Complement levels at admission as a reflection of coronavirus disease 2019 (COVID-19) severity state.

Complement system hyperactivation has been proposed as a potential driver of adverse outcomes in severe acute respiratory syndrome coronavirus 2 infected patients, given prior research of complement deposits found in tissue and blood samples, as well as evidence of clinical improvement with anticomplement therapy. Its role in augmenting thrombotic microangiopathy mediated organ damage has also been implicated in coronavirus disease 2019 (COVID-19). This study aimed to examine associations between complement parameters and progression to severe COVID-19 illness, as well as correlations with other systems. Blood samples of COVID-19 patients presenting to the emergency department (ED) were analyzed for a wide panel of complement and inflammatory biomarkers. The primary outcome was COVID-19 severity at index ED visit, while the secondary outcome was peak disease severity over the course of illness. Fifty-two COVID-19 patients were enrolled. C3a (p = 0.018), C3a/C3 ratio (p = 0.002), and sC5b-9/C3 ratio (p = 0.021) were significantly elevated in with severe disease at ED presentation. Over the course of illness, C3a (p = 0.028) and C3a/C3 ratio (p = 0.003) were highest in the moderate severity group. In multivariate regression controlled for confounders, complement hyperactivation failed to predict progression to severe disease. C3a, C3a/C3 ratio, and sC5b-9/C3 ratio were correlated positively with numerous inflammatory biomarkers, fibrinogen, and VWF:Ag, and negatively with plasminogen and ADAMTS13 activity. We found evidence of complement hyperactivation in COVID-19, associated with hyperinflammation and thrombotic microangiopathy. Complement inhibition should be further investigated for potential benefit in patients displaying a hyperinflammatory and microangiopathic phenotype.

Clinical relevance of membrane attack complex deposition in children with IgA nephropathy and Henoch-Schönlein purpura.

BACKGROUND: IgA nephropathy (IgAN) and Henoch-Schönlein purpura are common glomerular disorders in children sharing the same histopathologic pattern of IgA deposits within the mesangium, even if their physiopathology may be different. Repeated exposure to pathogens induces the production of abnormal IgA1. The immune complex deposition in the renal mesangium in IgAN or potentially in small vessels in Henoch-Schönlein purpura induces complement activation via the alternative and lectin pathways. Recent studies suggest that levels of membrane attack complex (MAC) in the urine might be a useful indicator of renal injury. Because of the emerging availability of therapies that selectively block complement activation, the aim of the present study is to investigate whether MAC immunostaining might be a useful marker of IgA-mediated renal injury. METHODS: We conducted immunohistochemistry analysis of the MAC on renal biopsies from 67 pediatric patients with IgAN and Henoch-Schönlein purpura. We classified their renal biopsies according to the Oxford classification, retrieved symptoms, biological parameters, treatment, and follow-up. RESULTS: We found MAC expression was significantly related to impaired renal function and patients whose clinical course required therapy. MAC deposits tend to be more abundant in patients with decreased glomerular filtration rate (p = 0.02), patients with proteinuria > 0.750 g/day/1.73 m2, and with nephrotic syndrome. No correlation with histological alterations was observed. CONCLUSIONS: We conclude that MAC deposition could be a useful additional indicator of renal injury in patients with IgAN and Henoch-Schönlein purpura, independent of other indicators.

Glomerular membrane attack complex is not a reliable marker of ongoing C5 activation in lupus nephritis.

Complement plays an important role in the pathogenesis of lupus nephritis (LN). With the emergence of therapeutic complement inhibition, there is a need to identify patients in whom complement-driven inflammation is a major cause of kidney injury in LN. Clinical and histopathological data were obtained retrospectively from 57 biopsies with class III, IV, and V LN. Biopsies were stained for complement components C9, C5b-9, C3c, and C3d and for the macrophage marker CD68. C9 and C5b-9 staining were highly correlated (r = 0.92 in the capillary wall). C5b-9 staining was detected in the mesangium and/or capillary wall of both active and chronic proliferative LN in all but one biopsy and in the capillary wall of class V LN in all biopsies. C5b-9 staining intensity in the tubular basement membrane correlated with markers of tubulointerstitial damage, and more intense capillary wall C5b-9 staining was significantly associated with nonresponse to conventional treatment. Glomerular C5b-9 staining intensity did not differ between active and chronic disease; in contrast, C3c and CD68 staining were associated with active disease. Evaluation of serial biopsies and comparison of staining in active and chronic LN demonstrated that C5b-9 staining persisted for months to years. These results suggest that C5b-9 staining is almost always present in LN, resolves slowly, and is not a reliable marker of ongoing glomerular C5 activation. This limits the utility of C5b-9 staining to identify patients who are most likely to benefit from C5 inhibition.

