The C5a receptor antagonist PMX205 ameliorates experimentally induced colitis associated with increased IL-4 and IL-10

Revisiting the relationship between complement and ulcerative colitis

Ulcerative colitis (UC) is an inflammatory bowel disorder (IBD) characterized by relapsing chronic inflammation of the colon that causes continuous mucosal inflammation. The global incidence of UC is steadily increasing. Immune mechanisms are involved in the pathogenesis of UC, of which complement is shown to play a critical role by inducing local chronic inflammatory responses that promote tissue damage. However, the function of various complement components in the development of UC is complex and even paradoxical. Some components (e.g. C1q, CD46, CD55, CD59, and C6) are shown to safeguard the intestinal barrier and reduce intestinal inflammation, while others (e.g. C3, C5, C5a) can exacerbate intestinal damage and accelerate the development of UC. The complement system was originally thought to function primarily in an extracellular mode; however, recent evidence indicates that it can also act intracellularly as the complosome. The current study provides an overview of current studies on complement and its role in the development of UC. While there are few studies that describe how intracellular complement contributes to UC, we discuss potential future directions based on related publications. We also highlight novel methods that target complement for IBD treatment.

Complement System Inhibitory Drugs in a Zebrafish (Danio rerio) Model: Computational Modeling

The dysregulation of complement system activation usually results in acute or chronic inflammation and can contribute to the development of various diseases. Although the activation of complement pathways is essential for innate defense, exacerbated activity of this system may be harmful to the host. Thus, drugs with the potential to inhibit the activation of the complement system may be important tools in therapy for diseases associated with complement system activation. The synthetic peptides Cp40 and PMX205 can be highlighted in this regard, given that they selectively inhibit the C3 and block the C5a receptor (C5aR1), respectively. The zebrafish (Danio rerio) is a robust model for studying the complement system. The aim of the present study was to use in silico computational modeling to investigate the hypothesis that these complement system inhibitor peptides interact with their target molecules in zebrafish, for subsequent in vivo validation. For this, we analyzed molecular docking interactions between peptides and target molecules. Our study demonstrated that Cp40 and the cyclic peptide PMX205 have positive interactions with their respective zebrafish targets, thus suggesting that zebrafish can be used as an animal model for therapeutic studies on these inhibitors.

The role of C5a receptors in autoimmunity

The complement system is an essential component of the innate immune response and plays a vital role in host defense and inflammation. Dysregulation of the complement system, particularly involving the anaphylatoxin C5a and its receptors (C5aR1 and C5aR2), has been linked to several autoimmune diseases, indicating the potential for targeted therapies. C5aR1 and C5aR2 are seven-transmembrane receptors with distinct signaling mechanisms that play both partially overlapping and opposing roles in immunity. Both receptors are expressed on a broad spectrum of immune and non-immune cells and are involved in cellular functions and physiological processes during homeostasis and inflammation. Dysregulated C5a-mediated inflammation contributes to autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, epidermolysis bullosa acquisita, antiphospholipid syndrome, and others. Therefore, targeting C5a or its receptors may yield therapeutic innovations in these autoimmune diseases by reducing the recruitment and activation of immune cells that lead to tissue inflammation and injury, thereby exacerbating the autoimmune response. Clinical trials focused on the inhibition of C5 cleavage or the C5a/C5aR1-axis using small molecules or monoclonal antibodies hold promise for bringing novel treatments for autoimmune diseases into practice. However, given the heterogeneous nature of (systemic) autoimmune diseases, there are still several challenges, such as patient selection, optimal dosing, and treatment duration, that require further investigation and development to realize the full therapeutic potential of C5a receptor inhibition, ideally in the context of a personalized medicine approach. Here, we aim to provide a brief overview of the current knowledge on the function of C5a receptors, the involvement of C5a receptors in autoimmune disorders, the molecular mechanisms underlying C5a receptor-mediated autoimmunity, and the potential for targeted therapies to modulate their activity.

GNA12 regulates C5a-induced migration by downregulating C5aR1-PLCβ2-PI3K-AKT-ERK1/2 signaling

Gna12 has been identified as one of the reported inflammatory bowel disease (IBD) susceptibility genes in genome-wide association studies (GWAS). However, the function of GNA12 in intestinal homeostasis remains unknown. Here we report that GNA12, a G-protein α subunit, regulates C5a-induced migration in macrophages. Deficiency of GNA12 results in enhanced migration induced by C5a in macrophages. Mechanistically, GNA12 suppresses C5a-induced migration by downregulating the C5aR1-PLCβ2-PI3K-AKT-ERK1/2 signaling. Therefore, our study reveals that GNA12 is an anti-inflammatory factor, which might alleviate the development of inflammation by inhibiting the excessive chemotactic migration of macrophages.

Serum Depletion of Complement Component 5a Is Associated With Increased Inflammation and Poor Clinical Outcomes in Patients With Perianal Fistulas

BACKGROUND

Persistent disease is a significant issue in the management of perianal fistulas, with up to 50% of patients requiring additional treatment after surgery.

OBJECTIVE

This study aimed to identify a novel prognostic modality in hopes of risk-stratifying patients for persistent disease following corrective surgery.

DESIGN

This was a retrospective study based on prospectively collected data using a combination of histopathology, high-throughput proteomic arrays, and ELISA-based methods.

SETTINGS

This study used data obtained from patients who underwent corrective surgery for perianal fistulas at the University of Illinois Hospital between June 2019 and July 2020.

PATIENTS

A cohort of 22 consecutive patients who had corrective surgery for perianal fistulas were included in this study. The patients were divided into 2 groups: those with resolving fistulas (N = 13) and those with persisting fistulas (N = 9).

MAIN OUTCOME MEASURES

Nonresolving fistulas were determined by disease representation within 2 months of corrective surgery.

RESULTS

Serum samples from patients with persistent perianal fistulas displayed a consistent decrease in the expression of complement pathway component C5a compared with either healthy controls or patients with resolving forms of disease. This was paralleled by an increase in the fistula expression of C5a and an associated increase in tissue infiltrating leukocytes and interleukin-1β expression.

LIMITATIONS

This study was limited by its retrospective design, relatively small sample size, and single-center data analysis.

CONCLUSIONS

These results suggest that C5a is modestly depleted in patients with nonresolving forms of disease and traffics to the site of tissue damage and inflammation. Accordingly, serum C5a warrants continued investigation as a prognostic biomarker and predictor of recurrence in patients presenting with perianal fistulas. See Video Abstract at http://links.lww.com/DCR/B982 .

