Different Complement Activation Patterns Following C5 Cleavage in MOGAD and AQP4-IgG+NMOSD.

OBJECTIVES: In myelin oligodendrocyte glycoprotein IgG-associated disease (MOGAD) and aquaporin-4 IgG+ neuromyelitis optica spectrum disorder (AQP4+NMOSD), the autoantibodies are mainly composed of IgG1, and complement-dependent cytotoxicity is a primary pathomechanism in AQP4+NMOSD. We aimed to evaluate the CSF complement activation in MOGAD. METHODS: CSF-C3a, CSF-C4a, CSF-C5a, and CSF-C5b-9 levels during the acute phase before treatment in patients with MOGAD (n = 12), AQP4+NMOSD (n = 11), multiple sclerosis (MS) (n = 5), and noninflammatory neurologic disease (n = 2) were measured. RESULTS: CSF-C3a and CSF-C5a levels were significantly higher in MOGAD (mean ± SD, 5,629 ± 1,079 pg/mL and 2,930 ± 435.8 pg/mL) and AQP4+NMOSD (6,017 ± 3,937 pg/mL and 2,544 ± 1,231 pg/mL) than in MS (1,507 ± 1,286 pg/mL and 193.8 ± 0.53 pg/mL). CSF-C3a, CSF-C4a, and CSF-C5a did not differ between MOGAD and AQP4+NMOSD while CSF-C5b-9 (membrane attack complex, MAC) levels were significantly lower in MOGAD (17.4 ± 27.9 ng/mL) than in AQP4+NMOSD (62.5 ± 45.1 ng/mL, p = 0.0019). Patients with MOGAD with severer attacks (Expanded Disability Status Scale [EDSS] ≥ 3.5) had higher C5b-9 levels (34.0 ± 38.4 ng/m) than those with milder attacks (EDSS ≤3.0, 0.9 ± 0.7 ng/mL, p = 0.044). DISCUSSION: The complement pathway is activated in both MOGAD and AQP4+NMOSD, but MAC formation is lower in MOGAD, particularly in those with mild attacks, than in AQP4+NMOSD. These findings may have pathogenetic and therapeutic implications in MOGAD.

Autocrine vitamin D signaling switches off pro-inflammatory programs of TH1 cells.

The molecular mechanisms governing orderly shutdown and retraction of CD4+ type 1 helper T (TH1) cell responses remain poorly understood. Here we show that complement triggers contraction of TH1 responses by inducing intrinsic expression of the vitamin D (VitD) receptor and the VitD-activating enzyme CYP27B1, permitting T cells to both activate and respond to VitD. VitD then initiated the transition from pro-inflammatory interferon-γ+ TH1 cells to suppressive interleukin-10+ cells. This process was primed by dynamic changes in the epigenetic landscape of CD4+ T cells, generating super-enhancers and recruiting several transcription factors, notably c-JUN, STAT3 and BACH2, which together with VitD receptor shaped the transcriptional response to VitD. Accordingly, VitD did not induce interleukin-10 expression in cells with dysfunctional BACH2 or STAT3. Bronchoalveolar lavage fluid CD4+ T cells of patients with COVID-19 were TH1-skewed and showed de-repression of genes downregulated by VitD, from either lack of substrate (VitD deficiency) and/or abnormal regulation of this system.

Complement Overactivation and Consumption Predicts In-Hospital Mortality in SARS-CoV-2 Infection.

