Dynamic control of the complement system by modulated expression of regulatory proteins

Filtration and tubular handling of EWE-hC3Nb1, a complement inhibitor nanobody, in wild type mice and a mouse model of proteinuric kidney disease

Tubular activation and deposition of filtered complement proteins have been implicated in the progression of proteinuric kidney disease. The potent C3b-specific nanobody inhibitor of the alternative pathway, EWE-hC3Nb1, is likely freely filtered in the glomerulus to allow complement inhibition in the tubular lumen and may provide a novel treatment option to prevent tubulointerstitial injury. However, more information on the pharmacokinetic properties and renal tubular handling of EWE-hC3Nb1 nanobody is required for its pharmacological application in relation to kidney disease. Here, we examined the pharmacokinetic properties of free EWE-hC3Nb1 in mouse plasma and urine, following subcutaneous injection in wild-type control and podocin knock out (KO) mice with severe proteinuria. Tubular handling of filtered EWE-hC3Nb1 was assessed by immunohistochemistry (IHC) on kidney tissue from control, proteinuric mice, and KO mice deficient in the proximal tubule endocytic receptor megalin. Rapid plasma absorption and elimination of EWE-hC3Nb1 was observed in both control and proteinuric mice; however, urinary excretion of EWE-hC3Nb1 was markedly increased in proteinuric mice. Urinary EWE-hC3Nb1 excretion was amplified in megalin KO mice, and substantial accumulation of EWE-hC3Nb1 was observed in megalin-expressing renal proximal tubules by IHC. Moreover, free EWE-hC3Nb1 was found to be rapidly cleared from plasma. In conclusion, filtered EWE-hC3Nb1 is reabsorbed by a megalin-dependent process in the proximal tubules. Increased load of filtered proteins in the tubular fluid may inhibit the megalin-dependent uptake of EWE-hC3Nb1 in proteinuric mice. Treatment with EWE-hC3Nb1 may allow investigation of the effects of complement inhibition in the tubular fluid.

Pharmacological and clinical profile of ravulizumab 100 mg/mL formulation for paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome

INTRODUCTION

Paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS) are two rare and severe conditions caused by chronic complement (C') system dysregulation. Treatment with eculizumab, a recombinant, humanized monoclonal antibody against complement C5, changed the natural history of both diseases inducing remission and improving patient outcome. Ravulizumab, a new long-acting next-generation C5 inhibitor has been recently approved for treatment of PNH and aHUS.

AREAS COVERED

Main characteristics of ravulizumab are described: composition, dosing, efficacy and safety profile. Further, an overview of seminal studies and clinical trials using ravulizumab to treat PNH and aHUS in children and adults is detailed. Literature review was performed using the following key words: paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, and ravulizumab.

EXPERT OPINION

Ravulizumab profile to treat PNH and aHUS is equivalent to eculizumab in efficacy and safety but allows extended dosing interval to every 4-8 weeks based on patient weight, and requires reduced infusion time. Less travels to infusion centers and medical visits and decreasing job and school absences, significantly increases patient and families' QoL, while reducing cost. Further infusion time is reduced Ravulizumab will possibly become the treatment of choice for patients with PNH and aHUS on chronic C5 inhibition.

The role of the complement system in kidney glomerular capillary thrombosis

The complement system is part of the innate immune system. The crucial step in activating the complement system is the generation and regulation of C3 convertase complexes, which are needed to generate opsonins that promote phagocytosis, to generate C3a that regulates inflammation, and to initiate the lytic terminal pathway through the generation and activity of C5 convertases. A growing body of evidence has highlighted the interplay between the complement system, coagulation system, platelets, neutrophils, and endothelial cells. The kidneys are highly susceptible to complement-mediated injury in several genetic, infectious, and autoimmune diseases. Atypical hemolytic uremic syndrome (aHUS) and lupus nephritis (LN) are both characterized by thrombosis in the glomerular capillaries of the kidneys. In aHUS, congenital or acquired defects in complement regulators may trigger platelet aggregation and activation, resulting in the formation of platelet-rich thrombi in the kidneys. Because glomerular vasculopathy is usually noted with immunoglobulin and complement accumulation in LN, complement-mediated activation of tissue factors could partly explain the autoimmune mechanism of thrombosis. Thus, kidney glomerular capillary thrombosis is mediated by complement dysregulation and may also be associated with complement overactivation. Further investigation is required to clarify the interaction between these vascular components and develop specific therapeutic approaches.

