Complement Activation Assays Research Articles

Immunological properties of silica nanoparticles: a structure–activity relationship study

Silica nanoparticles are increasingly considered for drug delivery applications. These applications require an understanding of their biocompatibility, including their interactions with the immune system. However, systematic studies for silica nanoparticle immunological safety profiles are lacking. To fill this gap, we conducted an in vitro study investigating various aspects of silica nanoparticles’ interactions with blood and immune cells. Four types of silica nanoparticles with variations in size and porosity were studied. These included nonporous Stöber silica nanoparticles with average diameters of approximately 50 and 100 nm (SNP50 and SNP100), mesoporous silica nanoparticles of approximately 100 nm (Meso100), and hollow mesoporous silica nanoparticles of approximately 100 nm (HMSNP100) in diameter, respectively. The hematological compatibility was assessed using hemolysis, complement activation, platelet aggregation, and plasma coagulation assays. The effects of nanoparticles on immune cell function were studied using in vitro phagocytosis, chemotaxis, natural killer cell cytotoxicity, leukocyte proliferation, human lymphocyte activation, colony-forming unit granulocyte-macrophage, and leukocyte procoagulant activity assays. The in vitro findings suggest that at high concentrations, corresponding to the in vivo human dose of 40 mg/kg, silica nanoparticles demonstrated an array of immunotoxic effects that depended on their physicochemical properties. However, all types of silica nanoparticles studied were not immunotoxic at concentrations corresponding to lower doses (≤ 8 mg/kg) comparable to that of nanocarriers in other nanomedicines currently used in the clinic. These findings are promising for using silica nanoparticles for the systemic delivery of bioactive and imaging agents.

Lipopolysaccharide with long O-antigen is crucial for Salmonella Enteritidis to evade complement activity and to facilitate bacterial survival in vivo in the Galleria mellonella infection model

Bacterial resistance to serum is a key virulence factor for the development of systemic infections. The amount of lipopolysaccharide (LPS) and the O-antigen chain length distribution on the outer membrane, predispose Salmonella to escape complement-mediated killing. In Salmonella enterica serovar Enteritidis (S. Enteritidis) a modal distribution of the LPS O-antigen length can be observed. It is characterized by the presence of distinct fractions: low molecular weight LPS, long LPS and very long LPS. In the present work, we investigated the effect of the O-antigen modal length composition of LPS molecules on the surface of S. Enteritidis cells on its ability to evade host complement responses. Therefore, we examined systematically, by using specific deletion mutants, roles of different O-antigen fractions in complement evasion. We developed a method to analyze the average LPS lengths and investigated the interaction of the bacteria and isolated LPS molecules with complement components. Additionally, we assessed the aspect of LPS O-antigen chain length distribution in S. Enteritidis virulence in vivo in the Galleria mellonella infection model. The obtained results of the measurements of the average LPS length confirmed that the method is suitable for measuring the average LPS length in bacterial cells as well as isolated LPS molecules and allows the comparison between strains. In contrast to earlier studies we have used much more precise methodology to assess the LPS molecules average length and modal distribution, also conducted more subtle analysis of complement system activation by lipopolysaccharides of various molecular mass. Data obtained in the complement activation assays clearly demonstrated that S. Enteritidis bacteria require LPS with long O-antigen to resist the complement system and to survive in the G. mellonella infection model.

Interaction Studies of Hexameric and Pentameric IgMs with Serum-Derived C1q and Recombinant C1q Mimetics.

The interaction between IgM and C1q represents the first step of the classical pathway of the complement system in higher vertebrates. To identify the significance of particular IgM/C1q interactions, recombinant IgMs were used in both hexameric and pentameric configurations and with two different specificities, along with C1q derived from human serum (sC1q) and two recombinant single-chain variants of the trimeric globular region of C1q. Interaction and complement activation assays were performed using the ELISA format, and bio-layer interferometry measurements to study kinetic behavior. The differences between hexameric and pentameric IgM conformations were only slightly visible in the interaction assay, but significant in the complement activation assay. Hexameric IgM requires a lower concentration of sC1q to activate the complement compared to pentameric IgM, leading to an increased release of C4 compared to pentameric IgM. The recombinant C1q mimetics competed with sC1q in interaction assays and were able to inhibit complement activation. The bio-layer interferometry measurements revealed KD values in the nanomolar range for the IgM/C1q interaction, while the C1q mimetics exhibited rapid on and off binding rates with the IgMs. Our results make C1q mimetics valuable tools for developing recombinant C1q, specifically its variants, for further scientific studies and clinical applications.

