With complements: C3 inhibition in the clinic

C3 is a key complement protein, located at the nexus of all complement activation pathways. Extracellular, tissue, cell-derived, and intracellular C3 plays critical roles in the immune response that is dysregulated in many diseases, making it an attractive therapeutic target. However, challenges such as very high concentration in blood, increased acute expression, and the elevated risk of infections have historically posed significant challenges in the development of C3-targeted therapeutics. This is further complicated because C3 activation fragments and their receptors trigger a complex network of downstream effects; therefore, a clear understanding of these is needed to provide context for a better understanding of the mechanism of action (MoA) of C3 inhibitors, such as pegcetacoplan. Because of C3's differential upstream position to C5 in the complement cascade, there are mechanistic differences between pegcetacoplan and eculizumab that determine their efficacy in patients with paroxysmal nocturnal hemoglobinuria. In this review, we compare the MoA of pegcetacoplan and eculizumab in paroxysmal nocturnal hemoglobinuria and discuss the complement-mediated disease that might be amenable to C3 inhibition. We further discuss the current state and outlook for C3-targeted therapeutics and provide our perspective on which diseases might be the next success stories in the C3 therapeutics journey.

Inside-Out of Complement in Cancer

The role of complement in cancer has received increasing attention over the last decade. Recent studies provide compelling evidence that complement accelerates cancer progression. Despite the pivotal role of complement in fighting microbes, complement seems to suppress antitumor immunity via regulation of host cell in the tumor microenvironment. Although most studies link complement in cancer to complement activation in the extracellular space, the discovery of intracellular activation of complement, raises the question: what is the relevance of this process for malignancy? Intracellular activation is pivotal for the survival of immune cells. Therefore, complement can be important for tumor cell survival and growth regardless of the role in immunosuppression. On the other hand, because intracellular complement (the complosome) is indispensable for activation of T cells, these functions will be essential for priming antitumor T cell responses. Here, we review functions of complement in cancer with the consideration of extra and intracellular pathways of complement activation and spatial distribution of complement proteins in tumors and periphery and provide our take on potential significance of complement as biomarker and target for cancer therapy.

SARS-CoV-2 drives JAK1/2-dependent local complement hyperactivation

Patients with coronavirus disease 2019 (COVID-19) present a wide range of acute clinical manifestations affecting the lungs, liver, kidneys, and gut. Angiotensin-converting enzyme 2 (ACE2), the best-characterized entry receptor for the disease-causing virus SARS-CoV-2, is highly expressed in the aforementioned tissues. However, the pathways that underlie the disease are still poorly understood. Here, we unexpectedly found that the complement system was one of the intracellular pathways most highly induced by SARS-CoV-2 infection in lung epithelial cells. Infection of respiratory epithelial cells with SARS-CoV-2 generated activated complement component C3a and could be blocked by a cell-permeable inhibitor of complement factor B (CFBi), indicating the presence of an inducible cell-intrinsic C3 convertase in respiratory epithelial cells. Within cells of the bronchoalveolar lavage of patients, distinct signatures of complement activation in myeloid, lymphoid, and epithelial cells tracked with disease severity. Genes induced by SARS-CoV-2 and the drugs that could normalize these genes both implicated the interferon-JAK1/2-STAT1 signaling system and NF-κB as the main drivers of their expression. Ruxolitinib, a JAK1/2 inhibitor, normalized interferon signature genes and all complement gene transcripts induced by SARS-CoV-2 in lung epithelial cell lines but did not affect NF-κB–regulated genes. Ruxolitinib, alone or in combination with the antiviral remdesivir, inhibited C3a protein produced by infected cells. Together, we postulate that combination therapy with JAK inhibitors and drugs that normalize NF-κB signaling could potentially have clinical application for severe COVID-19.