A Rare Case of Atypical Hemolytic Uremia Syndrome Triggered by Influenza Vaccination

Atypical hemolytic uremic syndrome (aHUS) occurs in patients with defective alternative complement pathways, making them susceptible to thrombotic microangiopathy (thrombocytopenia, intravascular hemolysis, and renal failure), and is usually triggered by infectious agents. Influenza and Streptococcus pneumonia are known triggers for aHUS. However, influenza vaccination triggering aHUS is rarely reported. We present a 30-year-old male who presented with chills, abdominal discomfort, and night sweats after receiving the influenza vaccine. The patient had thrombocytopenia, elevated creatinine, blood urea nitrogen, liver enzymes, and bilirubin with schistocytes with peripheral smear. ADAMTS13 activity was normal so the patient was diagnosed with aHUS. The patient improved with eculizumab and was ultimately found to have a mutation in CD46, which made him susceptible to aHUS. This case shows patients with dysregulated alternative complement pathways may be predisposed to develop aHUS after receiving influenza vaccination.

Elevated Expression Levels of Lung Complement Anaphylatoxin, Neutrophil Chemoattractant Chemokine IL-8, and RANTES in MERS-CoV-Infected Patients: Predictive Biomarkers for Disease Severity and Mortality

The complement system, a network of highly-regulated proteins, represents a vital part of the innate immune response. Over-activation of the complement system plays an important role in inflammation, tissue damage, and infectious disease severity. The prevalence of MERS-CoV in Saudi Arabia remains significant and cases are still being reported. The role of complement in Middle East Respiratory Syndrome coronavirus (MERS-CoV) pathogenesis and complement-modulating treatment strategies has received limited attention, and studies involving MERS-CoV-infected patients have not been reported. This study offers the first insight into the pulmonary expression profile including seven complement proteins, complement regulatory factors, IL-8, and RANTES in MERS-CoV infected patients without underlying chronic medical conditions. Our results significantly indicate high expression levels of complement anaphylatoxins (C3a and C5a), IL-8, and RANTES in the lungs of MERS-CoV-infected patients. The upregulation of lung complement anaphylatoxins, C5a, and C3a was positively correlated with IL-8, RANTES, and the fatality rate. Our results also showed upregulation of the positive regulatory complement factor P, suggesting positive regulation of the complement during MERS-CoV infection. High levels of lung C5a, C3a, factor P, IL-8, and RANTES may contribute to the immunopathology, disease severity, ARDS development, and a higher fatality rate in MERS-CoV-infected patients. These findings highlight the potential prognostic utility of C5a, C3a, IL-8, and RANTES as biomarkers for MERS-CoV disease severity and mortality. To further explore the prediction of functional partners (proteins) of highly expressed proteins (C5a, C3a, factor P, IL-8, and RANTES), the computational protein–protein interaction (PPI) network was constructed, and six proteins (hub nodes) were identified.

EGFR modulates complement activation in head and neck squamous cell carcinoma

Background

The epidermal growth factor receptor (EGFR) is pivotal for growth of epithelial cells and is overexpressed in several epithelial cancers like head and neck squamous cell carcinoma (HNSCC). EGFR signalling is also involved in diverse innate immune functions in epithelia. We previously found a role for EGFR in modulating the complement system in skin, this prompted an investigation into EGFR role in complement modulation in HNSCC.

Methods

We used patient derived HNSCC cell lines with varying sensitivities to EGFR inhibitors, and generated EGFR inhibition resistant cell lines to study the role of EGFR in modulating complement in HNSCC.