LA DEPLECIN SRICA DEL COMPONENTE A DEL COMPLEMENTO SE ASOCIA CON UN AUMENTO DE LA INFLAMACIN Y MALOS RESULTADOS CLNICOS EN PACIENTES CON FSTULAS PERIANALES

ANTECEDENTES:La persistencia de la enfermedad es un problema significativo en el manejo de las fístulas perianales, presente hasta en el 50 % de los pacientes después de la cirugía y que requieren tratamiento adicional.OBJETIVO:DISEÑO:Se trata de un estudio retrospectivo basado en datos recolectados prospectivamente usando una combinación de histopatología, arreglos proteómicos de alto rendimiento y métodos basados en ELISA.ENTORNO CLÍNICO:Este estudio utilizó datos de pacientes que se sometieron a cirugía correctiva por fístulas perianales en el Hospital de la Universidad de Illinois entre junio de 2019 y julio de 2020.PACIENTES:Se incluyó en este estudio una cohorte de 22 pacientes consecutivos que se sometieron a cirugía correctiva de fístulas perianales. Los pacientes se dividieron en 2 grupos: aquellos con fístulas en resolución (N = 13) y aquellos con fístulas persistentes (N = 9).PRINCIPALES MEDIDAS DE VALORACIÓN:Las fístulas que no se resuelven fueron determinadas por la reaparición de la enfermedad dentro de los 2 meses posteriores a la cirugía correctiva.RESULTADOS:Las muestras de suero de pacientes con fístulas perianales persistentes mostraron una disminución constante en la expresión del componente C5a de la vía del complemento en comparación con controles sanos o pacientes con formas de resolución de la enfermedad. Esto fue paralelo a un aumento en la expresión de C5a en la fístula y un aumento asociado en los leucocitos que se infiltran en el tejido y la expresión de IL-1β.LIMITACIONES:El estudio estuvo limitado por su diseño retrospectivo, tamaño de muestra relativamente pequeño y análisis de datos de un solo centro.CONCLUSIONES:Estos resultados sugieren que C5a se reduce moderadamente en pacientes con formas de enfermedad que no se resuelven y se desplaza al sitio del daño tisular e inflamación. En consecuencia, el C5a sérico justifica una investigación continua como biomarcador pronóstico y predictor de recurrencia en pacientes que presentan fístulas perianales. Consulte Video Resumen en http://links.lww.com/DCR/B982 . (Traducción- Dr. Ingrid Melo ).

The Complement Pathway: New Insights into Immunometabolic Signaling in Diabetic Kidney Disease

Significance: The metabolic disorder, diabetes mellitus, results in microvascular complications, including diabetic kidney disease (DKD), which is partly believe to involve disrupted energy generation in the kidney, leading to injury that is characterized by inflammation and fibrosis. An increasing body of evidence indicates that the innate immune complement system is involved in the pathogenesis of DKD; however, the precise mechanisms remain unclear. Recent Advances: Complement, traditionally thought of as the prime line of defense against microbial intrusion, has recently been recognized to regulate immunometabolism. Studies have shown that the complement activation products, Complement C5a and C3a, which are potent pro-inflammatory mediators, can mediate an array of metabolic responses in the kidney in the diabetic setting, including altered fuel utilization, disrupted mitochondrial respiratory function, and reactive oxygen species generation. In diabetes, the lectin pathway is activated via autoreactivity toward altered self-surfaces known as danger-associated molecular patterns, or via sensing altered carbohydrate and acetylation signatures. In addition, endogenous complement inhibitors can be glycated, whereas diet-derived glycated proteins can themselves promote complement activation, worsening DKD, and lending support for environmental influences as an additional avenue for propagating complement-induced inflammation and kidney injury. Critical Issues: Recent evidence indicates that conventional renoprotective agents used in DKD do not target the complement, leaving this web of inflammatory stimuli intact. Future Directions: Future studies should focus on the development of novel pharmacological agents that target the complement pathway to alleviate inflammation, oxidative stress, and kidney fibrosis, thereby reducing the burden of microvascular diseases in diabetes. Antioxid. Redox Signal. 37, 781-801.

Increased Levels of C5a in Gingival Crevicular Fluid and Saliva of Patients with Periodontal Disease

C5a is a powerful complement effector molecule that is considered to be an important proinflammatory mediator in several systemic chronic inflammatory diseases. However, its levels in periodontal diseases are yet to be assessed. We aimed to analyse the secretion of C5a in gingival crevicular fluid (GCF) and saliva of patients with periodontal disease. Twenty-eight patients diagnosed with stage 3–4 periodontitis and 16 periodontally healthy subjects participated in this study. GCF was collected from sites with the deepest probing depth of each patient, and volume was measured using a Periotron 8000^®. One mL of unstimulated saliva was also collected. Samples were analysed using a commercially available ELISA kit. The data were analysed using the Mann–Whitney U test, Pearson’s bivariate testing, and receiver operating characteristic curve. C5a was present in GCF from patients with periodontitis (1.06 ± 0.25 ng/mL) whilst it was undetected in controls. Saliva concentration was also significantly higher in periodontitis (1.82 ± 2.31 ng/mL) than controls (0.60 ± 0.72 ng/mL, p = 0.006). C5a levels were more pronounced in periodontitis in both oral fluids assessed by the present pilot study. These results suggest that the more pronounced levels of C5a in oral fluids from periodontitis patients indicate a potential role of this molecule in this disease pathogenesis, deserving to be better explored in subsequent studies.

Zebrafish fin regeneration involves generic and regeneration-specific osteoblast injury responses

Successful regeneration requires the coordinated execution of multiple cellular responses to injury. In amputated zebrafish fins, mature osteoblasts dedifferentiate, migrate towards the injury and form proliferative osteogenic blastema cells. We show that osteoblast migration is preceded by cell elongation and alignment along the proximodistal axis, which require actomyosin, but not microtubule turnover. Surprisingly, osteoblast dedifferentiation and migration can be uncoupled. Using pharmacological and genetic interventions, we found that NF-ĸB and retinoic acid signalling regulate dedifferentiation without affecting migration, while the complement system and actomyosin dynamics affect migration but not dedifferentiation. Furthermore, by removing bone at two locations within a fin ray, we established an injury model containing two injury sites. We found that osteoblasts dedifferentiate at and migrate towards both sites, while accumulation of osteogenic progenitor cells and regenerative bone formation only occur at the distal-facing injury. Together, these data indicate that osteoblast dedifferentiation and migration represent generic injury responses that are differentially regulated and can occur independently of each other and of regenerative growth. We conclude that successful fin bone regeneration appears to involve the coordinated execution of generic and regeneration-specific responses of osteoblasts to injury.

Mitochondrial damage-associated molecular patterns trigger arginase-dependent lymphocyte immunoregulation

Tissue damage leads to loss of cellular and mitochondrial membrane integrity and release of damage-associated molecular patterns, including those of mitochondrial origin (mitoDAMPs). Here, we describe the lymphocyte response to mitoDAMPs. Using primary cells from mice and human donors, we demonstrate that natural killer (NK) cells and T cells adopt regulatory phenotypes and functions in response to mitoDAMPs. NK cell-mediated cytotoxicity, interferon gamma (IFN-γ) production, T cell proliferation, and in vivo anti-viral T cell activation are all interrupted in the presence of mitoDAMPs or mitoDAMP-rich irradiated cells in in vitro and in vivo assays. Mass spectrometry analysis of mitoDAMPs demonstrates that arginase and products of its enzymatic activity are prevalent in mitoDAMP preparations. Functional validation by arginase inhibition and/or arginine add-back shows that arginine depletion is responsible for the alteration in immunologic polarity. We conclude that lymphocyte responses to mitoDAMPs reflect a highly conserved mechanism that regulates inflammation in response to tissue injury.

