Clinical and histological characteristics of renal AA amyloidosis: a retrospective study of 68 cases with a special interest to amyloid-associated inflammatory response

Renal alterations in cats (Felis catus) housed in shelters and affected by systemic AA-amyloidosis: Clinicopathological data, histopathology, and ultrastructural features

AA-amyloidosis is frequent in shelter cats, and chronic kidney disease is the foremost cause of death. The aims were to describe kidney laboratory and microscopic findings in shelter cats with AA-amyloidosis. Cats were included if kidney specimens were collected post-mortem and laboratory data were available within 6 months before death. Renal lesions were evaluated with optical and electron microscopy. Mass spectrometry was used to characterize amyloid. Nine domestic short-hair cats were included; 4 females and 5 males with a median age of 8 years (range = 2-13). All cats had blood analyses and urinalyses available. Serum creatinine concentrations were increased in 6 cats and symmetric dimethylarginine was increased in all of the cats. All of the cats had proteinuria. Eight of 9 cats had amyloid in the medulla, and 9 had amyloid in the cortex (glomeruli). All cats had amyloid in the interstitium. Six cats had concurrent interstitial nephritis and 1 had membranoproliferative glomerulonephritis. All cats had extrarenal amyloid deposits. Amyloid was AA in each case. In conclusion, renal deposition of amyloid occurs in both cortex and medulla in shelter cats and is associated with azotemia and proteinuria. Renal involvement of systemic AA-amyloidosis should be considered in shelter cats with chronic kidney disease. The cat represents a natural model of renal AA-amyloidosis.

2024 Update on Classification, Etiology, and Typing of Renal Amyloidosis: A Review

Amyloidosis is a protein folding disease that causes organ injuries and even death. In humans, 42 proteins are now known to cause amyloidosis. Some proteins become amyloidogenic as a result of a pathogenic variant as seen in hereditary amyloidoses. In acquired forms of amyloidosis, the proteins form amyloid in their wild-type state. Four types (serum amyloid A, transthyretin, apolipoprotein A-IV, and β2-macroglobulin) of amyloid can occur either as acquired or as a mutant. Iatrogenic amyloid from injected protein medications have also been reported and AIL1RAP (anakinra) has been recently found to involve the kidney. Finally, the mechanism of how leukocyte cell-derived chemotaxin 2 (ALECT2) forms amyloid remains unknown. This article reviews the amyloids that involve the kidney and how they are typed.

Systemic Amyloidosis and Kidney Transplantation: An Update

Amyloidosis is a heterogeneous disorder characterized by abnormal protein aggregate deposition that often leads to kidney involvement and end-stage kidney disease. With advancements in diagnostic techniques and treatment options, the prevalence of patients with amyloidosis requiring chronic dialysis has increased. Kidney transplantation is a promising avenue for extending survival and enhancing quality of life in these patients. However, the complex and heterogeneous nature of amyloidosis presents challenges in determining optimal referral timing for transplantation and managing post-transplantation course. This review focuses on recent developments and outcomes of kidney transplantation for amyloidosis-related end-stage kidney disease. This review also aims to guide clinical decision-making and improve management of patients with amyloidosis-associated kidney disease, offering insights into optimizing patient selection and post-transplant care for favorable outcomes.

A comparative urinary proteomic and metabolomic analysis between renal aa amyloidosis and membranous nephropathy with clinicopathologic correlations

Urinary omics has become a powerful tool for elucidating pathophysiology of glomerular diseases. However, no urinary omics analysis has been performed yet on renal AA amyloidosis. Here, we performed a comparative urine proteomic and metabolomic analysis between recently diagnosed renal AA amyloidosis (AA) and membranous nephropathy (MN) patients. Urine samples of 22 (8 AA, 8 MN and 6 healthy control) patients were analyzed with nLC-MS/MS and GC/MS for proteomic and metabolomic studies, respectively. Pathological specimens were scored for glomerulosclerosis and tubulointerstitial fibrosis grades. Functional enrichment analysis between AA and control groups showed enrichment in cell adhesion related sub-domains. Uromodulin (UMOD) was lower, whereas ribonuclease 1 (RNase1) and α-1-microglobulin/bikunin precursor (AMBP) were higher in AA compared to MN group. Correlations were demonstrated between UMOD-proteinuria (r = -0.48, p = 0.03) and AMBP-eGFR (r = -0.69, p = 0.003) variables. Metabolomic analysis showed myo-inositol and urate were higher in AA compared to MN group. A positive correlation was detected between RNase1 and urate independent of eGFR values (r = 0.63, p = 0.01). Enrichment in cell adhesion related domains suggested a possible increased urinary shear stress due to amyloid fibrils. UMOD, AMBP and myo-inositol were related with tubulointerstitial damage, whereas RNase1 and urate were believed to be related with systemic inflammation in AA amyloidosis. SIGNIFICANCE: Urinary omics studies have become a standard tool for biomarker studies. However, no urinary omics analysis has been performed yet on renal AA amyloidosis. Here, we performed a comparative urinary omics analysis between recently diagnosed renal AA amyloidosis (AA), membranous nephropathy (MN) patients and healthy controls. Pathological specimens were scored with glomerulosclerosis (G) and tubulointerstitial fibrosis (IF) grades to consolidate the results of the omics studies and correlation analyzes. Functional enrichment analysis showed enrichment in cell adhesion related sub-domains due to downregulation of cadherins; which could be related with increased urinary shear stress due to amyloid deposition and disruption of tissue micro-architecture. In comparative proteomic analyzes UMOD was lower, whereas RNase1 and AMBP were higher in AA compared to MN group. Whereas in metabolomic analyzes; myo-inositol, urate and maltose were higher in AA compared to MN group. Correlations were demonstrated between UMOD-proteinuria (r = -0.48, p = 0.03), AMBP-eGFR (r = -0.69, p = 0.003) and between RNase1-Urate independent of eGFR values (r = 0.63, p = 0.01). This study is the first comprehensive urinary omics analysis focusing on renal AA Amyloidosis to the best of our knowledge. Based on physiologic roles and clinicopathologic correlations of the molecules; UMOD, AMBP and myo-inositol were related with tubulointerstitial damage, whereas RNase1 and urate were believed to be increased with systemic inflammation and endothelial damage in AA amyloidosis.