This research was financed by the National Heart, Lung, and Blood Institute of the NIH (grant 5K22HL125593 to M. Kazemian; R01HL119215 to J.R.S.); National Institute of General Medical Sciences of the NIH (grant R35GM138283 to M. Kazemian); and Deutsche Forschungsgemeinschaft (fellowship FR3851/2-1 to T. Freiwald) and supported, in part, by the Intramural Research Program of the NIH; the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) (project number ZIA/DK075149 to B.A.); the National Heart, Lung, and Blood Institute (NHLBI) (project number ZIA/Hl006223 to C.K.); and the National Institute of Allergy and Infectious Diseases (NIAID) (project number ZIA/AI001175 to M.S.L.). T. Frum is supported by T32DE007057. Funding for part of the work was provided by the University of Michigan Biological Scholars Program (to C.E.W.), LifeARC Charity (to S.K.), and CRUK KHP Centre (to S.K.).

Mitochondrial C5aR1 activity in macrophages controls IL-1β production underlying sterile inflammation

While serum-circulating complement destroys invading pathogens, intracellularly active complement, termed the “complosome,” functions as a vital orchestrator of cell-metabolic events underlying T cell effector responses. Whether intracellular complement is also nonredundant for the activity of myeloid immune cells is currently unknown. Here, we show that monocytes and macrophages constitutively express complement component (C) 5 and generate autocrine C5a via formation of an intracellular C5 convertase. Cholesterol crystal sensing by macrophages induced C5aR1 signaling on mitochondrial membranes, which shifted ATP production via reverse electron chain flux toward reactive oxygen species generation and anaerobic glycolysis to favor IL-1β production, both at the transcriptional level and processing of pro–IL-1β. Consequently, atherosclerosis-prone mice lacking macrophage-specific C5ar1 had ameliorated cardiovascular disease on a high-cholesterol diet. Conversely, inflammatory gene signatures and IL-1β produced by cells in unstable atherosclerotic plaques of patients were normalized by a specific cell-permeable C5aR1 antagonist. Deficiency of the macrophage cell-autonomous C5 system also protected mice from crystal nephropathy mediated by folic acid. These data demonstrate the unexpected intracellular formation of a C5 convertase and identify C5aR1 as a direct modulator of mitochondrial function and inflammatory output from myeloid cells. Together, these findings suggest that the complosome is a contributor to the biologic processes underlying sterile inflammation and indicate that targeting this system could be beneficial in macrophage-dependent diseases, such as atherosclerosis.

Mentalizing Glasses: Multifocal Attention in Mentalization-Based Treatment and the Role of the Supervision

Bifocal attention has been conceptualized differently by various scholars; however, all converge in the idea that the therapeutic process includes the need for the therapist to focus his attention on more than one aspect of the therapeutic setting. We propose a novel view in the application of bifocal attention within the mentalizing framework (MBT) of working with children, adolescents, and their families. We start by providing a short history of the evolution of the construct of bifocal attention, followed by a brief description of the structure of MBT for children and adolescents, emphasizing the crucial role of bifocal and multiple attentions in the mentalizing therapist. We close by discussing the importance of continued supervision in facilitating the maintaining of mentalizing glasses in therapy.

The C3-like molecule CD109 controls Th1 versus Th17 induction in CD4+ T cells

Recent workdefined an unexpected and critical role for intracellular/autocrine active complement in human Th1 biology. Specifically, autocrine stimulation of CD46via TCR-induced C3b generation is needed for IFN-γ production by human CD4+ T cells. Thus, CD46-deficient patients are unable to generate normal Th1 responses. Analysis of the CD46-driven gene signature in Th1 cells revealed CD109 as a direct target of CD46. Indeed, T cells from CD46 deficient patients and from healthy donors in which CD46 expression was ablated via CRISPR-Cas9 technology failed to upregulate CD109. CD109 is aGPI-linked surface protein, mostly expressed on non-immune cells, and belongs to the complement C3 protein family. Though CD109 has been reported as a major negative regulator of TGF-β receptor signaling, direct functional activity for of CD109 on T cells remains unexplored.

Knock-out of CD109 in human CD4+ T cells with CRISPR-Cas9 technology induced uncontrolled Th1 and Th17 activation upon in vitro stimulation under non-skewing conditions. Similarly, CD4+T cells from Cd109−/− mice displayed augmented Th1 and Th17 in vitro responses and caused significantly more tissue pathology and weight loss in a T cell-transfer colitis model. Surprisingly, on T cells, CD109 does not restrain IFN-γ and/or IL-17 induction via modulation of TGF-β receptor activity. Instead, CD109 engages with a non-canonical costimulatory molecule and controls stemness- and metabolism-related signaling pathways.