Development of Potent and Selective Agonists for Complement C5a Receptor 1 with In Vivo Activity

The anaphylatoxin C5a is a complement peptide associated with immune-related disorders. C5a binds with equal potency to two GPCRs, C5aR1 and C5aR2. Multiple C5a peptide agonists have been developed to interrogate the C5a receptor function but none show selectivity for C5aR1. To address these limitations, we developed potent and stable peptide C5aR1 agonists that display no C5aR2 activity and over 1000-fold selectivity for C5aR1 over C3aR. This includes BM213, which induces C5aR1-mediated calcium mobilization and pERK1/2 signaling but not β-arrestin recruitment, and BM221, which exhibits no signaling bias. Both ligands are functionally similar to C5a in human macrophage cytokine release assays and in a murine in vivo neutrophil mobilization assay. BM213 showed antitumor activity in a mouse model of mammary carcinoma. We anticipate that these C5aR1-selective agonists will be useful research tools to investigate C5aR1 function.

Optimisation of a Microfluidic Method for the Delivery of a Small Peptide

Peptides hold promise as therapeutics, as they have high bioactivity and specificity, good aqueous solubility, and low toxicity. However, they typically suffer from short circulation half-lives in the body. To address this issue, here, we have developed a method for encapsulation of an innate-immune targeted hexapeptide into nanoparticles using safe non-toxic FDA-approved materials. Peptide-loaded nanoparticles were formulated using a two-stage microfluidic chip. Microfluidic-related factors (i.e., flow rate, organic solvent, theoretical drug loading, PLGA type, and concentration) that may potentially influence the nanoparticle properties were systematically investigated using dynamic light scattering and transmission electron microscopy. The pharmacokinetic (PK) profile and biodistribution of the optimised nanoparticles were assessed in mice. Peptide-loaded lipid shell-PLGA core nanoparticles with designated size (~400 nm) and a sustained in vitro release profile were further characterized in vivo. In the form of nanoparticles, the elimination half-life of the encapsulated peptide was extended significantly compared with the peptide alone and resulted in a much higher distribution into the lung. These novel nanoparticles with lipid shells have considerable potential for increasing the circulation half-life and improving the biodistribution of therapeutic peptides to improve their clinical utility, including peptides aimed at treating lung-related diseases.

Tissue-Type Plasminogen Activator and Tenecteplase-Mediated Increase in Blood Brain Barrier Permeability Involves Cell Intrinsic Complement

Background: Tissue-type plasminogen activator (t-PA) has been the mainstay of therapeutic thrombolysis for patients with acute ischaemic stroke (AIS). However, t-PA can cause devastating intracerebral hemorrhage. t-PA can also influence the CNS in part by modulation of BBB permeability. Complement activation also occurs after AIS and has also been reported to increase BBB permeability. The complement components, C3 and C5, can also be activated by t-PA via plasmin formation and cell intrinsic complement may be involved in this process. Tenecteplase (TNK-tPA) is a t-PA variant with a longer plasma half-life, yet the ability of TNK-tPA to modulate the BBB and complement is less clear.

Aim: To evaluate the effect of C5 and C5a-receptor 1 (C5aR1) inhibitors on t-PA- and TNK-tPA-mediated opening of the BBB.

Methods: We used an in vitro model of the BBB where human brain endothelial cells and human astrocytes were co-cultured on the opposite sides of a porous membrane assembled in transwell inserts. The luminal (endothelial) compartment was stimulated with t-PA or TNK-tPA together with plasminogen, in the presence of PMX205 (a non-competitive C5aR1 antagonist), Avacopan (a competitive C5aR1 antagonist) or Eculizumab (a humanized monoclonal inhibitor of human C5). BBB permeability was assessed 5 and 24 h later. Immunofluorescence was also used to detect changes in C5 and C5aR1 expression in endothelial cells and astrocytes.

Results: PMX205, but not Avacopan or Eculizumab, blocked t-PA-mediated increase in BBB permeability at both the 5 and 24 h time points. PMX205 also blocked TNK-tPA-mediated increase in BBB permeability. Immunofluorescence analysis revealed intracellular staining of C5 in both cell types. C5aR1 expression was also detected on the cell surfaces and also located intracellularly in both cell types.

Conclusion: t-PA and TNK-tPA-mediated increase in BBB permeability involves C5aR1 receptor activation from cell-derived C5a. Selective inhibitors of C5aR1 may have therapeutic potential in AIS.

Arginase impedes the resolution of colitis by altering the microbiome and metabolome

Arginase 1 (Arg1), which converts l-arginine into ornithine and urea, exerts pleiotropic immunoregulatory effects. However, the function of Arg1 in inflammatory bowel disease (IBD) remains poorly characterized. Here, we found that Arg1 expression correlated with the degree of inflammation in intestinal tissues from IBD patients. In mice, Arg1 was upregulated in an IL-4/IL-13- and intestinal microbiota-dependent manner. Tie2-Cre Arg1fl/fl mice lacking Arg1 in hematopoietic and endothelial cells recovered faster from colitis than Arg1-expressing (Arg1fl/fl) littermates. This correlated with decreased vessel density, compositional changes in intestinal microbiota, diminished infiltration by myeloid cells, and an accumulation of intraluminal polyamines that promote epithelial healing. The proresolving effect of Arg1 deletion was reduced by an l-arginine-free diet, but rescued by simultaneous deletion of other l-arginine-metabolizing enzymes, such as Arg2 or Nos2, demonstrating that protection from colitis requires l-arginine. Fecal microbiota transfers from Tie2-Cre Arg1fl/fl mice into WT recipients ameliorated intestinal inflammation, while transfers from WT littermates into Arg1-deficient mice prevented an advanced recovery from colitis. Thus, an increased availability of l-arginine as well as altered intestinal microbiota and metabolic products accounts for the accelerated resolution from colitis in the absence of Arg1. Consequently, l-arginine metabolism may serve as a target for clinical intervention in IBD patients.

Pharmacological characterisation of small molecule C5aR1 inhibitors in human cells reveals biased activities for signalling and function

The complement fragment C5a is a core effector of complement activation. C5a, acting through its major receptor C5aR1, exerts powerful pro-inflammatory and immunomodulatory functions. Dysregulation of the C5a-C5aR1 axis has been implicated in numerous immune disorders, and the therapeutic inhibition of this axis is therefore imperative for the treatment of these diseases. A myriad of small-molecule C5aR1 inhibitors have been developed and independently characterised over the past two decades, however the pharmacological properties of these compounds has been difficult to directly compare due to the wide discrepancies in the model, read-out, ligand dose and instrumentation implemented across individual studies. Here, we performed a systematic characterisation of the most commonly reported and clinically advanced small-molecule C5aR1 inhibitors (peptidic: PMX53, PMX205 and JPE1375; non-peptide: W545011, NDT9513727, DF2593A and CCX168). Through signalling assays measuring C5aR1-mediated cAMP and ERK1/2 signalling, and β-arrestin 2 recruitment, this study highlighted the signalling-pathway dependence of the rank order of potencies of the C5aR1 inhibitors. Functional experiments performed in primary human macrophages demonstrated the high insurmountable antagonistic potencies for the peptidic inhibitors as compared to the non-peptide compounds. Finally, wash-out studies provided novel insights into the duration of inhibition of the C5aR1 inhibitors, and confirmed the long-lasting antagonistic properties of PMX53 and CCX168. Overall, this study revealed the potent and prolonged antagonistic activities of selected peptidic C5aR1 inhibitors and the unique pharmacological profile of CCX168, which thus represent ideal candidates to fulfil diverse C5aR1 research and clinical therapeutic needs.

