Diagnostic significance of hypocomplementemia

Characterization of the plasma proteomic profile of Fabry disease: Potential sex- and clinical phenotype-specific biomarkers

Fabry disease (FD) is a X-linked rare lysosomal storage disorder caused by deficient α-galactosidase A (α-GalA) activity. Early diagnosis and the prediction of disease course are complicated by the clinical heterogeneity of FD, as well as by the frequently inconclusive biochemical and genetic test results that do not correlate with clinical course. We sought to identify potential biomarkers of FD to better understand the underlying pathophysiology and clinical phenotypes. We compared the plasma proteomes of 50 FD patients and 50 matched healthy controls using DDA and SWATH-MS. The >30 proteins that were differentially expressed between the 2 groups included proteins implicated in processes such as inflammation, heme and haemoglobin metabolism, oxidative stress, coagulation, complement cascade, glucose and lipid metabolism, and glycocalyx formation. Stratification by sex revealed that certain proteins were differentially expressed in a sex-dependent manner. Apolipoprotein A-IV was upregulated in FD patients with complications, especially those with chronic kidney disease, and apolipoprotein C-III and fetuin-A were identified as possible markers of FD with left ventricular hypertrophy. All these proteins had a greater capacity to identify the presence of complications in FD patients than lyso-GB3, with apolipoprotein A-IV standing out as being more sensitive and effective in differentiating the presence and absence of chronic kidney disease in FD patients than renal markers such as creatinine, glomerular filtration rate and microalbuminuria. Identification of these potential biomarkers can help further our understanding of the pathophysiological processes that underlie the heterogeneous clinical manifestations associated with FD.

Complement inhibitors in pediatric kidney diseases: new therapeutic opportunities

Historically, the complement system (classical, lectin, alternative, and terminal pathways) is known to play a crucial role in the etiopathogenesis of many kidney diseases. Direct or indirect activation in these settings is revealed by consumption of complement proteins at the serum level and kidney tissue deposition seen by immunofluorescence and electron microscopy. The advent of eculizumab has shown that complement inhibitors may improve the natural history of certain kidney diseases. Since then, the number of available therapeutic molecules and experimental studies on complement inhibition has increased exponentially. In our narrative review, we give a summary of the main complement inhibitors that have completed phase II and phase III studies or are currently used in adult and pediatric nephrology. The relevant full-text works, abstracts, and ongoing trials (clinicaltrials.gov site) are discussed. Data and key clinical features are reported for eculizumab, ravulizumab, crovalimab, avacopan, danicopan, iptacopan, pegcetacoplan, and narsoplimab. Many of these molecules have been shown to be effective in reducing proteinuria and stabilizing kidney function in different complement-mediated kidney diseases. Thanks to their efficacy and target specificity, these novel drugs may radically improve the outcome of complement-mediated kidney diseases, contributing to an improvement in our understanding of their underlying pathophysiology.

Complement

The role of complement in human autoimmune, inflammatory, and infectious diseases is reviewed, focusing on clinical applicability. A typical case is presented in which serum testing for C3 and C4 is performed to help assess a syndrome with a broad differential diagnosis. The review includes a discussion of complement deficiency states, consumption of complement by diseases characterized by immune-complex formation and deposition, usefulness and interpretation of laboratory tests for complement, and development of drugs targeting specific components of the complement pathway for a growing number of indications.

The correlates of neonatal complement component 3 and 4 protein concentrations with a focus on psychiatric and autoimmune disorders

Complement components have been linked to schizophrenia and autoimmune disorders. We examined the association between neonatal circulating C3 and C4 protein concentrations in 68,768 neonates and the risk of six mental disorders. We completed genome-wide association studies (GWASs) for C3 and C4 and applied the summary statistics in Mendelian randomization and phenome-wide association studies related to mental and autoimmune disorders. The GWASs for C3 and C4 protein concentrations identified 15 and 36 independent loci, respectively. We found no associations between neonatal C3 and C4 concentrations and mental disorders in the total sample (both sexes combined); however, post-hoc analyses found that a higher C3 concentration was associated with a reduced risk of schizophrenia in females. Mendelian randomization based on C4 summary statistics found an altered risk of five types of autoimmune disorders. Our study adds to our understanding of the associations between C3 and C4 concentrations and subsequent mental and autoimmune disorders.

A Transcriptome Array-Based Approach to Link SGLT-2 and Intrarenal Complement C5 Synthesis in Diabetic Nephropathy

Diabetic nephropathy is a common microvascular complication of diabetes mellitus. It is characterized by progressive chronic kidney disease (CKD) with decline of kidney function by hyperfiltration. On a mechanistic level, activation of the complement system has been implicated in the pathogenesis of diabetic nephropathy. Therefore, here we pursued a transcriptome array-based approach to link intrarenal SGLT-2 and the synthesis of distinct complement components in diabetic nephropathy. Publicly available datasets for SLC5A2 (encoding SGLT-2) and complement system components were extracted specifically from microdissected tubulointerstitial (healthy controls: n = 31, diabetic nephropathy: n = 17) and glomerular compartments (healthy controls: n = 21, diabetic nephropathy: n = 12). First, we compared tubulointerstitial and glomerular log2SLC5A2 mRNA expression levels and confirmed a predominant synthesis within the tubulointerstitial compartment. Among various complement components and receptors, the only significant finding was a positive association between SLC5A2 and the tubulointerstitial synthesis of the complement component C5 in diabetic nephropathy (p = 0.0109). Finally, intrarenal expression of SLC5A2 was associated predominantly with pathways involved in metabolic processes. Interestingly, intrarenal complement C5 synthesis was also associated with enrichment of metabolic signaling pathways, overlapping with SLC5A2 for "metabolism" and "biological oxidations". These observations could be of relevance in the pathogenesis of diabetic nephropathy and implicate a mechanistic link between SGLT-2 and intrarenal complement synthesis.

Does kidney biopsy in pediatric lupus patients "complement" the management and outcomes of silent lupus nephritis? Lessons learned from a pediatric cohort

BACKGROUND

Silent lupus nephritis (SLN) is systemic lupus erythematosus (SLE) without clinical and laboratory features of kidney involvement but with biopsy-proven nephritis. This study aims to describe and compare the baseline characteristics and outcomes of pediatric SLN with overt LN (OLN) and to identify associated risk factors and biochemical markers.

