Inappropriate Complement Activation Research Articles

Protective role of complement factor H against the development of preeclampsia.

Pregnancy is an immunologically regulated, complex process. A tightly controlled complement system plays a crucial role in the successful establishment of pregnancy and parturition. Complement inhibitors at the feto-maternal interface are likely to prevent inappropriate complement activation to protect the fetus. In the present study, we aimed to understand the role of Factor H (FH), a negative regulator of complement activation, in normal pregnancy and in a model of pathological pregnancy, i.e. preeclampsia (PE). The distribution and expression of FH was investigated in placental tissues, various placental cells, and in the sera of healthy (CTRL) or PE pregnant women via immunohistochemistry, RT-qPCR, ELISA, and Western blot. Our results showed a differential expression of FH among the placental cell types, decidual stromal cells (DSCs), decidual endothelial cells (DECs), and extravillous trophoblasts (EVTs). Interestingly, FH was found to be considerably less expressed in the placental tissues of PE patients compared to normal placental tissue both at mRNA and protein levels. Similar results were obtained by measuring circulating FH levels in the sera of third trimester CTRL and PE mothers. Syncytiotrophoblast microvesicles, isolated from the placental tissues of PE and CTRL women, downregulated FH expression by DECs. The present study appears to suggest that FH is ubiquitously present in the normal placenta and plays a homeostatic role during pregnancy.

Inhibition of the Complement Alternative Pathway by Chemically Modified DNA Aptamers That Bind with Picomolar Affinity to Factor B.

The complement system is a conserved component of innate immunity that fulfills diverse roles in defense and homeostasis. Inappropriate activation of complement contributes to many inflammatory diseases, however, which has led to a renewed emphasis on development of therapeutic complement inhibitors. Activation of complement component C3 is required for amplification of complement and is achieved through two multisubunit proteases called C3 convertases. Of these, the alternative pathway (AP) C3 convertase is responsible for a majority of the C3 activation products in vivo, which renders it an attractive target for inhibitor discovery. In this study, we report the identification and characterization of two related slow off-rate modified DNA aptamers (SOMAmer) reagents that inhibit formation of the AP C3 convertase by binding to the proprotease, factor B (FB). These aptamers, known as SL1102 (31 bases) and SL1103 (29 bases), contain uniform substitutions of 5-(N-2-naphthylethylcarboxyamide)-2'-deoxyuridine for deoxythymidine. SL1102 and SL1103 bind FB with K d values of 49 and 88 pM, respectively, and inhibit activation of C3 and lysis of rabbit erythrocytes under AP-specific conditions. Cocrystal structures of SL1102 (3.4 Å) and SL1103 (3.1 Å) bound to human FB revealed that SL1102 and SL1103 recognize a site at the juncture of the CCP1, CCP3, and vWF domains of FB. Consistent with these structures and previously published information, these aptamers inhibited FB binding to C3b and blocked formation of the AP C3 convertase. Together, these results demonstrate potent AP inhibition by modified DNA aptamers and expand the pipeline of FB-binding molecules with favorable pharmacologic properties.

Essential Role of Complement in Pregnancy: From Implantation to Parturition and Beyond.

The complement cascade was identified over 100 years ago, yet investigation of its role in pregnancy remains an area of intense research. Complement inhibitors at the maternal-fetal interface prevent inappropriate complement activation to protect the fetus. However, this versatile proteolytic cascade also favorably influences numerous stages of pregnancy, including implantation, fetal development, and labor. Inappropriate complement activation in pregnancy can have adverse lifelong sequelae for both mother and child. This review summarizes the current understanding of complement activation during all stages of pregnancy. In addition, consequences of complement dysregulation during adverse pregnancy outcomes from miscarriage, preeclampsia, and pre-term birth are examined. Finally, future research directions into complement activation during pregnancy are considered.

Inhibition of complement pathway activation with Pozelimab, a fully human antibody to complement component C5.