Complement-mediated microangiopathy in IgA nephropathy and IgA vasculitis with nephritis.

Complement factor C4d was recently observed in renal biopsies from patients who had IgA nephropathy and a poor prognosis. We previously reported that C4d is a common denominator in microangiopathies. In this retrospective cohort study, we investigated whether C4d is a marker of microangiopathy in both IgA nephropathy and IgA vasculitis with nephritis, and whether patients with C4d and microangiopathy have poor renal outcome. We examined 128 renal biopsies from adult and pediatric patients, including normotensive and hypertensive patients, who presented with IgA nephropathy or IgA vasculitis with nephritis. Biopsies were re-evaluated in accordance with the Oxford classification, scored for additional lesions, and stained for complement proteins using immunohistochemistry, including C4d and C5b-9. Clinical data were collected with a mean (±SD) follow-up period of 51 ± 39 months. Changes in estimated glomerular filtration rate over time were compared using linear mixed-effects models. Renal survival was analyzed using multivariable Cox regression. Microangiopathic lesions were present in 20% of all biopsies (23% and 9% of patients with IgA nephropathy and IgA vasculitis with nephritis, respectively). Microangiopathy was associated with C4d and C5b-9 deposits, a higher number of chronic lesions, and hypertension (all p < 0.05). Patients with C4d and microangiopathic lesions had significantly poorer renal survival than patients without these findings, corrected for hypertension (p < 0.01). In conclusion, patients with IgA nephropathy or IgA vasculitis with nephritis with a combination of C4d positivity and microangiopathy comprise a clinical subgroup with an increased number of chronic lesions, lower estimated glomerular filtration rate, and poorer renal survival, even when corrected for hypertension. These data suggest that complement activation is involved in the development of microangiopathy in patients with IgA nephropathy and IgA vasculitis with nephritis, and that complement-mediated microangiopathy contributes to disease progression.

An Ex Vivo Test of Complement Activation on Endothelium for Individualized Eculizumab Therapy in Hemolytic Uremic Syndrome.

RATIONALE & OBJECTIVE: Although primary atypical hemolytic uremic syndrome (aHUS) is associated with abnormalities in complement genes and antibodies to complement factor H, the role of complement in secondary aHUS remains debatable. We evaluated the usefulness of an ex vivo test to: (1) detect complement activation within the endothelium in primary and secondary aHUS, (2) differentiate active disease from remission, (3) monitor the effectiveness of eculizumab therapy, and (4) identify relapses during eculizumab dosage tapering and after discontinuation of treatment. STUDY DESIGN: Case series. SETTING & PARTICIPANTS: 121 patients with primary aHUS and 28 with secondary aHUS. Serum samples were collected during acute episodes, following remission, and during eculizumab treatment and were assessed using a serum-induced ex vivo C5b-9 endothelial deposition test. RESULTS: Serum-induced C5b-9 deposition on cultured microvascular endothelium was quantified by calculating the endothelial area covered by C5b-9 staining; values were expressed as percentage of C5b-9 deposits induced by a serum pool from healthy controls. Testing with adenosine diphosphate-activated endothelium demonstrated elevated C5b-9 deposits for all untreated patients with aHUS independent of disease activity, while testing with unstimulated endothelium demonstrated deposits only in active disease. Similar findings were observed in secondary aHUS. Serum-induced C5b-9 deposits on activated and unstimulated endothelium normalized during eculizumab treatment. 96% (22/23) of patients receiving eculizumab at extended 3- or 4-week dosing intervals demonstrated normal C5b-9 deposits on activated endothelium, despite most patients having CH50Eq (serum complement activity) > 20 UEq/mL, indicating that adequate complement control was achieved even with incomplete blockade of circulating C5. During eculizumab dosage tapering or after treatment discontinuation, all patients experiencing relapses versus only 6% (1/17) of those in stable remission had elevated C5b-9 deposits on unstimulated endothelium. LIMITATIONS: The C5b-9 endothelial deposition test can be performed in only specialized laboratories. Findings on eculizumab dosage tapering need to be confirmed with longitudinal monitoring of C5b-9 deposition. CONCLUSIONS: The C5b-9 endothelial deposition assay may represent an advance in our ability to monitor aHUS activity and individualize therapy.