METHODS

In this retrospective, observational study, multivariate logistic regression and receiver operating characteristic (ROC) analyses studied age, sex, race, serum complements, anti-double-stranded-DNA antibody, anti-Smith antibody, eGFR, and proliferative nephritis.

RESULTS

In our cohort of 69 patients, 47 were OLN, and 22 were SLN. OLN (OR = 4.9, p = 0.03) and non-African Americans (AA) (OR = 13.0, p < 0.01) had higher odds, and increasing C3 and C4 were associated with lower odds of proliferative nephritis (OR 0.95 and 0.65 per one unit increase in C3 and C4, respectively, p < 0.01). They demonstrated a good discriminative ability to detect proliferative nephritis as assessed by the area under the ROC curve (C3 = 0.78, C4 = 0.78). C3 and C4 in proliferative SLN and OLN were comparable and significantly lower than their non-proliferative counterparts. No association was observed between age, sex, anti-double-stranded-DNA antibody, anti-Smith antibody, eGFR, and proliferative nephritis. Proliferative SLN and OLN patients received similar treatments. Adverse events were identified in the proliferative OLN only.

CONCLUSIONS

Lower complement levels are associated with proliferative lesions in pediatric LN-both SLN and OLN. The non-AA population had higher odds of having proliferative nephritis than the AA. Prospective, randomized, long-term follow-up of proliferative SLN patients is needed to ascertain the beneficial effect of early diagnosis and treatment. A higher resolution version of the Graphical abstract is available as Supplementary information.

Incidence of serum sickness following Indian polyvalent antivenom therapy in a cohort of snake-envenomed patients in rural Sri Lanka

INTRODUCTION

Serum sickness is a poorly reported delayed adverse reaction following snake antivenom therapy. We aimed to assess the frequency of serum sickness associated with administering Indian polyvalent antivenom in Sri Lanka.

METHODS

We recruited patients from the Anuradhapura snakebite cohort who were admitted to a rural tertiary care hospital in Sri Lanka over one year period. Patients were interviewed over the phone 21 to 28 days post-envenoming to collect data on clinical effects: fever/chills, arthralgia/myalgia, rash, malaise, headache, abdominal pain, and nausea/vomiting. The presence of three or more symptoms between the 5th to 20th days after snake envenoming was defined as serum sickness.

RESULTS

We were able to contact 98/122 (80%) patients who received antivenom and 423/588 (72%) who did not receive antivenom during the study period. The treated patients received a median dose of 20 vials (interquartile range: 20-30) of Indian polyvalent antivenom and of them, 92 (92%) received premedication. However, 67/98 (68%) developed acute adverse reactions to antivenom, including 19/98 (19%) developing anaphylaxis. Only 4/98 (4%) who received antivenom met the criteria for serum sickness, compared to none who did not receive antivenom therapy. All patients who developed serum sickness were envenomed by Russell's vipers, were premedicated, and received VINS Bioproducts antivenom. Three of them were treated with hydrocortisone in the acute stage, as premedication or as a treatment for acute adverse reactions of antivenom. Although all four patients sought medical advice for their symptoms, only one was clinically suspected to be serum sickness and treated, while the others were treated for infections.

CONCLUSIONS

We confirmed that Indian polyvalent antivenom use in Sri Lanka is associated with high rates of acute adverse reactions. In contrast to studies of other antivenoms only a small proportion of patients developed serum sickness.

The complement system and human autoimmune diseases

Genetic deficiencies of early components of the classical complement activation pathway (especially C1q, r, s, and C4) are the strongest monogenic causal factors for the prototypic autoimmune disease systemic lupus erythematosus (SLE), but their prevalence is extremely rare. In contrast, isotype genetic deficiency of C4A and acquired deficiency of C1q by autoantibodies are frequent among patients with SLE. Here we review the genetic basis of complement deficiencies in autoimmune disease, discuss the complex genetic diversity seen in complement C4 and its association with autoimmune disease, provide guidance as to when clinicians should suspect and test for complement deficiencies, and outline the current understanding of the mechanisms relating complement deficiencies to autoimmunity. We focus primarily on SLE, as the role of complement in SLE is well-established, but will also discuss other informative diseases such as inflammatory arthritis and myositis.

Alternative pathway diagnostics

Uncontrolled alternative pathway activation is the primary driver of several diseases, and it contributes to the pathogenesis of many others. Consequently, diagnostic tests to monitor this arm of the complement system are increasingly important. Defects in alternative pathway regulation are strong risk factors for disease, and drugs that specifically block the alternative pathway are entering clinical use. A range of diagnostic tests have been developed to evaluate and monitor the alternative pathway, including assays to measure its function, expression of alternative pathway constituents, and activation fragments. Genetic studies have also revealed many disease-associated variants in alternative pathway genes that predict the risk of disease and prognosis. Newer imaging modalities offer the promise of non-invasively detecting and localizing pathologic complement activation. Together, these various tests help in the diagnosis of disease, provide important prognostic information, and can help guide therapy with complement inhibitory drugs.

The role of the complement system in kidney glomerular capillary thrombosis

The complement system is part of the innate immune system. The crucial step in activating the complement system is the generation and regulation of C3 convertase complexes, which are needed to generate opsonins that promote phagocytosis, to generate C3a that regulates inflammation, and to initiate the lytic terminal pathway through the generation and activity of C5 convertases. A growing body of evidence has highlighted the interplay between the complement system, coagulation system, platelets, neutrophils, and endothelial cells. The kidneys are highly susceptible to complement-mediated injury in several genetic, infectious, and autoimmune diseases. Atypical hemolytic uremic syndrome (aHUS) and lupus nephritis (LN) are both characterized by thrombosis in the glomerular capillaries of the kidneys. In aHUS, congenital or acquired defects in complement regulators may trigger platelet aggregation and activation, resulting in the formation of platelet-rich thrombi in the kidneys. Because glomerular vasculopathy is usually noted with immunoglobulin and complement accumulation in LN, complement-mediated activation of tissue factors could partly explain the autoimmune mechanism of thrombosis. Thus, kidney glomerular capillary thrombosis is mediated by complement dysregulation and may also be associated with complement overactivation. Further investigation is required to clarify the interaction between these vascular components and develop specific therapeutic approaches.