Complement is a key component of the innate immune system. Inappropriate complement activation underlies the pathophysiology of a variety of diseases. Complement component 5 (C5) is a validated therapeutic target for complement-mediated diseases, but the development of new therapeutics has been limited by a paucity of preclinical models to evaluate the pharmacokinetic (PK) and pharmacodynamic (PD) properties of candidate therapies. The present report describes a novel humanized C5 mouse and its utility in evaluating a panel of fully human anti-C5 antibodies. Surprisingly, humanized C5 mice revealed marked differences in clearance rates amongst a panel of anti-C5 antibodies. One antibody, pozelimab (REGN3918), bound C5 and C5 variants with high affinity and potently blocked complement-mediated hemolysis in vitro. In studies conducted in both humanized C5 mice and cynomolgus monkeys, pozelimab demonstrated prolonged PK and durable suppression of hemolytic activity ex vivo. In humanized C5 mice, a switch in dosing from in-house eculizumab to pozelimab was associated with normalization of serum C5 concentrations, sustained suppression of hemolytic activity ex vivo, and no overt toxicity. Our findings demonstrate the value of humanized C5 mice in identifying new therapeutic candidates and treatment options for complement-mediated diseases.

Novel insights into the treatment of complement-mediated hemolytic anemias.

Complement-mediated hemolytic anemias can either be caused by deficiencies in regulatory complement components or by autoimmune pathogenesis that triggers inappropriate complement activation. In paroxysmal nocturnal hemoglobinuria (PNH) hemolysis is entirely complement-driven. Hemolysis is also thought to be complement-dependent in cold agglutinin disease (CAD) and in paroxysmal cold hemoglobinuria (PCH), whereas warm antibody autoimmune hemolytic anemia (wAIHA) is a partially complement-mediated disorder, depending on the subtype of wAIHA and the extent of complement activation. The pathophysiology, clinical presentation, and current therapies for these diseases are reviewed in this article. Novel, complement-directed therapies are being rapidly developed. Therapeutic terminal complement inhibition using eculizumab has revolutionized the therapy and prognosis in PNH but has proved less efficacious in CAD. Upstream complement modulation is currently being investigated and appears to be a highly promising therapy, and two such agents have entered phase II and III trials. Of these, the anti-C1s monoclonal antibody sutimlimab has shown favorable activity in CAD, while the anti-C3 cyclic peptide pegcetacoplan appears to be promising in PNH as well as CAD, and may also have a therapeutic potential in wAIHA.

Distribution of exogenous complement factor H in mice invivo.

Factor H is an important regulator of complement activation in plasma and on cell surfaces in both humans and mice. If FH function is compromised, inappropriate complement activation on self-surfaces can have disastrous effects as seen in the kidney diseases atypical haemolytic uremic syndrome (aHUS) and C3 glomerulopathy. As FH constructs have been proposed to be used in treatment for these diseases, we studied the distribution of exogenous FH fragments in mice. Full-length mFH, mFH1-5 and mFH18-20 fragments were radiolabelled, and their distribution was examined in WT, FH-/- and FH-/- C3-/- mice invivo. Whole body scintigraphy revealed accumulation of radioactivity in the abdominal part of the mice, but also to the thyroid gland and urinary bladder. At organ level in WT mice, some full-length FH accumulated in internal organs, but most of it remained in the circulation. Both of the mFH fragments accumulated in the kidneys and were excreted in urine. For mFH1-5, urinary secretion is the likely cause for the accumulation. Concentration of mFH18-20 to kidneys was slower, and at tissue level, mFH18-20 was localized at the proximal tubuli in WT and FH-/- C3-/- mice. No C3-independent binding to glomeruli was detected. In conclusion, these results show that glomerular glycosaminoglycans and sialic acids alone do not collect FH in kidneys. Deposition of C3 fragments is also needed, which implies that in aHUS, the problem is in simultaneous recognition of C3 fragments and glycosaminoglycans or sialic acids by FH, not just the inability of FH to recognize glomerular endothelium as such.