Absence of Distinct Immunohistochemical Distribution of Annexin A5, C3b, C4d, and C5b-9 in Placentas From Patients With Antiphospholipid Antibodies, Preeclampsia, and Systemic Lupus Erythematosus.

INTRODUCTION: In pregnancy, the presence of preeclampsia (PEC), systemic lupus erythematosus (SLE), and/or antiphospholipid antibody syndrome (APLS) is characterized by poor obstetric outcomes, with potential adverse effects for both mother and fetus. Although the histopathologic changes observed in these entities have been well established, the pathogenic mediators associated with tissue injury are poorly understood. METHODS: Forty placentas were evaluated, including 10 patients with preeclampsia, 9 with SLE, 11 with APLS, and 10 disease-free controls. Each case was subjected to a panel of immunohistochemical markers including C3b, C4d, Annexin A5, and C5b-9. Staining was graded on intensity and distribution. RESULTS: C4d staining was distinctly different among disease groups and controls. Moreover, 6/10 PEC cases, 3/9 SLE cases, and 4/11 APLS cases showed at least focal staining for C4d. All controls were negative. Annexin A5 (AnxA5) staining showed intrinsic variability in all disease groups, while 10/10 controls showed diffuse, strong staining (2+ or 3+). C3b staining was heterogeneous among groups. DISCUSSION: Previously, antiphospholipid antibody (aPLA)-associated pregnancy complications have been thought to be a consequence of a unique aPLA-mediated pathogenic mechanism. However, the immunohistochemical similarity (increased complement and decreased AnxA5 staining) observed in placentas from patients with APLS, PEC, and SLE suggests that aPLA-associated pregnancy complications may reflect a more general autoimmune mechanism.

High levels of urinary complement proteins are associated with chronic renal damage and proximal tubule dysfunction in immunoglobulin A nephropathy.

AIM: Complement activation is involved in the pathogenesis and progression of immunoglobulin A nephropathy (IgAN); however, the clinical implication of abnormal complement protein levels in serum and urine is not clear. To address this we analyzed the correlation between disease activity and complement proteins in serum and urine from IgAN patients, and compared to patients with other types of chronic kidney disease (CKD) as well as healthy controls. METHODS: We included 85 Chinese patients with IgAN, 23 patients with non-proliferative CKD, and 20 healthy individuals. Patients were divided according to the Oxford classification of M0E0S0T0 (group 1, n = 20), M1E1S0-1 T0-1 (group 2, n = 25), M1E1S0-1 T2 or M0E0S1T1-2 (group 3, n = 40). Complement factor H (CFH), mannose-binding lectin and membrane attack complex in serum and urine were measured by enzyme-linked immunosorbent assay. RESULTS: Urinary CFH, membrane attack complex and serum CFH were increased in both IgAN and CKD patients compared with healthy controls. The urinary excretion of CFH was the highest in IgAN patients with most tubulointerstitial damage (IgAN group 3). Urinary CFH and mannose-binding lectin levels were significantly higher in IgAN patients with crescents formation (C1-2) than in patients without (C0). Urinary complement protein excretion correlated negatively with estimated glomerular filtration rate, and positively with urinary retinol-binding protein and α1-microglobulin excretion indicating proximal tubule dysfunction. CONCLUSION: Increased urinary excretion of complement proteins in IgAN is related to chronic injury and tubular dysfunction. This warrants caution using urinary complement proteins as markers of disease activity.

Complement activation products in the circulation and urine of primary membranous nephropathy.