AA amyloidosis With Ig-Dominant Staining and Diagnostically Unusual Features

Introduction

Although serum amyloid A (AA) amyloid may occasionally show nonspecific staining by immunofluorescence (IF), the correct diagnosis can usually be determined by integrating pathologic features and clinical scenario, and using AA amyloid immunohistochemistry (IHC) and/or mass spectrometry. A recent mass spectrometry-based study described false-positive Ig IF staining in a subset of AA amyloid cases.

Methods

We sought to delineate clinicopathologic features of AA amyloid with Ig-dominant staining by using a retrospective review.

Results

AA amyloid with Ig-dominant staining was identified in 10 patients from 5 institutions, representing 1.2% to 4% of AA amyloid kidney biopsies. Evidence of a monoclonal protein was documented in 0% to 2.7% of patients with AA amyloid screened for inclusion, but 30% of those with Ig-dominant staining. The patient population had equal sex distribution and presented at median age of 68.5 years with nephrotic proteinuria and kidney impairment. Etiologies of AA amyloid included injection drug use (30%), autoimmune disease (20%), and chronic infection (10%); 40% had no identified clinical association. On biopsy, heavy chain (co)dominant staining by IF (in 80%), discordant distribution in Ig staining (in 20%), tubulointerstitial nephritis (in 30%), and/or crescents (in 10%) were present. Two of 3 patients with paraproteinemia had concordant heavy and/or light chain dominant staining within the AA amyloid. Two cases were initially misdiagnosed as Ig-associated amyloidosis.

Conclusion

We describe the morphologic spectrum of AA amyloidosis with Ig-dominant staining which may have clinical, laboratory, and pathologic overlap with amyloid light chain (AL), amyloid heavy chain, and heavy and light chain (AHL) amyloidosis.

Renal amyloid-A amyloidosis in cats: Characterization of proteinuria and biomarker discovery, and associations with kidney histology

BACKGROUND

Amyloid A (AA) amyloidosis is a protein misfolding disease arising from serum amyloid A (SAA). Systemic AA amyloidosis recently was shown to have a high prevalence in shelter cats in Italy and was associated with azotemia and proteinuria.

OBJECTIVES

Investigate urine protein profiles and diagnostic biomarkers in cats with renal AA amyloidosis.

ANIMALS

Twenty-nine shelter cats.

METHODS

Case-control study. Cats with renal proteinuria that died or were euthanized between 2018 and 2021 with available necropsy kidney, liver and spleen samples, and with surplus urine collected within 30 days before death, were included. Histology was used to characterize renal damage and amyloid amount and distribution; immunohistochemistry was used to confirm AA amyloidosis. Urine protein-to-creatinine (UPC) and urine amyloid A-to-creatinine (UAAC) ratios were calculated, and sodium dodecyl sulfate-agarose gel electrophoresis (SDS-AGE) and liquid chromatography-mass spectrometry (LC-MS) of proteins were performed.

RESULTS

Twenty-nine cats were included. Nineteen had AA amyloidosis with renal involvement. Cats with AA amyloidosis had a higher UPC (median, 3.9; range, 0.6-12.7 vs 1.5; 0.6-3.1; P = .03) and UAAC ratios (median, 7.18 × 10-3 ; range, 23 × 10-3 -21.29 × 10-3 vs 1.26 × 10-3 ; 0.21 × 10-3 -6.33 × 10-3 ; P = .04) than unaffected cats. The SDS-AGE identified mixed-type proteinuria in 89.4% of cats with AA amyloidosis and in 55.6% without AA amyloidosis (P = .57). The LC-MS identified 63 potential biomarkers associated with AA amyloidosis (P < .05). Among these, urine apolipoprotein C-III was higher in cats with AA amyloidosis (median, 1.38 × 107 ; range, 1.85 × 105 -5.29 × 107 vs 1.76 × 106 ; 0.0 × 100 -1.38 × 107 ; P = .01). In the kidney, AA-amyloidosis was associated with glomerulosclerosis (P = .02) and interstitial fibrosis (P = .05).

CONCLUSIONS AND CLINICAL IMPORTANCE

Renal AA amyloidosis is associated with kidney lesions, increased proteinuria and increased urine excretion of SAA in shelter cats. Additional studies are needed to characterize the role of lipid transport proteins in the urine of affected cats.

Renal AA amyloidosis: presentation, diagnosis, and current therapeutic options: a review

Amyloid A amyloidosis is thought to be the second most common form of systemic amyloidosis behind amyloidosis secondary to monoclonal Ig. It is the result of deposition of insoluble fibrils in the extracellular space of tissues and organs derived from the precursor protein serum amyloid A, an acute phase reactant synthesized excessively in the setting of chronic inflammation. The kidney is the most frequent organ involved. Most patients present with proteinuria and kidney failure. The diagnosis is made through tissue biopsy with involvement of the glomeruli in most cases, but also often of the vessels and the tubulointerstitial compartment. The treatment usually targets the underlying etiology and consists increasingly of blocking the inflammatory cascade of cytokines with interleukin-1 inhibitors, interleukin-6 inhibitors, and tumor necrosis factor-α inhibitors to reduce serum amyloid A protein formation. This strategy has also shown efficacy in cases where an underlying etiology cannot be readily identified and has significantly improved the prognosis of this entity. In addition, there has been increased interest at developing effective therapies able to clear amyloid deposits from tissues, albeit with mitigated results so far.

Renal Amyloidosis: Epidemiological, Clinical, and Laboratory Profile in Adults from One Nephrology Center

Background

Renal amyloidosis is one of the main differential diagnoses of nephrotic proteinuria in adults and the elderly. The aim of this study with the most important series in our country is to contribute to the epidemiological, clinical, and etiological study of the renal amyloidosis.

Methods

In a retrospective study carried out between 1975 and 2019, 310 cases of histologically proven and typed renal amyloidosis were selected for this study.

Results

There were 209 men and 101 women with a mean age of 53.8 ± 15.4 years (range, 17–84 years). Of the 310 cases, 255 (82.3%) were diagnosed with AA renal amyloidosis and 55 (17.7%) with non-AA amyloidosis. Infections were the main cause of AA amyloidosis, and tuberculosis was the most frequent etiology. The period from the onset of the underlying disease to diagnosis of the renal amyloidosis was an average of 177 months. The most frequent manifestations at the time of diagnosis were nephrotic syndrome (84%), chronic renal failure (30.3%), and end-stage renal disease (37.8%). After a medium follow-up of 16 months (range, 0–68 months), mortality occurred in 60 cases.