Assessment of C3 and C4 component of complement system in aborted women infected with Toxoplasma gondii

Background: The complement system consists of more than 30 proteins that are either present as soluble proteins in the blood or present as membrane-associated proteins. Inappropriate complement activation and complement deficiencies are the underlying cause of the pathophysiology of many diseases.Methods: A case-control study was conducted to asses role of complement system during toxoplasmosis in Najaf province. Thirty five sera of infected women with toxoplasmosis by investigation antibody against toxoplasmosis for IgG and IgM by ELISA technique were tested to determine the levels of C3 and C4 by using single radial immunodiffusion technique and compared with the ten of control sera of non infected subjects and non-aborted.Results: The high C3 in significant differences(P<0.05) and C4 with no significant differences(P>0.05) levels were found in aborted toxo-positive women in compared with control. Likewise, it was found that association between concentration of C3,C4 and number of abortion.Conclusion: complement were play role in immune response of pregnant women especially against toxoplasmosis that cause abortion to these women.

Complement: A primer for the coming therapeutic revolution.

The complement system is an important part of the innate and adaptive immune systems. Originally characterized as a single serum component contributing to the killing of bacteria, we now know that there are close to sixty complement proteins, multiple activation pathways and a wide range of effector functions mediated by complement. The system plays a critical role in host defense against bacteria, viruses, fungi and other pathogens. However, inappropriate complement activation contributes to the pathophysiology of autoimmune diseases and many inflammatory syndromes. Over the last several decades, therapeutic approaches to inhibit complement activation at various steps in the pathways have met with initial success, particularly at the level of the terminal pathway. This success, combined with insight from animal model studies, has lead to an unprecedented effort by biotech and pharmaceutical companies to begin developing complement inhibitors. As a result, complement has been brought for the first time to the attention of pharmacologists, toxicologists, project managers and others in the drug development industry, as well as those in the investment world. The purpose of this primer is to provide a broad overview of complement immunobiology to help those new to complement understand the rationale behind the current therapeutic directions and the investment potential of these new therapeutics.

Regulation of Complement and Contact System Activation via C1 Inhibitor Potentiation and Factor XIIa Activity Modulation by Sulfated Glycans - Structure-Activity Relationships.

The serpin C1 inhibitor (C1-INH) is the only regulator of classical complement activation as well as the major regulator of the contact system. Its importance is demonstrated by hereditary angioedema (HAE), a severe disease with potentially life-threatening attacks due to deficiency or dysfunction of C1-INH. C1-INH replacement is the therapy of choice in HAE. In addition, C1-INH showed to have beneficial effects in other diseases characterized by inappropriate complement and contact system activation. Due to some limitations of its clinical application, there is a need for improving the efficacy of therapeutically applied C1-INH or to enhance the activity of endogenous C1-INH. Given the known potentiating effect of heparin on C1-INH, sulfated glycans (SG) may be such candidates. The aim of this study was to characterize suitable SG by evaluating structure-activity relationships. For this, more than 40 structurally distinct SG were examined for their effects on C1-INH, C1s and FXIIa. The SG turned out to potentiate the C1s inhibition by C1-INH without any direct influence on C1s. Their potentiating activity proved to depend on their degree of sulfation, molecular mass as well as glycan structure. In contrast, the SG had no effect on the FXIIa inhibition by C1-INH, but structure-dependently modulated the activity of FXIIa. Among the tested SG, β-1,3-glucan sulfates with a Mr ≤ 10 000 were identified as most promising lead candidates for the development of a glycan-based C1-INH amplifier. In conclusion, the obtained information on structural characteristics of SG favoring C1-INH potentiation represent an useful elementary basis for the development of compounds improving the potency of C1-INH in diseases and clinical situations characterized by inappropriate activation of complement and contact system.

Drusen maculopathy: a risk factor for visual deterioration.