Emerging Insights into the Structure and Function of Complement C5a Receptors

Complement factor C5a is an integral constituent of the complement cascade critically involved in the innate immune response, and it exerts its functions via two distinct receptors, C5aR1 and C5aR2. While C5aR1 is a prototypical G-protein-coupled receptor (GPCR), C5aR2 lacks functional coupling to heterotrimeric G proteins, although both receptors efficiently recruit β arrestins (βarrs). Here, we discuss the recent studies providing direct structural details of ligand-receptor interactions, and a framework of functional bias in this system, including the differences in terms of structural motifs and transducer coupling. We also discuss the functional analogy of C5aR2 with the atypical chemokine receptors (ACKRs), and highlight the future directions to elucidate the mechanistic basis of the functional divergence of these receptors activated by a common natural agonist.

Preclinical Pharmacokinetics of Complement C5a Receptor Antagonists PMX53 and PMX205 in Mice

The cyclic hexapeptides PMX53 and PMX205 are potent noncompetitive inhibitors of complement C5a receptor 1 (C5aR1). They are widely utilized to study the role of C5aR1 in mouse models, including central nervous system (CNS) disease, and are dosed through a variety of routes of administration. However, a comprehensive pharmacokinetics analysis of these drugs has not been reported. In this study, the blood and CNS pharmacokinetics of PMX53 and PMX205 were performed in mice following intravenous, intraperitoneal, subcutaneous, and oral administration at identical doses. The absorption and distribution of both drugs were rapid and followed a two-compartment model with elimination half-lives of ∼20 min for both compounds. Urinary excretion was the major route of elimination following intravenous dosing with ∼50% of the drug excreted unchanged within the first 12 h. Oral bioavailability of PMX205 was higher than that of PMX53 (23% versus 9%), and PMX205 was also more efficient than PMX53 at entering the intact CNS. In comparison to other routes, subcutaneous administration of PMX205 resulted in high bioavailability (above 90%), as well as prolonged plasma and CNS exposure. Finally, repeated daily oral or subcutaneous administration of PMX205 demonstrated no accumulation of drug in blood, the brain, or the spinal cord, promoting its safety for chronic dosing. These results will be helpful in correlating the desired therapeutic effects of these C5aR1 antagonists with their pharmacokinetic profile. It also suggests that subcutaneous dosing of PMX205 may be an appropriate route of administration for future clinical testing in neurological disease.

Complement alone drives efficacy of a chimeric antigonococcal monoclonal antibody

Multidrug-resistant Neisseria gonorrhoeae is a global health problem. Monoclonal antibody (mAb) 2C7 recognizes a gonococcal lipooligosaccharide epitope that is expressed by >95% of clinical isolates and hastens gonococcal vaginal clearance in mice. Chimeric mAb 2C7 (human immunoglobulin G1 [IgG1]) with an E430G Fc modification that enhances Fc:Fc interactions and hexamerization following surface-target binding and increases complement activation (HexaBody technology) showed significantly greater C1q engagement and C4 and C3 deposition compared to mAb 2C7 with wild-type Fc. Greater complement activation by 2C7-E430G Fc translated to increased bactericidal activity in vitro and, consequently, enhanced efficacy in mice, compared with “Fc-unmodified” chimeric 2C7. Gonococci bind the complement inhibitors factor H (FH) and C4b-binding protein (C4BP) in a human-specific manner, which dampens antibody (Ab)-mediated complement-dependent killing. The variant 2C7-E430G Fc overcame the barrier posed by these inhibitors in human FH/C4BP transgenic mice, for which a single 1 μg intravenous dose cleared established infection. Chlamydia frequently coexists with and exacerbates gonorrhea; 2C7-E430G Fc also proved effective against gonorrhea in gonorrhea/chlamydia-coinfected mice. Complement activation alone was necessary and sufficient for 2C7 function, evidenced by the fact that (1) “complement-inactive” Fc modifications that engaged Fc gamma receptor (FcγR) rendered 2C7 ineffective, nonetheless; (2) 2C7 was nonfunctional in C1q^−/− mice, when C5 function was blocked, or in C9^−/− mice; and (3) 2C7 remained effective in neutrophil-depleted mice and in mice treated with PMX205, a C5a receptor (C5aR1) inhibitor. We highlight the importance of complement activation for antigonococcal Ab function in the genital tract. Elucidating the correlates of protection against gonorrhea will inform the development of Ab-based gonococcal vaccines and immunotherapeutics.

A chimeric antibody that contains a "complement-enhancing" mutation in Fc (so-called HexaBody technology) shows increased bactericidal activity compared to antibody bearing wild-type Fc and may represent a promising immunotherapeutic approach against multidrug-resistant gonorrhea.

Running promotes chronicity of arthritis by local modulation of complement activators and impairing T regulatory feedback loops

OBJECTIVES

The mechanisms driving onset of joint inflammation in arthritides such as rheumatoid arthritis and spondyloarthritis and the conversion to disease chronicity are poorly understood. We hypothesised mechanostrain could play an instrumental role herein by engaging local and/or systemic pathways, thereby attenuating disease course and outcome.

METHODS

The development of collagen antibody-induced arthritis (CAIA) in C57BL/6 mice was evaluated both clinically and histologically under different loading regimens: control, voluntary running or hindpaw unloading. Bone surface porosity was quantified by high-resolution µ-CT. Gene expression analyses were conducted by microarrays and qPCR on microdissected entheses, murine and human synovial tissues (both normal and inflamed). Serum cytokines and chemokines were measured by ELISA. The influence of complement activation and T regulatory (Treg) cell function on the induction and resolution phase of disease was studied by respectively pharmacological modulation and conditional Treg depletion.

RESULTS

Voluntary running strongly impacts the course of arthritis by impairing the resolution phase of CAIA, leading to more persistent inflammation and bone surface porosity. Mechanical strain induced local complement activation, increased danger-associated molecular pattern expression, activating Fcγ receptors as well as changes in fibroblast phenotype. Interestingly, complement C5a receptor blockade inhibited the enhanced joint pathology caused by voluntary running. Moreover, Treg depletion led to a loss of disease resolution in CAIA mice, which was not observed under voluntary running conditions.

CONCLUSIONS

Running promotes onset and chronicity of arthritis by local upregulation of complement activators and hampering regulatory T cell feedback loops.

C5a anaphylatoxin and its role in critical illness-induced organ dysfunction

Critical illness is an aetiologically and clinically heterogeneous syndrome that is characterised by organ failure and immune dysfunction. Mortality in critically ill patients is driven by inflammation-associated organ damage and a profound vulnerability to nosocomial infection. Both factors are influenced by the activated complement protein C5a, released by unbridled activation of the complement system during critical illness. C5a exerts deleterious effects on organ systems directly and suppresses antimicrobial functions of key immune cells. Whilst several recent reports have added key knowledge of the cellular signalling pathways triggered by C5a, there remain a number of areas that are incompletely understood and therapeutic opportunities are still being evaluated. In this review, we summarise the cellular basis for C5a-induced vulnerability to nosocomial infection and organ dysfunction. We focus on cells of the innate immune system, highlighting the major areas in need of further research and potential avenues for targeted therapies.