Together, these data suggest that the complement-related protein CD109 serves as an important and novel molecular switch on CD4+ T-cells, where it regulates the balance between Th1 and Th17-induction pathways.

SARS-CoV-2 drives JAK1/2-dependent local complement hyperactivation

Patients with coronavirus disease 2019 (COVID-19) present a wide range of acute clinical manifestations affecting the lungs, liver, kidneys and gut. Angiotensin converting enzyme (ACE) 2, the best-characterized entry receptor for the disease-causing virus SARS-CoV-2, is highly expressed in the aforementioned tissues. However, the pathways that underlie the disease are still poorly understood. Here, we unexpectedly found that the complement system was one of the intracellular pathways most highly induced by SARS-CoV-2 infection in lung epithelial cells. Infection of respiratory epithelial cells with SARS-CoV-2 generated activated complement component C3a and could be blocked by a cell-permeable inhibitor of complement factor B (CFBi), indicating the presence of an inducible cell-intrinsic C3 convertase in respiratory epithelial cells. Within cells of the bronchoalveolar lavage of patients, distinct signatures of complement activation in myeloid, lymphoid and epithelial cells tracked with disease severity. Genes induced by SARS-CoV-2 and the drugs that could normalize these genes both implicated the interferon-JAK1/2-STAT1 signaling system and NF-B as the main drivers of their expression. Ruxolitinib, a JAK1/2 inhibitor, normalized interferon signature genes and all complement gene transcripts induced by SARS-CoV-2 in lung epithelial cell lines, but did not affect NF-B-regulated genes. Ruxolitinib, alone or in combination with the antiviral remdesivir, inhibited C3a protein produced by infected cells. Together, we postulate that combination therapy with JAK inhibitors and drugs that normalize NF-B-signaling could potentially have clinical application for severe COVID-19.

Diapedesis-Induced Integrin Signaling via LFA-1 Facilitates Tissue Immunity by Inducing Intrinsic Complement C3 Expression in Immune Cells

Intrinsic complement C3 activity is integral to human T helper type 1 (Th1) and cytotoxic T cell responses. Increased or decreased intracellular C3 results in autoimmunity and infections, respectively. The mechanisms regulating intracellular C3 expression remain undefined. We identified complement, including C3, as among the most significantly enriched biological pathway in tissue-occupying cells. We generated C3-reporter mice and confirmed that C3 expression was a defining feature of tissue-immune cells, including T cells and monocytes, occurred during transendothelial diapedesis, and depended on integrin lymphocyte-function-associated antigen 1 (LFA-1) signals. Immune cells from patients with leukocyte adhesion deficiency type 1 (LAD-1) had reduced C3 transcripts and diminished effector activities, which could be rescued proportionally by intracellular C3 provision. Conversely, increased C3 expression by T cells from arthritis patients correlated with disease severity. Our study defines integrins as key controllers of intracellular complement, demonstrates that perturbations in the LFA-1-C3-axis contribute to primary immunodeficiency, and identifies intracellular C3 as biomarker of severity in autoimmunity.

T cell-intrinsic C5L2 activation protects against uncontrolled inflammatory Th responses and autoimmunity

Intracellular/autocrine complement proteins have emerged as critical regulators of human Th1 induction and contraction. T cells contain both intracellular C3 and C5 activation systems, with intracellular C3aR1 and C5aR1 stimulation driving T cell homeostatic survival and normal Th1 IFN-gamma production, respectively. Here we demonstrate how the intracellular/autocrine C5 system is regulated by using T cells from the first described patient with C5aR2 deficiency. This patient suffers from an autoinflammatory syndrome, with enhanced inflammatory Th responses and a profound loss of naïve CD4 T cells (95% of CD4 T cells in the blood have a memory T cell phenotype). Thus, in contrast to intracellular C5aR1 stimulation, cell surface expressed C5aR2 is an important negative regulator of inflammatory Th induction. While both C5aR1 and C5aR2 can bind C5a, we found that the carboxypeptidase-processed form of C5a, C5a-desArg, was twice as potent as C5a in reducing Th1 induction. In addition, carboxypeptidase M (CPM) expression was highly induced upon T cell activation indicating that CPM may be mediating T cell-derived C5a-desArg generation and thus, C5aR2 stimulation. In this vein, activation of T cells in the presence of a CPM inhibitor induced Th1 hyper-induction, which was rescued by addition of a C5aR2 agonist and reduced by adding C5a-desArg, but not C5a. The in vivo importance of T cell-expressed CPM and autocrine C5aR2 activation is demonstrated by the fact that CPM−/− mice have enhanced inflammatory Th responses and CPM−/− T cells cause increased pathology in an in vivo T cell transfer colitis model. These data highlight the complex auto-regulatory functions of complement in T cell responses.