Age-related macular degeneration (AMD), the most common cause of visual loss after the age of 65, displays a degeneration of the retinal pigment epithelial (RPE) cells and photoreceptors in the retinal centre (macula). The central macula (fovea) that contains mostly cone photoreceptors mediates the high visual acuity. Drusen maculopathy may lead to visual deterioration. Drusen are extracellular deposits of debris that accumulate on Bruch's membrane. Drusen attract inflammatory, immunological and vasoactive stimuli. RPE and photoreceptor cells overlying drusen exhibit biochemical and morphological signs of degeneration. Strong and intermittent light exposure (photons) induces the formation of free radicals in the very high oxygen tension milieu of the retina. The negative effects of irradiation stimulate accumulation of lipofuscin in RPE and photoreceptor cells leading to mitochondrial dysfunction and apoptotic cell death. A hydrophobic barrier is built up in Bruch's membrane reducing diffusion to the choroid. Hereditary and inflammatory factors modify the risk for AMD. There is a genetic dysregulation of the complement system leading to inappropriate complement activation. The genetic polymorphism of complement factor H (CFH) and age-related maculopathy susceptibilty 2 (ARMS2) increase the risk of progression to advanced AMD. The photoelectric effect creates free radicals, resulting in a continuous increase of lipofuscin formation and impairing mitochondrial activity. In addition, inflammation and complement dysregulation contribute to the formation of drusen and vasoproliferative reactions with neovascularization. Antioxidants neutralize reactive oxygen species and reduce lipofuscin accumulation in RPE and photoreceptor cells. For prophylactic treatment of drusen maculopathy, high doses of antioxidants such as vitamins C and E, lutein, zeaxanthine and zinc are used according to the Age-Related Eye Disease Study 2 (AREDS 2). The risk of developing advanced AMD was reduced by 27% at 10years follow-up. No adverse events were noted.

The relative merits of therapies being developed to tackle inappropriate (‘self’-directed) complement activation

The complement system is an enzyme cascade that helps defend against infection. Many complement proteins occur in serum as inactive enzyme precursors or reside on cell surfaces. Complement components have many biologic functions and their activation can eventually damage the plasma membranes of cells and some bacteria. Although a direct link between complement activation and autoimmune diseases has not been found, there is increasing evidence that complement activation significantly contributes to the pathogenesis of a large number of inflammatory diseases that may have autoimmune linkage. The inhibition of complement may therefore be very important in a variety of autoimmune diseases since their activation may be detrimental to the individual involved. However, a complete and long-term inhibition of complement may have some contra side effects such as increased susceptibility to infection. The site of complement activation will, however, determine the type of inhibitor to be used, its route of application and dosage level. Compared with conventional drugs, complement inhibitors may be the best option for treatment of autoimmune diseases. The review takes a critical look at the relative merits of therapies being developed to tackle inappropriate complement activation that are likely to result in sporadic autoimmune diseases or worsen already existing one. It covers the complement system, general aspects of complement inhibition therapy, therapeutic strategies and examples of complement inhibitors. It concludes by highlighting on the possibility that a better inhibitor of complement activation when found will help provide a formidable treatment for autoimmune diseases as well as preventing one.

Complement, a target for therapy in inflammatory and degenerative diseases.

The complement system is a key innate immune defence against infection and an important driver of inflammation; however, these very properties can also cause harm. Inappropriate or uncontrolled activation of complement can cause local and/or systemic inflammation, tissue damage and disease. Complement provides numerous options for drug development as it is a proteolytic cascade that involves nine specific proteases, unique multimolecular activation and lytic complexes, an arsenal of natural inhibitors, and numerous receptors that bind to activation fragments. Drug design is facilitated by the increasingly detailed structural understanding of the molecules involved in the complement system. Only two anti-complement drugs are currently on the market, but many more are being developed for diseases that include infectious, inflammatory, degenerative, traumatic and neoplastic disorders. In this Review, we describe the history, current landscape and future directions for anti-complement therapies.

A novel factor I activity in Nipah virus inhibits human complement pathways through cleavage of C3b.