Results

We found that HNSCC cell lines activate the complement system when incubated with human serum. This complement activation was increased in cell lines sensitive to EGFR inhibition following the use of the tyrosine kinase inhibitor Iressa. Sensitive cell line made resistant to EGFR-inhibitors displayed complement activation and a decrease in complement regulatory proteins even in the absence of EGFR-inhibitors. Complement activation did not cause lysis of HNSCC cells, and rather led to increased extracellular signal-regulated kinase (ERK) phosphorylation in one cell line.

Conclusion

These data indicate that EGFR has a complement modulatory role in HNSCC, and that a prolonged EGFR-inhibition treatment in sensitive cancer cells increases complement activation. This has implications in understanding the response to EGFR inhibitors, in which resistance and inflammatory skin lesions are two major causes for treatment cessation.

Complement system activation and peritoneal membrane alterations: Culprit or innocent bystander?

Peritoneal dialysis (PD) accounts for approximately 10% of the dialysis population worldwide. Major concern limiting long-term PD success is the loss of the peritoneal membrane function after prolonged exposure to dialysis solutions. The complement system is a major component of the innate immune system, which provides a first-line defense against pathogens. Uncontrolled activation of the complement system directly contributes to the pathophysiology of rare and common kidney diseases and to a growing number of nonrenal diseases. Here, we review currently available evidence of complement activation in patients treated with PD and its association with structural and functional alterations of the peritoneal membrane. Mainly, evidence point toward a local, intraperitoneal, production of complement molecules in response to PD exposure. Dialysis fluids, particularly glucose, play a role in complement activation and dysregulation leading to untoward PD-related pathophysiological processes such as peritoneal fibrosis, angiogenesis, and vasculopathy and, perhaps, encapsulating peritoneal fibrosis development. These findings could lead to further development and use of anticomplement therapeutics in PD patients to prevent membrane damage.

Time-resolved dual RNA-seq of tissue uncovers Pseudomonas plecoglossicida key virulence genes in host-pathogen interaction with Epinephelus coioides

Bacterial pathogen-host interactions are highly dynamic, regulated processes that have been primarily investigated using in vitro assays. The dynamics of bacterial pathogen-host interplay in vivo are poorly understood. Using time-resolved dual RNA-seq in a Pseudomonas plecoglossicida-Epinephelus coioides infection model, we observed that bacterial genes encoding classical virulence factors and host genes involved in immune regulation were dynamically expressed during infection. Using network inferencing, we were able to predict interspecies regulatory networks linking bacterial virulence genes to host immune genes. Together with gene co-expression network analysis of the pathogen, secY was predicted to be a key virulence gene for P. plecoglossicida pathogenicity in the host, fliN was predicted to be a less important virulence gene. The results of bioinformatics prediction were confirmed by animal infection experiments. Our work provides the first paradigm to study dynamic alterations of bacterial pathogen and host interactions based on the elucidation of time-resolved interactive transcriptomes in vivo, and may be developed into a novel and universal method for revealing the true complexity of the bacterial infection process.

Complement regulatory proteins in kidneys of patients with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis

The complement system activation is involved in the development of anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV). The study aimed to investigate the expression of complement regulatory proteins (CRPs) CD46, CD55 and CD59 in kidneys of 51 AVV patients. The expression of CD46, CD55 and CD59 in kidneys was detected by immunohistochemistry and double immunofluorescence staining. The immunohistochemical examination revealed that expression of the three CRPs could be detected in the glomeruli and tubules of both AAV patients and normal controls. The expression levels of the three CRPs in glomeruli of patients with AAV were significantly lower than those of normal controls. The scores of CD46 and CD55 expression in the tubules of AAV patients were significantly lower than those of normal controls, while there was no significant difference between the scores of CD59 expression in tubules of AAV patients and those of normal controls. Among AAV patients, the expression level of CD46 in glomeruli correlated inversely with the proportion of normal glomeruli, while it correlated with tubular atrophy in renal interstitium (r = -0·305, P = 0·026; r = 0·330, P = 0·023, respectively). The expression levels of CD55 and CD59 in glomeruli correlated with the proportion of total crescents (r = 0·384, P = 0·006; r = 0·351, P = 0·011, respectively). Double immunofluorescence staining indicated that all three CRPs were expressed on endothelial cells, podocytes and mesangial cells in glomeruli. The expression levels of the three CRPs were dysregulated in kidneys of patients with AAV. The expression levels of CD46, CD55 and CD59 were associated with the severity of renal injury of AAV patients.