The association between lupus serology and disease outcomes: A systematic literature review to inform the treat-to-target approach in systemic lupus erythematosus

INTRODUCTION

Serological markers such as anti-double stranded (ds)DNA antibodies and complement fractions C3/C4, are integral components of disease activity assessment in patients with systemic lupus erythematosus (SLE). However, it remains uncertain whether treatment should aim at restoration of serological abnormalities.

OBJECTIVES

To analyze and critically appraise the literature on the prognostic impact of active lupus serology despite clinical disease quiescence.

METHODS

A systematic literature review was performed in PubMed and EMBASE using the PICOT(S) (population, index, comparator, outcome(s), timing, setting) system to identify studies evaluating the association of serum anti-dsDNA, C3 and C4 levels assessed at the time of clinical remission or during the disease course, against the risk for impending flares and organ damage. Risk of bias was determined by the Quality in Prognosis Studies and ROB2 tools for observational and randomized controlled studies, respectively.

RESULTS

Fifty-three studies were eligible, the majority having moderate (70.6%) or high (11.8%) risk of bias and not adequately controlling for possible confounders. C3 hypocomplementemia during stable/inactive disease was associated with increased risk (2.0 to 3.8-fold) for subsequent flare in three out of seven relevant studies. Three out of four studies reported a significant effect of C4 hypocomplementemia on flare risk, including one study in lupus nephritis (likelihood ratio-positive 12.0). An increased incidence of flares (2.0 to 2.8-fold) was reported in 11 out of 16 studies assessing the prognostic effect of high anti-dsDNA, and similarly, the majority of studies yielded significant relationships with renal flares. Six studies examined the effect of combined (rather than individual) serological activity, confirming the increased risk (2.0 to 2.7-fold) for relapses. No consistent association was found with organ damage.

CONCLUSION

Notwithstanding the heterogeneity and risk of bias, existing evidence indicates a modest association between abnormal serology and risk for flare in patients with stable/inactive SLE. These findings provide limited support for inclusion of serology in the treat-to-target approach but rationalize to further investigate their prognostic implications especially in lupus nephritis.

Clinical Characteristics of Cryoglobulinemia With Cardiac Involvement in a Single Center

Background: Cryoglobulinemia is a syndrome characterized by the presence of cryoglobulins (CGs) in serum, and cardiac involvement is a rare occurrence that can affect treatment and prognosis. This study aimed to explore the clinical characteristics of cryoglobulinemia with cardiac involvement.

Methods: 108 patients diagnosed with cryoglobulinemia who were admitted and treated in Peking Union Medical College Hospital (PUMCH) between June 1985 and June 2019 were enrolled in the present study. Clinical characteristics, therapy, and prognosis of patients with cardiac involvement were retrospectively analyzed.

Results: The cryoglobulinemia with cardiac involvement was found in 7 patients, thus reaching the incidence of 6.5%. Heart failure was the main cardiac manifestation found in these patients, all with the involvement of external cardiac organs. Laboratory examinations showed significant elevation of N-terminal brain natriuretic peptide precursor (NT-proBNP) and brain natriuretic peptide (BNP) with negative troponin (cTnI). Electrocardiogram (ECG) was generally normal or only showed low-flat and biphasic multi-lead T waves. Echocardiography was performed in 6 patients, all of whom showed enlargement of heart cavity. Five patients had reduced left ventricular myocardial contractible motion with decreased ejection fraction, 3 patients had pericardial effusion, and 1 patient had left ventricular hypertrophy or severe aortic insufficiency. Cardiac magnetic resonance imaging showed delayed myocardial enhancement in 2 patients. One patient underwent a myocardial biopsy, which showed perivasculitis. Condition in 6 patients who received active treatment targeting improved in the early stage. Three patients (3/7, 42.9%) died due to disease progression during follow-up period.

Conclusions: Cryoglobulinemia with cardiac involvement is a rare but serious condition that has relatively high risk of death. When patients with cryoglobulinemia without underlying heart disease experience heart failure, chest pain, or elevation of asymptomatic NT-proBNP and BNP, there is a high possibility of cardiac involvement, even if the electrocardiogram and troponin are negative. Further examinations such as echocardiography, cardiac magnetic resonance imaging, and myocardial biopsy examination could contribute to the diagnosis. Cardiac manifestations could be timely reversed after active targeted treatment. NT-proBNP and echocardiography could be used for the monitoring of disease efficacy.

The Contribution of Serum Complement Component 3 Levels to 90-Day Mortality in Living Donor Liver Transplantation

The contributions of the complement system have been elucidated in the process of solid organ transplantation, including kidney transplantation. However, the role of complement in liver transplantation is unknown. We sought to elucidate the time-dependent changes of peritransplantational serum complement levels and the relationships with posttransplant outcomes and other immunological biomarkers. We enrolled 82 patients who underwent living-related donor liver transplantation (LDLT). Nine patients (11%) died within 90 days after LDLT (non-survivors). The following immunomarkers were collected preoperatively and at 1, 2, and 4 week(s) after LDLT: serum C3, C4, immunoglobulin G (IgG), and peripheral blood leukocyte populations characterized by CD3, CD4, CD8, CD16, CD19, CD20, CD22, and CD56. Consequently, C3 and C4 increased time-dependently after LDLT. Preoperatively, C3 was negatively correlated with the MELD score, Child–Pugh score, CD16-positive leukocyte percentage, and the CD56-positive leukocyte percentage. Non-survivors had lower levels of C3 at 2 weeks in comparison to survivors (median [interquartile range]: 56 [49-70] mg/dL vs. 88 [71-116] mg/dL, p=0.0059). When the cutoff value of C3 at 2 weeks to distinguish non-survivors was set to 71 mg/dL, the sensitivity, specificity, and area under the ROC curve were 87.5%, 75.0%, and 0.80, respectively. A principal component analysis showed an inverse relationship between the C3 and C4 levels and the percentage of CD8-, CD16-, and CD56-positive leukocytes at 1 and 2 week(s). All non-survivors were included in the cluster that showed higher percentages of CD8-, CD16-, and CD56-positive leukocytes at 2 weeks. In conclusion, we demonstrated the relationship between complement, outcomes, and other immunomarkers in LDLT and suggested the usefulness of C3 at 2 weeks after LDLT in distinguishing the mortality.

