Magdalena Riedl

An international consensus approach to the management of atypical hemolytic uremic syndrome in children

Atypical hemolytic uremic syndrome (aHUS) emerged during the last decade as a disease largely of complement dysregulation. This advance facilitated the development of novel, rational treatment options targeting terminal complement activation, e.g., using an anti-C5 antibody (eculizumab). We review treatment and patient management issues related to this therapeutic approach. We present consensus clinical practice recommendations generated by HUS International, an international expert group of clinicians and basic scientists with a focused interest in HUS. We aim to address the following questions of high relevance to daily clinical practice: Which complement investigations should be done and when? What is the importance of anti-factor H antibody detection? Who should be treated with eculizumab? Is plasma exchange therapy still needed? When should eculizumab therapy be initiated? How and when should complement blockade be monitored? Can the approved treatment schedule be modified? What approach should be taken to kidney and/or combined liver–kidney transplantation? How should we limit the risk of meningococcal infection under complement blockade therapy? A pressing question today regards the treatment duration. We discuss the need for prospective studies to establish evidence-based criteria for the continuation or cessation of anticomplement therapy in patients with and without identified complement mutations.

Complement Factor H–Related Protein 1 Deficiency and Factor H Antibodies in Pediatric Patients with Atypical Hemolytic Uremic Syndrome

BACKGROUND AND OBJECTIVES This study evaluated the relevance of complement factor H (CFH)-related protein (CFHR) 1 deficiency in pediatric patients with atypical hemolytic uremic syndrome (aHUS) by evaluating both the frequency of deletions in CFHR1 and the presence of complement factor H (CFH) antibodies. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS A total of 116 patients (mainly from central Europe) and 118 healthy blood donors were included from 2001 to 2012. The presence of CFHR1 gene deletions was determined in 90 pediatric patients with aHUS and 118 controls by an easy, fast, and cheap PCR assay; 100 patients with aHUS and 42 controls were tested for CFH antibodies by ELISA. Questionnaires were administered to evaluate the clinical and laboratory data. RESULTS Homozygous deletion in CFHR1 was detected in 32% of the patients with aHUS tested, compared with 2.5% of controls (P<0.001). CFH antibodies were present in 25% of the patients and none of the controls. CFH antibodies were detected in 82% of patients with homozygous CFHR1 gene deletion and in 6% of patients without. CFH antibody-positive patients with aHUS showed a significantly lower platelet nadir at disease onset and significantly less frequent involvement of the central nervous system than did antibody-negative patients. Antibody-positive patients also received plasma therapy more often. CONCLUSION Homozygous deletion in CFHR1 is strongly associated with occurrence of CFH antibodies in pediatric patients with aHUS. However, despite this apparent genetic disease predisposition, it cannot be considered an exclusive cause for aHUS. Initial presentation of Shiga toxin-negative HUS with severe thrombocytopenia and no central nervous system complications in pediatric patients is especially suspicious for CFH antibody aHUS.

Spectrum of complement-mediated thrombotic microangiopathies: pathogenetic insights identifying novel treatment approaches.

Thrombotic microangiopathy (TMA) is a rare but severe disorder characterized by endothelial cell activation and thrombus formation. It manifests with the triad of hemolytic anemia, thrombocytopenia, and organ failure. Prompt diagnosis and treatment initiation are crucial for long-term outcome. TMA often manifests subsequent to infectious events, of which (enterohemorrhagic) Escherichia coli is the most frequently reported. TMA also occurs on the background of genetic/autoimmune defects in the complement system (atypical hemolytic uremic syndrome [aHUS]) and underlying conditions, such as pregnancy, transplantation, drugs, other glomerulopathies, vasculitides, or metabolic defects. Complement activation or defects in its regulation have now been described in an increasing number of acquired diseases with TMA. Coinciding with this expanding spectrum of complement-mediated diseases, the question arises which patients might benefit from a complement-targeted therapy. Success of therapy depends on the individual contribution of complement activation in disease pathogenesis. The advent of eculizumab, a monoclonal antibody that blocks terminal complement activation, has markedly improved outcome and quality of life in patients with aHUS. This review discusses the contribution of complement and highlights its complex interaction with inflammation, coagulation, and the endothelium. Treatment experiences focusing on eculizumab therapy are discussed in detail across the emerging spectrum of complement-mediated thrombotic microangiopathies.