Diapedesis and LFA-1 mediate tissue immune cell effector activity via intrinsic complement C3 licensing

Intracellularly generated and autocrine-functioning complement component C3 is a critical integral part of normal human CD4+ Th1 and cytotoxic CD8+ T cells responses. Increased or decreased intracellular C3 result in autoimmunity and infections, respectively. The mechanisms regulating intracellular C3 expression are, however, undefined. By comparing transcriptomes from blood and tissue, we identified the complement system, including C3, as one of the most significantly enriched biological pathways in tissue-occupying cells of human macrophages, CD4+ and CD8+ T cells. By leveraging a novel C3 reporter mouse, we confirmed that C3 gene transcription is a feature of immune cells in tissues, is induced during trans-endothelial diapedesis, and is dependent on the integrin intercellular adhesion molecule (ICAM)-1 liganding lymphocyte function-associated antigen (LFA)-1. Consequently, monocytes and T cells from patients with leukocyte adhesion deficiency (LAD)-1 had reduced C3 and diminished effector activities, which could be rescued proportionally by normalization of intracellular C3. In synovia of patients with rheumatoid arthritis (RA), C3 transcript expression by CD4+ T cells was linearly associated with disease severity and acted as a biomarker distinguishing inflamed versus uninflamed RA. Our study defines the integrin network as a novel and key controller of intracellular complement, demonstrates that perturbations in the LFA-1–C3 axis contribute to primary human immunodeficiency and identifies T cell C3 production as a biomarker of the severity of autoimmunity.

The C3-like molecule CD109 controls Th1 versus Th17 induction in CD4+ T cells

Recent work defined an unexpected and critical role for intracellular/autocrine active complement in human Th1 biology. Specifically, autocrine stimulation of CD46 via TCR-induced C3b generation is needed for IFN-γ production by human CD4+T cells. Analysis of the CD46-driven gene signature in Th1 cells revealed CD109, a C3-like surface protein known to regulate TGF-β signaling, as a direct target of CD46. We confirmed that T cells from patients with CD46 deficiency, which suffer from recurrent infection due to reduced Th1 responses, and from healthy donors knocked-out for CD46 via CRISPR-Cas9 technology failed to upregulate CD109. CD109 is expressed on keratinocytes, endothelial and stem cells and overexpression is connected with cancer but its function on T cells remains unexplored.

In vitro activation of mouse Cd109−/− CD4+ T-cells showed a strong increase of Th1- and Th17-related cytokines compare to their WT counterpart. In line with this observation, Cd109−/− mouse CD4+ T cells showed an increase in IL-17A+ and IFN-γ+/IL-17A+ T cell numbers in vivo and caused significantly more weight loss and disease pathology in a T cell-transfer colitis model. Although CD109 is known to regulate TGF-β signaling, our RNA-sequencing analysis of activated Cd109−/− mouse T cells revealed that this molecule is restraining Th17 induction rather via impact on cell cycle and apoptosis related pathways, which we are investigating now.

Together, these data suggest that the complement-related protein CD109 serves as an important and novel molecular switch on CD4+ T-cells, where it regulates the balance between Th1 and Th17-induction pathways.