Complement is an innate immune system that most animal viruses must face during natural infections. Given that replication and dissemination of the highly pathogenic Nipah virus (NiV) include exposure to environments rich in complement factors, we tested the in vitro sensitivity of NiV to complement-mediated neutralization. Here we show that NiV was completely resistant to in vitro neutralization by normal human serum (NHS). Treatment of purified NiV with NHS activated complement pathways, but there was very little C3 deposition on virus particles. In in vitro reconstitution experiments, NiV particles provided time- and dose-dependent factor I-like protease activity capable of cleaving C3b into inactive C3b (iC3b). NiV-dependent inactivation of C3b only occurred with the cofactors factor H and soluble CR1 but not with CD46. Purified NiV particles did not support C4b cleavage. Electron microscopy of purified NiV particles showed immunogold labeling with anti-factor I antibodies. Our results suggest a novel mechanism by which NiV evades the human complement system through a unique factor I-like activity. Viruses have evolved mechanisms to limit complement-mediated neutralization, some of which involve hijacking cellular proteins involved in control of inappropriate complement activation. Here we report a previously unknown mechanism whereby NiV provides a novel protease activity capable of in vitro cleavage and inactivation of C3b, a key component of the complement cascade. These data help to explain how an enveloped virus such as NiV can infect and disseminate through body fluids that are rich in complement activity. Disruption of the ability of NiV to recruit complement inhibitors could form the basis for the development of effective therapies and safer vaccines to combat these highly pathogenic emerging viruses.

Prediction of inflammatory responses induced by biomaterials in contact with human blood using protein fingerprint from plasma

Inappropriate complement activation is often responsible for incompatibility reactions that occur when biomaterials are used. Complement activation is therefore a criterion included in legislation regarding biomaterials testing. However, no consensus is yet available regarding appropriate complement-activation-related test parameters. We examined protein adsorption in plasma and complement activation/cytokine release in whole blood incubated with well-characterized polymers. Strong correlations were found between the ratio of C4 to its inhibitor C4BP and generation of 10 (mainly pro-inflammatory) cytokines, including IL-17, IFN-γ, and IL-6. The levels of complement activation products correlated weakly (C3a) or not at all (C5a, sC5b-9), confirming their poor predictive values. We have demonstrated a direct correlation between downstream biological effects and the proteins initially adhering to an artificial surface after contact with blood. Consequently, we propose the C4/C4BP ratio as a robust, predictor of biocompatibility with superior specificity and sensitivity over the current gold standard.

A novel CRIg‐targeted complement inhibitor protects cells from complement damage

The inappropriate activation of complement may contribute to various immune diseases. The alternative pathway (AP) predominates during complement activation regardless of the initiating pathways. Hence, the main AP regulator factor H (FH) holds great potential as an attractive therapeutic intervention. In addition, complement receptor of the immunoglobulin superfamily (CRIg) has been demonstrated to inhibit AP and, more notably, still specifically binds to C3b/iC3b. We thus developed novel CRIg-targeted complement inhibitors by connecting the functional domains of CRIg and FH, which we termed CRIg-FH and CRIg-L-FH. CRIg-L-FH, slightly more potent than CRIg-FH, considerably inhibited both AP- and also classical pathway (CP)-mediated hemolysis and successfully eliminated the deposition of C3b/iC3b. Kinetic analysis further revealed that the binding affinity constant (KD) of CRIg/FH was in the micromolar range, consistent with its long-lasting binding to complement-attacked cells. CRIg-L-FH efficiently protected aberrant erythrocytes of patients with paroxysmal nocturnal hemoglobinuria (PNH) from AP- and CP-mediated complement damage (IC50 was 22.43 and 64.69 nM, respectively). Moreover, CRIg-L-FH was found to inhibit complement activation induced by the anti-Thy1 antibody in a mesangioproliferative glomerulonephritis (MPGN) rat model. Hence, CRIg-L-FH protects glomerular mesangial cells (GMCs) from complement-mediated injury and proliferative lesions. These findings strongly suggest that CRIg/FH is a potential therapeutic drug candidate for a range of complement-mediated diseases.

