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The complement system is an important humoral immune surveillance mechanism against tumours. However, many malignant tumours are resistant to complement mediated lysis. Here, we report secretion of complement factor H related protein 5 (FHR5) by primary tumour cells derived from Glioblastoma multiforme (GBM) patients. We investigated whether the secreted FHR5 exhibited functional activity similar to factor H, including inhibition of complement mediated lysis, acting as a co-factor for factor I mediated cleavage of C3b, and decay acceleration of C3 convertase. Immunoblotting analysis of primary GBM cells (B30, B31 and B33) supernatant showed the active secretion of FHR5, but not of Factor H. ELISA revealed that the secretion of soluble GBM-FHR5 by cultured GBM cells increased in a time-dependent manner. Primary GBM-FHR5 inhibited complement mediated lysis, possessed co-factor activity for factor I mediated cleavage and displayed decay acceleration of C3 convertase. In summary, we detected the secretion of FHR5 by primary GBM cells B30, B31 and B33. The results demonstrated that GBM-FHR5 shares biological function with FH as a mechanism primary GBM cells potentially use to resist complement mediated lysis. [ABSTRACT FROM AUTHOR]

Although kidney transplantation is the best treatment for end stage kidney disease, the benefits are limited by factors such as the short fall in donor numbers, the burden of immunosuppression and graft failure. Although there have been improvements in one-year outcomes, the annual rate of graft loss beyond the first year has not significantly improved, despite better therapies to control the alloimmune response. There is therefore a need to develop alternative strategies to limit kidney injury at all stages along the transplant pathway and so improve graft survival. Complement is primarily part of the innate immune system, but is also known to enhance the adaptive immune response. There is increasing evidence that complement activation occurs at many stages during transplantation and can have deleterious effects on graft outcome. Complement activation begins in the donor and occurs again on reperfusion following a period of ischemia. Complement can contribute to the development of the alloimmune response and may directly contribute to graft injury during acute and chronic allograft rejection. The complexity of the relationship between complement activation and allograft outcome is further increased by the capacity of the allograft to synthesise complement proteins, the contribution complement makes to interstitial fibrosis and complement's role in the development of recurrent disease. The better we understand the role played by complement in kidney transplant pathology the better placed we will be to intervene. This is particularly relevant with the rapid development of complement therapeutics which can now target different the different pathways of the complement system. Combining our basic understanding of complement biology with preclinical and observational data will allow the development and delivery of clinical trials which have best chance to identify any benefit of complement inhibition. [ABSTRACT FROM AUTHOR]

Remarkable advances have been made over past decades in understanding the pathogenesis of complement-mediated diseases. This has led to development of new therapies for, and in some cases re-classification of, complement-driven diseases. This success is due to not only insight from human patients but also studies using transgenic animal models. Animal models that mimic human diseases are useful tools to understand the mechanism of disease and develop new therapies but there are also limitations due to species differences in their complement systems. This review provides a summary of transgenic animal models for three human diseases that are at the forefront of anti-complement therapy, paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G). They are discussed here as examples to highlight the values and limitations of animal modeling in complement-driven diseases. [ABSTRACT FROM AUTHOR]

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by complement-mediated cell lysis due to deficiency of GPI-anchored complement regulators. Blockage of the lytic pathway by eculizumab is the only available therapy for PNH patients and shows remarkable benefits, but regularly yields PNH erythrocytes opsonized with fragments of complement protein C3, rendering such erythrocytes prone to extravascular hemolysis. This effect is associated with insufficient responsiveness seen in a subgroup of PNH patients. Novel C3-opsonin targeted complement inhibitors act earlier in the cascade, at the level of activated C3 and are engineered from parts of the natural complement regulator Factor H (FH) or complement receptor 2 (CR2). This inhibitor class comprises three variants of “miniFH” and the clinically developed “FH-CR2” fusion-protein (TT30). We show that the approach of FH-CR2 to target C3-opsonins was more efficient in preventing complement activation induced by foreign surfaces, whereas the miniFH variants were substantially more active in controlling complement on PNH erythrocytes. Subtle differences were noted in the ability of each version of miniFH to protect human PNH cells. Importantly, miniFH and FH-CR2 interfered only minimally with complement-mediated serum killing of bacteria when compared to untargeted inhibition of all complement pathways by eculizumab. Thus, the molecular design of each C3-opsonin targeted complement inhibitor determines its potency in respect to the nature of the activator/surface providing potential functionality in PNH. [ABSTRACT FROM AUTHOR]