The anaphylatoxin C3a primes model colonic epithelial cells for expression of inflammatory mediators through Gαi

Multiple studies have identified that complement becomes activated during inflammation of the intestines yet it is unclear what roles the split complement molecules play. The epithelium, in particular, may be impacted and accordingly, we first discovered that colonic cell lines indeed possess the C5aR. Here we examined whether these cells also possess the C3aR. We determined that T84, HT-29 and Caco2 all possess C3aR mRNA and protein; T84 and HT29 were used to further explore the consequence of C3a binding the C3aR. C3a led to increased mRNA for CXCL2, CXCL8 and CXCL11. Polarized T84 monolayers responded to apically applied C3a with increased CXCL8 mRNA more rapidly than if the C3a was applied basolaterally. Polarized monolayers also increased permeability when treated with C3a. ERK1/2 was activated by C3a and the increase in CXCL8 mRNA was ERK-dependent in both T84 and HT-29. C3a resulted in activation of Gαi, determined by the ERK1/2 signal showing sensitivity to pertussis toxin. The transmembrane signal was further mapped to include Ras and c-Raf. Finally, we show that the C3aR is expressed by primary cells in mouse enteroids. We conclude that complement activation will contribute to the epithelial response during inflammation through C3a binding to the C3aR including by priming the cells to upregulate mRNA for selected chemokines.

The critical role of C5a as an initiator of neutrophil-mediated autoimmune inflammation of the joint and skin

The deposition of IgG autoantibodies in peripheral tissues and the subsequent activation of the complement system, which leads to the accumulation of the anaphylatoxin C5a in these tissues, is a common hallmark of diverse autoimmune diseases, including rheumatoid arthritis (RA) and pemphigoid diseases (PDs). C5a is a potent chemoattractant for granulocytes and mice deficient in its precursor C5 or its receptor C5aR1 are resistant to granulocyte recruitment and, consequently, to tissue inflammation in several models of autoimmune diseases. However, the mechanism whereby C5a/C5aR regulates granulocyte recruitment in these diseases has remained elusive. Mechanistic studies over the past five years into the role of C5a/C5aR1 in the K/BxN serum arthritis mouse model have provided novel insights into the mechanisms C5a/C5aR1 engages to initiate granulocyte recruitment into the joint. It is now established that the critical actions of C5a/C5aR1 do not proceed in the joint itself, but on the luminal endothelial surface of the joint vasculature, where C5a/C5aR1 mediate the arrest of neutrophils on the endothelium by activating β₂ integrin. Then, C5a/C5aR1 induces the release of leukotriene B₄ (LTB₄) from the arrested neutrophils. The latter, subsequently, initiates by autocrine/paracrine actions via its receptor BLT1 the egress of neutrophils from the blood vessel lumen into the interstitial. Compelling evidence suggests that this C5a/C5aR1-LTB₄/BLT1 axis driving granulocyte recruitment in arthritis may represent a more generalizable biological principle critically regulating effector cell recruitment in other IgG autoantibody-induced diseases, such as in pemphigoid diseases. Thus, dual inhibition of C5a and LTB₄, as implemented in nature by the lipocalin coversin in the soft-tick Ornithodoros moubata, may constitute a most effective therapeutic principle for the treatment of IgG autoantibody-driven diseases.

The intestinal complement system in inflammatory bowel disease: Shaping intestinal barrier function

The complement system is part of innate sensor and effector systems such as the Toll-like receptors (TLRs). It recognizes and quickly systemically and/or locally respond to microbial-associated molecular patterns (MAMPs) with a tailored defense reaction. MAMP recognition by intestinal epithelial cells (IECs) and appropriate immune responses are of major importance for the maintenance of intestinal barrier function. Enterocytes highly express various complement components that are suggested to be pivotal for proper IEC function. Appropriate activation of the intestinal complement system seems to play an important role in the resolution of chronic intestinal inflammation, while over-activation and/or dysregulation may worsen intestinal inflammation. Mice deficient for single complement components suffer from enhanced intestinal inflammation mimicking the phenotype of patients with chronic inflammatory bowel disease (IBD) such as Crohn's disease (CD) or ulcerative colitis (UC). However, the mechanisms leading to complement expression in IECs seem to differ markedly between UC and CD patients. Hence, how IECs, intestinal bacteria and epithelial cell expressed complement components interact in the course of IBD still remains to be mostly elucidated to define potential unique patterns contributing to the distinct subtypes of intestinal inflammation observed in CD and UC.

Complement C5a Receptor 1 Exacerbates the Pathophysiology of N. meningitidis Sepsis and Is a Potential Target for Disease Treatment

Sepsis caused by Neisseria meningitidis (meningococcus) is a rapidly progressing, life-threatening disease. Because its initial symptoms are rather unspecific, medical attention is often sought too late, i.e., when the systemic inflammatory response is already unleashed. This in turn limits the success of antibiotic treatment. The complement system is generally accepted as the most important innate immune determinant against invasive meningococcal disease since it protects the host through the bactericidal membrane attack complex. However, complement activation concomitantly liberates the C5a peptide, and it remains unclear whether this potent anaphylatoxin contributes to protection and/or drives the rapidly progressing immunopathogenesis associated with meningococcal disease. Here, we dissected the specific contribution of C5a receptor 1 (C5aR1), the canonical receptor for C5a, using a mouse model of meningococcal sepsis. Mice lacking C3 or C5 displayed susceptibility that was enhanced by >1,000-fold or 100-fold, respectively, consistent with the contribution of these components to protection. In clear contrast, C5ar1^−/− mice resisted invasive meningococcal infection and cleared N. meningitidis more rapidly than wild-type (WT) animals. This favorable outcome stemmed from an ameliorated inflammatory cytokine response to N. meningitidis in C5ar1^−/− mice in both in vivo and ex vivo whole-blood infections. In addition, inhibition of C5aR1 signaling without interference with the complement bactericidal activity reduced the inflammatory response also in human whole blood. Enticingly, pharmacologic C5aR1 blockade enhanced mouse survival and lowered meningococcal burden even when the treatment was administered after sepsis induction. Together, our findings demonstrate that C5aR1 drives the pathophysiology associated with meningococcal sepsis and provides a promising target for adjunctive therapy.

The devastating consequences of N. meningitidis sepsis arise due to the rapidly arising and self-propagating inflammatory response that mobilizes antibacterial defenses but also drives the immunopathology associated with meningococcemia. The complement cascade provides innate broad-spectrum protection against infection by directly damaging the envelope of pathogenic microbes through the membrane attack complex and triggers an inflammatory response via the C5a peptide and its receptor C5aR1 aimed at mobilizing cellular effectors of immunity. Here, we consider the potential of separating the bactericidal activities of the complement cascade from its immune activating function to improve outcome of N. meningitidis sepsis. Our findings demonstrate that the specific genetic or pharmacological disruption of C5aR1 rapidly ameliorates disease by suppressing the pathogenic inflammatory response and, surprisingly, allows faster clearance of the bacterial infection. This outcome provides a clear demonstration of the therapeutic benefit of the use of C5aR1-specific inhibitors to improve the outcome of invasive meningococcal disease.

Complement Receptor C5aR1 Plays an Evolutionarily Conserved Role in Successful Cardiac Regeneration

BACKGROUND

Defining conserved molecular pathways in animal models of successful cardiac regeneration could yield insight into why adult mammals have inadequate cardiac regeneration after injury. Insight into the transcriptomic landscape of early cardiac regeneration from model organisms will shed light on evolutionarily conserved pathways in successful cardiac regeneration.