Inhibition of complement C1s in patients with cold agglutinin disease: lessons learned from a named patient program

Cold agglutinin disease (CAD) causes predominantly extravascular hemolysis and anemia via complement activation. Sutimlimab is a novel humanized monoclonal antibody directed against classical pathway complement factor C1s. We aimed to evaluate the safety and efficacy of long-term maintenance treatment with sutimlimab in patients with CAD. Seven CAD patients treated with sutimlimab as part of a phase 1B study were transitioned to a named patient program. After a loading dose, patients received biweekly (once every 2 weeks) infusions of sutimlimab at various doses. When a patient's laboratory data showed signs of breakthrough hemolysis, the dose of sutimlimab was increased. Three patients started with a dose of 45 mg/kg, another 3 with 60 mg/kg, and 1 with a fixed dose of 5.5 g every other week. All CAD patients responded to re-treatment, and sutimlimab increased hemoglobin from a median initial level of 7.7 g/dL to a median peak of 12.5 g/dL (P = .016). Patients maintained near normal hemoglobin levels except for a few breakthrough events that were related to underdosing and which resolved after the appropriate dose increase. Four of the patients included were eventually treated with a biweekly 5.5 g fixed-dose regimen of sutimlimab. None of them had any breakthrough hemolysis. All patients remained transfusion free while receiving sutimlimab. There were no treatment-related serious adverse events. Overlapping treatment with erythropoietin, rituximab, or ibrutinib in individual patients was safe and did not cause untoward drug interactions. Long-term maintenance treatment with sutimlimab was safe, effectively inhibited hemolysis, and significantly increased hemoglobin levels in re-exposed, previously transfusion-dependent CAD patients.

Repeated Administration of Clinical Doses of Tramadol and Tapentadol Causes Hepato- and Nephrotoxic Effects in Wistar Rats

Tramadol and tapentadol are fully synthetic and extensively used analgesic opioids, presenting enhanced therapeutic and safety profiles as compared with their peers. However, reports of adverse reactions, intoxications and fatalities have been increasing. Information regarding the molecular, biochemical, and histological alterations underlying their toxicological potential is missing, particularly for tapentadol, owing to its more recent market authorization. Considering the paramount importance of liver and kidney for the metabolism and excretion of both opioids, these organs are especially susceptible to toxicological damage. In the present study, we aimed to characterize the putative hepatic and renal deleterious effects of repeated exposure to therapeutic doses of tramadol and tapentadol, using an in vivo animal model. Male Wistar rats were randomly divided into six experimental groups, composed of six animals each, which received daily single intraperitoneal injections of 10, 25 or 50 mg/kg tramadol or tapentadol (a low, standard analgesic dose, an intermediate dose and the maximum recommended daily dose, respectively). An additional control group was injected with normal saline. Following 14 consecutive days of administration, serum, urine and liver and kidney tissue samples were processed for biochemical, metabolic and histological analysis. Repeated administration of therapeutic doses of both opioids led to: (i) increased lipid and protein oxidation in liver and kidney, as well as to decreased total liver antioxidant capacity; (ii) decreased serum albumin, urea, butyrylcholinesterase and complement C3 and C4 levels, denoting liver synthesis impairment; (iii) elevated serum activity of liver enzymes, such as alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and γ-glutamyl transpeptidase, as well as lipid profile alterations, also reflecting hepatobiliary commitment; (iv) derangement of iron metabolism, as shown through increases in serum iron, ferritin, haptoglobin and heme oxygenase-1 levels. In turn, elevated serum cystatin C, decreased urine creatinine output and increased urine microalbumin levels were detected upon exposure to tapentadol only, while increased serum amylase and urine N-acetyl-β-D-glucosaminidase activities were observed for both opioids. Collectively, these results are compatible with kidney injury. Changes were also found in the expression levels of liver- and kidney-specific toxicity biomarker genes, upon exposure to tramadol and tapentadol, correlating well with alterations in lipid profile, iron metabolism and glomerular and tubular function. Histopathological analysis evidenced sinusoidal dilatation, microsteatosis, mononuclear cell infiltrates, glomerular and tubular disorganization, and increased Bowman's spaces. Although some findings are more pronounced upon tapentadol exposure, our study shows that, when compared with acute exposure, prolonged administration of both opioids smooths the differences between their toxicological effects, and that these occur at lower doses within the therapeutic range.

Complement and the Kidney: An Overview

The complement cascade was first recognized as a downstream effector system of antibody-mediated cytotoxicity. Consistent with this view, it was discovered in the 1960s that complement is activated in the glomeruli of patients with immune complex glomerulonephritis. More recently, research has shown that complement system has many additional functions relating to regulation of the immune response, homeostasis, and metabolism. It has also become clear that the complement system is important to the pathogenesis of many non-immune complex mediated kidney diseases. In fact, in atypical hemolytic uremic syndrome and C3 glomerulopathy, uncontrolled complement activation is the primary driver of disease. Complement activation generates multiple pro-inflammatory fragments, and if not properly controlled it can cause fulminant tissue injury. Furthermore, the mechanisms of complement activation and complement-mediated injury vary from disease to disease. Many new drugs that target the complement cascade are in clinical development, so it is important to fully understand the biology of the complement system and its role in disease.

Hypocomplementemia as a Risk Factor for Organ Damage Accrual in Patients with Systemic Lupus Erythematosus

While it is a common practice to monitor complement levels in patients with systemic lupus erythematosus to aid in flare prediction and detection, it is unclear if this strategy is helpful in preventing subsequent organ damage. We studied longitudinal complement levels in 102 SLE patients during a median follow-up of 13.8 years (IQR 7.0, 23.1). Low complement was defined as C3 < 0.84 g/L and/or C4 < 0.08 g/L, disease activity by clinical SLEDAI-2K, and organ damage by SLICC-DI. We calculated a time averaged clinical SLEDAI score (cWAS) and performed multivariate regression models to assess the independent predictive value of low complement for organ damage at last visit. Hypocomplementemia (HC) was observed in 67% of all patients and was more often due to low C3 (97%) than low C4 (54%). Compared to patients not developing HC (33%), HC patients were more frequently positive for anti-dsDNA Ab (72% vs 36%, p < 0.01) and aPL (74% vs 40%, p < 0.01) but HC was concurrently present with anti-dsDNA Ab in only half the cases. The time-adjusted cWAS scores (1.9 vs 1.2, p = 0.9), frequency (SDI > 0, n = 60), and type of organ damage accrual were similar for patients with and without HC (OR 1.08, p > 0.20). Intermittent or sustained HC has no predictive value for damage accrual in SLE or the underlying disease activity over time. This together with significant discrepancies in the concurrence of low C3, C4, and anti-dsDNA Ab indicates frequent activation of the complement pathway by other factors than immune complexes in SLE.