BACKGROUND: Complement activation plays a substantial role in the pathogenesis of primary membranous nephropathy (pMN). C5b-9, C3c, MBL, and factor B have been documented in the subepithelial immune deposits. However, the changing of complement activation products in circulation and urine is not clear. METHODS: We measured the circulating and urinary levels of C1q, MBL, C4d, Bb, properdin, C3a, C5a, and sC5b-9, in 134 patients with biopsy-proven pMN, by enzyme-linked immunosorbent assay. All the plasma values were corrected by eGFR and all the urinary values were corrected by urinary creatinine and urinary protein excretion. Anti-PLA2R antibodies were measured in all patients. RESULTS: The plasma complement activation products were elevated both in the patients with and without anti-PLA2R antibodies. C3a levels were remarkably increased in the circulation and urine, much higher than the elevated levels of C5a. C5b-9 was in normal range in plasma, but significantly higher in urine. The urinary C5a had a positive correlation with anti-PLA2R antibody levels and urinary protein. The plasma level of C4d was elevated, but C1q and MBL were comparable to healthy controls. Positive correlations were observed between plasma C4d/MBL and urinary protein, only in the patients with positive anti-PLA2R antibodies but not in those without. The plasma level of Bb was elevated and had positive correlation with urinary protein only in the patients without anti-PLA2R antibodies. CONCLUSION: Complement activation products were remarkable increased in pMN and may serve as sensitive biomarkers of disease activity. The complement may be activated through lectin pathway with the existence of anti-PLA2R antibodies, while through alternative pathway in the absence of antibody.

Early Increase in Complement Terminal Pathway Activation Marker sC5b-9 Is Predictive for the Development of Thrombotic Microangiopathy after Stem Cell Transplantation.

Hematopoietic stem cell transplantation (HSCT)-associated thrombotic microangiopathy (TA-TMA) is a multifactorial complication, and its prediction is largely unresolved. Our aim was to analyze changes of complement profile after HSCT to identify potential markers of TA-TMA development. Thirty-three consecutive pediatric patients (9.6 ± 4.4 years old) who underwent allogeneic HSCT due to malignant (n = 17) or nonmalignant (n = 16) indications were included in this study. Graft-versus-host disease (GVHD) was diagnosed using Glucksberg criteria, viral reactivation was monitored, 5 different TA-TMA diagnostic criteria were applied, and all important clinical and laboratory parameters of TA-TMA activity were registered. Complement pathway activities, components and terminal pathway activation marker (sC5b-9) levels were systematically measured before transplantation and on days 28, 56, and 100 after HSCT. During the first 100 days after HSCT, 1 of 33 patients died (day 50, multiple organ failure), whereas 10 subjects met the criteria for TA-TMA, typically on day 61 (range, 16 to 98 days). TA-TMA was preceded by acute GVHD in 3 of 10 patients, by viral reactivation in 2 of 10, or by both in 4 of 10 cases. Baseline sC5b-9 levels did not differ in patients without (200 [interquartile range, 144 to 266] ng/mL), or with (208 [interquartile range, 166 to 271] ng/mL) subsequent TA-TMA; however, on day 28 significant differences were observed (201 [interquartile range, 185 to 290] ng/mL versus 411 [interquartile range, 337 to 471] ng/mL; P = .004). Importantly, all 10 patients with TMA showed increase in sC5b-9 level from baseline level to day 28, whereas in patients without TMA the same tendency was observed for only 9 of 23 patients (P = .031). No additional complement parameters were closely associated with the development of TA-TMA. Development of TA-TMA occurred in 30% of our patients, typically after GVHD and/or viral reactivation. However, early raise of sC5b-9 activation marker was predictive for later development of TA-TMA, and should therefore be considered as an alarming sign necessitating a careful monitoring of all TA-TMA activity markers. Further studies enrolling a higher number of patients are necessary to determine if terminal pathway activation is an independent predictor of TA-TMA.

Complement activation predicts adverse pregnancy outcome in patients with systemic lupus erythematosus and/or antiphospholipid antibodies.