Complement and the Regulation of T Cell Responses

The complement system is an evolutionarily ancient key component of innate immunity required for the detection and removal of invading pathogens. It was discovered more than 100 years ago and was originally defined as a liver-derived, blood-circulating sentinel system that classically mediates the opsonization and lytic killing of dangerous microbes and the initiation of the general inflammatory reaction. More recently, complement has also emerged as a critical player in adaptive immunity via its ability to instruct both B and T cell responses. In particular, work on the impact of complement on T cell responses led to the surprising discoveries that the complement system also functions within cells and is involved in regulating basic cellular processes, predominantly those of metabolic nature. Here, we review current knowledge about complement's role in T cell biology, with a focus on the novel intracellular and noncanonical activities of this ancient system.

Brain-based treatment-A new approach or a well-forgotten old one?

For a relatively long period of time, mental functioning was mainly associated with personal profile while brain functioning went by the wayside. After the 90s of the 20th century, or the so called "Decade of the Brain", today, contemporary specialists work on the boundary between fundamental science and medicine. This brings neuroscience, neuropsychology, psychiatry, and psychotherapy closer to each other. Today, we definitely know that brain structures are being built and altered thanks to experience. Psychotherapy can be more effective when based on a neuropsychological approach-this implies identification of the neural foundations of various disorders and will lead to specific psychotherapeutic conclusions. The knowledge about the brain is continually enriched, which leads to periodic rethinking and updating of the therapeutic approaches to various diseases of the nervous system and brain dysfunctions. The aim of translational studies is to match and combine scientific areas, resources, experience and techniques to improve prevention, diagnosis and therapies, and "transformation" of scientific discoveries into potential treatments of various diseases done in laboratory conditions. Neuropsychological studies prove that cognition is a key element that links together brain functioning and behaviour. According to Dr. Kandel, all experimental events, including psychotherapeutic interventions, affect the structure and function of neuronal synapses. The story of why psychotherapy works is a story of understanding the brain mechanisms of psychic processes, a story of how the brain has been evolving to ensure learning, forgetting, and the mechanisms of permanent psychological change. The new evidence on brain functioning necessitates the integration of neuropsychological achievements in the psychotherapeutic process. An integrative approach is needed to take into account the dynamic interaction between brain functioning, psyche, soul, spirit, and social interaction, ie, development of a model of psychotherapeutic work based on cerebral plasticity! Brain-based psychotherapy aims at changing brain functioning not directly, but through experiences. This is neuro-psychologically informed psychotherapy.

Targeting complement-mediated immunoregulation for cancer immunotherapy

Complement was initially discovered as an assembly of plasma proteins "complementing" the cytolytic activity of antibodies. However, our current knowledge places this complex system of several plasma proteins, receptors, and regulators in the center of innate immunity as a bridge between the initial innate responses and adaptive immune reactions. Consequently, complement appears to be pivotal for elimination of pathogens, not only as an early response defense, but by directing the subsequent adaptive immune response. The discovery of functional intracellular complement and its roles in cellular metabolism opened novel avenues for research and potential therapeutic implications. The recent studies demonstrating immunoregulatory functions of complement in the tumor microenvironment and the premetastatic niche shifted the paradigm on our understanding of functions of the complement system in regulating immunity. Several complement proteins, through their interaction with cells in the tumor microenvironment and in metastasis-targeted organs, contribute to modulating tumor growth, antitumor immunity, angiogenesis, and therefore, the overall progression of malignancy and, perhaps, responsiveness of cancer to different therapies. Here, we focus on recent progress in our understanding of immunostimulatory vs. immunoregulatory functions of complement and potential applications of these findings to the design of novel therapies for cancer patients.