Objectives: Uncontrolled thromboinflammation plays an important role in the pathogenesis of coronavirus disease (COVID-19) caused by SARS-CoV-2 virus. Complement was implicated as key contributor to this process, therefore we hypothesized that markers of the complement profile, indicative for the activation state of the system, may be related to the severity and mortality of COVID-19. Methods: In this prospective cohort study samples of 102 hospitalized and 26 outpatients with PCR-confirmed COVID-19 were analyzed. Primary outcome was in-hospital, COVID-19 related mortality, and secondary outcome was COVID-19 severity as assessed by the WHO ordinal scale. Complement activity of alternative and classical pathways, its factors, regulators, and activation products were measured by hemolytic titration, turbidimetry, or enzyme-immunoassays. Clinical covariates and markers of inflammation were extracted from hospital records. Results: Increased complement activation was characteristic for hospitalized COVID-19 patients. Complement activation was significantly associated with markers of inflammation, such as interleukin-6, C-reactive protein, and ferritin. Twenty-five patients died during hospital stay due to COVID-19 related illness. Patients with uncontrolled complement activation leading to consumption of C3 and decrease of complement activity were more likely to die, than those who had complement activation without consumption. Cox models identified anaphylatoxin C3a, and C3 overactivation and consumption (ratio of C3a/C3) as predictors of in-hospital mortality [HR of 3.63 (1.55-8.45, 95% CI) and 6.1 (2.1-17.8), respectively]. Conclusion: Increased complement activation is associated with advanced disease severity of COVID-19. Patients with SARS-CoV-2 infection are more likely to die when the disease is accompanied by overactivation and consumption of C3. These results may provide observational evidence and further support to studies on complement inhibitory drugs for the treatment of COVID-19.

Complement and Chlamydia psittaci: Early Complement-Dependent Events Are Important for DC Migration and Protection During Mouse Lung Infection.

The zoonotic intracellular bacterium Chlamydia psittaci causes life-threatening pneumonia in humans. During mouse lung infection, complement factor C3 and the anaphylatoxin C3a augment protection against C. psittaci by a so far unknown mechanism. To clarify how complement contributes to the early, innate and the late, specific immune response and resulting protection, this study addresses the amount of C3, the timing when its presence is required as well as the anaphylatoxin receptor(s) mediating its effects and the complement-dependent migration of dendritic cells. Challenge experiments with C. psittaci on various complement KO mice were combined with transient decomplementation by pharmacological treatment, as well as the analysis of in vivo dendritic cells migration. Our findings reveal that a plasma concentration of C3 close to wildtype levels was required to achieve full protection. The diminished levels of C3 of heterozygote C3+/- mice permitted already relative effective protection and improved survival as compared to C3-/- mice, but overall recovery of these animals was delayed. Complement was in particular required during the first days of infection. However, additionally, it seems to support protection at later stages. Migration of CD103+ dendritic cells from the infected lung to the draining lymph node-as prerequisite of antigen presentation-depended on C3 and C3aR and/or C5aR. Our results provide unique mechanistic insight in various aspects of complement-dependent immune responses under almost identical, rather physiological experimental conditions. Our study contributes to an improved understanding of the role of complement, and C3a in particular, in infections by intracellular bacteria.

Pharmacological approach for the reduction of inflammatory and prothrombotic hyperactive state in COVID-19 positive patients by acting on complement cascade.

The novel Coronavirus SARS-CoV-2 is the viral pathogen responsible for the ongoing global pandemic, COVID-19 (Coronavirus disease 2019). To date, the data recorded indicate 1.62 Mln deaths and 72.8 Mln people infected (WHO situation report Dec 2020). On December 27, the first anti-COVID-19 vaccinations started in Europe. There are no direct antivirals against SARS-CoV-2. Understanding the pathophysiological and inflammatory/immunological processes of SARS-CoV-2 infection is essential to identify new drug therapies. In the most severe COVID-19 cases, an unregulated immunological/inflammatory system results in organ injury that can be fatal to the host in some cases. Pharmacologic approaches to normalize the unregulated inflammatory/immunologic response is an important therapeutic solution. Evidence associates a non-regulation of the "complement system" as one of the causes of generalized inflammation causing multi-organ dysfunction. Serum levels of a complement cascade mediator, factor "C5a", have been found in high concentrations in the blood of COVID-19 patients with severe disease. In this article we discuss the correlation between complement system and COVID-19 infection and pharmacological solutions directed to regulate.

The Complement C3a and C3a Receptor Pathway in Kidney Diseases.