Conclusions

Given the high frequency of AA amyloidosis in our country, awareness of the proper management of infectious and chronic inflammatory diseases remains a priority in reducing the occurrence of this serious disease.

Prognostic value of histopathological scoring and grading in patients with renal AA amyloidosis

OBJECTIVE

The amount and distribution pattern of amyloid deposits may contribute to renal function and outcome, given the great diversity of renal involvement in amyloidosis. The aim of this study was to analyze the impact of histological characteristics of patients with biopsy-proven renal AA amyloidosis (AAA) on renal outcome.

METHODS

Renal biopsies of 37 patients with AAA were re-evaluated. The distribution pattern of glomerular amyloid (GA) deposits was classified, the extent of amyloid deposits in glomeruli, vessel, and interstitium and other histopathologic lesions were scored, and renal amyloid prognostic score (RAPS) was determined by summing all scores. Their potential prognostic relevance on renal outcome was investigated.

RESULTS

GA and vascular amyloid (VA) deposits were noted in all cases, interstitial amyloid (IA) was detected in 70.2%. GA deposits were predominantly seen in diffuse mesengiocapillary fashions (class IV) (51.4%). GA class, the extent of GA, VA, IA deposit, and RAPS, as well as interstitial fibrosis (IF) and interstitial inflammation were correlated to renal function at diagnosis. During the median follow-up of 52 months, 13 patients developed doubling of serum creatinine or end stage renal disease and they had a higher degree of GA and VA load (p = 0.03 and p = 0.042, respectively) as compared to the remaining patients. VA load, but not GA and RAPS grade, was associated with poor renal outcome (HR 3.016, 95% CI 1.45-6.25, p = 0.003).

CONCLUSIONS

Baseline renal function is closely linked to the extent of AA amyloid deposit in renal parenchyma but only VA load was a predictor of renal outcome in AAA patients.

A rare presentation of kidney failure in a patient with giant cell arteritis: case report and review of literature

Although giant cell arteritis, also called temporal arteritis, is the most common primary vasculitis in the elderly, an association with AA amyloidosis has rarely been reported. AA amyloidosis is a disorder that results from the extracellular deposition of proteolytic cleavage products of serum amyloid A, which occurs in the setting of long-standing inflammation. We present a case of a patient with giant cell arteritis who developed a rapidly deteriorating kidney function, due to AA amyloidosis. Early recognition of this rare phenomenon is crucial as prompt treatment may be beneficial in the salvage of renal function.

Infections and AA amyloidosis: An overview

BACKGROUND

Amyloidoses are a heterogeneous group of systemic diseases characterised by extracellular accumulation of insoluble amyloid fibrils derived from unfolded proteins. Inflammatory (AA) amyloidosis can complicate various inflammatory disorders that are associated with a sustained acute phase response and serum amyloid A (SAA) protein overproduction. Chronic infections were the first recognised cause of amyloidoses. However, with the better management of underlying diseases, the frequency of AA amyloidosis is decreasing.

PURPOSE

The aim of this overview was to discuss the several infections associated with AA amyloidosis and the relative frequency of infections as aetiological factors.

METHODS

A search of the literature was performed using the PubMed database using the MeSH terms "Amyloidosis" and "Infections," from inception to December 31st, 2019. Articles written in other languages than English or French were excluded.

RESULTS

The frequency of AA amyloidosis secondary to infections decreased from more than 50% to less than 20% after the 2000s, with a parallel increase in the frequency of AA amyloidosis secondary to inflammatory diseases and to an unknown cause.

CONCLUSION

Whereas new antibiotics have been developed and sanitary conditions are better, infections still represent 5%-30% of the causes of AA amyloidosis, including in developed countries. These data argue for better screening of chronic infections to prevent AA amyloidosis and the development of new strategies to manage recurrent infections.

[Familial Mediterranean fever in 2020]

Familial Mediterranean fever is the most frequent autoinflammatory disease with autosomal recessive transmission. Most patients carry mutations in the MEFV gene encoding the protein marenostrin/pyrin. It is characterised by short ant recurrent attacks of fever and serositis with abdominal or thoracic pain, usually lasting less than 3 days, raised inflammatory biologic markers in an individual of Mediterranean origin. Colchicine has been shown to be effective in prevention of inflammatory attacks and development of amyloidosis which is responsible of nephrotic syndrome and chronic renal failure. Better knowledge in pathogenic mechanisms permitted identification of interleukin-1 beta (Il-1 β) as the main cytokine target. Anti-IL-1 therapy must be considered as a second line treatment in case of persistent inflammation or colchicine intolerance.

[Retrospective clinical and morphological analysis of patients with AL amyloidosis (the 2008 to 2015 nephrobiopsies)]

OBJECTIVE

To study correlations between the clinical signs of dysfunction and pathological structural changes in the renal parenchyma in a group of Russian patients with AL amyloidosis in 2008-2015.

SUBJECTS AND METHODS

A total group (At) including Group 1 with AL (kappa + lambda light chains) (n=46) was divided into subgroups: 2λ) 40 patients with AL-lambda (AL-λ); 3κ) 6 patients with AL-kappa (AL-κ). All the patients underwent standard laboratory and instrumental studies: determinations of the peak systolic and diastolic blood pressures (SBP and DBP, respectively, mm Hg), glomerular filtration rate (GFR) (ml/min/1.73 m²) by the EPI equation, daily protein loss (g/day). Polyclonal antibodies against kappa and lambda light chains, AA component, and transthyretin (DAKO, Denmark) were used as immunomorphological markers. Light optical structural changes were semiquantitatively assessed, by ranking the following analyzed sign: interstitial focal sclerosis (FS), tubular atrophy (TA), interstitial inflammatory infiltration (II) semi-quantitatively (0 - no; 1 - < 25%; 2 - <50%, 3 - >50% of the volume of a histological compartment). Glomerulosclerosis (GS) was defined as the percentage of sclerotic glomeruli. The extent of amyloid depositions in the renal parenchyma structures was estimated according to the procedure proposed by Ying Yao et al., 2013.