Keeping It All Going-Complement Meets Metabolism

The complement system is an evolutionary old and crucial component of innate immunity, which is key to the detection and removal of invading pathogens. It was initially discovered as a liver-derived sentinel system circulating in serum, the lymph, and interstitial fluids that mediate the opsonization and lytic killing of bacteria, fungi, and viruses and the initiation of the general inflammatory responses. Although work performed specifically in the last five decades identified complement also as a critical instructor of adaptive immunity—indicating that complement’s function is likely broader than initially anticipated—the dominant opinion among researchers and clinicians was that the key complement functions were in principle defined. However, there is now a growing realization that complement activity goes well beyond “classic” immune functions and that this system is also required for normal (neuronal) development and activity and general cell and tissue integrity and homeostasis. Furthermore, the recent discovery that complement activation is not confined to the extracellular space but occurs within cells led to the surprising understanding that complement is involved in the regulation of basic processes of the cell, particularly those of metabolic nature—mostly via novel crosstalks between complement and intracellular sensor, and effector, pathways that had been overlooked because of their spatial separation. These paradigm shifts in the field led to a renaissance in complement research and provide new platforms to now better understand the molecular pathways underlying the wide-reaching effects of complement functions in immunity and beyond. In this review, we will cover the current knowledge about complement’s emerging relationship with the cellular metabolism machinery with a focus on the functional differences between serum-circulating versus intracellularly active complement during normal cell survival and induction of effector functions. We will also discuss how taking a closer look into the evolution of key complement components not only made the functional connection between complement and metabolism rather “predictable” but how it may also give clues for the discovery of additional roles for complement in basic cellular processes.

Experimentally-induced anti-myeloperoxidase vasculitis does not require properdin, MASP-2 or bone marrow-derived C5

Anti-neutrophil cytoplasmic antibody vasculitis is a systemic autoimmune disease with glomerulonephritis and pulmonary haemorrhage as major clinical manifestations. The name reflects the presence of autoantibodies to myeloperoxidase and proteinase-3, which bind to both neutrophils and monocytes. Evidence of the pathogenicity of these autoantibodies is provided by the observation that injection of anti-myeloperoxidase antibodies into mice causes a pauci-immune focal segmental necrotizing glomerulonephritis which is histologically similar to the changes seen on renal biopsy in patients. Previous studies in this model have implicated the alternative pathway of complement activation and the anaphylatoxin C5a. Despite this progress, the factors that initiate complement activation have not been defined. In addition, the relative importance of bone marrow-derived and circulating C5 is not known. This is of interest given the recently identified roles for complement within leukocytes. We induced anti-myeloperoxidase vasculitis in mice and confirmed a role for complement activation by demonstrating protection in C3-deficient mice. We showed that neither MASP-2- nor properdin-deficient mice were protected, suggesting that alternative pathway activation does not require properdin or the lectin pathway. We induced disease in bone marrow chimaeric mice and found that circulating and not bone marrow-derived C5 was required for disease. We have therefore excluded properdin and the lectin pathway as initiators of complement activation and this means that future work should be directed at other potential factors within diseased tissue. In addition, in view of our finding that circulating and not bone marrow-derived C5 mediates disease, therapies that decrease hepatic C5 secretion may be considered as an alternative to those that target C5 and C5a. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Complement Regulates Nutrient Influx and Metabolic Reprogramming during Th1 Cell Responses

Expansion and acquisition of Th1 cell effector function requires metabolic reprogramming; however, the signals instructing these adaptations remain poorly defined. Here we found that in activated human T cells, autocrine stimulation of the complement receptor CD46, and specifically its intracellular domain CYT-1, was required for induction of the amino acid (AA) transporter LAT1 and enhanced expression of the glucose transporter GLUT1. Furthermore, CD46 activation simultaneously drove expression of LAMTOR5, which mediated assembly of the AA-sensing Ragulator-Rag-mTORC1 complex and increased glycolysis and oxidative phosphorylation (OXPHOS), required for cytokine production. T cells from CD46-deficient patients, characterized by defective Th1 cell induction, failed to upregulate the molecular components of this metabolic program as well as glycolysis and OXPHOS, but IFN-γ production could be reinstated by retrovirus-mediated CD46-CYT-1 expression. These data establish a critical link between the complement system and immunometabolic adaptations driving human CD4⁺ T cell effector function.

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CD46 regulates GLUT1 and LAT1 and enhances glucose and AA uptake in T cells

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LAMTOR5 mediates Ragulator-Rag-mTORC1 assembly in activated T cells

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Complement drives glycolysis and oxidative phosphorylation critical to Th1 cell induction

Detection of cell membrane-bound CD46 using flow cytometry

CD46 is an important regulator of the complement system by preventing unwanted deposition of the complement activation products and opsonins C3b/C4b onto self-tissue. Recently, intracellular signals mediated by CD46 activation on several distinct human cell types have demonstrated that CD46 also plays decisive roles in immuneregulation. The growing recognition of CD46 as key regulator in several vital biological processes, led to increased demand in sensitive methods for monitoring CD46 expression and changes thereof on cells and in tissues. Here we describe a method, which allows for studying CD46 expression on the surface of cells using specific antibodies in combination with fluorescence-activated cell sorting (FACS) analysis.