Invasive meningococcal disease due to a non-capsulated Neisseria meningitidis strain in a patient with IgG4-related disease

Background

Invasive Meningococcal Disease (IMD) is a rare and critical disease in Japan. Most of these cases are caused by capsulated Neisseria meningitidis strains. Non-capsulated (non-typable) strains are considered relatively low-pathogenic and can colonize in the nasopharynx of healthy children and young adults. As far as could be ascertained, only twelve IMD cases due to non-capsulated strains have been reported in the literature. No clear risk factors could be identified in a literature review (unknown or immunocompetent, seven cases; C6 deficiency, three cases).

Case presentation

We report a Japanese male taxi driver with bacteremia and meningitis due to non-capsulated N. meningitidis. He had a fever and shaking chills. Ceftriaxone was administered, and the patient finally recovered. During the clinical course, relative adrenal insufficiency occurred and was treated with hydrocortisone. A hidden co-morbidity, immunoglobulin G4 (IgG4)-related disease, was revealed in the past surgical history (a resection of bilateral orbital tumors), which included symptoms (swelling lachrymal glands and lymph nodes), elevated IgG4, immunoglobulin E, and hypocomplementemia. He recovered finally and no recurrence was observed.

Conclusions

Our IMD case is the first reported in Japan, where IMD is not considered pandemic. The patient had a history of IgG4-related disease, although we could not establish a clear relationship between the patient’s IMD and co-morbidity. A collection of further clinical cases might establish the risk factors and characteristics of IMD that could be caused by this neglected pathogen, non-capsulated N. meningitidis.

Systemic lupus erythematosus biomarkers: the challenging quest

SLE, a multisystem heterogeneous disease, is characterized by production of antibodies to cellular components, with activation of both the innate and the adaptive immune system. Decades of investigation of blood biomarkers has resulted in incremental improvements in the understanding of SLE. Owing to the heterogeneity of immune dysregulation, no single biomarker has emerged as a surrogate for disease activity or prediction of disease. Beyond identification of surrogate biomarkers, a multitude of clinical trials have sought to inhibit elevated SLE biomarkers for therapeutic benefit. Armed with new -omics technologies, the necessary yet daunting quest to identify better surrogate biomarkers and successful therapeutics for SLE continues with tenacity.

A wolf in another wolf's clothing

This case of infective endocarditis masquerading as mixed cryoglobulinemia in a man with a history of intravenous drug use (IVDU) and hepatitis C virus (HCV) highlights the importance of maintaining a broad differential and continually re-evaluating the working diagnosis as new information presents itself. The patient presented to an outside hospital and was treated for presumptive mixed cryoglobulinemia with corticosteroid therapy. When the patient did not improve, he was transferred to a tertiary care center for possible Rituximab and/or plasmapheresis. Further investigation revealed Enterococcus bacteremia with subsequent workup consistent with infective endocarditis (IE). This case highlights a diagnostic dilemma and demonstrates the importance of a thorough evaluation as it pertains to overlapping features of IE and mixed cryoglobulinemia.

All Things Complement

The complement (C) cascade is an ancient system of proteins whose primary role is to initiate and modulate immune responses. During C activation, circulating proteins are cleaved and nascent cleavage fragments participate in a broad range of downstream innate and adaptive immune functions. Although the majority of these functions are either homeostatic or protective, a large body of experimental and clinical evidence also highlights a central role for the C system in the pathogenesis of many types of glomerular disease. From classic pathway activation in lupus nephritis to alternative pathway dysregulation in C3 glomerulopathy, our understanding of the spectrum of C involvement in kidney disease has expanded greatly in recent years. However, the characteristics that make the glomerulus so uniquely susceptible to C-mediated injury are not fully understood, and this remains an area of ongoing investigation. Several C inhibitors have been approved for clinical use, and additional C inhibitory drugs are in development. The use of these drugs in patients with kidney disease will expand our understanding of the benefits and limitations of C inhibition.

Complement Activation in Patients with Focal Segmental Glomerulosclerosis

Background

Recent pre-clinical studies have shown that complement activation contributes to glomerular and tubular injury in experimental FSGS. Although complement proteins are detected in the glomeruli of some patients with FSGS, it is not known whether this is due to complement activation or whether the proteins are simply trapped in sclerotic glomeruli. We measured complement activation fragments in the plasma and urine of patients with primary FSGS to determine whether complement activation is part of the disease process.

Study Design

Plasma and urine samples from patients with biopsy-proven FSGS who participated in the FSGS Clinical Trial were analyzed.

Setting and Participants

We identified 19 patients for whom samples were available from weeks 0, 26, 52 and 78. The results for these FSGS patients were compared to results in samples from 10 healthy controls, 10 patients with chronic kidney disease (CKD), 20 patients with vasculitis, and 23 patients with lupus nephritis.

Outcomes

Longitudinal control of proteinuria and estimated glomerular filtration rate (eGFR).

Measurements

Levels of the complement fragments Ba, Bb, C4a, and sC5b-9 in plasma and urine.

Results

Plasma and urine Ba, C4a, sC5b-9 were significantly higher in FSGS patients at the time of diagnosis than in the control groups. Plasma Ba levels inversely correlated with the eGFR at the time of diagnosis and at the end of the study. Plasma and urine Ba levels at the end of the study positively correlated with the level of proteinuria, the primary outcome of the study.

Limitations

Limited number of patients with samples from all time-points.

Conclusions

The complement system is activated in patients with primary FSGS, and elevated levels of plasma Ba correlate with more severe disease. Measurement of complement fragments may identify a subset of patients in whom the complement system is activated. Further investigations are needed to confirm our findings and to determine the prognostic significance of complement activation in patients with FSGS.

