by indirect competitive ELISA in all sera. Complement binding capacity was studied by IIF using antibodies to C3 after incubation of skin section with autoantibodies and source of fresh complement. CP autoantibodies reacting with the 230-240 kD and/or the 180-kD epidermal bands showed an IgG4/IgG1 subclass restriction, with a predominance of IgG4 in 10 cases, of IgG1 in four. In BP sera, IgG4 and IgG1 autoantibodies were detected with a similar frequency (100% and 83%, respectively). In EBA sera, autoantibodies reacting with the 290 kD and 145 kD dermal bands also showed an IgG1/IgG4 restriction. Concordant results were obtained by IIF. However, the IIF method had a lower sensitivity for the detection of IgG4 CP antibodies and IgG1 EBA antibodies than immunoblotting. Finally, when CP antibodies were analyzed for their complement-binding activity, it was found that sera containing IgG4 autoantibodies alone never fixed complement whereas all complement-fixing CP sera had IgG1 autoantibodies, suggesting that only this subclass of antibodies is capable of fixing complement.

The lectin jacalin from jackfruit seeds shows a human IgA-subclass specificity by gel precipitation and Western blotting. However, its reactivity with IgA2 is a matter of controversy. We further studied the immunoglobulin isotype specificity of jacalin by affinity chromatography with myeloma sera and by inhibition of jacalin binding to solid-phase IgA1 by purified monoclonal immunoglobulins. The lectin proved to bind IgA2 of both allotypes with a lower apparent affinity than for IgA1 and IgD.

Measurement of antibodies to the capsular polysaccharide polyribosylribitolphosphate (PRP) of Haemophilus influenzae type b by ELISA is made difficult by the poor binding of this antigen to the solid phase. Six coating conditions were compared using immune and non-immune human sera. Direct coating with PRP was inefficient. Precoating with protamine or poly-L-lysine (PLL) yielded irreproducible results and high background levels. Assays with PRP conjugated with PLL as coat were not sensitive enough. In addition, anti-PRP antibodies, especially those belonging to the IgM class, crossreacted with PLL. Coating with avidin or streptavidin followed by incubation with biotin-coupled PRP was not satisfactory either, due to binding of certain sera in the absence of PRP. Coating with PRP coupled to tyramine resulted in low backgrounds and acceptable specific binding levels. However, the finding that the binding of a few sera was only partially inhibited by soluble PRP led us to include an inhibition step in every experiment. Only optical densities inhibited by the antigen were taken into account. In view of the lack of parallelism of dilution curves from different sera, no attempt was made to express the results in weight units. They were expressed in arbitrary units calculated by comparison with internal standards. Under such conditions, the assay permitted a reproducible (interassay coefficients of variation around 10%) determination of PRP-Ab belonging to the various immunoglobulin classes and IgG subclasses and showed a good correlation with results obtained using the Farr assay.

Serum IgG subclasses were measured by a competitive indirect immunoassay with monoclonal antibodies in 31 leukemic patients before and after bone marrow transplantation. Antibodies to Hemophilus influenzae type b (Hib) capsular polysaccharide were determined in 28 cases. Abnormally low or borderline subclass (mostly IgG2 and IgG4) levels were found late after transplant in 23 infected and noninfected patients. These levels persisted for as long as 25 months, in association with low or borderline IgA levels in 78% of the cases. IgG2, IgG4, and IgA often showed a parallel evolution, whereas IgG1, IgG3, and IgM often varied together in the opposite way. Class but not subclass deficiencies were more frequent in patients with graft-v-host disease (GVHD). Subclass abnormalities predominated in infected patients, with mean levels correlating with the severity of infections; however, the abnormalities are not clearly predictive of infections in individual cases. Most patients with Hib pneumonia showed virtually no IgG antibody response to Hib, and one-half of the patients had a moderate IgM and IgA response. In the whole series, many sera collected greater than 1 year after graft contained very low or undetectable antibodies. Correlation between anti-Hib antibody and IgG2 levels was significant but weak because of discrepancies that were only partially explained by the subclass distribution of the antibodies.

A competitive indirect ELISA is described for the measurement of IgG4 levels. It uses a monoclonal anti-subclass and antibody and purified monoclonal IgG4 as standards. This method is sensitive and reproducible and more accurate than hemagglutination inhibition and radial immunodiffusion. Serum IgG4 levels in 173 normal adults were less than 0.01-2.1 mg/ml (mean 0.30 mg/ml) in women and less than 0.01-1.87 mg/ml (mean 0.465 mg/ml) in men.