RESULTS

The AL group showed a female preponderance (65.21%). The patients' mean age was 62±11 years. There were no significant differences in daily proteinuria and the levels of serum creatinine, GFR, SBP, and DBP between the groups. The predominant clinical manifestation in the patients was nephrotic syndrome. A comparative analysis of the pathomorphological criteria for the spread of amyloid masses and the markers of fibroplastic processes revealed no statistically significant differences in the studied groups. Correlation analysis of the spread of AL deposits in the renal parenchyma in the patients of Group 1 and Subgroup 2λ, as well as laboratory data showed that there were significant (p<0.05) correlations with GFR, serum creatinine, unlike in Subgroup 3κ. At the same time, the analysis demonstrated that daily proteinuria had a significant positive correlation with VA, IA, GA, and TA values in Subgroup 3κ, unlike in Group 1 and Subgroup 2λ. Positive correlations were found between glomerulosclerosis and VA in Subgroup 2 λ and IA in Group 1. Sclerotic (FS and TA) changes in the tubular interstitium (TIN) were significantly positively correlated with all the indicators of AL (GA, VA, IA, TA) in the examinees in Group 1 and Subgroup 2λ, but not in Subgroup 3κ. Inflammatory TIN infiltration showed statistically significant (p<0.05) positive correlations with IA and VA in Group 1 and Subgroup 2λ and their absence in subgroup 3κ.

CONCLUSION

: The retrospective analysis of nephrobiopsy specimens from of patients with AL amyloidosis revealed that kidney damage was mainly associated with the development of λ-associated AL amyloidosis. The clinical and laboratory parameters were correlated with the pathomorphological criteria for loading the renal parenchyma with amyloid masses. The findings suggest that there are clinical and morphological features of the subclasses of AL amyloidosis, which may be of value for predicting the course and progression of the disease.

A histopathological scoring and grading system to predict outcome for patients with AA amyloidosis

PURPOSE

Renal involvement is associated with significant morbidity and mortality in AA amyloidosis. Extend of amyloid deposition in kidney biopsies may be predictive for clinical manifestations and outcomes. The aim of our study is to assess clinical features of patients with biopsy-proven renal AA amyloidosis and to evaluate the relationship between histopathological scoring and grading of renal amyloid deposition with clinical findings and outcomes.

METHODS

The study included 86 patients who were diagnosed with renal AA amyloidosis. The demographic and clinical features at the time of biopsy and follow-up data were retrospectively collected. Amyloid deposition in glomeruli, interstitium, vessels and tubulointerstitial findings were scored and renal amyloid prognostic score (RAPS) was assigned by adding all scores. RAPS was further divided into three grades (RAPS grade I, II, III).

RESULTS

Median age was 50 (36-59) years. Familial Mediterranean fever was the leading cause. RAPS grade and interstitial inflammatory infiltration were associated with baseline eGFR and glomerular amyloid deposition was associated with proteinuria. During the follow-up period (median 50 months), 39 patients developed ESRD. Extensive (involving > 50%) glomerular amyloid deposition, baseline eGFR and proteinuria were independent risk factors for progression to end stage renal disease. Death censored renal survival was significantly lower among patients with RAPS grade III compared to those with RAPS grade I and II. Patient survival rate was not different according to RAPS grade.

CONCLUSIONS

Degree of renal amyloid accumulation is associated with renal function and outcome. The scoring and grading system may be predictive in clinical outcome and contribute to understanding of disease mechanism.

Correlation between amyloid deposits affecting renal compartments and glomerular filtration rate during renal biopsy in a renal amyloidosis case series

Amyloidosis comprises a group of disorders that accumulate modified autologous proteins in organs, mainly the kidneys. Few studies have addressed the amyloid compartmental distribution and associated clinical outcomes. The aim of this study was to present a case series of renal amyloidosis correlating histopathological data with glomerular filtration rate (GFR) during kidney biopsy. We studied 53 cases reviewed by nephropathologists from 2000 to 2018 in a single kidney biopsy center in Brazil. GFR was estimated using the CKD-EPI formula. Cases were divided into Group A ≥60 and Group B <60 mL·min⁻¹·(1.73 m²)⁻¹ using the estimated GFR during kidney biopsy. Semiquantitative histopathological study was performed, including extension and distribution of amyloid deposits by compartments (glomeruli, tubulointerstitial tissue, and vessels). Statistical analyses were made to understand associations with lower GFR. No difference was seen for age, gender, proteinuria, hematuria, subtype of amyloid protein, arteriosclerosis, interstitial fibrosis/infiltrate, or glomerular and interstitial amyloid deposits. After a previous P value <0.1 in the descriptive analysis, the following variables were selected: globally sclerotic glomeruli, high blood pressure, and the extension of vascular amyloid deposition. A binary logistic regression model with GFR as the dependent variable showed history of hypertension and vascular amyloid to be robust and independent predictors of Group B <60 mL·min⁻¹·(1.73 m²)⁻¹. Beyond the histopathologic diagnosis of amyloidosis, a semiquantitative approach on renal biopsy could provide new insights. Vascular amyloid is an independent predictor of renal dysfunction in cases of renal amyloidosis.

Renal amyloidosis: validation of a proposed histological scoring system in an independent cohort

Background

In systemic amyloidosis, the kidney is frequently affected and renal involvement has a major impact on survival. Renal involvement is clinically characterized by decreased estimated glomerular filtration rate (eGFR) and proteinuria. The two most common renal amyloidosis types are light chain-related amyloidosis (AL) and serum amyloid A (AA) amyloidosis. Standardized histopathological scoring of amyloid deposits is crucial to assess disease progression. Therefore, we aimed to validate the proposed scoring system from Rubinstein et al. (Novel pathologic scoring tools predict end-stage kidney disease in light chain (AL) amyloidosis. Amyloid 2017; 24: 205–211) in an independent patient cohort.

Methods

We attempt to reproduce the scoring system, consisting of an amyloid score (AS) and a composite scarring injury score (CSIS), in a multicentre AL and AA case series. Additionally, we analysed all renal amyloidosis kidney biopsies performed in the Netherlands between 1993 and 2012.

Results

Similar to the original study, AS and CSIS correlated to eGFR (r = −0.45, P = 0.0061 and r = −0.60, P < 0.0001, respectively) but not to proteinuria at diagnosis. Furthermore, AS, but not CSIS, was associated with renal outcome. The scoring system was not reproducible in AA patients. The median incidence rate for renal amyloidosis in the Netherlands was 2.3 per million population per year, and increased during the study period.

Conclusions

In our AL case series and the original study, AS and CSIS were correlated to eGFR but not to proteinuria, and AS correlated with renal outcome. Overall, we regard this scoring system as competent for standardized histopathological assessment of amyloid deposits burden and thereby disease advancement in renal biopsies.