Synovitis in a Patient with IgG4-related Disease

A 71-year-old man was admitted to our department due to arthralgia and renal dysfunction. A physical examination disclosed swelling of the right shoulder and left wrist joints. Laboratory tests showed elevated serum IgG4 and creatinine levels, and magnetic resonance imaging of the wrist revealed bone erosion and synovitis. In addition, fluorodeoxyglucose positron emission tomography showed uptake in the submandibular glands, pancreas, kidneys, and affected joints and a renal biopsy revealed tubulointerstitial nephritis with the infiltration of IgG4+ plasma cells. The patient was subsequently diagnosed with IgG4-related disease (IgG4-RD) and successfully treated with corticosteroid therapy. This case suggests that erosive arthritis may occur in patients with IgG4-RD.

Utility of immunologic testing in suspected rheumatologic disease

The use of diagnostic testing in the clinical practice of medicine has been a shifting landscape from the time that the first blood test was utilized. This is no different in the field of immunology and in particular rheumatology. As the field of immunology is relatively young, the clinical tests are not well established and therefore guidelines for use are still under debate. In this review, we seek to look at some of the key autoantibodies, as well as other tests that are available to diagnose suspected rheumatologic disease, and examine how to best use these tests in the clinic. In particular, we will focus on the anti-nuclear antibodies, anti-neutrophil cytoplasmic antibodies, complement, cryoglobulins, rheumatoid factor, and anti-citrullinated protein antibodies.

Noninvasive detection of complement activation through radiologic imaging

A wealth of experimental and clinical data demonstrates that the complement system is involved in the pathogenesis of numerous inflammatory diseases. Complement activation contributes to injury in disorders that involve nearly every tissue in the body. Concerted effort has been expended in recent years to develop therapeutic complement inhibitors. Eculizumab, an inhibitory antibody to C5, was recently approved for the treatment of several diseases, and many other complement inhibitors are in clinical development. As these drugs are developed, the need for improved methods of detecting and monitoring complement activation within particular tissues will be increasingly important. We have developed a magnetic resonance imaging (MRI)-based method for noninvasive detection of complement activation. This method utilizes iron-oxide nanoparticles that are targeted to sites of complement activation with a recombinant protein that contains the C3d-binding region of complement receptor (CR) 2. Iron-oxide nanoparticles darken (negatively enhance) images obtained by T2-weighted MRI. We have demonstrated that the CR2-targeted nanoparticles bind within the kidneys of mice with lupus-like kidney disease (MRL/1pr mice), causing a decrease in the T2 signal within the kidneys. This method discriminates diseased kidneys from healthy controls, and the magnitude of the negative enhancement in the cortex of MRL/lpr mice correlates with their disease severity. This method may be useful for identifying those patients most likely to benefit from complement inhibitors and for monitoring the response of these patients to treatment. These results may open up new avenues to develop tools for the monitoring of disease progression in complement-dependent diseases.

Therapeutic regulation of complement in patients with renal disease - where is the promise?

Numerous renal diseases are characterized by complement activation within the kidney, and several lines of evidence implicate complement activation as an important part of the pathogenesis of these diseases. Investigators have long anticipated that complement inhibitors would be important and effective therapies for renal diseases. Eculizumab is a monoclonal antibody to the complement protein C5 that has now been administered to patients with several types of renal disease. The apparent efficacy of this agent may herald a new era in the treatment of renal disease, but many questions about the optimal use of therapeutic complement inhibitors remain. Herein we review the rationale for using complement inhibitors in patients with renal disease and discuss several drugs and approaches that are currently under development.

Thrombotic thrombocytopenic purpura with an autoantibody to ADAMTS13 complicating Sjögren's syndrome: two cases and a literature review

An association between thrombotic thrombocytopenic purpura (TTP) and Sjögren's syndrome (SS) is rare. This is the first report of two patients with TTP who had inhibitory autoantibodies to ADAMTS13 (a disintegrin-like and metalloprotease with thrombospondin type 1 repeats) complicating primary SS. A rapid diagnosis of TTP, which is a potentially lethal condition, made it possible to treat the two cases successfully. Only eight similar cases with TTP complicating SS have been reported in the literature. The possible presentation of primary SS without classic sicca symptoms, but with haematological abnormalities including TTP, should be recognised. Furthermore, it is important to measure ADAMTS13 activity and anti-ADAMTS13 antibodies, because TTP with SS seems to be a concurrent overlapping autoimmune disorder. We suggest that plasma exchanges in combination with corticosteroids should be administered as early as possible, since they appeared to be effective in treating TTP with SS, including in our cases.

Complement C3 in Bernese Mountain dogs

BACKGROUND

Previous research suggests that low serum concentrations of the third component of complement (C3) are associated with both the susceptibility to infectious agents such as Borrelia burgdorferi and the development of glomerular disease. We hypothesized that low levels of C3 are associated with the coincident occurrence of B. burgdorferi infection and glomerulonephritis in Bernese Mountain dogs.

OBJECTIVES

The aims of this study were to evaluate the serum concentration of C3 in Bernese Mountain dogs with and without antibodies against B. burgdorferi and to compare this concentration with that of healthy control dogs.

METHODS

Eighty-three clinically healthy Bernese Mountain dogs and 46 control dogs were included. Antibodies against B. burgdorferi were determined using an ELISA with a whole cell sonicate as antigen. Results were confirmed using Western blot. C3 was measured using a single radial immunodiffusion test. Results were reported as the percentage concentration of C3 compared with that in pooled preserved canine serum (100% C3 concentration).

RESULTS

Median C3 concentration was 128.5% in Bernese Mountain dogs with antibodies against B. burgdorferi, 133.5% in B. burgdorferi-negative Bernese Mountain dogs, 87.8% in positive control dogs, and 102.2% in negative control dogs. Within Bernese Mountain and control groups, C3 was lower in dogs with antibodies against B. burgdorferi compared with those without. Percentage concentration of C3 was higher in healthy Bernese Mountain dogs compared with control dogs.

CONCLUSION

Low C3 concentration is not an explanation for the high prevalence of B. burgdorferi infections and glomerular disease in Bernese Mountain dogs.