OBJECTIVE: Studies in mouse models implicate complement activation as a causative factor in adverse pregnancy outcomes (APOs). We investigated whether activation of complement early in pregnancy predicts APOs in women with systemic lupus erythematosus (SLE) and/or antiphospholipid (aPL) antibodies. METHODS: The PROMISSE Study enrolled pregnant women with SLE and/or aPL antibodies (n=487) and pregnant healthy controls (n=204) at <12 weeks gestation and evaluated them monthly. APOs were: fetal/neonatal death, preterm delivery <36 weeks because of placental insufficiency or preeclampsia and/or growth restriction <5th percentile. Complement activation products were measured on serial blood samples obtained at each monthly visit. RESULTS: APO occurred in 20.5% of SLE and/or aPL pregnancies. As early as 12-15 weeks, levels of Bb and sC5b-9 were significantly higher in patients with APOs and remained elevated through 31 weeks compared with those with normal outcomes. Moreover, Bb and sC5b-9 were significantly higher in patients with SLE and/or aPL without APOs compared with healthy controls. In logistic regression analyses, Bb and sC5b-9 at 12-15 weeks remained significantly associated with APO (ORadj=1.41 per SD increase; 95% CI 1.06 to 1.89; P=0.019 and ORadj=1.37 per SD increase; 95% CI 1.05 to 1.80; P=0.022, respectively) after controlling for demographic and clinical risk factors for APOs in PROMISSE. When analyses were restricted to patients with aPL (n=161), associations between Bb at 12-15 weeks and APOs became stronger (ORadj=2.01 per SD increase; 95% CI 1.16 to 3.49; P=0.013). CONCLUSION: In pregnant patients with SLE and/or aPL, increased Bb and sC5b-9 detectable early in pregnancy are strongly predictive of APOs and support activation of complement, particularly the alternative pathway, as a contributor to APOs.

Membrane Attack Complex and Factor H in Humans with Acute Kidney Injury.

BACKGROUND AND AIMS: Complement system seems to play an important role in the pathogenesis of Acute Kidney Injury (AKI). The aim of this study was to investigate the role of complement system in the pathogenesis of human AKI. For this purpose, we studied Membrane Attack Complex (MAC) and factor H in plasma and kidney tissue in AKI. METHODS: Plasmatic concentrations of MAC and Factor H were studied in patients with hospital-acquired AKI and their respective controls. MAC and Factor H expression and localization within the kidney were studied by immunohistochemistry in kidney tissue samples from autopsies. Demographical, past medical, and laboratory data in patients on admission and 3 years after discharge were recorded. RESULTS: Plasmatic MAC concentrations were significantly higher in AKI-patients (5848±3604 vs 3703±1483 mAU/mL, p< 0.01), mainly in the severe cases, as measured by the need of renal replacement therapy, non-recovery of renal function, RIFLE classification and CKD development. MAC deposition was observed in tubular epithelial cell basal membranes, showing a larger number of tubules with MAC deposition, larger perimeter of affected tubules and greater intensity of MAC immunostaining in AKI patients. Factor H concentrations were higher in AKI patients (0.86±0.05 vs 0.60±0.04 mg/mL, p=0.007), showing a strong positive association with plasmatic MAC (r=0.7, p< 0.01)). Factor H immunostaining showed a tubular cytoplasmic pattern, with significant variations in the staining intensity, associated with the severity of histologic damage. CONCLUSION: Our data confirm that complement system is involved in human AKI, through the lytic action of MAC in tubular epithelial cells. These results suggest that complement system activation in AKI could be related with CKD development.

FcγRIIIa-Syk Co-signal Modulates CD4+ T-cell Response and Up-regulates Toll-like Receptor (TLR) Expression.

CD4(+) T-cells in systemic lupus erythematosus (SLE) patients show altered T-cell receptor signaling, which utilizes Fc-receptor γ-chain FcRγ-Syk. A role for FcγRIIIa activation from immune complex (IC) ligation and sublytic terminal complement complex (C5b-9) in CD4(+) T-cell responses is not investigated. In this study, we show that the ICs present in SLE patients by ligating to FcγRIIIa on CD4(+) T-cells phosphorylate Syk and provide a co-stimulatory signal to CD4(+) T-cells in the absence of CD28 signal. This led to the development of pathogenic IL-17A(+) and IFN-γ(high) CD4(+) T-cells in vitro. Cytokines IL-1ß, IL-6, TGF-ß1, and IL-23 were the only requirement for the development of both populations. SLE patients CD4(+) T-cells that expressed CD25, CD69, and CD98 bound to ICs showed pSyk and produced IFN-γ and IL-17A. This FcγRIIIa-mediated co-signal differentially up-regulated the expression of IFN pathway genes compared with CD28 co-signal. FcγRIIIa-pSyk up-regulated several toll-like receptor genes as well as the HMGB1 and MyD88 gene transcripts. ICs co-localized with these toll-like receptor pathway proteins. These results suggest a role for the FcγRIIIa-pSyk signal in modulating adaptive immune responses.

C5 nephritic factors drive the biological phenotype of C3 glomerulopathies.