Overexpression of Human CD55 and CD59 or Treatment with Human CD55 Protects against Renal Ischemia-Reperfusion Injury in Mice

Deficiency in the membrane-bound complement regulators CD55 and CD59 exacerbates renal ischemia-reperfusion injury (IRI) in mouse models, but the effect of increasing CD55 and CD59 activity has not been examined. In this study, we investigated the impact of overexpression of human (h) CD55 ± hCD59 or treatment with soluble rhCD55 in a mouse model of renal IRI. Unilaterally nephrectomised mice were subjected to 18 (mild IRI) or 22 min (moderate IRI) warm renal ischemia, and analyzed 24 h after reperfusion for renal function (serum creatinine and urea), complement deposition (C3b/c and C9), and infiltration of neutrophils and macrophages. Transgenic mice expressing hCD55 alone were protected against mild renal IRI, with reduced creatinine and urea levels compared with wild type littermates. However, the renal function of the hCD55 mice was not preserved in the moderate IRI model, despite a reduction in C3b/c and C9 deposition and innate cell infiltration. Mice expressing both hCD55 and hCD59, on the other hand, were protected in the moderate IRI model, with significant reductions in all parameters measured. Wild type mice treated with rhCD55 immediately after reperfusion were also protected in the moderate IRI model. Thus, manipulation of CD55 activity to increase inhibition of the C3 and C5 convertases is protective against renal IRI, and the additional expression of hCD59, which regulates the terminal complement pathway, provides further protection. Therefore, anti-complement therapy using complement regulatory proteins may provide a potential clinical option for preventing tissue and organ damage in renal IRI.

HUS and atypical HUS

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy characterized by intravascular hemolysis, thrombocytopenia, and acute kidney failure. HUS is usually categorized as typical, caused by Shiga toxin-producing Escherichia coli (STEC) infection, as atypical HUS (aHUS), usually caused by uncontrolled complement activation, or as secondary HUS with a coexisting disease. In recent years, a general understanding of the pathogenetic mechanisms driving HUS has increased. Typical HUS (ie, STEC-HUS) follows a gastrointestinal infection with STEC, whereas aHUS is associated primarily with mutations or autoantibodies leading to dysregulated complement activation. Among the 30% to 50% of patients with HUS who have no detectable complement defect, some have either impaired diacylglycerol kinase ε (DGKε) activity, cobalamin C deficiency, or plasminogen deficiency. Some have secondary HUS with a coexisting disease or trigger such as autoimmunity, transplantation, cancer, infection, certain cytotoxic drugs, or pregnancy. The common pathogenetic features in STEC-HUS, aHUS, and secondary HUS are simultaneous damage to endothelial cells, intravascular hemolysis, and activation of platelets leading to a procoagulative state, formation of microthrombi, and tissue damage. In this review, the differences and similarities in the pathogenesis of STEC-HUS, aHUS, and secondary HUS are discussed. Common for the pathogenesis seems to be the vicious cycle of complement activation, endothelial cell damage, platelet activation, and thrombosis. This process can be stopped by therapeutic complement inhibition in most patients with aHUS, but usually not those with a DGKε mutation, and some patients with STEC-HUS or secondary HUS. Therefore, understanding the pathogenesis of the different forms of HUS may prove helpful in clinical practice.

Adeno-associated virus mediated delivery of an engineered protein that combines the complement inhibitory properties of CD46, CD55 and CD59

BACKGROUND

A variety of disorders are associated with the activation of complement. CD46, CD55 and CD59 are the major membrane associated regulators of complement on human cells. Previously, we have found that independent expression of CD55, CD46 or CD59 through gene transfer protects murine tissues against human complement mediated attack. In the present study, we investigated the potential of combining the complement regulatory properties of CD46, CD55 and CD59 into single gene products expressed from an adeno-associated virus (AAV) vector in a soluble non-membrane anchored form.