The pathogenesis of some kidney diseases is closely associated with complement activation, where the C3a/C3a receptor (C3aR) might play a crucial role. C3a/C3aR has dual roles and may exert anti-inflammatory or pro-inflammatory effects depending on different cell types and diseases. In the kidneys, C3aR is primarily expressed on the tubular epithelium and less in glomerular podocytes. C3aR expression is enhanced and the levels of C3a in the plasma and urine are increased in kidney diseases of several types, and are associated with disease progression and severity. The C3a/C3aR pathway facilitates the progression of glomerular and tubulointerstitial diseases, while it has opposite effects on urinary tract infections. Clinical trials targeting C3a/C3aR in kidney diseases are lacking. Here, we reviewed the studies on the C3a/C3aR pathway in kidney disease, with the aim of understanding in-depth its controversial roles and its potential therapeutic value.

The Value of Targeting Complement Components in Asthma.

Asthma is an important respiratory illness. Though pharmacological and biological treatment is well established and is staged according to endotypes and their responses to treatment, novel avenues are being explored. Our focus is complement. In this viewpoint, we evaluate the approach to target complement in this complex hypersensitivity reaction that develops chronicity and has a personal-as well as a societal-cost.

The activation of complement system in different types of renal replacement therapy.

The complement cascade is a part of innate immune system that responds rapidly to defend the host against invading microorganisms and complete the action of immune cells. The activation of the complement system leads to increased inflammatory response, fibrosis of tubulointestinal tissue and progression of chronic kidney disease (CKD). The purpose of this study was to determine whether the type of renal replacement therapy has an effect on activation of the complement system. The study included 79 patients with CKD stages 4 - 5 according to Kidney Disease Improving Global Outcomes (KDIGO) guidelines on conservative treatment (CKD4-5) (n = 28), on peritoneal dialysis (PD) (n = 21) and undergoing chronic haemodialysis (HD) (n = 30). The concentrations of complement components C3a, C5a and C5b-9 were determined in plasma using the ELISA method. The highest concentration of C3a was found in PD group and differed significantly from HD group, both before and after haemodialysis treatment and CKD4-5 patients (P = 0.00001). The C5a concentration in HD patients was significantly higher than in PD patients and CKD4-5 group (P = 0.0001). The C5a and C5b-9 concentrations significantly increased during the haemodialysis session (P = 0.027 and P = 0.01, respectively). The values of C5b-9 observed in PD and CKD4-5 groups were significantly lower, than in HD patients (P = 0.0005). In HD patients the negative correlations were found between the time of haemodialysis treatment and C5b-9 concentration, both before and after haemodialysis session (Rs = -0.436, P = 0.016 and Rs = -0.365, P = 0.046, respectively). The type of renal replacement therapy influences the complement activation, which is the most intense during the haemodialysis treatment and correlates negatively with the haemodialysis vintage. The promising therapeutic intervention may be an improvement of HD biocompatibility.

Complement in sepsis-when science meets clinics.

Sepsis as life-threatening organ dysfunction caused by microorganisms represents a dreadful challenge for the immune system. The role of the complement system as major column of innate immunity has been extensively studied in various sepsis models, but its translational value remains in the dark. Complement activation products, such as C3a and C5a, and their corresponding receptors provide useful diagnostic tools and promising targets to improve organ function and outcome. However, a monotherapeutic complement intervention irrespective of the current immune function seems insufficient to reverse the complex sepsis mechanisms. Indeed, sepsis-induced disturbances of cross talking complement, coagulation, and fibrinolytic cascades lead to systemic 'thromboinflammation', ultimately followed by multiple-organ failure. We propose to reliably monitor the complement function in the patient and to re-establish the immune balance by patient-tailored combined therapies, such as complement and Toll-like receptor inhibition. Our working hypothesis aims at blocking the 'explosive' innate immune recognition systems early on before downstream mediators are released and the inflammatory response becomes irreversible, a strategy that we name 'upstream approach'.

Characterization of Anaphylatoxin Receptor Expression and C3a/C5a Functions in Anaphylatoxin Receptor Reporter Mice.