Immune checkpoint inhibitor–associated renal amyloid A amyloidosis: A case series and review of the literature

Immune checkpoint inhibitors are a cornerstone in the management of many oncological disorders, and their indications continue to grow. However, as with any therapy we must remain vigilant of the possible adverse effects. Although interstitial nephritis is a reported cause of immune checkpoint inhibitor–related kidney injury, immune-mediated glomerular disease has rarely been described. Here, we present three patients being treated with checkpoint inhibitors for colon cancer, metastatic squamous cell carcinoma of the lung, and melanoma, who developed biopsy-proven amyloid A amyloidosis. In all three cases, the malignancies were in remission, yet continued inflammation and amyloid deposition occurred, pointing toward a primary role of the immune checkpoint inhibitor. Treatment generally remains a challenge due to a paucity of reported cases, thus further study of cytokine profile is prudent. In one case, the patient was given tocilizumab in the setting of elevated interleukin-6 levels; unfortunately no appreciable renal benefit was noted and the patient became dialysis dependent. In the other two cases, the patients were treated with colchicine and steroids. One patient had a substantial decrease in proteinuria and inflammatory markers while no significant response was noted in the other. Knowledge of immune checkpoint inhibitor–associated amyloid A amyloidosis is important for the oncologist and the nephrologists.

Revisiting renal amyloidosis with clinicopathological characteristics, grading, and scoring: A single-institutional experience

INTRODUCTION:

Kidney involvement is a major cause of mortality in systemic amyloidosis. Glomerulus is the most common site of deposition in renal amyloidosis, and nephrotic syndrome is the most common presentation. Distinction between AA and AL is done using immunofluorescence (IF) and immunohistochemistry (IHC). Renal biopsy helps in diagnosis and also predicting the clinical course by applying scoring and grading to the biopsy findings.

MATERIALS AND METHODS:

The study includes all cases of biopsy-proven renal amyloidosis from January 2008 to May 2017. Light microscopic analysis; Congo red with polarization; IF; IHC for Amyloid A, kappa, and lambda; and bone marrow evaluation were done. Classification of glomerular amyloid deposition and scoring and grading are done as per the guidelines of Sen S et al.

RESULTS:

There are 40 cases of biopsy-proven renal amyloidosis with 12 primary and 23 secondary cases. Mean age at presentation was 42.5 years. Edema was the most common presenting feature. Secondary amyloidosis cases were predominant. Tuberculosis was the most common secondary cause. Multiple myeloma was detected in four primary cases. Grading of renal biopsy features showed a good correlation with the class of glomerular involvement.

CONCLUSION:

Clinical history, IF, and IHC are essential in amyloid typing. Grading helps provide a subtle guide regarding the severity of disease in the background of a wide range of morphological features and biochemical values. Typing of amyloid is also essential for choosing the appropriate treatment.

Profile of renal AA amyloidosis in older and younger individuals: a single-centre experience

OBJECTIVE

In epidemiological studies of amyloid A (AA) amyloidosis from Turkey, the most frequently cause was familial Mediterranean fever (FMF) and it occurs generally in young age population. However, there are no sufficient data regarding aetiology, clinical presentation and prognosis of renal AA amyloidosis in advanced age patients. In this study, we aimed to investigate demographic, clinical presentation, aetiology and outcomes of adults aged 60 years or older patients with biopsy-proven renal AA amyloidosis.

METHODS

This is a retrospective study involving 53 patients who were diagnosed with AA amyloidosis by kidney biopsy from 2006 to 2016. In all patients, kidney biopsies were performed due to asymptomatic proteinuria, nephrotic syndrome and/or renal insufficiency. The patients were separated into two groups on the basis of age (group I: ≥60 years and group II: <60 years). Outcomes of patients in terms of the requirement of renal replacement therapy and mortality were recorded.

RESULTS

In patients with group I, the causes of AA amyloidosis were as follows: FMF 16 (50%), bronchiectasis 7 (23%), chronic osteomyelitis 2 (6%), inflammatory bowel disease 2 (6%), rheumatoid arthritis 2 (6%), ankylosing spondylitis 1 (3%) and unknown aetiology 2 (6%). The underlying disorders of AA amyloidosis in group II patients were as follows: FMF 17 (81%), Behcet's disease 1 (5%) and unknown aetiology 3 (14%). No statistically significant differences were detected between two groups with regard to systolic and diastolic blood pressures, albumin, proteinuria and lipids. The combination of chronic kidney disease and nephrotic syndrome was the most common clinical presentation in group I (73%) and group II (43%) (p = .05). Compared to the group II, estimated glomerular filtration rate was significantly lower in group I at the time of kidney biopsy (p = .003). At 12-month follow-up, 61% of the group I and 33% of the group II developed end-stage kidney disease requiring dialysis, while 11% of the group I died.

CONCLUSION

Our results indicated that renal AA amyloidosis is a rare disease in advanced age patients. At baseline and follow-up period, advanced age patients had worse kidney disease and outcomes.

[Familial Mediterranean fever]

Familial Mediterranean Fever (FMF) is the most frequent monogenic auto-inflammatory disease. FMF is an autosomal recessive disease, which affects populations from Mediterranean origin and is associated with MEFV gene mutations encoding for the protein pyrin. Pyrin activation enhances the secretion of interleukin 1 by myelo-monocytic cells. Main features of the disease are acute attacks of serositis mainly located on the abdomen, less frequently on chest and joints, accompanied by fever and biological inflammatory markers elevation. Usually attacks last 1 to 3 days and spontaneously stop. A daily oral colchicine intake of 1 to 2mg/day is able to prevent attack's occurrence, frequency, intensity and duration among most patients. Colchicine is also able to prevent the development of inflammatory amyloidosis, the most severe complication of FMF. This state of the art article will focus on the diagnosis of FMF, the treatment and an update on the pathophysiology including the recent described dominant form of MEFV-associated new auto-inflammatory diseases.