Bupleurum chinense exerts a mild antipyretic effect on LPS-induced pyrexia rats involving inhibition of peripheral TNF-α production.

Bupleuri Radix, the dried roots of Bupleurum chinense DC. (BC) or Bupleurum scorzonerifolium Willd., is one of the most frequently used traditional Chinese medicines. As the species in Xiao-Chai-Hu decoction, BC has been used as an antipyretic medicine with a long history. However, its antipyretic characteristics and underlying mechanism(s) remain unclear. To elucidate the antipyretic characteristics and mechanism(s) of BC used in its traditional way. The water extract of BC (BCE) was prepared according to the traditional decocting mode. Murine fever and endotoxemia models were induced by intravenous injection of lipopolysaccharide (LPS). In vitro complement activation assay and the levels of TNF-α, IL-6, IL-1β, and C5a were determined by ELISA. BCE exerted a confirmed but mild antipyretic effect on LPS-induced fever of rat. In vitro, it significantly lowered LPS-elevated TNF-α in the supernatant of rat complete blood cells and THP-1cells, but failed to decrease IL-6 and IL-1β. In murine endotoxemia models, BCE markedly decreased serum TNF-α, but had no impact on IL-6 and IL-1β. BCE also restricted complement activation in vitro and in vivo. Nevertheless, the mixture of saikosaponin A and D could not suppress supernatant TNF-α of monocytes and serum TNF-α of endotoxemia mice. The present study dissects the peripheral mechanism for the antipyretic effect of BC used in the traditional way. Our findings indicate that BCE directly suppresses monocyte-produced TNF-α, thus decreasing circulating TNF-α, which may be responsible for its mild but confirmed antipyretic action.

Autoantibodies against complement factor B in rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disorder affecting the joints. Many patients carry anti-citrullinated protein autoantibodies (ACPA). Overactivation of the complement system seems to be part of the pathogenesis of RA, and autoantibodies against the pathway initiators C1q and MBL, and the regulator of the complement alternative pathway, factor H (FH), were previously reported. Our aim was to analyze the presence and role of autoantibodies against complement proteins in a Hungarian RA cohort. To this end, serum samples of 97 ACPA-positive RA patients and 117 healthy controls were analyzed for autoantibodies against FH, factor B (FB), C3b, C3-convertase (C3bBbP), C1q, MBL and factor I. In this cohort, we did not detect any patient with FH autoantibodies but detected C1q autoantibodies in four patients, MBL autoantibodies in two patients and FB autoantibodies in five patients. Since the latter autoantibodies were previously reported in patients with kidney diseases but not in RA, we set out to further characterize such FB autoantibodies. The isotypes of the analyzed autoantibodies were IgG2, IgG3, IgGκ, IgGλ and their binding site was localized in the Bb part of FB. We detected in vivo formed FB-autoanti-FB complexes by Western blot. The effect of the autoantibodies on the formation, activity and FH-mediated decay of the C3 convertase in solid phase convertase assays was determined. In order to investigate the effect of the autoantibodies on complement functions, hemolysis assays and fluid phase complement activation assays were performed. The autoantibodies partially inhibited the complement-mediated hemolysis of rabbit red blood cells, inhibited the activity of the solid phase C3-convertase and C3 and C5b-9 deposition on complement activating surfaces. In summary, in ACPA-positive RA patients we identified FB autoantibodies. The characterized FB autoantibodies did not enhance complement activation, rather, they had inhibitory effect on complement. These results support the involvement of the complement system in the pathomechanism of RA and raise the possibility that protective autoantibodies may be generated in some patients against the alternative pathway C3 convertase. However, further analyses are needed to assess the exact role of such autoantibodies.

A Flow Cytometry-Based Assay to Measure C3b Deposition on Protozoan Parasites Such as Toxoplasma gondii.