Functional analysis of CD59 using complement-dependent cytotoxicity assay

CD59 overexpression has been shown to confer the resistance of tumors to complement lysis. Complement lysis is one of the two major killing mechanisms of therapeutic anticancer antibodies. This chapter provides a method that allows studying the extent of complement protection of tumors by CD59.

Detection of CD59 using flow cytometry

CD59 is the single regulator of the terminal complement pathway. It has been implicated in disease such as Paroxysmal nocturnal hemoglobinuria (PMH) and cancer. Expression of CD59 protects normal and malignant cells from the cytotoxic potential of the complement system. Here we describe a method, which allows for studying its expression on the surface of cells.

Enzymatic Reactions and Detection of C3 Cleavage Fragments

The complement component C3 is the major effector molecule of the complement system. C3 circulates in the blood and interstitial fluids as pro-enzyme and is activated by enzymatic cleavage into a C3a portion, a classic anaphylatoxin that functions as chemoattractant and immune cell activator, and the C3b portion, the body's most potent opsonin. C3 cleavage is in most cases mediated by an enzyme complex called the C3 convertase. However, it is now becoming increasingly clear that the cleavage of C3 by a range of 'single' proteases into bioactive C3a and C3b fragments is of high physiological significance. Here, we describe a protocol for the enzymatic cleavage of human C3 by the serine protease cathepsin L and the detection of the cleavage products C3a and C3b by western blotting as an example for this kind of enzymatic reactions.

Intracellular complement activation sustains T cell homeostasis and mediates effector differentiation

Complement is viewed as a critical serum-operative component of innate immunity, with processing of its key component, C3, into activation fragments C3a and C3b confined to the extracellular space. We report here that C3 activation also occurred intracellularly. We found that the T cell-expressed protease cathepsin L (CTSL) processed C3 into biologically active C3a and C3b. Resting T cells contained stores of endosomal and lysosomal C3 and CTSL and substantial amounts of CTSL-generated C3a. While “tonic” intracellular C3a generation was required for homeostatic T cell survival, shuttling of this intracellular C3-activation-system to the cell surface upon T cell stimulation induced autocrine proinflammatory cytokine production. Furthermore, T cells from patients with autoimmune arthritis demonstrated hyperactive intracellular complement activation and interferon-γ production and CTSL inhibition corrected this deregulated phenotype. Importantly, intracellular C3a was observed in all examined cell populations, suggesting that intracellular complement activation might be of broad physiological significance.

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Complement C3 is activated intracellularly in human T cells by cathepsin L

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Intracellular C3 activation mediates cell survival and Th1 induction

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Increased intracellular C3 activation underlies T effector dysregulation in arthritis

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Patients with serum C3-deficiency retain intracellular C3a generation

Complement in cancer and cancer immunotherapy

Recently, there has been an increase of interest in the use of biological or immune-based therapies for patients with malignancies. This has been informed by the deeper understanding of the crosstalk between the host immune system and malignant tumours, as well as the potential advantages of immunotherapy-high specificity and less toxicity compared to standard approaches. The particular emphasis of this article is on the role of the complement system in tumour growth and antibody-based cancer immunotherapy. The functional consequences from overexpression of complement regulators by tumours and the development of strategies for overcoming this are discussed in detail. This review discusses these issues with a view to inspiring the development of new agents that could be useful for the treatment of cancer.

Interplay between REST and nucleolin transcription factors: a key mechanism in the overexpression of genes upon increased phosphorylation

Non-malignant cells can be transformed via the activation of kinases that control degradation of neural-restrictive silencer factor (REST). Here, we identify a mechanism that contributes to the activation of genes, expression of which is controlled by responsive elements containing overlapping binding sites for REST and nucleolin. We demonstrate that both phosphorylated and non-phosphorylated nucleolin-bound DNA; however, only phosphorylated nucleolin successfully competed with either full-length REST or a REST-derived DNA-binding peptide, REST68, for binding to the overlapping binding sites. We show that this interplay between the two transcription factors regulates the activation of cell survival and immunomodulatory genes in tumors and non-malignant cells with activated protein kinase C, which is accompanied with alterations in cell proliferation and apoptosis. We propose a model for the regulation of these genes, which brings a new insight into the molecular mechanisms that control cellular transformation driven by activation of protein kinases.