Molecular basis of complete complement C4 deficiency in two North-African families with systemic lupus erythematosus

Complete deficiency of complement C4 is among the strongest genetic risk factors for human systemic lupus erythematosus (SLE). C4 is a constituent of the RP-C4-CYP21-TNX (RCCX) module in the human leukocyte antigen (HLA) that exhibits inter-individual copy-number and gene-size variations. Here, we studied two North-African families with complete C4 deficiency and SLE. The first included a Moroccan male SLE patient (1P) and a sibling, who were both homozygous for HLA-A*02 B*17 DRB1*07. The second had an Algerian female SLE patient (2P) homozygous for HLA-A*01 B*17 DRB1*13. Early SLE disease onset, the presence of photosensitive rashes, anti-Ro/SSA, renal disease and high titers of antinuclear antibodies were the common features of complete C4 deficiency. Southern blot analyses showed that 1P had monomodular RCCX with a long C4A, whereas 2P had bimodular RCCX with one long C4A and one short C4B. Genomic DNA fragments for these mutant genes were amplified and sequenced. A C>T transition that created the R540X nonsense mutation in C4A was found in 1P. An identical 4-bp insertion that generated the Y1537X nonsense mutation was discovered in both C4A and C4B of 2P. The high concordance of SLE and C4 deficiency among patients with non-DR3 and non-DR2 haplotypes underscores the importance of C4 proteins in the protection against SLE.

Long-term follow-up of juvenile acute nonproliferative glomerulitis (JANG)

This report concerns a 9-year-old boy who was diagnosed with atypical type II membranoproliferative glomerulonephritis and later proved to have juvenile acute nonproliferative glomerulitis (JANG). To the best of our knowledge, this is the first report on the long-term clinical and pathological follow-up of JANG.

Streptococcal pyrogenic exotoxin B antibodies in a mouse model of glomerulonephritis

Streptococcal pyrogenic exotoxin B is an extracellular cysteine protease. Only nephritis-associated strains of group A streptococci secrete this protease and this may be involved in the pathogenesis of post-streptococcal glomerulonephritis. Mice were actively immunized with a recombinant protease inactive exotoxin B mutant or passively immunized with exotoxin B antibody. Characteristics of glomerulonephritis were measured using histology, immunoglobulin deposition, complement activation, cell infiltration, and proteinuria. None of the mice given bovine serum albumin or exotoxin A as controls showed any marked changes. Immunoglobulin deposition, complement activation, and leukocyte infiltration occurred only in the glomeruli of exotoxin B-hyperimmunized mice. One particular anti-exotoxin B monoclonal antibody, 10G, was cross-reactive with kidney endothelial cells and it caused kidney injury and proteinuria when infused into mice. This cross-reactivity may be involved in the pathogenesis of glomerulonephritis following group A streptococcal infection.

Three distinct profiles of serum complement C4 proteins in pediatric systemic lupus erythematosus (SLE) patients: tight associations of complement C4 and C3 protein levels in SLE but not in healthy subjects

The serial changes of serum complement proteins C4 and C3 in SLE were characterized in 33 pediatric SLE patients with defined C4 genotypes. Three distinct groups of C4 protein profiles were observed. The first group was characterized by persistently low C4 levels (<10 mg/dL) throughout the course of the study. Patients with this profile had mild disease manifestations and low to medium copy numbers of C4 genes. The second group featured periodic fluctuations of serum C4 protein concentrations above and below 10 mg/dL, paralleled with ups and downs of SLE disease activities. Most patients with the second profile had unequal copy numbers of C4A and C4B genes and relatively severe disease. The third group had normal serum C4 levels (>15 mg/dL) most of the time and occasionally low C4 and C3 levels that were mostly coincident with disease flares prior to effective medical treatment. Most patients in this group

Serum concentrations of the third component of complement in healthy dogs and dogs with protein-losing nephropathy

OBJECTIVE

To develop a method for determining the concentration of the third component of complement (C3) in canine serum, to establish a reference range for C3 in healthy dogs, and to evaluate dogs with protein-losing nephropathy (PLN) to determine whether PLN is associated with decreased serum C3 concentrations.

ANIMALS

30 healthy dogs and 49 dogs with PLN.

PROCEDURES

Serum samples were obtained from healthy dogs at the time of examination, whereas serum samples were obtained from dogs with PLN at the time of diagnosis. All samples were frozen at -70 degrees C until analyzed. Serum C3 concentrations were determined by use of a sandwich ELISA. Concentrations were expressed as the number of dilutions in which C3 could be detected.

RESULTS

C3 was detectable in healthy control dogs (range, 1,920,000 to 15,400,000 dilutions; median, 9,600,000 dilutions). This represented a range of four 2-fold serum dilutions. In addition, C3 was detectable in dogs with PLN (range, 1,460,000 to 30,070,000 dilutions; median, 7,680,000 dilutions), which represented a range of six 2-fold serum dilutions. There was no significant difference in C3 concentrations between the 2 groups.

CONCLUSIONS AND CLINICAL RELEVANCE

C3 is a critical part of the immune defense system that has not been extensively examined in veterinary medicine. An ELISA was developed for measuring C3 concentrations, and a reference range for healthy dogs was established. Significant decreases in C3 concentrations were not detected in any dog with PLN. Additional studies will be required to definitively determine the importance of serum C3 concentrations in PLN.

Long-term follow-up of atypical membranoproliferative glomerulonephritis: are steroids indicated?

Atypical membranoproliferative glomerulonephritis (MPGN) has been reported to have a good prognosis when treated with corticosteroids. However, this recommendation is based on uncontrolled trials and is associated with many complications. The purpose of our study is to determine whether steroid therapy is indicated for atypical MPGN. The cases of seven patients with atypical MPGN are reported in this study. Urinary abnormalities of five of them were detected by urine screening at school, of two because of macrohematuria. Hypocomplementemia was noted in six patients. All but one patient were treated without corticosteroids, and five with angiotensin-converting enzyme inhibitors (ACEI) and/or the Chinese herbal medicine Sairei-to (TJ-114). One patient recovered spontaneously from proteinuria and was therefore not treated, and one who developed severe proteinuria during observation was treated with corticosteroids. After an average follow-up period of 10.0 years, five patients showed normal urinary findings, one had hematuria and one proteinuria. At the most recent follow-up, the renal function of all patients remained within the normal range, and serum C3 had returned to normal levels in five out of six. These findings suggest that the indication of steroid therapy for atypical MPGN should be re-examined, since most of the patients with atypical MPGN seem to have an excellent prognosis without treatment with corticosteroids.