Flow cytometry is a powerful tool that can be used to study protozoan parasite interactions with the complement system. We developed a flow cytometric assay to measure the deposition of complement activation product C3b and to assess resistance to complement-mediated lysis. This assay involves exposing cultured parasites to human serum (the source of human complement) and staining parasites with antibodies against complement proteins to detect and quantify complement components on the parasite surface by flow cytometry. The assay can be used to compare complement activation across a variety of different species of protozoan parasites. As a proof of concept, we describe protocols to study C3 deposition on the single-cell protist Toxoplasma gondii. This parasite actively regulates C3 deposition and proteolytic inactivation to eliminate the formation of lytic pores targeted to the parasite surface coat, which is the end-product of the complement cascade. The antibodies used in this assay recognize both active and inactive forms of C3 deposited on parasite surfaces. Hence, the assay facilitates the identification and characterization of parasite resistance factors that regulate complement deposition and catabolic inactivation. © Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Basic Protocol 1: Culturing human foreskin fibroblasts and Toxoplasma gondii strains Basic Protocol 2: In vitro complement activation assay Support Protocol: Screening of normal human serum Basic Protocol 3: Flow cytometric analysis of C3b deposition.

Mechanistic investigation of thermosensitive liposome immunogenicity and understanding the drivers for circulation half-life: A polyethylene glycol versus 1,2-dipalmitoyl-sn-glycero-3-phosphodiglycerol study

Various thermosensitive liposome (TSL) formulations have been described to date and it is currently unclear which are optimal for solid tumor treatment. Sufficient circulation half-life is important and most liposomes obtain this by polyethylene glycol (PEG) surface modification. 1,2-dipalmitoyl-sn-glycero-3-phosphodiglycerol (DPPG2) has been described as a promising alternative which increases TSL circulation half-life and facilitates rapid drug release under mild hyperthermia at 20–30 mol%. The present work describes an investigation of the DPPG2-TSL protein corona, blood cell interactions, complement activation in human plasma/blood and hypersensitivity reactions in rats. Furthermore, accelerated blood clearance (ABC) was investigated to obtain a complete assessment of DPPG2-TSL interactions with components of the blood and identify drivers for circulation half-life. A higher mol% DPPG2 increased Apolipoprotein E (ApoE) adsorption and decreased complement activation and granulocyte interaction in vitro. In contrast to PEG-TSL, DPPG2-TSL showed no ABC effect. In vivo hypersensitivity assessment by eicosanoid measurements, platelet and lymphocyte counting resembled the results of in vitro complement activation assays although here all DPPG2-TSL formulations induced hypersensitive responses upon i.v. administration. Prolonged circulation half-life of DPPG2-TSL may be ApoE-induced and the absent ABC effect demonstrates an advantage over PEG-TSL. Low complement activation in human plasma and blood for 20–30 mol% DPPG2-TSL presents a unique formulation attribute with the potential to strengthen clinical evaluation.

Preparation and characterization of an elastin nanogel with enhanced biocompatibility and improved entrapment efficiency in prostate cancer cells

Nanogels represent an emerging class of drug delivery systems with enhanced renal clearance and serum half-life. However, synthetic polymeric nanogels are immunogenic and less biodegradable than other systems. Protein nanogels, being non-immunogenic; biodegradable; biocompatible; and mechanically, spatially, and temporally tunable, are gaining widespread attention. Elastin, a natural structural component of connective tissue, has enhanced vascular mobility and is highly biodegradable, biocompatible, temperature and pH sensitive, inert in the bloodstream, able to self-assemble, and able to permeate the blood-brain-barrier. In this study, the development of an Elastin Nanogel (ENG) and its functional capacity as a next generation injectable nano-drug carrier was studied. ENG was prepared via an inverse mini-emulsion technique and was characterized and found to be stable at room temperature and cytocompatible with five different prostate cancer cell lines of varied etiologies. Rhodamine-loaded ENG showed enhanced cellular uptake. Blood smear, hemolysis, CBC, PT/APTT, and C3a complement activation assays showed that ENG is vascular tissue compatible and hence meets the objectives of injectable nanogels. The formulated ENG can be efficiently used as an injectable nano-drug carrier for cancer therapy. Moreover, ENG has the potential to encapsulate hydrophobic drugs for targeted drug delivery.