METHODS

Minigenes encoding the complement regulatory domains from CD46, CD55 and CD59 (SACT) or CD55 and CD59 (DTAC) were cloned into an AAV vector. The specific regulatory activity of each component of SACT and DTAC was measured in vitro. The recombinant AAV vectors were injected into the peritoneum of mice and the efficacy of the transgene products for being able to protect murine liver vasculature against human complement, specifically the membrane attack complex (MAC), was measured.

RESULTS

SACT and DTAC exhibited properties similar to CD46, CD55 and CD59 or CD55 and CD59, respectively, in vitro. AAV mediated delivery of SACT or DTAC protected murine liver vasculature from human MAC deposition by 63.2% and 56.7%, respectively.

CONCLUSIONS

When delivered to mice in vivo via an AAV vector, SACT and DTAC are capable of limiting human complement mediated damage. SACT and DTAC merit further study as potential therapies for complement mediated disorders when delivered via a gene therapy approach.

Complement regulatory protein genes in channel catfish and their involvement in disease defense response

Complement system is one of the most important defense systems of innate immunity, which plays a crucial role in disease defense responses in channel catfish. However, inappropriate and excessive complement activation could lead to potential damage to the host cells. Therefore the complement system is controlled by a set of complement regulatory proteins to allow normal defensive functions, but prevent hazardous complement activation to host tissues. In this study, we identified nine complement regulatory protein genes from the channel catfish genome. Phylogenetic and syntenic analyses were conducted to determine their orthology relationships, supporting their correct annotation and potential functional inferences. The expression profiles of the complement regulatory protein genes were determined in channel catfish healthy tissues and after infection with the two main bacterial pathogens, Edwardsiella ictaluri and Flavobacterium columnare. The vast majority of complement regulatory protein genes were significantly regulated after bacterial infections, but interestingly were generally up-regulated after E. ictaluri infection while mostly down-regulated after F. columnare infection, suggesting a pathogen-specific pattern of regulation. Collectively, these findings suggested that complement regulatory protein genes may play complex roles in the host immune responses to bacterial pathogens in channel catfish.

On the Functional Overlap between Complement and Anti-Microbial Peptides

Intriguingly, activated complement and anti-microbial peptides share certain functionalities; lytic, phagocytic, and chemo-attractant activities and each may, in addition, exert cell instructive roles. Each has been shown to have distinct LPS detoxifying activity and may play a role in the development of endotoxin tolerance. In search of the origin of complement, a functional homolog of complement C3 involved in opsonization has been identified in horseshoe crabs. Horseshoe crabs possess anti-microbial peptides able to bind to acyl chains or phosphate groups/saccharides of endotoxin, LPS. Complement activity as a whole is detectable in marine invertebrates. These are also a source of anti-microbial peptides with potential pharmaceutical applicability. Investigating the locality for the production of complement pathway proteins and their role in modulating cellular immune responses are emerging fields. The significance of local synthesis of complement components is becoming clearer from in vivo studies of parenchymatous disease involving specifically generated, complement-deficient mouse lines. Complement C3 is a central component of complement activation. Its provision by cells of the myeloid lineage varies. Their effector functions in turn are increased in the presence of anti-microbial peptides. This may point to a potentiating range of activities, which should serve the maintenance of health but may also cause disease. Because of the therapeutic implications, this review will consider closely studies dealing with complement activation and anti-microbial peptide activity in acute inflammation (e.g., dialysis-related peritonitis, appendicitis, and ischemia).

Improving immunogenicity and efficacy of vaccines for genital herpes containing herpes simplex virus glycoprotein D

No vaccines are approved for prevention or treatment of genital herpes. The focus of genital herpes vaccine trials has been on prevention using herpes simplex virus type 2 (HSV-2) glycoprotein D (gD2) alone or combined with glycoprotein B. These prevention trials did not achieve their primary end points. However, subset analyses reported some positive outcomes in each study. The most recent trial was the Herpevac Trial for Women that used gD2 with monophosphoryl lipid A and alum as adjuvants in herpes simplex virus type 1 (HSV-1) and HSV-2 seronegative women. Unexpectedly, the vaccine prevented genital disease by HSV-1 but not HSV-2. Currently, HSV-1 causes more first episodes of genital herpes than HSV-2, highlighting the importance of protecting against HSV-1. The scientific community is conflicted between abandoning vaccine efforts that include gD2 and building upon the partial successes of previous trials. We favor building upon success and present approaches to improve outcomes of gD2-based subunit antigen vaccines.