Kidney biopsy in AA amyloidosis: impact of histopathology on prognosis

In AA amyloidosis, while kidney biopsy is widely considered for diagnosis by clinicians, there is no evidence that the detailed investigation of renal histopathology can be utilized for the prognosis and clinical outcomes. In this study, we aimed to obtain whether histopathologic findings in kidney biopsy of AA amyloidosis might have prognostic and clinical value. This is a retrospective cohort study that included 38 patients who were diagnosed with AA amyloidosis by kidney biopsy between 2005 and 2013.The kidney biopsy specimens of patients were evaluated and graded for several characteristics of histopathological lesions and their relationship with renal outcomes. Segmental amyloid deposition in the kidney biopsy was seen in 29%, global amyloid deposition in 71, diffuse involvement of glomeruli in 84.2%, focal involvement in 7%, glomerular enlargement in 53%, tubular atrophy in 75% and interstitial fibrosis in 78% of patients. Histopathologically, glomerular enlargement, interstitial fibrosis, tubular atrophy, interstitial inflammation and global amyloid deposition were significantly associated with lower estimated glomerular filtration rate (eGFR) (p = .02, p < .001, p = .001, p = .009, p = .002, respectively) in univariate analysis. In multivariate analysis, tubular atrophy was the only predictor of eGFR (p = .019 B = -20.573). In the follow-up at an average of 27 months, 18 patients developed end-stage renal disease (ESRD). Among them, global amyloid deposition was the only risk factor for the development of ESRD (p = .01, OR = 18.750, %95 CI= 2.021-173.942). This is the first study showing that the histopathological findings in kidney biopsy of AA amyloidosis might have a prognostic and clinical value for renal outcomes.

Clinical Presentation of Tubulointerstitial Nephritis Caused by Amyloid Light-chain Amyloidosis in a Patient with Sjögren's Syndrome

We report a 70-year-old woman with Sjögren's syndrome who had severe renal dysfunction with mild proteinuria and elevated urinary low-molecular-weight proteins. Based on these clinical presentations, interstitial nephritis due to Sjögren's syndrome was strongly suspected. Unexpectedly, renal pathology revealed amyloid light-chain (AL) lambda-type depositions predominantly in the vasculatures with severe tubulointerstitial damage. Concentrated urine immunofixation was positive for Bence Jones lambda-type monoclonal proteins. Given the involvement in other organs, systemic AL amyloidosis was diagnosed. The patient underwent chemotherapy, but hemodialysis was ultimately instituted. It should be remembered that renal amyloidosis occurs as a clinical presentation of interstitial nephritis.

Deposition, Clearance, and Reinduction of Amyloid A Amyloid in Interleukin 1 Receptor Antagonist Knockout Mice

Amyloid A (AA) amyloidosis is characterized by the extracellular deposition of AA amyloid and results in the irreversible dysfunction of parenchymal organs. In experimental models, AA amyloid deposits are cleared following a decrease in circulating serum amyloid A (SAA) concentrations. Additional inflammatory stimuli during this recovery process may induce more severe amyloid redeposition. In the present study, we confirmed the deposition, clearance, and reinduction of AA amyloid deposits in interleukin 1 receptor antagonist knockout mice (IL-1raKO) and studied the SAA levels and amyloid-enhancing factor activity based on the time-dependent changes of amyloid deposition. Histopathologically, following initial (day 0) injection of amyloid-enhancing factor in combination with an inflammatory stimulus (silver nitrate [AgNO₃]), amyloid deposition peaked by day 20, and its deposition gradually decreased after day 35. SAA concentrations in serum were precipitously elevated on day 1 but returned to normal levels by day 10, whereas the SAA dimer was detected in serum after day 45. An additional AgNO₃ injection was administered to mice with amyloidosis on day 5, 10, 35, or 50, and all mice developed large amyloid deposits. Amyloid deposition was most severe in mice treated with AgNO₃ on day 35. The inoculation of sera from mice with AA amyloidosis, combined with AgNO₃, induced AA amyloidosis. Serum samples collected on days 35 and 50, which contained high concentrations of the SAA dimer, induced amyloidosis in a high proportion (83%) of mice. Therefore, increased SAA and/or its dimer in serum during the recovery process may markedly exacerbate the development of AA amyloidosis.

Novel Type of Renal Amyloidosis Derived from Apolipoprotein-CII

Amyloidosis is characterized by extracellular deposition of misfolded proteins as insoluble fibrils. Most renal amyloidosis cases are Ig light chain, AA, or leukocyte chemotactic factor 2 amyloidosis, but rare hereditary forms can also involve the kidneys. Here, we describe the case of a 61-year-old woman who presented with nephrotic syndrome and renal impairment. Examination of the renal biopsy specimen revealed amyloidosis with predominant involvement of glomeruli and medullary interstitium. Proteomic analysis of Congo red-positive deposits detected large amounts of the Apo-CII protein. DNA sequencing of the APOC2 gene in the patient and one of her children detected a heterozygous c.206A→T transition, causing an E69V missense mutation. We also detected the mutant peptide in the proband's renal amyloid deposits. Using proteomics, we identified seven additional elderly patients with Apo-CII-rich amyloid deposits, all of whom had kidney involvement and histologically exhibited nodular glomerular involvement. Although prior in vitro studies have shown that Apo-CII can form amyloid fibrils and that certain mutations in this protein promote amyloid fibrillogenesis, there are no reports of this type of amyloidosis in humans. We propose that this study reveals a new form of hereditary amyloidosis (AApoCII) that is derived from the Apo-CII protein and appears to manifest in the elderly and preferentially affect the kidneys.

[Pathological and clinical correlations in renal AA amyloidosis: A Moroccan series of 30 cases]

OBJECTIVE

Study of histological and clinical correlations of 30 cases of renal amyloidosis AA diagnosed between November 2010 and December 2012.

RESULTS

The main causes associated with amyloidosis AA were represented by chronic infectious diseases (60%). Nephrotic syndrome and renal failure were observed in 94% and 73% respectively. The distribution of amyloid deposits: 90% of patients had a glomerular form and 10% had a vascular form. Inflammatory reaction associated with AA renal amyloidosis was present in 50% of cases. This inflammation was observed near amyloid deposits associated with a deposition of immunoglobulin chains and/or complement factors.

CONCLUSION

Our study confirms the predominance of AA amyloidosis complicating chronic infectious diseases, especially tuberculosis. Our data point out a relationship between the morphology of renal AA amyloidosis, its clinical presentation and prognosis.