Corrigendum

Cellular MicrobiologyVolume 23, Issue 1 e13286 CORRIGENDUMFree Access Corrigendum This article corrects the following: Borrelia burgdorferi outer surface protein C (OspC) binds complement component C4b and confers bloodstream survival Jennifer A. Caine, Yi-Pin Lin, Julie R. Kessler, Hiromi Sato, John M. Leong, Jenifer Coburn, Volume 19Issue 12Cellular Microbiology First Published online: September 26, 2017 First published: 09 November 2020 https://doi.org/10.1111/cmi.13286AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat In “Borrelia burgdorferi outer surface protein C (OspC) binds complement component C4b and confers bloodstream survival”, by Caine et al. (2017)which was published in volume 19, issue 12, September 2017, the authors wish to notify readers that we have not been able to reliably reproduce the data in Figure 5. The corresponding text “To determine if OspC is able to directly inhibit the complement cascade allowing WT B. burgdorferi to survive in the bloodstream of mice, we performed an ELISA-based complement activation assay. Plates were coated with initiators of each pathway of the complement cascade; Immunoglobulin M (IgM; classical pathway), mannan (lectin pathway), lipopolysaccharide (LPS; alternative pathway), or buffer (negative control). Coated plates were incubated with a mixture of pooled active human serum and various concentrations of purified GST-OspC B31, GST, or buffer, and complement deposition was measured in each well by ELISA (Figure 5). Wells coated with IgM or mannan and incubated with 1000 nM GST- OspC have significantly lower levels of deposited complement compared to wells incubated in GST (Figure 5a,b). This effect is not seen in LPS coated wells, where the addition of GST-OspC does not inhibit complement deposition compared to GST at any concentration tested (Figure 5c) and Figure 5” should be removed from the paper. In addition, Experimental Procedures section 4.13 “Complement Inhibition ELISAs” should be removed. All other data shown are reproducible, so our primary conclusion is supported. REFERENCE Caine, JA, Lin, Y-P, Kessler, JR, Sato, H, Leong, JM, and Coburn, J. Borrelia burgdorferi outer surface protein C (OspC) binds complement component C4b and confers bloodstream survival. Cellular Microbiology, 2017; 19:e12786. PMID 28873507, PMCID PMC5680108. https://doi.org/10.1111/cmi.12786 Volume23, Issue1January 2021e13286 ReferencesRelatedInformation

Development of Pharmacodynamic Assays to Assess Ex Vivo Masp-2 Inhibition and Their Use to Characterize the Pharmacodynamics of Narsoplimab (OMS721) in Humans and Monkeys