C3 Glomerulopathies, which include Dense Deposit Disease and C3 Glomerulonephritis, are associated with genetic and acquired dysregulation of the C3 convertase alternative pathway of complement. The potential role of the activation of the C5 convertase has not been studied extensively. Here we analyzed IgG samples from patients with C3 Glomerulopathies to identify circulating autoantibodies that stabilize the C3 alternative pathway (C3 Nephritic Factors) as well as C5 convertases (C5 Nephritic Factors), thus preventing decay of these enzyme complexes. Rare variants in alternative pathway genes were found in 28 of 120 tested patients. C3 and C5 Nephritic Factors were found in 76 of 101 (75%) and 29 of 59 (49%) of the patients, respectively. Therefore, we compared the results of the assays for the C3 and C5 nephritic factors functional activity: 29% were positive for C3 Nephritic Factors alone, 39% were positive for both C3 and C5 Nephritic Factors, and 10% were positive for C5 Nephritic Factors alone. We found that the addition of properdin-enhanced stabilization of C3 convertase in the presence of IgG doubly positive for both Nephritic Factors, while it did not modify the stabilization mediated by IgG solely positive for C3 Nephritic Factors. Both C3 and C5 Nephritic Factors correlated with C3 consumption, while only C5 Nephritic Factors correlated with sC5b9 levels. C5 Nephritic Factors-positive patients were more likely to have C3 Glomerulonephritis than Dense Deposit Disease. Thus, dysregulation of the C5 convertase contributes to C3 Glomerulopathies inter-disease differences and may have direct therapeutic implications.

Complement and contact system activation in acute congestive heart failure patients.

Recent experimental data indicate a pathogenic role of complement activation in congestive heart failure (CHF). The aim of this study was to evaluate contact and complement systems activation in patients hospitalized for an acute episode of CHF. Forty-two of 80 consecutive patients admitted at our hospital with confirmed diagnosis of acute CHF were enrolled. They underwent blood sampling within 24 h from admission (T0) and at clinical stability (T1). Patients were stratified for ejection fraction (EF) based on echocardiographic test. We measured plasma levels of C3, C4, sC5b-9 and cleaved high molecular weight kininogen (contact activation marker). At T1, C3 levels increased significantly compared to T0 (97 ± 2 versus 104 ± 3% of total pooled plasma, P < 0·01). Classifying patients according to EF, only patients with preserved EF presented a significant increase of C3 from T0 to T1 (99 ± 3 versus 108 ± 4%, P = 0·03). When the sample was stratified according to clinical outcome, C3 (98 ± 3 versus 104 ± 4%, P = 0·03) and sC5b-9 levels (204 ± 10 versus 230 ± 11 ng/ml, P = 0·03) were increased in patients who had positive outcome after hospitalization. CHF patients with preserved EF and positive outcome after hospitalization showed higher levels of sC5b-9 in the T1 period compared with T0 (211 ± 14 versus 243 ± 14 ng/ml, P = 0·04). Our results suggest that the complement system reacts differently if CHF occurs with preserved or reduced EF. This finding is interesting if we consider the difference in epidemiology, pathogenesis and possible therapeutic approaches of these two clinical entities.

Plasma complement biomarkers distinguish multiple sclerosis and neuromyelitis optica spectrum disorder.

BACKGROUND: Multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) are autoimmune inflammatory demyelinating diseases of the central nervous system. Although distinguished by clinicoradiological and demographic features, early manifestations can be similar complicating management. Antibodies against aquaporin-4 support the diagnosis of NMOSD but are negative in some patients. Therefore, there is unmet need for biomarkers that enable early diagnosis and disease-specific intervention. OBJECTIVE: We investigated whether plasma complement proteins are altered in MS and NMOSD and provide biomarkers that distinguish these diseases. METHODS: Plasma from 54 NMOSD, 40 MS and 69 control donors was tested in multiplex assays measuring complement activation products and proteins. Using logistic regression, we tested whether combinations of complement analytes distinguished NMOSD from controls and MS. RESULTS: All activation products were elevated in NMOSD compared to either control or MS. Four complement proteins (C1inh, C1s, C5 and FH) were higher in NMOSD compared to MS or controls. A model comprising C1inh and terminal complement complex (TCC) distinguished NMOSD from MS (area under the curve (AUC): 0.98), while C1inh and C5 distinguished NMOSD from controls (AUC: 0.94). CONCLUSION: NMOSD is distinguished from MS by plasma complement biomarkers. Selected complement analytes enable differential diagnosis. Findings support trials of anti-complement therapies in NMOSD.