Candida tropicalis is an opportunistic fungal pathogen and is one of the most frequently isolated non-albicans species. It can cause localised as well as invasive systemic infections particularly in immunocompromised patients. Increased resistance to common anti-fungal drugs is an emerging problem. In order to establish disseminated infections, C andida has evolved several strategies to escape the host immune system. A detailed understanding of how C. tropicalis escapes the host immune attack is needed as it can help develop novel anti-fungal therapies. Secreted aspartyl proteinases (Saps) of C. albicans have been shown to be determinants of virulence and immune evasion. However, the immune evasion properties of C. tropicalis Saps have been poorly characterised. This study investigated the immune evasion properties of C. tropicalis secreted aspartic protease 1 (Sapt1). Sapt1 was recombinantly produced using a Kluyveromyces lactis yeast expression system. A range of complement proteins and immunogloublins were screened to test if Sapt1 had any proteolytic activity. Sapt1 efficiently cleaved human mannose-binding lectin (MBL) and collectin-11, which are the initiating molecules of the lectin pathway of the complement system, but not l -ficolin. In addition, Sapt1 cleaved DC-SIGN, the receptor on antigen presenting dendritic cells. Proteolysis was prominent in acidic condition (pH 5.2), a characteristic of aspartyl protease. No proteolytic activity was detected against complement proteins C1q, C3, C3b, IgG and IgA. In view of the ability of Sapt1 to cleave MBL and collectin-11, we found that Sapt1 could prevent activation of the complement lectin pathway. RT-qPCR analysis using three different C. tropicalis clinical isolates (oral, blood and peritoneal dialysis fluid) revealed relatively higher levels of mRNA expression of Sapt1 gene when compared to a reference strain; Sapt1 protein was found to be secreted by all the tested strains. Lectin pathway and its initiating components are crucial to provide front line defence against Candida infections. For the first time, we have shown that a Candida protease can proteolytically degrade the key initiating components of lectin pathway and inhibit complement activation. Findings from this study highlight the importance of exploring Sapt1 as a potential therapeutic target. We conclude that C. tropicalis secretes Sapt1 to target the complement lectin pathway, a key pattern recognition and clearance mechanism, for its survival and pathogenesis. [ABSTRACT FROM AUTHOR]

Abstract: Therapeutic modulation of the complement system has become increasingly important in line with the growing recognition of the role of complement in numerous diseases. Compstatin, a peptidic inhibitor that acts at the central level of the complement cascade, is currently in clinical evaluation but routes to improve its efficacy have not yet been fully explored. Here, we report improvements in both the inhibitory potency and pharmacokinetic parameters of compstatin that broaden its clinical applications. Selective modification of the compstatin N-terminus with non-proteinogenic amino acids resulted in the first analogue with subnanomolar binding affinity (K D =0.5nM) and other similarly potent derivatives with improved solubility in clinically relevant solvents. Detailed structure–activity relationship studies based on biophysical and computational methods revealed key structural determinants for the observed improvements. Importantly, pharmacokinetic evaluation in non-human primates revealed target-driven elimination kinetics with plasma half-life values exceeding expectations for peptidic drugs (close to 12h). This successful optimization strategy is expected to pave the way for systemic administration of compstatin in a range of clinical conditions. [Copyright &y& Elsevier]

Abstract: This study assessed variation in plasma levels of the complement regulatorC1 inhibitor (C1inh) in patients with age related macular degeneration (AMD) and controls. Plasma from391 AMD cases and 370 controls was assayed by rate nephelometry to determine C1inh protein levels. Protein levels were analysed for relationships with age, gender, smoking, AMD disease status and genetic variation in the SERPING1 gene, which encodes C1inh, using a multivariate analysis. t-Tests show a significant difference in C1inh levels in AMD cases compared with controls (p =2.340E-6), smokers compared to non-smokers (p =1.022E-4) and females compared to males (p =1.661E-7). Multivariate analysis shows that after accounting for gender and smoking AMD status remained significant. Age was included in the model but was not significant. Including genetic variation in the model shows that one significant SNP (rs2649663) 5′ of the SERPING1 gene is associated with C1inh levels though this SNP is not associated with AMD. This suggests that genetic variation in the promoter region of the SERPING1 gene may influence expression of the gene. [Copyright &y& Elsevier]

Abstract: Despite multiple reports on autoantibody-initiated complement activation in autoimmune hepatitis (AIH), how does the humoral immunity contribute to the pathogenesis of AIH remained unclear. In this report, by adoptively transferring a polyclonal rabbit anti-OVA antibody into Hep-OVA Tg mice in which OVA is selectively expressed on the surface of hepatocytes, we found that excessive complement activation initiated by the autoantibody overwhelmed the protection of intrinsic cell surface complement regulators, and induced hepatocytes injury both in vitro and in vivo. The anti-OVA antibody induced hepatic injury in Hep-OVA Tg but not WT C57BL/6 mice as assessed by serum ALT levels and liver histopathology. Immunohistochemical analyses showed that after the antibody administration, there was massive complement activation on anti-OVA IgG coated hepatocytes in Hep-OVA Tg mice, but not in WT mice. Consistent with these results, depleting complement by cobra venom factor (CVF) prior to antibody injections protected Hep-OVA Tg mice from anti-OVA IgG induced hepatic injury. In addition, treating Hep-OVA Tg mice with recombinant mouse decay accelerating factor, a native complement inhibitor, protected them from autoantibody induced hepatitis. These results suggest that complement could play a pivotal role in liver specific autoantibody mediated hepatocyte injury in AIH, and that complement inhibitors could be, in principle, developed as novel therapeutics against AIH. [Copyright &y& Elsevier]

The complement system is a key player in innate immunity and a modulator of the adaptive immune system. Among the three pathways of complement, the alternative pathway (AP) accounts for most of the complement activation. Factor B (FB) is a major protease of the AP, making it a promising target to inhibit the AP activity in conditions of uncontrolled complement activation. Based on the data obtained from sequence analysis and conformational changes associated with FB, we expressed and purified a recombinant FB fragment (FBfr). We tested the inhibitory activity of the protein against the AP by in vitro assays. FBfr protein was proven to inhibit the complement AP activity when tested by C3b deposition assay and rabbit erythrocyte hemolytic assay. Our recombinant FBfr was able to compete with the native human FB, which allowed it to inhibit the AP activity. This novel compound is a good candidate for further characterization and testing to be used in complement diagnostic tests and as a drug lead in the field of complement therapeutics. [ABSTRACT FROM AUTHOR]