Introduction Narsoplimab (OMS721) is a fully human monoclonal antibody that binds to and inhibits mannan-binding lectin-associated serine protease 2 (MASP-2). MASP-2 is the key enzyme responsible for activation of the lectin pathway of the complement system. The lectin pathway is activated when plasma is exposed to molecular patterns present on microbes and injured host cell surfaces, initiating a proteolytic cascade that results in the activation of complement components C4, C2, C3 and C5 to yield multiple biologically active products. Inhibiting MASP-2 activity prevents lectin-mediated generation of complement activation products, thereby reducing inflammation and tissue injury. Narsoplimab is the first lectin pathway-specific complement inhibitor in clinical development. In published clinical studies and case reports, improvement has been observed in narsoplimab-treated patients with hematopoietic stem cell transplant-associated thrombotic microangiopathy, immunoglobulin A (IgA) nephropathy and atypical hemolytic uremic syndrome. Here we describe the development of pharmacodynamic (PD) assays to quantify MASP-2 inhibition ex vivo and their use to study duration of action and to establish the pharmacokinetic (PK)/PD relationship of narsoplimab in monkeys and humans. Methods PD assays to measure lectin pathway activity, a measure of MASP-2 activity, in minimally diluted (90%) serum from human and monkey were developed using immobilized mannan as a lectin pathway-specific complement activator with C4b as the activation endpoint. ELISA and flow cytometry assay platforms were employed to assess the PD response of monkeys or normal healthy human volunteers administered narsoplimab, respectively. The PD response was used to characterize the time-course and dose-response of lectin pathway inhibition by narsoplimab. Drug concentration data obtained from matched serum samples were used to estimate the ex vivo EC50 of lectin pathway inhibition in monkeys and humans. Lectin pathway-specific complement activation assays applicable to minimally diluted serum samples were developed by evaluating the time-course of lectin-induced complement activation response under varying reaction temperatures and selecting optimized test conditions within the dynamic range of the assay platform. The test methods were used to characterize monkey and human lectin pathway inhibition profiles of narsoplimab in vitro, and the flow cytometric method was validated for analysis of human serum samples. Results The PD assays were used to characterize the PD response of monkeys administered a single intravenous (IV) bolus injection of narsoplimab at 0.05, 0.15, 0.5, 1.5 or 5 mg/kg, and of normal human healthy volunteers administered a single IV infusion of the drug at 0.25, 0.625 or 2 mg/kg, or 6 weekly IV infusions at 2 or 4 mg/kg. A clear, dose-dependent initial PD response was observed in monkeys in the dose range of 0.5 mg/kg to 5 mg/kg, which subsequently declined over time. In humans, a minimal PD response was observed at 0.025 mg/kg. A near maximal initial PD response was seen at 0.675 mg/kg or higher, followed by a decline over time. In the 6-week repeat-dose study, once-weekly dosing of narsoplimab at 2 mg/kg resulted in a mean trough PD response of ~55% lectin pathway inhibition, which increased to an ~80% mean trough response with once-weekly dosing of 4 mg/kg. PK sample analysis revealed a clear PK/PD relationship in monkeys and humans. Modeling of the PK/PD relationship in monkeys indicated an EC50 value of ~7 µg/mL (~ 46 nM), which is comparable to the IC50 value of lectin pathway inhibition in vitro (33 nM). In humans, modeling of the PK/PD relationship data indicated an EC50 value of ~500 ng/mL (3.3 nM), again very similar to the IC50 value of lectin pathway inhibition in vitro (3.4 nM). Conclusion We successfully developed PD assays to monitor blockade of lectin pathway activation in monkeys and humans administered narsoplimab. Using a validated PD assay, we demonstrate that a high level of lectin pathway blockade can be maintained in normal human healthy volunteers by once-weekly administration of narsoplimab at 4 mg/kg IV. We also demonstrate a consistent PK/PD relationship across the study population, indicating that narsoplimab concentration ranges can be used to target the desired level of lectin pathway inhibition. Figure 1 Disclosures Freeman: Omeros Corporation: Current Employment. Cummings:Omeros Corporation: Current Employment. Chuidian:Omeros Corporation: Current Employment. Dudler:Omeros Corporation: Current Employment.

A clinical trial comparing aliskiren with enalapril for the treatment of C3 glomerulopathy

Abstract Introduction To date there is no established, effective treatment for C3 glomerulopathy, encompassing both Dense Deposit Disease and C3 glomerulonephritis. We have previously reported that renin mediates complement activation by cleaving C3 and found that the direct renin inhibitor aliskiren blocked complement activation by renin and inhibited complement activation systemically and in the kidneys in three patients with Dense Deposit Disease. Theoretically enalapril should increase renin without blocking its effect and therefore we will conduct a clinical trial to compare these two treatments. Material and methods We will include patients to be treated with aliskiren or enalapril (15 in each arm). Recruitment will take place in Swedish hospitals. Children 6 years or older with a glomerular filtration rate equal to or above 50 ml/min/1.73 m2 and adults equal to or above 30 ml/min/1.73 m2 will be included. Patients will be randomized for treatment with aliskiren or enalapril, as monotherapy or in combination with immune suppressive medications. After 6 months patients will switch to the other treatment and continue on the second treatment for an additional 2.5 years. Patients will be followed regularly regarding renal function, proteinuria, blood pressure, activation of the renin-angiotensin system and complement activation assays. After 1–3 years, when medically indicated or at the end of the study, a repeat renal biopsy will be performed to validate the effect of treatment on renal morphology and complement deposition. Conclusions The results of this study may provide more scientific evidence for, or against, the use of aliskiren in patients with C3 glomerulopathy.

A novel complement inhibitor sMAP-FH targeting both the lectin and alternative complement pathways.