The epidermal growth factor receptor is a regulator of epidermal complement component expression and complement activation

The complement system is activated in response to tissue injury. During wound healing, complement activation seems beneficial in acute wounds but may be detrimental in chronic wounds. We found that the epidermal expression of many complement components was only increased to a minor extent in skin wounds in vivo and in cultured keratinocytes after exposure to supernatant from stimulated mononuclear cells. In contrast, the epidermal expression of complement components was downregulated in ex vivo injured skin lacking the stimulation from infiltrating inflammatory cells but with intact injury-induced epidermal growth factor receptor (EGFR)-mediated growth factor response. In cultured primary keratinocytes, stimulation with the potent EGFR ligand, TGF-α, yielded a significant downregulation of complement component expression. Indeed, EGFR inhibition significantly enhanced the induction of complement components in keratinocytes and epidermis following stimulation with proinflammatory cytokines. Importantly, EGFR inhibition of cultured keratinocytes either alone or in combination with proinflammatory stimulus promoted activation of the complement system after incubation with serum. In keratinocytes treated solely with the EGFR inhibitor, complement activation was dependent on serum-derived C1q, whereas in keratinocytes stimulated with a combination of proinflammatory cytokines and EGFR inhibition, complement activation was found even with C1q-depleted serum. In contrast to human keratinocytes, EGFR inhibition did not enhance complement component expression or cause complement activation in murine keratinocytes. These data demonstrate an important role for EGFR in regulating the expression of complement components and complement activation in human epidermis and keratinocytes and, to our knowledge, identify for the first time a pathway important for the epidermal regulation of complement activation.

The role of the complement system in acute kidney injury

Acute kidney injury is a common and severe clinical problem. Patients who develop acute kidney injury are at increased risk of death despite supportive measures such as hemodialysis. Research in recent years has shown that tissue inflammation is central to the pathogenesis of renal injury, even after nonimmune insults such as ischemia/reperfusion and toxins. Examination of clinical samples and preclinical models has shown that activation of the complement system is a critical cause of acute kidney injury. Furthermore, complement activation within the injured kidney is a proximal trigger of many downstream inflammatory events within the renal parenchyma that exacerbate injury to the kidney. Complement activation also may account for the systemic inflammatory events that contribute to remote organ injury and patient mortality. Complement inhibitory drugs have now entered clinical use and may provide an important new therapeutic approach for patients suffering from, or at high risk of developing, acute kidney injury.

Complement activation by heme as a secondary hit for atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is characterized by genetic and acquired abnormalities of the complement system leading to alternative pathway (AP) overactivation and by glomerular endothelial damage, thrombosis, and mechanical hemolysis. Mutations per se are not sufficient to induce aHUS, and nonspecific primary triggers are required for disease manifestation. We investigated whether hemolysis-derived heme contributes to aHUS pathogenesis. We confirmed that heme activates complement AP in normal human serum, releasing C3a, C5a, and sC5b9. We demonstrated that heme-exposed endothelial cells also activate the AP, resulting in cell-bound C3 and C5b9. This was exacerbated in aHUS by genetic abnormalities associated with AP overactivation. Heme interacted with C3 close to the thioester bond, induced homophilic C3 complexes, and promoted formation of an overactive C3/C5 convertase. Heme induced decreased membrane cofactor protein (MCP) and decay-accelerating factor (DAF) expression on endothelial cells, giving Factor H (FH) a major role in complement regulation. Finally, heme promoted a rapid exocytosis of Weibel-Palade bodies, with membrane expression of P-selectin known to bind C3b and trigger the AP, and the release of the prothrombotic von Willebrand factor. These results strongly suggest that hemolysis-derived heme represents a common secondary hit amplifying endothelial damage and thrombosis in aHUS.