Complement and Its Receptors: New Insights into Human Disease

Although new activation and regulatory mechanisms are still being identified, the basic architecture of the complement system has been known for decades. Two major roles of complement are to control certain bacterial infections and to promote clearance of apoptotic cells. In addition, although inappropriate complement activation has long been proposed to cause tissue damage in human inflammatory and autoimmune diseases, whether this is indeed true has been uncertain. However, recent studies in humans, especially those using newly available biological therapeutics, have now clearly demonstrated the pathophysiologic importance of the complement system in several rare diseases. Beyond these conditions, recent genetic studies have strongly supported an injurious role for complement in a wide array of human inflammatory, degenerative, and autoimmune diseases. This review includes an overview of complement activation, regulatory, and effector mechanisms. It then focuses on new understandings gained from genetic studies, ex vivo analyses, therapeutic trials, and animal models as well as on new research opportunities.

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Introduction: Atypical hemolytic-uremic syndrome is a rare constellation of hemolytic anemia, thrombocytopenia, and renal impairment caused by uncontrolled complement activation in the absence of Shiga-like toxin producing bacteria or streptococci. 80% of cases are sporadic, triggered by HIV infection, organ transplantation, pregnancy, use of certain anticancer, immunotherapeutic, or antiplatelet agents. 50% of sporadic cases have no identifiable trigger. Mortality may be as high as 25% with 50% of patients progressing to end-stage renal disease. Recently, eculizumab, a humanized monoclonal antibody which inhibits complement activation, has been used to treat atypical hemolytic-uremic syndrome. We present a case of atypical hemolytic-uremic syndrome in an adult ICU patient successfully treated with eculizumab. A 71-year-old man with a history of squamous cell lung carcinoma treated with definitive radiation therapy 5 months previously, presented with 4 days of right-sided chest pain, and 2 days of worsening shortness of breath, chills, and productive cough. Physical exam revealed tachycardia and crackles at the right lung base. Chest radiography revealed right middle and lower lobe infiltrates with right-sided pleural effusion. Pertinent laboratory studies demonstrated a WBC of 24.4, and creatinine of 1.5 mg/dL. Cultures were obtained and he was started on broad spectrum antibiotics for presumed pneumonia. On hospital day 2 his respiratory status decompensated and a chest tube was placed to manage the pleural effusion. His mental status became increasingly altered and despite aggressive treatment he progressed to respiratory failure requiring intubation. He developed worsening anemia (hemoglobin 8.2 g/dL), thrombocytopenia (platelet count 32), and was found to have spontaneous pulmonary hemorrhage on bronchoscopy. His renal failure (creatinine 3.77 mg/dL) worsened and he was started on continuous renal replacement therapy. Further laboratory analysis revealed a LDH of 1173, an undetectable haptoglobin, and a peripheral smear with >10 schistocytes per high power field confirming a hemolytic process. He continued to have a waxing and waning mental status despite metabolic improvement with renal replacement therapy, as well as progressive anemia and thrombocytopenia. Results from ADAMTS13 enzyme assay returned, revealing 46% activity, not consistent with the diagnosis of TTP. He was therefore thought unlikely to benefit from plasma exchange. Complement levels were found to be low, and he was started on high dose corticosteroids for the presumed diagnosis of atypical hemolytic-uremic syndrome secondary to either sepsis (despite persistently negative cultures) or underlying lung cancer (despite lack of disseminated disease). With minimal improvement over several days, the decision was made to pursue eculizumab therapy. 5 days after initiation of eculizumab his hemoglobin began to rise and his platelet count increased to more than 100. His mental status cleared and he was extubated successfully. 20 days after initiation of eculizumab he no longer required renal replacement therapy. He was discharged from the hospital on a taper of eculizumab. Treatment of atypical hemolytic-uremic syndrome with eculizumab has been discussed in 2 recent case reports (1 neonate and 1 renal transplant patient) and a pair of published phase 2 trials, but never, to our knowledge, in a critically ill adult. While rare, atypical hemolytic-uremic syndrome should be considered in ICU patients with anemia, thrombocytopenia, and renal dysfunction, even in the absence of a known trigger. The terminal complement inhibitor eculizumab is a novel monoclonal antibody that has demonstrated good efficacy in controlling the inappropriate complement activation that underlies the pathogenesis of atypical hemolytic-uremic syndrome. Current clinical trials are underway to further explore this novel therapy.