METHODS

Here we describe a cross-species transcriptomic screen in 3 model organisms for cardiac regeneration: axolotl, neonatal mice, and zebrafish. Apical resection to remove ≈10% to 20% of ventricular mass was carried out in these model organisms. RNA-sequencing analysis was performed on the hearts harvested at 3 time points: 12, 24, and 48 hours after resection. Sham surgery was used as internal control.

RESULTS

Genes associated with inflammatory processes were found to be upregulated in a conserved manner. Complement receptors (activated by complement components, part of the innate immune system) were found to be highly upregulated in all 3 species. This approach revealed induction of gene expression for complement 5a receptor 1 in the regenerating hearts of zebrafish, axolotls, and mice. Inhibition of complement 5a receptor 1 significantly attenuated the cardiomyocyte proliferative response to heart injury in all 3 species. Furthermore, after left ventricular apical resection, the cardiomyocyte proliferative response was diminished in mice with genetic deletion of complement 5a receptor 1.

CONCLUSIONS

These data reveal that activation of complement 5a receptor 1 mediates an evolutionarily conserved response that promotes cardiomyocyte proliferation after cardiac injury and identify complement pathway activation as a common pathway of successful heart regeneration.

Pharmacological inhibition of complement C5a-C5a1 receptor signalling ameliorates disease pathology in the hSOD1G93A mouse model of amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE

Amyotrophic lateral sclerosis (ALS) is a fatal and rapidly progressing motor neuron disease without effective treatment. The complement system is up-regulated in ALS, with recent studies indicating that the activation product C5a accelerates disease progression via the C5a₁ receptor (C5aR1). We therefore examined the therapeutic effect of C5a₁ receptor antagonism in hSOD1^G93A mice, the most widely used preclinical model of ALS.

EXPERIMENTAL APPROACH

The selective and orally active C5a₁ receptor antagonist, PMX205, was administered to hSOD1^G93A mice in drinking water, both pre- and post-disease onset. Blood, brain and spinal cord pharmacokinetics were performed using LC-MS/MS methods. Effects of PMX205 on hSOD1^G93A disease progression was determined using body weight, hindlimb grip strength, survival time and blood analysis.

KEY RESULTS

PMX205 entered the intact CNS at pharmacologically active concentrations, with increased entry observed in hSOD1^G93A mice as the disease progressed, in line with augmented blood-brain barrier breakdown. hSOD1^G93A mice treated with PMX205 before disease onset had significantly improved hindlimb grip strength, slower disease progression and extended survival, compared with vehicle treatment. These improvements were associated with reductions in pro-inflammatory monocytes and granulocytes and increases in T-helper lymphocytes in peripheral blood. PMX205 treatment beginning 3 weeks following disease onset also attenuated disease progression, significantly extending survival.

CONCLUSION AND IMPLICATIONS

These results confirm that C5a₁ receptors play a pathogenic role in hSOD1^G93A mice, further validating the C5a-C5a₁ receptor signalling axis as a potential therapeutic target to slow disease progression in ALS.

Properdin deficiency protects from 5-fluorouracil-induced small intestinal mucositis in a complement activation-independent, interleukin-10-dependent mechanism

Intestinal mucositis is a serious complication of chemotherapy that leads to significant morbidity that may require dose or drug adjustments. Specific mitigating strategies for mucositis are unavailable, due partly to an incomplete understanding of the pathogenic mechanisms. We have previously shown an effect of properdin, a positive regulator of complement activation, in models of colitis. Here we use properdin-deficient (P^KO ) mice to interrogate the role of properdin and complement in small intestinal mucositis. Mucositis was induced by five daily injections of 5-fluorouracil (5-FU) in wild-type (WT), P^KO , interleukin (IL)-10^-/- and properdin/IL-10^-/- double knock-out (DKO) mice. At the time of euthanasia their jejunum was collected for histology, immunohistochemistry and cytokine and complement activation measurements. Complement became activated in mice receiving 5-FU, indicated by increased intestinal levels of C3a and C5a. Compared to WT, P^KO mice experienced significantly less mucositis, despite C3a levels as high as inflamed WT mice and slightly less C5a. Conversely, P^KO mice had higher intestinal levels of IL-10. IL-10 expression was mainly by epithelial cells in both uninflamed and inflamed P^KO mice. IL-10^-/- mice proved to be highly susceptible to mucositis and DKO mice were equally susceptible, demonstrating that a lack of properdin does not protect mice lacking IL-10. We interpret our findings to indicate that, to a significant extent, the inflammation of mucositis is properdin-dependent but complement activation-independent. Additionally, the benefit achieved in the absence of properdin is associated with increased IL-10 levels, and IL-10 is important in limiting mucositis.

Netrin-1 Reduces Monocyte and Macrophage Chemotaxis towards the Complement Component C5a

Netrin-1, acting at its cognate receptor UNC5b, has been previously demonstrated to inhibit CC chemokine-induced immune cell migration. In line with this, we found that netrin-1 was able to inhibit CCL2-induced migration of bone marrow derived macrophages (BMDMs). However, whether netrin-1 is capable of inhibiting chemotaxis to a broader range of chemoattractants remains largely unexplored. As our initial experiments demonstrated that RAW264.7 and BMDMs expressed high levels of C5a receptor 1 (C5aR1) on their surface, we aimed to determine the effect of netrin-1 exposure on monocyte/macrophage cell migration induced by C5a, a complement peptide that plays a major role in multiple inflammatory pathologies. Treatment of RAW264.7 macrophages, BMDMs and human monocytes with netrin-1 inhibited their chemotaxis towards C5a, as measured using two different real-time methods. This inhibitory effect was found to be dependent on netrin-1 receptor signalling, as an UNC5b blocking antibody was able to reverse netrin-1 inhibition of C5a induced BMDM migration. Treatment of BMDMs with netrin-1 had no effect on C5aR1 proximal signalling events, as surface C5aR1 expression, internalisation and intracellular Ca²⁺ release following C5aR1 ligation remained unaffected after netrin-1 exposure. We next examined receptor distal events that occur following C5aR1 activation, but found that netrin-1 was unable to inhibit C5a induced phosphorylation of ERK1/2, Akt and p38, pathways important for cellular migration. Furthermore, netrin-1 treatment had no effect on BMDM cytoskeletal rearrangement following C5a stimulation as determined by microscopy and real-time electrical impedance sensing. Taken together these data highlight that netrin-1 inhibits monocyte and macrophage cell migration, but that the mechanism behind this effect remains unresolved. Nevertheless, netrin-1 and its cognate receptors warrant further investigation as they may represent a potential avenue for the development of novel anti-inflammatory therapeutics.

CYP4F18-Deficient Neutrophils Exhibit Increased Chemotaxis to Complement Component C5a

CYP4Fs were first identified as enzymes that catalyze hydroxylation of leukotriene B4 (LTB4). CYP4F18 has an unusual expression in neutrophils and was predicted to play a role in regulating LTB4-dependent inflammation. We compared chemotaxis of wild-type and Cyp4f18 knockout neutrophils using an in vitro assay. There was no significant difference in the chemotactic response to LTB4, but the response to complement component C5a increased 1.9-2.25-fold in knockout cells compared to wild-type (P < 0.01). This increase was still observed when neutrophils were treated with inhibitors of eicosanoid synthesis. There were no changes in expression of other CYP4 enzymes in knockout neutrophils that might compensate for loss of CYP4F18 or lead to differences in activity. A mouse model of dextran sodium sulfate colitis was used to investigate the consequences of increased C5a-dependent chemotaxis in vivo, but there was no significant difference in weight loss, disease activity, or colonic tissue myeloperoxidase between wild-type and Cyp4f18 knockout mice. This study demonstrates the limitations of inferring CYP4F function based on an ability to use LTB4 as a substrate, points to expanding roles for CYP4F enzymes in immune regulation, and underscores the in vivo challenges of CYP knockout studies.