Inhibition of the complement activation has emerged as an option for treatment of a range of diseases. Activation of the lectin and alternative pathways (LP and AP, respectively) contribute to the deterioration of conditions in certain diseases such as ischemia-reperfusion injuries and age-related macular degeneration (AMD). In the current study, we generated dual complement inhibitors of the pathways MAp44-FH and sMAP-FH by fusing full-length MAp44 or small mannose-binding lectin-associated protein (sMAP), LP regulators, with the N-terminal five short consensus repeat (SCR) domains of complement factor H (SCR1/5-FH), an AP regulator. The murine forms of both fusion proteins formed a complex with endogenous mannose-binding lectin (MBL) or ficolin A in the circulation when administered in mice intraperitoneally. Multiple complement activation assays revealed that sMAP-FH had significantly higher inhibitory effects on activation of the LP and AP in vivo as well as in vitro compared to MAp44-FH. Human form of sMAP-FH also showed dual inhibitory effects on LP and AP activation in human sera. Our results indicate that the novel fusion protein sMAP-FH inhibits both the LP and AP activation in mice and in human sera, and could be an effective therapeutic agent for diseases in which both the LP and AP activation are significantly involved.

Three-Layered Silk Fibroin Tubular Scaffold for the Repair and Regeneration of Small Caliber Blood Vessels: From Design to in vivo Pilot Tests.

Silk fibroin (SF) is an eligible biomaterial for the development of small caliber vascular grafts for substitution, repair, and regeneration of blood vessels. This study presents the properties of a newly designed multi-layered SF tubular scaffold for vascular grafting (SilkGraf). The wall architecture consists of two electrospun layers (inner and outer) and an intermediate textile layer. The latter was designed to confer high mechanical performance and resistance on the device, while electrospun layers allow enhancing its biomimicry properties and host's tissues integration. In vitro cell interaction studies performed with adult Human Coronary Artery Endothelial Cells (HCAECs), Human Aortic Smooth Muscle Cells (HASMCs), and Human Aortic Adventitial Fibroblasts (HAAFs) demonstrated that the electrospun layers favor cell adhesion, survival, and growth. Once cultured in vitro on the SF scaffold the three cell types showed an active metabolism (consumption of glucose and glutamine, release of lactate), and proliferation for up to 20 days. HAAF cells grown on SF showed a significantly lower synthesis of type I procollagen than on polystyrene, meaning a lower fibrotic effect of the SF substrate. The cytokine and chemokine expression patterns were investigated to evaluate the cells' proliferative and pro-inflammatory attitude. Interestingly, no significant amounts of truly pro-inflammatory cytokines were secreted by any of the three cell types which exhibited a clearly proliferative profile. Good hemocompatibility was observed by complement activation, hemolysis, and hematology assays. Finally, the results of an in vivo preliminary pilot trial on minipig and sheep to assess the functional behavior of implanted SF-based vascular graft identified the sheep as the more apt animal model for next medium-to-long term preclinical trials.

Combining MAP‐1:CD35 or MAP‐1:CD55 fusion proteins with pattern‐recognition molecules as novel targeted modulators of the complement cascade

Dysregulation of the complement system is involved in the pathogenesis of several diseases, and its inhibition has been shown to be a feasible therapeutic option. Therefore, there is an interest in the development of complement modulators to treat complement activation-related inflammatory pathologies. Mannose-binding lectin (MBL)/ficolin/collectin-associated protein-1 (MAP-1) is a regulatory molecule of the lectin pathway (LP), whereas complement receptor 1 (CD35) and decay-accelerating factor (CD55) are membrane-anchored regulators with effects on the central effector molecule C3. In this study, we developed 2 novel soluble chimeric inhibitors by fusing MAP-1 to the 3 first domains of CD35 (CD351-3) or the 4 domains of CD55 (CD551-4) to modulate the complement cascade at 2 different stages. The constructs showed biologic properties similar to those of the parent molecules. In functional complement activation assays, the constructs were very efficient in inhibiting LP activation at the level of C3 and in the formation of terminal complement complex. This activity was enhanced when coincubated with recombinant LP recognition molecules MBL and ficolin-3. Recombinant MAP-1 fusion proteins, combined with recombinant LP recognition molecules to target sites of inflammation, represent a novel and effective therapeutic approach involving the initiation and the central and terminal effector functions of the complement cascade.-Pérez-Alós, L., Bayarri-Olmos, R., Skjoedt, M.-O., Garred, P. Combining MAP-1:CD35 or MAP-1:CD55 fusion proteins with pattern-recognition molecules as novel targeted modulators of the complement cascade.