The anaphylatoxins (AT) C3a and C5a are effector molecules of C3 and C5 exerting multiple biologic functions through binding and activation of their cognate G protein-coupled receptors. C3a interacts with the C3a receptor (C3aR), whereas C5a and its primary degradation product C5a-desArg engage C5aR1 and C5aR2. In the past, analysis of AT expression has been hampered by cross reaction of antibodies designed to recognize the different AT receptors. Furthermore, assessment of effects mediated by cell-specific activation has been difficult. Here, floxed AT receptor reporter mice are described as tools to monitor AT receptor expression in cells and tissues and to study the functions of C3a and C5a by cell-specific deletion of their cognate AT receptors. © 2020 The Authors. Basic Protocol 1: Genotyping of floxed GFP-C5aR1 knockin mice Support Protocol 1: Genotyping of LysMcre-C5ar1-/- mice Basic Protocol 2: Genotyping of floxed tdTomato-C3aR and -tdTomato-C5aR2 knockin mice Support Protocol 2: Preparation of genomic DNA Basic Protocol 3: Determination of C5aR1, C5aR2, and C3aR expression using floxed AT receptor reporter mice Support Protocol 3: Determination of C3aR expression using a C3aR-specific antibody Support Protocol 4: Determination of C5aR1, C5aR2, and C3aR mRNA expression in floxed GFP-C5aR1, floxed tdTomato-C5aR2 or -tdTomato C3aR positive cells Basic Protocol 4: Analysis of C5aR1-driven ERK1/2 phosphorylation in GFP-C5aR1+ cells Basic Protocol 5: Assessment of C3aR functions in cells obtained from floxed tdTomato-C3aR knockin mice- Determination of C3aR internalization Alternate Protocol: C3a-induced increase in intracellular Ca2+ Basic Protocol 6: C5aR2-driven IFN-γ production from NK cells Support Protocol 5: Isolation of splenic NK cells by FACS.

Heparin and non-anticoagulant heparin attenuate histone-induced inflammatory responses in whole blood.

Cytotoxic and pro-inflammatory histones are present in neutrophil extracellular traps (NETs) and are elevated in blood in several inflammatory conditions, sepsis being a major example. Compounds which can attenuate activities of histones are therefore of interest, with heparin being one such material that has previously been shown to bind to histones. Heparin, a successful anticoagulant for nearly a century, has been shown experimentally to bind to histones and exhibit a protective effect in inflammatory conditions. In the present study carried out in whole blood, heparin and selectively desulfated heparin reduced histone induced inflammatory markers such as interleukin 6 (IL 6), interleukin 8 (IL 8) and tissue factor and C3a, a complement component. The selectively desulfated heparins, with reduced anticoagulant activities, retained a high degree of effectiveness as an anti-histone agent, whereas fully desulfated heparin was found to be ineffective. The results from this study indicate that the presence of sulfate and other specific structural features are required for heparin to attenuate the inflammatory action of histones in whole blood.

In response to complement anaphylatoxin peptides C3a and C5a, human vascular endothelial cells migrate and mediate the activation of B-cells and polarization of T-cells.

The vascular endothelium has been discovered in the past several years to be important in shaping the cellular immune response. During the immune response the vascular endothelium is constantly perturbed by biologically potent molecules, including the complement activation peptides, C3a and C5a. Despite the importance of C3a and C5a in inflammation and immunity, their role in modulating lymphocyte function via activation of vascular endothelial cells is unknown. Accordingly, we investigated the regulated expression of the C3a and C5a receptors (complement anaphylatoxin C3a receptor [C3aR] and complement anaphylatoxin C5a receptor 1 [C5aR1]) on human umbilical vascular endothelial cells (HUVECs) and examined how C3a or C5a activation of HUVECs affects the activation and polarization of lymphatic cells. Our findings demonstrated that C3a and C5a increase C3aR and C5aR1 expression by HUVECs as well as directing their cellular transmigration and spreading through transwell filters. Moreover, C3a- or C5a-stimulated endothelial cells: (1) caused activation of B-lymphoblasts with significant increase in Fas Ligand (CD95L) (FasL), CD69, and IL-R1 expression, and (2) skewed T-lymphoblast cells toward a Th1 subtype, (CD4+ /CCR5+ ) that correlated with significant increase of IFN-γ. Collectively, these data indicate that C3a and C5a signaling is important in the activation and polarization of lymphocytes as they traffic through the vascular endothelium during the immune response.