Tailored Eculizumab Therapy in the Management of Complement Factor H–Mediated Atypical Hemolytic Uremic Syndrome in an Adult Kidney Transplant Recipient: A Case Report

Atypical hemolytic uremic syndrome (aHUS) is characterized by thrombocytopenia, microangiopathic hemolytic anemia, and acute kidney injury (AKI) which frequently progresses to end-stage renal disease (ESRD). In 50% of affected patients, mutations in complement regulatory proteins cause inappropriate complement activation with endothelial injury. Complement factor H (CFH) mutations cause 25% of aHUS cases; these patients have an 80% recurrence risk after kidney transplantation. Eculizumab, an anti-C5 antibody, is effective in limiting hemolysis episodes in patients with aHUS, but less is known about preventing recurrence after kidney transplantation. Herein we report the use of prophylactic eculizumab in an adult with aHUS who underwent kidney transplantation. A 31-year-old female presented with aHUS and progressive AKI associated with low complement 3 level leading to ESRD despite plasmapheresis and corticosteroids. She had a heterozygous nonsense mutation in CFH and reduced plasma CFH levels. She was given preoperative plasmapheresis and eculizumab and underwent living unrelated renal transplantation. Postoperatively, eculizumab was dosed to achieve low functional complement 5 levels and low soluble membrane attack complex levels and she has maintained excellent graft function without aHUS recurrence. We propose that eculizumab with titrated dosing should be used in CFH-mediated aHUS patients who are at a high risk of recurrence.

Maggot excretions affect the human complement system

The complement system plays an important role in the activation of the inflammatory response to injury, although inappropriate complement activation (CA) can lead to severe tissue damage. Maggot therapy is successfully used to treat infected wounds. In this study, we hypothesized that maggot excretions/secretions influence CA in order to modulate the host's inflammatory response. Therefore, the effect of maggot excretions on CA was investigated in preoperatively and postoperatively obtained sera from patients. Our results show that maggot excretions reduce CA in healthy and postoperatively immune-activated human sera up to 99.9%, via all pathways. Maggot excretions do not specifically initiate or inhibit CA, but break down complement proteins C3 and C4 in a cation-independent manner and this effect proves to be temperature tolerant. This study indicates a CA-reducing substrate that is already successfully used in clinical practice and may explain part of the improved wound healing caused by maggot therapy. Furthermore, the complement activation-reducing substance present in maggot excretions could provide a novel treatment modality for several diseases, resulting from an (over)active complement system.

The Role of Complement in the Antiphospholipid Syndrome: A Novel Mechanism for Pregnancy Morbidity

Despite the experimental research data on antiphospholipid syndrome (APS), the pathogenesis of thrombosis and fetal loss remains unknown. The objective of this study was to analyze the major advances in the field of complement activation as a possible thrombosis mechanism in the APS. The authors conducted a systemic analysis of the English literature and summarized both animal and human data that indicate the inappropriate complement activation as a mechanism causing thrombosis in the APS. The important role of complement activation in the pathogenesis of fetal loss was established using mice deficient in a complement regulatory protein. Further studies have shown that the infusion of human IgG antiphospholipid antibodies (aPL) induced fetal loss in pregnant mice, an effect that was abrogated by the concurrent administration of a C3 convertase inhibitor. Further studies suggested that C5a and neutrophils were the key components responsible for fetal injury. Moreover, use of F(ab)'2 fragments of aPL suggested the complement activation occurred mainly via the classical pathway. Other studies using models of induced thrombosis suggested that antibodies against β2GPI required the presence of terminal complement components to induce thrombus formation, and mice deficient in C3 or C5 were found to be resistant to aPL-induced thrombosis. Based on the aforementioned findings, it has been suggested that heparin prevents fetal loss in patients with APS by inhibiting complement activation rather than by its anticoagulant effect. The studies on complement are significant because they shift the focus of research in APS from thrombosis to inflammation. However, as human data are limited, more clinical research is necessary before the above findings translate in changes in the management of APS.