Local chemerin levels are positively associated with DSS-induced colitis but constitutive loss of CMKLR1 does not protect against development of colitis

Inflammatory bowel disease (IBD) is a family of disorders including ulcerative colitis and Crohn's disease that are characterized by chronic and relapsing intestinal inflammation. Increased production of proinflammatory mediators, possibly combined with low expression of anti-inflammatory mediators, is thought to promote the development and progression of IBD. In the current study, we demonstrate that expression, secretion, and processing of chemerin, a potent chemoattractant for cells expressing chemokine-like receptor 1 (CMKLR1), increased in the cecum and colon along a gradient positively associated with the severity of inflammation in dextran sodium sulfate (DSS)-induced colitis. We also show that levels of circulating bioactive chemerin increased following DSS treatment. At both 6-8 and 14-16 weeks of age, CMKLR1 knockout mice developed signs of clinical illness more slowly than wild type and had changes in circulating cytokine levels, increased spleen weight, and increased local chemerin secretion following DSS treatment. However, knockout mice ultimately developed similar levels of clinical illness and local inflammation as wild type. Finally, contrary to previous reports, intraperitoneal injection of bioactive chemerin had no effect on the severity of DSS-induced colitis. This suggests that local chemerin levels have a greater impact than circulating levels in the pathogenesis of colitis. Considered altogether, bioactive chemerin represents a novel biomarker for IBD severity, although strategies to modulate endogenous chemerin signaling other than chronic CMKLR1 loss are necessary in order to exploit chemerin as a therapeutic target for the treatment of IBD.

Properdin Regulation of Complement Activation Affects Colitis in Interleukin 10 Gene-Deficient Mice

BACKGROUND

Interleukin 10-deficient mice (IL-10(-/-)) are a popular model used to dissect the mechanisms underlying inflammatory bowel diseases. The role of complement, a host defense mechanism that bridges the innate and adaptive immune systems, has not been described in this model. We therefore studied the effect of deficiency of properdin, a positive regulator of complement, on colitis in mice with the IL-10(-/-) background.

METHODS

For acute colitis, IL-10(-/-) and IL-10/properdin double knockout (DKO) or radiation bone marrow-reconstituted chimeric mice, had piroxicam added to their powdered chow for 14 days. For chronic colitis, 2.5% dextran sodium sulfate was added to the animals' water for 4 days then the mice were killed 8 weeks later. Colons were assessed for inflammation, cell infiltration, and cytokine and complement measurements. Bacterial translocation was measured by cultivating bacteria from organs on Luria broth agar plates.

RESULTS

C3a and C5a levels and C9 deposition were all increased in piroxicam-fed IL-10(-/-) mice compared with mice not fed piroxicam. Piroxicam-fed DKO mice lacked increased C5a and C9 deposition combined with exacerbated colitis, reduced numbers of infiltrating neutrophils, and markedly higher local and systemic bacterial numbers compared with IL-10(-/-) mice. Bone marrow cells from IL-10(-/-) mice were sufficient to restore protection against the heightened colitis in piroxicam-fed DKO mice.

CONCLUSIONS

Complement is activated in the IL-10(-/-) mouse mucosa in a properdin-dependent manner. In the absence of terminal complement activation, the inflammation is heightened, likely due to a lack of neutrophil control over microbes escaping from the intestines.

Atypical Hemolytic Uremic Syndrome and Chronic Ulcerative Colitis Treated with Eculizumab

Background

Hemolytic-uremic syndrome (HUS) presents with hemolytic anemia, thrombocytopenia, and thrombotic microangiopathy of the kidney and usually results from Shiga-toxin induced activation of the alternative complement pathway. Gastroenteritis is a common feature of the Shiga-toxin producing Escherichia coli HUS, referred to as STEC-HUS. An inherited or acquired complement dysregulation may lead to HUS referred to as non-STEC or atypical (a)HUS. Although gastroenteritis is not a common presentation of aHUS, some patients develop ischemic colitis and may be misdiagnosed as acute appendicitis or acute ulcerative colitis (UC).

Case Diagnosis –Treatment

We present a patient with low circulating complement (C) 3 levels who developed aHUS in the course of chronic active UC. Resolution of renal and gastrointestinal manifestations in response to treatment with eculizumab, a humanized monoclonal antibody against terminal C5 protein suggests the role of alternative complement in the pathogenesis of both, aHUS and UC.

Conclusion

This case illustrates that dysregulation of the alternative complement pathway may manifest in other organs besides the kidney and that the circulating C3 levels do not correlate with the disease activity or the clinical response to eculizumab.

Regulation of the alternative pathway of complement modulates injury and immunity in a chronic model of dextran sulphate sodium-induced colitis

The role of complement in inflammatory bowel disease (IBD) has been studied primarily using acute models, and it is unclear how complement affects processes in more relevant chronic models of IBD in which modulation of adaptive immunity and development of fibrosis have pathogenic roles. Using mice deficient in C1q/mannose-binding lectin (MBL) or C3, we demonstrated an important role for these opsonins and/or the classical pathway C3 convertase in providing protection against mucosal injury and infection in a model of chronic dextran sulphate sodium (DSS)-induced colitis. In contrast, deficiency of the alternative pathway (fB(-/-) mice) had significantly less impact on injury profiles. Consequently, the effect of a targeted inhibitor of the alternative pathway was investigated in a therapeutic protocol. Following the establishment of colitis, mice were treated with CR2-fH during subsequent periods of DSS treatment and acute injury (modelling relapse). CR2-fH significantly reduced complement activation, inflammation and injury in the colon, and additionally reduced fibrosis. Alternative pathway inhibition also altered the immune response in the chronic state in terms of reducing numbers of B cells, macrophages and mature dendritic cells in the lamina propria. This study indicates an important role for the alternative pathway of complement in the pathogenesis and the shaping of an immune response in chronic DSS-induced colitis, and supports further investigation into the use of targeted alternative pathway inhibition for the treatment of IBD.

Properdin provides protection from Citrobacter rodentium-induced intestinal inflammation in a C5a/IL-6-dependent manner

Citrobacter rodentium is an attaching and effacing mouse pathogen that models enteropathogenic and enterohemorrhagic Escherichia coli in humans. The complement system is an important innate defense mechanism; however, only scant information is available about the role of complement proteins during enteric infections. In this study, we examined the impact of the lack of properdin, a positive regulator of complement, in C. rodentium-induced colitis. Following infection, properdin knockout (P(KO)) mice had increased diarrhea and exacerbated inflammation combined with defective epithelial cell-derived IL-6 and greater numbers of colonizing bacteria. The defect in the mucosal response was reversed by administering exogenous properdin to P(KO) mice. Then, using in vitro and in vivo approaches, we show that the mechanism behind the exacerbated inflammation of P(KO) mice is due to a failure to increase local C5a levels. We show that C5a directly stimulates IL-6 production from colonic epithelial cells and that inhibiting C5a in infected wild-type mice resulted in defective epithelial IL-6 production and exacerbated inflammation. These outcomes position properdin early in the response to an infectious challenge in the colon, leading to complement activation and C5a, which in turn provides protection through IL-6 expression by the epithelium. Our results unveil a previously unappreciated mechanism of intestinal homeostasis involving complement, C5a, and IL-6 during bacteria-triggered epithelial injury.