Complement Activation and Organ Damage After Trauma-Differential Immune Response Based on Surgical Treatment Strategy.

Background: The complement system is part of the innate immunity, is activated immediately after trauma and is associated with adult respiratory distress syndrome, acute lung injury, multiple organ failure, and with death of multiply injured patients. The aim of the study was to investigate the complement activation in multiply injured pigs as well as its effects on the heart in vivo and in vitro. Moreover, the impact of reamed vs. non-reamed intramedullary nailing was examined with regard to the complement activation after multiple trauma in pigs. Materials and Methods: Male pigs received multiple trauma, followed by femoral nailing with/without prior conventional reaming. Systemic complement hemolytic activity (CH-50 and AH-50) as well as the local cardiac expression of C3a receptor, C5a receptors1/2, and the deposition of the fragments C3b/iC3b/C3c was determined in vivo after trauma. Human cardiomyocytes were exposed to C3a or C5a and analyzed regarding calcium signaling and mitochondrial respiration. Results: Systemic complement activation increased within 6 h after trauma and was mediated via the classical and the alternative pathway. Furthermore, complement activation correlated with invasiveness of fracture treatment. The expression of receptors for complement activation were altered locally in vivo in left ventricles. C3a and C5a acted detrimentally on human cardiomyocytes by affecting their functionality and their mitochondrial respiration in vitro. Conclusion: After multiple trauma, an early activation of the complement system is triggered, affecting the heart in vivo as well as in vitro, leading to complement-induced cardiac dysfunction. The intensity of complement activation after multiple trauma might correlate with the invasiveness of fracture treatment. Reaming of the femoral canal might contribute to an enhanced "second hit" response after trauma. Consequently, the choice of fracture treatment might imply the clinical outcome of the critically injured patients and might be therefore crucial for their survival.

Effective inhibition of C3a-mediated pro-inflammatory response by a human C3a-specific protein binder.

Complement component 3a (C3a) plays a crucial role in the immune response and host defense, but it is also involved in pro-inflammatory responses, causing many inflammatory disorders. Blockade of C3a has been regarded as a potent therapeutic strategy for inflammatory diseases. Here, we present the development of a human C3a (hC3a)-specific protein binder, which effectively inhibits pro-inflammatory responses. The protein binder, which is composed of leucine-rich repeat modules, was selected against hC3a through phage display, and its binding affinity was matured up to 600 pM by further expanding the binding interface in a module-by-module manner. The developed protein binder was shown to have more than 10-fold higher specificity to hC3a compared with human C5a, exhibiting a remarkable suppression effect on pro-inflammatory response in monocyte, by blocking the interaction between hC3a and its receptor. The hC3a-specific protein binder is likely to have a therapeutic potential for C3a-mediated inflammatory diseases.

C3a elicits unique migratory responses in immature low-density neutrophils.

Neutrophils represent the immune system's first line of defense and are rapidly recruited into inflamed tissue. In cancer associated inflammation, phenotypic heterogeneity has been ascribed to this cell type, whereby neutrophils can manifest anti- or pro-metastatic functions depending on the cellular/micro-environmental context. Here, we demonstrate that pro-metastatic immature low-density neutrophils (iLDNs) more efficiently accumulate in the livers of mice bearing metastatic lesions compared with anti-metastatic mature high-density neutrophils (HDNs). Transcriptomic analyses reveal enrichment of a migration signature in iLDNs relative to HDNs. We find that conditioned media derived from liver-metastatic breast cancer cells, but not lung-metastatic variants, specifically induces chemotaxis of iLDNs and not HDNs. Chemotactic responses are due to increased surface expression of C3aR in iLDNs relative to HDNs. In addition, we detect elevated secretion of cancer-cell derived C3a from liver-metastatic versus lung-metastatic breast cancer cells. Perturbation of C3a/C3aR signaling axis with either a small molecule inhibitor, SB290157, or reducing the levels of secreted C3a from liver-metastatic breast cancer cells by short hairpin RNAs, can abrogate the chemotactic response of iLDNs both in vitro and in vivo, respectively. Together, these data reveal novel mechanisms through which iLDNs prefentially accumulate in liver tissue harboring metastases in response to tumor-derived C3a secreted from the liver-aggressive 4T1 breast cancer cells.