Rheumatoid factor, complement, and mixed cryoglobulinemia

Low serum level of complement component 4 (C4) that occurs in mixed cryoglobulinemia (MC) may be due to in vivo or ex vivo activation of complement by the classical pathway. Potential activators include monoclonal IgM rheumatoid factor (RF), IgG antibodies, and the complexing of the two in the cold, perhaps modulated by the rheology and stoichiometry of cryocomplexes in specific microcirculations. There is also the potential for activation of complement by the alternative and lectin pathways, particularly in the setting of chronic infection and immune stimulation caused by hepatitis C virus (HCV). Engagement of C1q and interaction with specific cell surface receptors serve to localize immune complexes (ICs) to the sites of pathology, notably the cutaneous and glomerular microcirculations. Defective or saturated clearance of ICs by CR1and/or Fc receptors may explain persistence in the circulation. The phlogistic potential of cryoprecipitable ICs depends upon the cleavage of complement components to generate fragments with anaphylatoxin or leukocyte mobilizing activity, and the assembly of the membrane attack complex (C5b-9) on cell surfaces. A research agenda would include further characterization of the effector arm of complement activation in MC, and elucidation of activation mechanisms due to virus and viral antigens in HCV infection.

Endothelial pentraxin 3 contributes to murine ischemic acute kidney injury

Toll-like receptor 4 (TLR4), a receptor for damage-associated molecular pattern molecules and also the lipopolysaccharide receptor, is required for early endothelial activation leading to maximal inflammation and injury during murine ischemic acute kidney injury. DNA microarray analysis of ischemic kidneys from TLR4-sufficient and -deficient mice showed that pentraxin 3 (PTX3) was upregulated only on the former while transgenic knockout of PTX3 ameliorated acute kidney injury. PTX3 was expressed predominantly on peritubular endothelia of the outer medulla of the kidney in control mice. Acute kidney injury increased PTX3 protein in the kidney and the plasma where it may be a biomarker of the injury. Stimulation by hydrogen peroxide, or the TLR4 ligands recombinant human high-mobility group protein B1 or lipopolysaccharide, induced PTX3 expression in the Mile Sven 1 endothelial cell line and in primary renal endothelial cells, suggesting that endothelial PTX3 was induced by pathways involving TLR4 and reactive oxygen species. This increase was inhibited by conditional endothelial knockout of myeloid differentiation primary response gene 88, a mediator of a TLR4 intracellular signaling pathway. Compared to wild-type mice, PTX3 knockout mice had decreased endothelial expression of cell adhesion molecules at 4 h of reperfusion, possibly contributing to a decreased early maladaptive inflammation in the kidneys of knockout mice. At 24 h of reperfusion, PTX3 knockout increased expression of endothelial adhesion molecules when regulatory and reparative leukocytes enter the kidney. Thus, endothelial PTX3 plays a pivotal role in the pathogenesis of ischemic acute kidney injury.

Complement Attack against Aspergillus and Corresponding Evasion Mechanisms

Invasive aspergillosis shows a high mortality rate particularly in immunocompromised patients. Perpetually increasing numbers of affected patients highlight the importance of a clearer understanding of interactions between innate immunity and fungi. Innate immunity is considered to be the most significant host defence against invasive fungal infections. Complement represents a crucial part of this first line defence and comprises direct effects against invading pathogens as well as bridging functions to other parts of the immune network. However, despite the potency of complement to attack foreign pathogens, the prevalence of invasive fungal infections is increasing. Two possible reasons may explain that phenomenon: First, complement activation might be insufficient for an effective antifungal defence in risk patients (due to, e.g., low complement levels, poor recognition of fungal surface, or missing interplay with other immune elements in immunocompromised patients). On the other hand, fungi may have developed evasion strategies to avoid recognition and/or eradication by complement. In this review, we summarize the most important interactions between Aspergillus and the complement system. We describe the various ways of complement activation by Aspergillus and the antifungal effects of the system, and also show proven and probable mechanisms of Aspergillus for complement evasion.