Clinicopathological features of renal amyloidosis: a single-center study on 47 cases

The correlations between the clinicopathological features and the long-term outcomes of renal amyloidosis (RA) were analyzed with a view to develop strategies for improving diagnosis and prognosis of RA. We retrospectively reviewed the clinicopathological characteristics of 47 patients diagnosed with RA between 2004 and 2014 at the Wuhan Union Hospital. The data on the renal histology, clinical manifestations, and prognosis of RA patients were retrieved from the hospital records and characteristic patterns were identified. The histological changes in the kidneys were correlated with the clinical manifestations of RA. Additionally, most RA patients in this study had decreased serum levels of κ light chain and increased urine levels of κ and λ light chains as well as presence of M-protein in the urine and serum. Patients with early RA showed no specific pathognomonic symptoms. Bleeding associated with diagnostic renal biopsy was rare. We recommend that the routine work-up of patients aged over 40 years and presenting with non-diabetic nephropathy includes the non-invasive tests for the measurement of serum and urine levels of κ and λ light chains as well as protein electrophoresis tests for the presence of urinary and serum M-protein. Additionally, such patients should undergo renal biopsy screening with Cong-red staining to ensure early diagnosis of RA and improve their survival, since the risk of hemorrhage related to renal biopsy screening is low at early stages of RA.

Cardiac amyloidosis: a challenging diagnosis

Cardiovascular involvement of amyloidosis is present in 90% of cases, which is frequently associated with the primary form of the disease (AL amyloidosis). Clinical manifestations are represented by heart failure due to restrictive myocardiopathy and electrical impulse conduction abnormalities, which are clinically remarkable in up to 50% of the cases. The prognosis of patients with systemic amyloidosis is directly associated with the presence of cardiac involvement, such that survival does not usually exceed 4 months after the onset of heart failure signs and symptoms. The authors report a case of primary systemic amyloidosis, diagnosed only at autopsy, with severe cardiac involvement.

Tocilizumab-induced remission of nephrotic syndrome accompanied by secondary amyloidosis and glomerulonephritis in a patient with rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune-mediated systemic disorder that primarily affects the musculoskeletal system. Patients with RA often present with kidney diseases, such as nephrotic syndrome. Causes of nephrotic syndrome include membranous nephropathy, IgA nephropathy and secondary amyloidosis. Recently, biological agents, including anti-tumor necrosis factor alpha and anti-interleukin 6 (IL-6) receptor antibodies, have been used for the treatment of RA. Anti-IL-6 receptor antibody therapy is believed to ameliorate RA-related kidney diseases, as IL-6 plays a central role in the pathogenesis of RA. We, herein, present the case of a patient with RA and related nephrotic syndrome whose proteinuria completely disappeared 1 month after tocilizumab treatment. A light microscopic examination of the pretreatment kidney biopsy specimen showed active glomerulonephritis with fibrocellular crescents and the deposition of amorphous substances stained weakly with hematoxylin-eosin and strongly with the Dylon method. Electron microscopy revealed the accumulation of microtubules ranging from 10 to 20 μm in width, primarily in the mesangial lesion. Amyloid A (AA) protein was positively stained in the mesangial area and vascular wall on immunohistochemistry. The final histologic diagnosis was RA-related glomerulonephritis and secondary AA amyloidosis. This case indicates that biological treatment targeting IL-6 is a promising therapeutic option for the treatment of kidney diseases associated with RA.

Renal Amyloidosis

Amyloidosis is an uncommon group of diseases in which soluble proteins aggregate and deposit extracellularly in tissue as insoluble fibrils, leading to tissue destruction and progressive organ dysfunction. More than 25 proteins have been identified as amyloid precursor proteins. Amyloid fibrils have a characteristic appearance on ultrastructural examination and generate anomalous colors under polarized light. Amyloidosis can be systemic or localized. The kidney is a prime site for amyloid deposition. Immunofluorescence, immunoperoxidase, and more recently laser microdissection and mass spectrometry are important tools used in the typing of renal amyloidosis.

Value of antibodies to free light chains in immunoperoxidase studies of renal biopsies

AIMS

Because immunoglobulin abnormalities may affect the kidney, investigation of renal biopsies requires immunohistological study of light chains. A problem is that most antibodies to light chains react with whole immunoglobulins as well as free light chains, and there are generally many more whole immunoglobulins than free light chains. The usefulness of antibodies that only detected free light chains was investigated.

METHODS

Antibodies to free light chains were used in an immunoperoxidase method on paraffin sections of 198 renal biopsies, and compared with conventional antibodies against light chains examined by immunofluorescence on 13 frozen sections and by immunoperoxidase on 46 paraffin sections.

RESULTS

Immunofluorescence and immunoperoxidase were concordant on 10 of 13 biopsies. Immunofluorescence detected slight deposition of light chains in three biopsies not shown by immunoperoxidase, of undetermined clinical significance. Using immunoperoxidase, the free light chain antibodies were more sensitive than conventional antibodies, giving much cleaner staining and better detection of deposits in AL amyloid, light chain deposition disease and cryoglobulinaemic glomerulonephritis. The free light chain antibodies showed discordance or ambiguity between immunohistological and clinical findings in seven (4%) of 185 patients with known immunoglobulin status. These included two of 28 cases of AL amyloid that showed no light chain deposition. The method was not designed for detection of light chain restriction in neoplastic plasma or lymphoplasmacytic cells.

CONCLUSIONS

Polyclonal antibodies to free light chains are an improvement on conventional antibodies in immunoperoxidase study of paraffin sections of renal biopsies and are useful in everyday practice.

Amyloid nephropathy

Amyloidosis is an uncommon disease that is characterized by abnormal extracellular deposition of misfolded protein fibrils leading to organ dysfunction. The deposited proteins display common chemical and histologic properties but can vary dramatically in their origin. Kidney disease is a common manifestation in patients with systemic amyloidosis with a number of amyloidogenic proteins discovered in kidney biopsy specimens. The emergence of mass spectrometry-based proteomics has added to the diagnostic accuracy and overall understanding of amyloidosis. This in-depth review discusses the general histopathologic features of renal amyloidosis and includes an in-depth discussion of specific forms of amyloid affecting the kidney.

AA amyloidosis: Mount Sinai experience, 1997-2012

BACKGROUND

AA amyloidosis is a systemic disease characterized by the extracellular deposition of amyloid fibrils derived from the acute-phase reactant serum amyloid A protein. It is typically a consequence of chronic inflammatory conditions like rheumatoid arthritis or Crohn's disease, although more patients are being identified who have more unusual causes or no known inflammatory stimulus.

METHODS

We performed a retrospective chart review of all patients with AA amyloidosis seen at Mount Sinai during the period of 1997-2012. Particular attention was paid to the patients' underlying diseases, extent of organ involvement, levels of inflammatory markers and proinflammatory cytokines, presence of pyrin gene mutations, and outcomes.