Interleukin-33 Amplifies Human Mast Cell Activities Induced by Complement Anaphylatoxins.

Both, aberrant mast cell responses and complement activation contribute to allergic diseases. Since mast cells are highly responsive to C3a and C5a, while Interleukin-33 (IL-33) is a potent mast cell activator, we hypothesized that IL-33 critically regulates mast cell responses to complement anaphylatoxins. We sought to understand whether C3a and C5a differentially activate primary human mast cells, and probe whether IL-33 regulates C3a/C5a-induced mast cell activities. Primary human mast cells were generated from peripheral blood precursors or isolated from healthy human lung tissue, and mast cell complement receptor expression, degranulation, mediator release, phosphorylation patterns, and calcium flux were assessed. Human mast cells of distinct origin express constitutively higher levels of C3aR1 than C5aR1, and both receptors are downregulated by anaphylatoxins. While C3a is a potent mast cell degranulation inducer, C5a is a weaker secretagogue with more delayed effects. Importantly, IL-33 potently enhances the human mast cell reactivity to C3a and C5a (degranulation, cytokine and chemokine release), independent of changes in C3a or C5a receptor expression or the level of Ca2+ influx. Instead, this reflects differential dynamics of intracellular signaling such as ERK1/2 phosphorylation. Since primary human mast cells respond differentially to anaphylatoxin stimulation, and that IL-33 is a key regulator of mast cell responses to complement anaphylatoxins, this is likely to aggravate Th2 immune responses. This newly identified cross-regulation may be important for controlling exacerbated complement- and mast cell-dependent Th2 responses and thus provides an additional rationale for targeting anti-IL33 therapeutically in allergic diseases.

Therapeutic Modulation of the Complement Cascade in Stroke.

Stroke is a leading cause of death and disability worldwide and an increasing number of ischemic stroke patients are undergoing pharmacological and mechanical reperfusion. Both human and experimental models of reperfused ischemic stroke have implicated the complement cascade in secondary tissue injury. Most data point to the lectin and alternative pathways as key to activation, and C3a and C5a binding of their receptors as critical effectors of injury. During periods of thrombolysis use to treat stroke, acute experimental complement cascade blockade has been found to rescue tissue and improves functional outcome. Blockade of the complement cascade during the period of tissue reorganization, repair, and recovery is by contrast not helpful and in fact is likely to be deleterious with emerging data suggesting downstream upregulation of the cascade might even facilitate recovery. Successful clinical translation will require the right clinical setting and pharmacologic strategies that are capable of targeting the key effectors early while not inhibiting delayed repair. Early reports in a variety of disease states suggest that such pharmacologic strategies appear to have a favorable risk profile and offer substantial hope for patients.

Measuring Circulating Complement Activation Products in Myeloperoxidase- and Proteinase 3-Antineutrophil Cytoplasmic Antibody-Associated Vasculitis.