NETosing Neutrophils Activate Complement Both on Their Own NETs and Bacteria via Alternative and Non-alternative Pathways

Neutrophils deposit antimicrobial proteins, such as myeloperoxidase and proteases on chromatin, which they release as neutrophil extracellular traps (NETs). Neutrophils also carry key components of the complement alternative pathway (AP) such as properdin or complement factor P (CFP), complement factor B (CFB), and C3. However, the contribution of these complement components and complement activation during NET formation in the presence and absence of bacteria is poorly understood. We studied complement activation on NETs and a Gram-negative opportunistic bacterial pathogen Pseudomonas aeruginosa (PA01, PAKwt, and PAKgfp). Here, we show that anaphylatoxin C5a, formyl-methionyl-leucyl-phenylalanine (fMLP) and phorbol myristate acetate (PMA), which activates NADPH oxidase, induce the release of CFP, CFB, and C3 from neutrophils. In response to PMA or P. aeruginosa, neutrophils secrete CFP, deposit it on NETs and bacteria, and induce the formation of terminal complement complexes (C5b–9). A blocking anti-CFP antibody inhibited AP-mediated but not non-AP-mediated complement activation on NETs and P. aeruginosa. Therefore, NET-mediated complement activation occurs via both AP- and non AP-based mechanisms, and AP-mediated complement activation during NETosis is dependent on CFP. These findings suggest that neutrophils could use their “AP tool kit” to readily activate complement on NETs and Gram-negative bacteria, such as P. aeruginosa, whereas additional components present in the serum help to fix non-AP-mediated complement both on NETs and bacteria. This unique mechanism may play important roles in host defense and help to explain specific roles of complement activation in NET-related diseases.

Treatment of enterohemorrhagic Escherichia coli-induced hemolytic uremic syndrome (eHUS).

Treatment of enterohemorrhagic Escherichia coli-induced hemolytic uremic syndrome (eHUS) still mostly relies on supportive intensive care regimens. Antibiotic treatment, as administered to eHUS patients during the 2011 O104:H4 outbreak, may reduce the shedding period, but this may apply only to this particular strain. In any case, there is no evidence for a beneficial use in the diarrheal phase and earlier warnings that antibiotic therapy at this stage may actually increase the likelihood of HUS remain unrefuted. Plasma exchange, a frequently chosen therapy in acute atypical HUS, was not beneficial for the outbreak patients and a prospective study of 274 pediatric eHUS patients even indicates a poorer long-term outcome. As eHUS is a disease where complement plays a pathophysiological role and individual beneficial treatments had been published, eculizumab was broadly administered during the outbreak, in particular to severely ill patients. The equally good outcome of treated versus untreated patients obviously does not allow a clear-cut statement, but rather points toward an advantageous use, at least for the severe cases. Although the role of complement should not be overestimated, the use of a complement blocker--not necessarily being a therapeutic option for uncomplicated eHUS--in severe disease may actually make the difference between favorable or detrimental outcome.

Enterohemorrhagic Escherichia coli O26:H11-Associated Hemolytic Uremic Syndrome: Bacteriology and Clinical Presentation.

Infection by enterohemorrhagic ESCHERICHIA COLI (EHEC) is the most frequent cause of hemolytic uremic syndrome (HUS) in childhood. During a 6-year period, all patients with the clinical diagnosis of HUS were registered in a prospective multicenter study in Austria and Germany. EHEC O26:H11 was the second most frequent detected serotype, accounting for 15.4% of all EHEC isolates. The presence of EHEC O26:H11 was significantly associated with young age at the disease onset ( P < 0.001). Patients infected with this serotype were not different in their clinical presentation than those infected with other serotypes. This study underlines the importance of EHEC serotypes other than O157 in the etiology of HUS and emphasizes the importance of implementation of appropriate diagnostic methods to identify the whole spectrum of EHEC associated with HUS.

Activity of Childhood Lupus Nephritis is Linked to Altered T Cell and Cytokine Homeostasis

PurposeStandard therapy for lupus nephritis is based on non-specific immunosuppression. We aimed to identify specific alterations in T cell and cytokine homeostasis and possible associations with disease activity in children with lupus nephritis (LN).MethodsThe phenotype of circulating T cells from children with LN and healthy controls (HC) was analyzed by flow cytometry. Intracellular expression of IL-17 and INF-γ was assessed after stimulation with anti-CD3 and anti-CD28. Serum concentrations of IP10, CCL2, TGF-β, IL-17, and IL-23 were measured by ELISA. Disease activity was determined using the Systemic Lupus Erythematosus Disease Activity Index 2000 update (SLEDAI-2K).ResultsChildren with active LN displayed increased frequencies of effector memory CD4+CD45RO+CCR7− and terminal differentiated CD4+CD45RA+CCR7− T cells and reduced naive CD4+CD45RA+CCR7+ T cells compared to those with inactive LN or HC. Circulating CD4+CXCR3+ and CD4+CCR2+ T cells correlated inversely with the renal SLEDAI-2K, whereas IP10 and CCL2 showed a positive correlation. Reduced CD4+Foxp3+ T cells and serum TFG-β levels in active LN were associated with high serum IL-17 and IL-23 levels and correlated inversely with the renal SLEDAI-2K (r = −0.5855, p = 0.0013 and r = −0.6246, p = 0.0005, respectively), whereas IL-17 and IL-23 correlated positively (r = 0.5516, p = 0.0029 and r = 0.6116, p = 0.0007, respectively). Expansion of Th17 and Th1/Th17 cells in children with LN was significantly greater than in HC (p = 0.0304 and p = 0.0067, respectively).ConclusionChildren with active LN display high levels of pro-inflammatory cytokines associated with an increase in effector T cells and reduction of regulatory T cells. Therapeutic regulation of the aberrant cytokine profile might specifically interrupt pathogenic mechanisms.