Relevance of C5b9 immunostaining in the diagnosis of neonatal hemochromatosis.

BACKGROUND: Neonatal hemochromatosis caused by a gestational alloimmune mechanism or gestational alloimmune liver disease (GALD) is a rare perinatal disorder characterized by intra- and extrahepatic iron overload. It is believed to result from complement-mediated liver injury, in which the classical complement pathway is activated by maternal antibody/fetal antigen complexes, leading to hepatocyte lysis by the membrane attack complex C5b9. According to some authors, C5b9 expression in more than 75% of liver parenchyma is specific for GALD. METHODS: We conducted a retrospective multicentric immunohistochemical study with anti-C5b9 in GALD cases (n = 25) and non-GALD cases with iron overload (n = 36) and without iron overload (n = 18). RESULTS: C5b9 was expressed in 100% of GALD cases but involved more than 75% of the liver parenchyma in only 26% of the cases. C5b9 was detected in 26.75% of the non-GALD cases with more than 75% of positive parenchyma in maternal erythrocytic alloimmunization, herpes and enterovirus hepatitis, bile acid synthetic defect, DGUOK mutation, Gaucher disease, cystic fibrosis, and giant-cell hepatitis with autoimmune hemolytic anemia. CONCLUSION: Diagnosis and therapeutic management of GALD cannot only be based on C5b9 expression in liver samples as it is not specific of this disease.

Plasma MASP-1 concentration and its relationship to recovery from coronary artery lesion in children with Kawasaki disease.

BACKGROUND: This study investigated prognostic factors for early recovery of coronary artery lesion (CAL) in children with Kawasaki disease (KD). METHODS: Patients hospitalized for KD were enrolled less than 2 wk from the onset of illness and divided into two groups: KD with CAL and KD without CAL. The CAL group was further divided into two subgroups according to the degree of CAL: mild (n = 31) and moderate/severe (n = 6) and further divided into two subgroups according to the age: younger than 1 y (n = 9) and older than 1 y (n = 28). Lectin pathway-related factors MASP-1, CD59, and C5b-9 were measured, along with C-reactive protein, white blood cell counts, erythrocyte sedimentation rate, and platelet count. Patients were followed up for 3 mo. Correlation between the measured factors and the length of time of recovery from CAL was analyzed. RESULTS: Plasma concentrations of MASP-1 in the CAL group were significantly lower than those without CAL. MASP-1 and gender positively correlated with the recovery time of CAL. There was no difference in MASP-1 between mild and moderate/severe CAL. At 3-mo follow-up, there was a positive correlation between plasma MASP-1 concentration and recovery time of the patients with CAL older than 1 y. CONCLUSION: Plasma MASP-1 concentration at the early stage of KD is predictive of length of time of recovery from CAL.

Complement Factor C4d Is a Common Denominator in Thrombotic Microangiopathy.

Complement activation has a major role in thrombotic microangiopathy (TMA), a disorder that can occur in a variety of clinical conditions. Promising results of recent trials with terminal complement-inhibiting drugs call for biomarkers identifying patients who might benefit from this treatment. The primary aim of this study was to determine the prevalence and localization of complement factor C4d in kidneys of patients with TMA. The secondary aims were to determine which complement pathways lead to C4d deposition and to determine whether complement activation results in deposition of the terminal complement complex. We examined 42 renal sections with histologically confirmed TMA obtained from a heterogeneous patient group. Deposits of C4d, mannose-binding lectin, C1q, IgM, and C5b-9 were scored in the glomeruli, peritubular capillaries, and arterioles. Notably, C4d deposits were present in 88.1% of TMA cases, and the various clinical conditions had distinct staining patterns within the various compartments of the renal vasculature. Classical pathway activation was observed in 90.5% of TMA cases. C5b-9 deposits were present in 78.6% of TMA cases and in 39.6% of controls (n=53), but the staining pattern differed between cases and controls. In conclusion, C4d is a common finding in TMA, regardless of the underlying clinical condition. Moreover, C5b-9 was present in >75% of the TMA samples, suggesting that terminal complement inhibitors may have a beneficial effect in these patients. C4d and C5b-9 should be investigated as possible diagnostic biomarkers in the clinical work-up of patients suspected of having complement-mediated TMA.