Therapeutic C3 inhibitor Cp40 abrogates complement activation induced by modern hemodialysis filters

Approximately 350,000 individuals in the United States rely on maintenance hemodialysis treatment because of end-stage renal disease. Despite improvements in dialysis technology, the mortality rate for patients treated with maintenance dialysis is still exceptionally high, with a 5-year survival rate of only 35%. Many patients succumb to conditions resulting at least in part from the chronic induction of inflammation. Among the triggers of inflammation, the complement system is of particular importance, being a well-appreciated mediator of inflammatory processes that is involved in many pathologic states. Here we used a refined pre-clinical model of hemodialysis in cynomolgus monkeys to confirm that even modern, polymer-based hemodialysis filters activate complement and to evaluate the potential of Cp40, a peptidic C3 inhibitor, to attenuate hemodialysis-induced complement activation. Our data show marked induction of complement activation even after only a single session of hemodialysis. Importantly, complete inhibition of complement activation was achieved in response to two distinct Cp40 treatment regimens. Further, we show that application of Cp40 during hemodialysis resulted in increased levels of the anti-inflammatory cytokine IL-10, indicating that Cp40 may be a potent and cost-effective treatment option for attenuating chronic inflammatory conditions in dialysis-dependent patients.

The complement system in inflammatory bowel disease

Complement is well appreciated to be a potent innate immune defense against microbes and is important in the housekeeping act of removal of apoptotic and effete cells. It is also understood that hyperactivation of complement, or the lack of regulators, may underlie chronic inflammatory diseases. A pipeline of products to intervene in complement activation, some already in clinical use, is being studied in various chronic inflammatory diseases. To date, the role of complement in inflammatory bowel disease has not received a lot of research interest. Novel genetically modified laboratory animals and experiments using antagonists to complement effector molecules have kindled important research observations implicating the complement system in inflammatory bowel disease pathogenesis. We review the evidence base for the role and potential therapeutic manipulation of the complement cascade in inflammatory bowel disease.

Regenerative medicine: prospects for the treatment of inflammatory bowel disease

This article reviews the current understanding of the processes driving the development and progression of inflammatory bowel disease (IBD), discusses how the dynamic crosstalk between resident microorganisms, host cells and the immune system is required in order to maintain immune homeostasis, and considers innovative strategies that allow the modification or modulation of the intestinal microorganismal community as a potential approach for treating IBD. This article next rationalizes the use of cell-based regenerative medicine as treatment for IBD, discusses the obstacles hindering its success, summarizes some of the results of recent clinical trials employing these therapies, and discusses ongoing work to enhance mesenchymal stem/stromal cells, making them better suited to the task of repairing the damage within the IBD gut.

Mucosal toll-like receptor 3-dependent synthesis of complement factor B and systemic complement activation in inflammatory bowel disease

BACKGROUND

Recent studies link Toll-like receptor 3 (TLR3) to the pathogenesis of inflammatory bowel disease (IBD). Screening TLR3-agonist response in an intestinal epithelial cell line, we found complement factor B mRNA (CFB) potently upregulated and went on to further study localization of complement factor B synthesis and systemic activation of complement in ulcerative colitis and Crohn's disease.

METHODS

In a transcriptome analysis of poly (I:C) stimulated HT-29 cells, we found CFB highly upregulated downstream of TLR3. We sought to confirm CFB upregulation in a microarray gene expression analysis on colonic biopsies from an IBD population (n = 133). Immunohistochemical staining and in situ hybridization were done to identify cellular sources of factor B and CFB. Systemic complement activation was assessed in plasma (n = 18) using neoepitope-based enzyme linked immunosorbent assay.

RESULTS

CFB mRNA and protein were abundantly expressed in the colonic epithelial cell line, and synthesis enhanced by the poly (I:C) TLR3 ligand. In inflamed versus normal colonic mucosa of ulcerative colitis and Crohn's disease, CFB mRNA was the most significantly overexpressed gene and the mRNA abundance ratio was among the 50 highest. Epithelial cells were the dominating site of factor B expression. Systemic complement activation was significantly higher in active than in nonactive IBD.

CONCLUSIONS

This study is the first to link TLR3 to activation of the alternative complement pathway. Complement factor B is potently upregulated locally in IBD in addition to having a possible central role in systemic complement activation. This suggests a prominent role for complement in IBD pathogenesis.

Treatment with the C5a receptor/CD88 antagonist PMX205 reduces inflammation in a murine model of allergic asthma

Allergic asthma is a chronic inflammatory airway disease arising from an aberrant immune response following exposure to environmental stimuli in genetically susceptible persons. The complement component 5 (C5)/C5a Receptor (C5aR/CD88) signaling pathway has been implicated in both experimental allergic asthma and human asthmatic disease. Targeting the C5a/C5aR signaling pathway in rodent models has been shown to either enhance or reduce allergic asthma consequences. Treatment with a recombinant humanized monoclonal antibody directed against C5 has shown unclear results in patients with asthma. The objective of this proof-of-concept animal study was to determine whether the low molecular weight C5aR peptidomimetic antagonist, PMX205, would reduce experimental allergic asthma consequences in mice. PMX205 or vehicle control was administered subcutaneously to BALB/c mice prior to and during standard ovalbumin (OVA) allergen sensitization and aerosolized challenge phases. PMX205 substantially reduced OVA-induced total cell (60%), neutrophil (66%) and eosinophil (65%) influxes in lavage fluid sampling. There were also significant reductions in OVA-induced lavage fluid IL-13 protein and lung Th2 cytokine gene expression with PMX205 administration. PMX205 treatment also diminished OVA-induced lung parenchyma cellular infiltration. PMX205 administration did not reduce OVA-induced serum IgE levels or epithelial mucous/goblet cell generation. There was no evidence of toxicity observed with PMX205 treatment in saline or OVA-challenged animals. These data provide evidence that pharmacologic blockade of C5aR by a low molecular weight antagonist (PMX205) reduces airway inflammatory cell and cytokine responses in experimental allergic asthma, and suggests that PMX205 might represent a novel therapeutic agent for reducing asthmatic outcomes.

Complement in immune and inflammatory disorders: therapeutic interventions

With the awareness that immune-inflammatory cross-talk is at the heart of many disorders, the desire for novel immunomodulatory strategies in the therapy of such diseases has grown dramatically. As a prime initiator and important modulator of immunological and inflammatory processes, the complement system has emerged as an attractive target for early and upstream intervention in inflammatory diseases and has moved into the spotlight of drug discovery. Although prevalent conditions such as age-related macular degeneration have attracted the most attention, the diverse array of complement-mediated pathologies, with distinct underlying mechanisms, demands a multifaceted arsenal of therapeutic strategies. Fortunately, efforts in recent years have not only introduced the first complement inhibitors to the clinic but also filled the pipelines with promising candidates. With a focus on immunomodulatory strategies, in this review we discuss complement-directed therapeutic concepts and highlight promising candidate molecules.