Inhibition of terminal complement activation in severe Shiga toxin-associated HUS - perfect example for a fast track from bench to bedside

Typical haemolytic uraemic syndrome (HUS) is a thrombotic microangiopathy, leading to severe renal disease as well as life‐threatening extrarenal complications. HUS is primarily caused by infections with enterohaemorrhagic Escherichia coli (EHEC) and 5–20% of EHEC infections result in HUS. EHEC bacteria produce several virulence factors, of which Shiga toxins are believed to play a central role. About 10% of all HUS cases are not caused by E. coli and are thus termed atypical HUS. These are observed as familial or sporadic forms and are most commonly caused by a dysregulation of the alternative pathway of the complement system due to inherited mutations of, or acquired auto‐antibodies against, complement regulator proteins. The, thereby, impaired control of complement, which plays a prominent role in the humoral immune system and in immune homeostasis, leads to a hyperactive state, including activation of endothelial cells and platelets, inflammation of small vessel and eventually to the destruction of the kidney and other organs (summarized in Orth et al, 2009). Lapeyraque et al have published the successful use of the licensed terminal complement C5 inhibitor eculizumab for the treatment of severe Shiga toxin‐associated HUS in three 3‐year‐old children with devastating prognoses (Lapeyraque et al, 2011). The three patients continued to show progression of the HUS despite having received multiple plasma exchanges. Treatment with eculizumab markedly improved their clinical status, in particular their neurological and renal functions, after two to four administrations of this complement inhibitor. Dialysis was reported to be discontinued after 3–16 days in all three patients. Recovery was attributed to eculizumab and absence of mutations of complement proteins …

Akt-Dependent Enhanced Migratory Capacity of Th17 Cells from Children with Lupus Nephritis

Th17 cells infiltrate the kidneys of patients with lupus nephritis (LN) and are critical for the pathogenesis of this disease. In this study, we show that enhanced activity of Stat3 in CD4+CD45RA−Foxp3− and Foxp3low effector T cells from children with LN correlates with increased frequencies of IL-17–producing cells within these T cell populations. The levels of retinoic acid-related orphan receptor c and IL-17 mRNA are significantly higher in PBMCs from children with LN than in those from controls. Mammalian target of rapamycin inhibition by rapamycin reduces both Stat3 activation in effector T cells and the frequency of IL-17–producing T cells in lupus patients. Complement factor C5a slightly increases the expression of IL-17 and induces activation of Akt in anti-CD3–activated lupus effector T cells. Th17 cells from children with LN exhibit high Akt activity and enhanced migratory capacity. Inhibition of the Akt signaling pathway significantly decreases Th17 cell migration. These findings indicate that the Akt signaling pathway plays a significant role in the migratory activity of Th17 cells from children with LN and suggest that therapeutic modulation of the Akt activity may inhibit Th17 cell trafficking to sites of inflammation and thus suppress chronic inflammatory processes in children with LN.

The autoimmune disease DEAP-hemolytic uremic syndrome.

DEAP-HUS (deficiency of CFHR plasma proteins and factor H [FH] autoantibody positive hemolytic uremic syndrome [HUS]) is a new form of HUS characterized by a deletion of genes coding for FH-related proteins and the presence of autoantibodies directed to FH. These disease-associated autoantibodies inhibit FH (CFH) surface binding functions, which results in a defective regulation of the alternative pathway and damage of endothelial cells. Here we describe two representative patients with DEAP-HUS who both developed end-stage renal failure with the background of homozygous deletion of CFHR1 and CFHR3 genes and the presence of FH autoantibodies. Based on the retrospective diagnosis of DEAP-HUS 2 to 12 months after the initial clinical presentation, subsequent immunosuppressive therapy was initiated. The autoantibody titers decreased, and the complement status of the patients improved, as indicated by increased C3 levels. Thus early diagnosis of DEAP-HUS and immunosuppressive treatments are important factors to treat this particular type of HUS.