RESULTS

Forty-three patients were seen at Mount Sinai with AA amyloidosis during this period. The most common underlying diseases were rheumatoid arthritis (21%) and Crohn's disease (16%), though 21% of patients were considered to have idiopathic AA amyloid after an extensive search found no underlying inflammatory disease. Almost all patients (95%) had renal involvement based on biopsy or clinical criteria, with 19 patients (44%) eventually requiring dialysis and 5 (12%) undergoing renal transplantation. Inflammatory markers were elevated in most patients; however, interleukin-6 was the only consistently elevated cytokine. Three patients (of 9 tested) were found to be positive for the E148Q pyrin gene mutation.

CONCLUSIONS

Our study confirms the increasing number of patients being seen with idiopathic AA amyloidosis. More research is needed to determine if these patients have an underlying genetic susceptibility encoded in pyrin or other genes. Our study also confirms the dominance of renal disease in this population. The elevated levels of interleukin-6, in comparison with other cytokines, could represent a therapeutic target.

Light chain renal amyloidosis with prominent giant cells

Clinical diagnosis of amyloidosis may be very challenging because signs, symptoms, and laboratory study results can be highly variable and may overlap with other disease entities. Amyloid has characteristic features on kidney biopsy, involving glomeruli, vessels, and/or interstitium as typically amorphous waxy material that is periodic acid-Schiff pale and Congo Red birefringent under polarized light. Electron microscopy demonstrates characteristic randomly oriented fibrils. However, in rare cases, amyloid may present with atypical morphologic features on kidney biopsy, closely mimicking other histopathologic diagnoses. We present a case of light chain (AL) κ amyloidosis with an unusual inflammatory infiltrate including prominent multinucleated giant cells in the interstitium and at the glomerular hilus. Amyloid was apparent within giant cells on Congo Red staining, as well as on ultrastructural evaluation. Together with prior studies of tumoral nonrenal amyloid and renal amyloid A, we suggest that the amyloid fibril constituents κ and serum amyloid A have some predilection for inciting the rare multinucleated giant cell reaction.

Human SAA1-derived amyloid deposition in cell culture: a consistent model utilizing human peripheral blood mononuclear cells and serum-free medium

Amyloid A (AA) amyloidosis is a fatal disease caused by extracellular deposition of fibrils derived from serum AA (SAA). AA amyloid fibril formation has previously been modeled in macrophage cultures using highly amyloidogenic mouse SAA1.1, but attempts to do the same with human SAA invariably failed. Our objective was to define conditions that support human SAA-derived amyloid formation in peripheral blood mononuclear cell (PBMC) cultures. Two conditions were found to be critical - omission of fetal calf serum and use of StemPro34, a lipid-enriched medium formulated for hematopoietic progenitor cells. Cultures maintained in serum-free StemPro34 and provided with recombinant human SAA1 in the complete absence of amyloid-enhancing factor exhibited amyloid deposition within 7 d. Amyloid co-localized with cell clusters that characteristically included cells of fibrocytic/dendritic morphology as well as macrophages. These cells formed networks that appeared to serve as scaffolding within and upon which amyloid accumulated. Cells in amyloid-forming cultures demonstrated increased adherence, survival and expression of extracellular matrix components. Of the three human SAA1 isoforms, SAA1.3 showed the most extensive amyloid deposition, consistent with it being the most prevalent isoform in Japanese patients with AA amyloidosis. Attesting to the reproducibility and general applicability of this model, amyloid formation has been documented in cultures established from eight PBMC donors.

Renal amyloidosis: origin and clinicopathologic correlations of 474 recent cases

BACKGROUND AND OBJECTIVES

The kidney is the organ most commonly involved in systemic amyloidosis. This study reports the largest clinicopathologic series of renal amyloidosis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study provides characteristics of 474 renal amyloidosis cases evaluated at the Mayo Clinic Renal Pathology Laboratory from 2007 to 2011, including age, sex, serum creatinine, proteinuria, type of amyloid, and tissue distribution according to type.

RESULTS

The type of amyloid was Ig amyloidosis in 407 patients (85.9%), AA amyloidosis in 33 (7.0%), leukocyte chemotactic factor 2 amyloidosis in 13 (2.7%), fibrinogen A α chain amyloidosis in 6 (1.3%), Apo AI, Apo AII, or Apo AIV amyloidosis in 3 (0.6%), combined AA amyloidosis/Ig heavy and light chain amyloidosis in 1 (0.2%), and unclassified in 11 (2.3%). Laser microdissection/mass spectrometry, performed in 147 cases, was needed to determine the origin of amyloid in 74 of the 474 cases (16%), whereas immunofluorescence failed to diagnose 28 of 384 light chain amyloidosis cases (7.3%). Leukocyte chemotactic factor 2 amyloidosis and Apo AI, Apo AII, or Apo AIV amyloidosis were characterized by diffuse interstitial deposition, whereas fibrinogen A α chain amyloidosis showed obliterative glomerular involvement. Compared with other types, Ig amyloidosis was associated with lower serum creatinine, higher degree of proteinuria, and amyloid spicules.

CONCLUSIONS

In the authors' experience, the vast majority of renal amyloidosis cases are Ig derived. The newly identified leukocyte chemotactic factor 2 amyloidosis form was the most common of the rarer causes of renal amyloidosis. With the advent of laser microdissection/mass spectrometry for amyloid typing, the origin of renal amyloidosis can be determined in >97% of cases.

Efficient amyloid A clearance in the absence of immunoglobulins and complement factors

Amyloid A amyloidosis is a protein misfolding disease characterized by deposition of extracellular aggregates derived from the acute-phase reactant serum amyloid A protein. If untreated, amyloid A amyloidosis leads to irreversible damage of various organs, including the kidneys, liver, and heart. Amyloid A deposits regress upon reduction of serum amyloid A concentration, indicating that the amyloid can be efficiently cleared by natural mechanisms. Clearance was proposed to be mediated by humoral immune responses to amyloid. Here, we report that amyloid clearance in mice lacking complement factors 3 and 4 (C3C4(-/-)) was equally efficient as in wild-type mice (C57BL/6), and was only slightly delayed in agammaglobulinemic mice (J(H-/-)). Hence, antibodies or complement factors are not necessary for natural amyloid clearance, implying the existence of alternative physiological pathways for amyloid removal.