OBJECTIVE: There is accumulating evidence that complement activation is important in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) pathogenesis. This study was undertaken to investigate complement activation in AAV with myeloperoxidase (MPO) positivity and AAV with proteinase 3 (PR3) positivity after determining optimal methods for measuring activated complement factors in circulation. METHODS: Participants included 98 patients with AAV (45 MPO-ANCA positive, 53 PR3-ANCA positive) and 35 healthy controls. Plasma was obtained from blood collected using EDTA tubes, with or without 100 µg/ml Futhan. Levels of Bb, C3a, C5a, soluble C5b-9 (sC5b-9), properdin, and C4d were measured by enzyme-linked immunosorbent assay. Group comparisons were made using Wilcoxon's 2-sample test. Paired data were analyzed using a matched pairs signed rank test. RESULTS: Compared to healthy controls, certain complement analyte levels were high in patients with active AAV with MPO positivity, including C3a (P < 0.0001), C5a (P = 0.0004), and sC5b-9 (P = 0.0007). During remission, levels of Bb (P = 0.001), C3a (P < 0.0001), and sC5b-9 (P = 0.003) were higher. Compared to healthy controls, C3a (P < 0.0001), C5a (P = 0.002), sC5b-9 (P = 0.0001), and C4d (P = 0.005) levels were higher in patients with active AAV with PR3 positivity; levels of C3a (P < 0.0001) and C4d (P = 0.007) were also higher duriing remission. There were no significant differences in any complement analyte for either ANCA serotype between patients with active disease and those with disease in remission. Among patients with paired samples, sC5-9 levels were significantly lower during disease remission compared to active disease. C5a was significantly lower among patients with disease in long-term remission who were not receiving therapy. For Bb, C5a, and sC5b-9, median levels and individual values were considerably higher in control and patient samples processed without Futhan compared to those processed with Futhan. CONCLUSION: Complement activation occurs in both MPO-positive AAV and PR3-positive AAV. The complement activation profile differs according to disease activity and possibly ANCA serotype. Futhan reduces in vitro complement activation and provides a more accurate measurement.

Targeting the Complement Pathway as a Therapeutic Strategy in Lung Cancer.

Lung cancer is the leading cause of cancer death in men and women. Lung adenocarcinoma (LUAD), represents approximately 40% of all lung cancer cases. Advances in recent years, such as the identification of oncogenes and the use of immunotherapies, have changed the treatment of LUAD. Yet survival rates still remain low. Additionally, there is still a gap in understanding the molecular and cellular interactions between cancer cells and the immune tumor microenvironment (TME). Defining how cancer cells with distinct oncogenic drivers interact with the TME and new strategies for enhancing anti-tumor immunity are greatly needed. The complement cascade, a central part of the innate immune system, plays an important role in regulation of adaptive immunity. Initially it was proposed that complement activation on the surface of cancer cells would inhibit cancer progression via membrane attack complex (MAC)-dependent killing. However, data from several groups have shown that complement activation promotes cancer progression, probably through the actions of anaphylatoxins (C3a and C5a) on the TME and engagement of immunoevasive pathways. While originally shown to be produced in the liver, recent studies show localized complement production in numerous cell types including immune cells and tumor cells. These results suggest that complement inhibitory drugs may represent a powerful new approach for treatment of NSCLC, and numerous new anti-complement drugs are in clinical development. However, the mechanisms by which complement is activated and affects tumor progression are not well understood. Furthermore, the role of local complement production vs. systemic activation has not been carefully examined. This review will focus on our current understanding of complement action in LUAD, and describe gaps in our knowledge critical for advancing complement therapy into the clinic.

Nephritic Factors: An Overview of Classification, Diagnostic Tools and Clinical Associations.

Nephritic factors comprise a heterogeneous group of autoantibodies against neoepitopes generated in the C3 and C5 convertases of the complement system, causing its dysregulation. Classification of these autoantibodies can be clustered according to their stabilization of different convertases either from the classical or alternative pathway. The first nephritic factor described with the capacity to stabilize C3 convertase of the alternative pathway was C3 nephritic factor (C3NeF). Another nephritic factor has been characterized by the ability to stabilize C5 convertase of the alternative pathway (C5NeF). In addition, there are autoantibodies against assembled C3/C5 convertase of the classical and lectin pathways (C4NeF). These autoantibodies have been mainly associated with kidney diseases, like C3 glomerulopathy and immune complex-associated-membranoproliferative glomerulonephritis. Other clinical situations where these autoantibodies have been observed include infections and autoimmune disorders such as systemic lupus erythematosus and acquired partial lipodystrophy. C3 hypocomplementemia is a common finding in all patients with nephritic factors. The methods to measure nephritic factors are not standardized, technically complex, and lack of an appropriate quality control. This review will be focused in the description of the mechanism of action of the three known nephritic factors (C3NeF, C4NeF, and C5NeF), and their association with human diseases. Moreover, we present an overview regarding the diagnostic tools for its detection, and the main therapeutic approach for the patients with nephritic factors.