DEHP Nanodroplets Leached From Polyvinyl Chloride IV Bags Promote Aggregation of IVIG and Activate Complement in Human Serum

Concerns regarding the impact of subvisible particulate impurities on the safety and efficacy of therapeutic protein products have led manufacturers to implement strategies to minimize protein aggregation and particle formation during manufacturing, storage, and shipping. However, once these products are released, manufacturers have limited control over product handling. In this work, we investigated the effect of di(2-ethylhexyl) phthalate (DEHP) nanodroplets generated in polyvinyl chloride (PVC) bags of intravenous (IV) saline on the stability and immunogenicity of IV immunoglobulin (IVIG) formulations. We showed that PVC IV bags containing saline can release DEHP droplets into the solution when agitated or transported using a pneumatic tube transportation system in a clinical setting. We next investigated the effects of emulsified DEHP nanodroplets on IVIG stability and immunogenicity. IVIG adsorbed strongly to DEHP nanodroplets, forming a monolayer. In addition, DEHP nanodroplets accelerated IVIG aggregation in agitated samples. The immunogenicity of DEHP nanodroplets and IVIG aggregates generated in these formulations were evaluated using an in vitro assay of complement activation in human serum. The results suggested DEHP nanodroplets shed from PVC IV bags could reduce protein stability and induce activation of the complement system, potentially contributing to adverse immune responses during the administration of therapeutic proteins.

Recognition protein C1q of innate immunity agglutinates nanodiamonds without activating complement

Nanodiamonds are promising nanomedicines for diagnostic and therapeutic applications. As nanodiamonds are mainly administered intravenously, it is critical to understand the humoral immune response upon exposure to nanodiamonds. Here, we report the interactions of pristine, oxidized, and PEG-functionalized nanodiamonds with human complement, an important part of our humoral innate immunity. In particular, we report the nanodiamond binding properties of the recognition protein of the classical complement pathway: C1q, which also takes part in many other physiological and pathological processes. Our results show similar trends in the effects of C1q on the three types of nanodiamonds. Complement activation assays using human serum show that the nanodiamonds trigger slight activities via the alternative pathway and no response via the classical pathway. Nevertheless, surface plasmon resonance shows that C1q binds the nanodiamonds and transmission electron microscopy reveals their agglutination. Studies with macrophages further show that C1q attachment affects their phagocytosis and cytokine response.

Chimeric proteins containing MAP-1 and functional domains of C4b-binding protein reveal strong complement inhibitory capacities

The complement system is a tightly regulated network of proteins involved in defense against pathogens, inflammatory processes, and coordination of the innate and adaptive immune responses. Dysregulation of the complement cascade is associated with many inflammatory disorders. Thus, inhibition of the complement system has emerged as an option for treatment of a range of different inflammatory diseases. MAP-1 is a pattern recognition molecule (PRM)-associated inhibitor of the lectin pathway of the complement system, whereas C4b-binding protein (C4BP) regulates both the classical and lectin pathways. In this study we generated chimeric proteins consisting of MAP-1 and the first five domains of human C4BP (C4BP1-5) in order to develop a targeted inhibitor acting at different levels of the complement cascade. Two different constructs were designed and expressed in CHO cells where MAP-1 was fused with C4BP1-5 in either the C- or N-terminus. The functionality of the chimeric proteins was assessed using different in vitro complement activation assays. Both chimeric proteins displayed the characteristic Ca2+-dependent dimerization and binding to PRMs of native MAP-1, as well as the co-factor activity of native C4BP. In ELISA-based complement activation assays they could effectively inhibit the lectin and classical pathways. Notably, MAP-1:C4BP1-5 was five times more effective than rMAP-1 and rC4BP1-5 applied at the same time, emphasizing the advantage of a single inhibitor containing both functional domains. The MAP-1/C4BP chimeras exert unique complement inhibitory properties and represent a novel therapeutic approach targeting both upstream and central complement activation.

Chimeric Proteins Containing MAP-1 and Functional Domains of C4b-Binding Protein Reveal Strong Complement Inhibitory Capacities.