Hypocomplementemia in systemic lupus erythematosus and primary antiphospholipid syndrome: prevalence and clinical significance in 667 patients

The objective of the study was to analyse the prevalence and clinical significance of hypocomplementemia in a large series of patients diagnosed either with systemic lupus erythematosus (SLE) or with primary antiphospholipid syndrome (APS) and its association with the main clinical, hematological and immunological features of these diseases. Between 1992 and 2003, complement determinations (C3 and C4 levels, CH50 activity) were performed in 597 consecutive patients diagnosed with SLE (530 women and 67 men, mean age 32.6 years) and 70 with primary APS (57 women and 13 men, mean age 38.7) visited in our department. Complement determinations are routinely made at the first visit of patients and yearly during the follow-up. SLE and primary APS were diagnosed according to current classification criteria. Hypocomplementemia was detected in 371 (62%) of SLE patients. Compared with patients with normal complement values, those with hypocomplementemia showed a higher prevalence of female gender (P < 0.001), fever (P = 0.021), nephropathy (P < 0.001), cutaneous vasculitis (P = 0.023), positive anti-dsDNA antibodies (P = 0.012) and cryoglobulinemia (P < 0.001). In addition, patients with hypocomplementemia showed a higher prevalence of APS-related features such as hemolytic anemia (P = 0.001) and antiphospholipid antibodies (P < 0.001). Hypocomplementemia was prospectively related to accumulated hospitalization in SLE patients but not with the accumulated number of lupus flares or with the survival after follow-up of five years. In contrast, 33 (47%) patients with primary APS presented low complement values, which were associated with a higher prevalence of livedo reticularis (P = 0.022), thrombocytopenia (P = 0.004), lupus anticoagulant (P = 0.013), positive IgM-aCL (P = 0.039), positive ANA (P = 0.002) and anti-dsDNA (P = 0.046). The diagnostic value of hypocomplementemia in patients with SLE is based on the association with disease activity, immune-complex mediated manifestations (glomerulonephritis, cryoglobulinemia) and APS-related features (livedo reticularis, hemolytic anemia and aPL). Hypocomplementemia was found in nearly half of patients with primary APS, and was associated with some APS features (livedo reticularis, thrombocytopenia, aPL) but also with SLE-related immunological markers (ANA and anti-dsDNA), identifying a subset of patients with primary APS with a higher risk of evolving to SLE. These results clearly support the routine determination of complement factors in the clinical follow-up of patients with SLE and primary APS.

A novel ELISA for the evaluation of the classical pathway of complement

Assessment of the overall function of the classical pathway of complement is traditionally performed by the hemolytic titration assay CH50. In the present study, we established a novel method for the quantitation of complement activity by measuring the deposition of C1q, C4, C3 and C9 on solid-phase IgM by an enzyme-linked immunosorbent assay (ELISA). Using the CH50 method as the reference, C9 deposition values displayed a sensitivity of 96.3% and a specificity of 99.4% in sera from patients with a variety of diseases. For C3, the sensitivity was 91.3% and the specificity 100%, for C4, the values were 95% and 100%, and for C1q the corresponding values were 52.9% and 98.9%. A close correlation was found between CH50 values below 30 U/ml and the deposition of C9 (r = 0.92), C3 (r = 0.91) and C4 (r = 0.92). In two patients with postinfectious glomerulonephritis normal C4 and C1q deposition was accompanied by decreased C3 and C9 deposition reflecting complement activation predominantly through the alternative pathway. In contrast, in two patients with complete C2 deficiency the deposition of C3 and C9 was undetectable together with normal C4 deposition values. Furthermore, in two patients with hereditary C1-inhibitor deficiency distinctly increased C1q deposition was accompanied by decreased C4 deposition values. In conclusion, the determination of complement deposition by ELISA represents a novel, quantitative method for the evaluation of complement activity. The measurement of C9 deposition alone or in combination with further complement proteins makes this ELISA a valuable tool for assessing the degree and level of complement consumption as well as localizing the missing protein in the case of complement deficiencies.

Serological characteristics of systemic lupus erythematosus from a hospital-based rheumatology clinic in Kuwait

Thirty-one consecutive patients with SLE were screened for antinuclear antibody (ANA), anti-DNA antibodies, extractable nuclear antigen antibodies (anti-ENAs) including anti-Sm, anti-RNP, anti-SSA (anti-Ro), anti-SSB; (anti-La), anti-Scl-70, rheumatoid factor (RF), C-reactive protein (CRP), C3 and C4 levels, anti-cardiolipin antibodies (aCL), biologically false positive serological test for syphilis (BF-STS) using VDRL test and Coombs' test. The age of the patients ranged from 11 to 52 year with a median of 29 year; female to male ratio of 5:1. There were 21 Kuwaitis, four Egyptians, three from the Indian subcontinent, two Filipinos and one Syrian. Main clinical categories of SLE were: mild cutaneous SLE in 12 (38.7%), clinical antiphospholipid syndrome (APS) secondary to SLE in 8 (25.8%), haematological manifestations of SLE in 5 (16.1%), renal lupus in four (12.9%), neuropsychiatric in three (9.7%), others (6.4%). Clinical features overlapped in several patients. ANA was positive in 96.8% (mean value 891.61 units/ml), anti-DNA in 35.5% (mean value 56.4 units) that was lower than expected and could be due to selection bias as the patients were from a rheumatology clinic, anti-ENA in 42%, anti-Sm 13% that was lower than other non-Caucasian populations, anti-RNP 13%, anti-SS-A in 35.5%, anti-SS-B in 19.4%, Scl-70 in 13%, CRP in 71% (moderate 58%, very high 13%); C3 mean 1.52 mg/ml (3.2% low levels), C4 mean 0.35 mg/ml (32% low levels), anticardiolipin mean GPL 35.35 units (high 58%), mean MPL 10.61 units (high 26%), BF-STS in 6%, Coombs' test in 6%, RF positive in 36%. The only significant positive clinical associations observed were those of renal involvement with anti-DNA antibodies (P = 0.042), and clinical antiphospholipid antibody syndrome with aCL antibodies (P = < 0.05).