The complement system is a tightly regulated network of proteins involved in defense against pathogens, inflammatory processes, and coordination of the innate and adaptive immune responses. Dysregulation of the complement cascade is associated with many inflammatory disorders. Thus, inhibition of the complement system has emerged as an option for treatment of a range of different inflammatory diseases. MAP-1 is a pattern recognition molecule (PRM)-associated inhibitor of the lectin pathway of the complement system, whereas C4b-binding protein (C4BP) regulates both the classical and lectin pathways. In this study we generated chimeric proteins consisting of MAP-1 and the first five domains of human C4BP (C4BP1−5) in order to develop a targeted inhibitor acting at different levels of the complement cascade. Two different constructs were designed and expressed in CHO cells where MAP-1 was fused with C4BP1−5 in either the C- or N-terminus. The functionality of the chimeric proteins was assessed using different in vitro complement activation assays. Both chimeric proteins displayed the characteristic Ca2+-dependent dimerization and binding to PRMs of native MAP-1, as well as the co-factor activity of native C4BP. In ELISA-based complement activation assays they could effectively inhibit the lectin and classical pathways. Notably, MAP-1:C4BP1−5 was five times more effective than rMAP-1 and rC4BP1−5 applied at the same time, emphasizing the advantage of a single inhibitor containing both functional domains. The MAP-1/C4BP chimeras exert unique complement inhibitory properties and represent a novel therapeutic approach targeting both upstream and central complement activation.

The Surface-Exposed Protein SntA Contributes to Complement Evasion in Zoonotic Streptococcus suis.

Streptococcus suis is an emerging zoonotic pathogen causing streptococcal toxic shock like syndrome (STSLS), meningitis, septicemia, and even sudden death in human and pigs. Serious septicemia indicates this bacterium can evade the host complement surveillance. In our previous study, a functionally unknown protein SntA of S. suis has been identified as a heme-binding protein, and contributes to virulence in pigs. SntA can interact with the host antioxidant protein AOP2 and consequently inhibit its antioxidant activity. In the present study, SntA is identified as a cell wall anchored protein that functions as an important player in S. suis complement evasion. The C3 deposition and membrane attack complex (MAC) formation on the surface of sntA-deleted mutant strain ΔsntA are demonstrated to be significantly higher than the parental strain SC-19 and the complementary strain CΔsntA. The abilities of anti-phagocytosis, survival in blood, and in vivo colonization of ΔsntA are obviously reduced. SntA can interact with C1q and inhibit hemolytic activity via the classical pathway. Complement activation assays reveal that SntA can also directly activate classical and lectin pathways, resulting in complement consumption. These two complement evasion strategies may be crucial for the pathogenesis of this zoonotic pathogen. Concerning that SntA is a bifunctional 2′,3′-cyclic nucleotide 2′-phosphodiesterase/3′-nucleotidase in many species of Gram-positive bacteria, these complement evasion strategies may have common biological significance.

The C3dg Fragment of Complement Is Superior to Conventional C3 as a Diagnostic Biomarker in Systemic Lupus Erythematosus.

In 2012, hypocomplementemia was included in the classification criteria of systemic lupus erythematosus (SLE). The suggested measurement of C3 or C4 often reflect disease activity poorly. Our objective was to establish an assay measuring C3dg, which is generated following complement activation, and to evaluate the assay in a cross-sectional SLE cohort. We included SLE patients (n = 169) and controls (n = 170) and developed a modified C3dg assay where C3dg fragments were separated from the large plasma proteins by polyethylene glycol (PEG), and the supernatant containing the C3dg fragment was used for analysis in an antibody-based sandwich-type assay. Gel permeation chromatography and western blotting were used to establish the optimal conditions for PEG precipitation. 16% PEG was optimal for separating C3dg from C3 and the larger protein fragments. The assay showed a high degree of stability when using EDTA plasma, and measurements correlated well with commercially available complement activation assays. SLE patients had higher concentrations in plasma of C3dg than controls (p < 0.05). ROC analysis showed that the C3dg activation fragment of C3 with an AUC of 0.96 (CI 0.94-0.98) was superior to C3 (AUC 0.52) in differentiating between patients and controls. Our results present a modified assay for the measurement of C3dg. We demonstrate that C3dg was superior to conventional C3 measurements in discriminating SLE patients from controls. We suggest that C3dg should be considered as a complement activation measurement in the SLE classification criteria.