Neuronal death in Alzheimer's disease and therapeutic opportunities

Alzheimer’s disease (AD) is an age-related neurodegenerative disease that affects approximately 24 million people worldwide. A number of different risk factors have been implicated in AD; however, neuritic (amyloid) plaques are considered as one of the defining risk factors and pathological hallmarks of the disease. In the past decade, enormous efforts have been devoted to understand the genetics and molecular pathogenesis leading to neuronal death in AD, which has been transferred into extensive experimental approaches aimed at reversing disease progression. Modern medicine is facing an increasing number of treatments available for vascular and neurodegenerative brain diseases, but no causal or neuroprotective treatment has yet been established. Almost all neurological conditions are characterized by progressive neuronal dysfunction, which, regardless of the pathogenetic mechanism, finally leads to neuronal death. The particular emphasis of this review is on risk factors and mechanisms resulting in neuronal loss in AD and current and prospective opportunities for therapeutic interventions. This review discusses these issues with a view to inspiring the development of new agents that could be useful for the treatment of AD.

Mannan-binding lectin deficiency modulates the humoral immune response dependent on the genetic environment

Mannan-binding lectin (MBL) is a plasma protein implicated in innate immune defence against a broad range of microorganisms, including viruses. It is also thought that MBL plays a role in the recruitment of the specific clonal immune response. This was studied by injecting soluble hepatitis B surface antigen (HBsAg) intravenously into mice deficient in both MBL-A and MBL-C (MBL DKO mice). The MBL DKO animals on mixed genetic background (SV129EvSv x C57BL/6) produced higher antibody titres than the wild-type littermates. After primary challenge with the antigen the immunoglobulin M anti-HBsAg antibody titres were threefold higher in the MBL DKO mice than in the wild-type mice. Following the boost, the immunoglobulin G anti-HBsAg antibody titres were 10-fold higher in the MBL DKO mice, suggesting that MBL plays a role in a negative feedback regulation of adaptive immunity. However, the modulating effect of MBL was dependent on the genetic environment. The MBL DKO mice backcrossed on a C57BL/6 background showed the opposite response with the MBL DKO mice now producing fewer antibodies than the wild-type animals, whereas MBL deficiency in mice with the SV129EvSv background did not show any effect in antibody production. These findings indicate that the modifying effect of MBL on the humoral immune response is influenced by the genetic environment.

Polymorphisms in mannan-binding lectin (MBL)-associated serine protease 2 affect stability, binding to MBL, and enzymatic activity

Mannan-binding lectin-associated serine protease 2 (MASP-2) is an enzyme of the innate immune system. MASP-2 forms complexes with the pattern recognition molecules mannan-binding lectin (MBL), H-ficolin, L-ficolin, or M-ficolin, and is activated when one of these proteins recognizes microorganisms and subsequently cleaves complement factors C4 and C2, thus initiating the activation of the complement system. Missense polymorphisms of MASP-2 exist in different ethnic populations. To further characterize the nature of these, we have produced and characterized rMASP-2s representing the following naturally occurring polymorphisms: R99Q, D120G, P126L, H155R, 156_159dupCHNH (CHNHdup), V377A, and R439H. Only very low levels of CHNHdup were secreted from the cells, whereas quantities similar to wild-type MASP-2 were found intracellularly, indicating that this mutation results in a misfolded protein. We found that D120G and CHNHdup could not associate with MBL, whereas R99Q, P126L, H155R, V377A, R439H, and wild-type MASP-2 bound equally well to MBL. Accordingly, when D120G and CHNHdup were mixed with MBL, no activation of complement factor C4 was observed, whereas R99Q, P126L, and V377A cleaved C4 with an activity comparable to wild-type MASP-2 and H155R slightly better. In contrast, the R439H variant was deficient in this process despite its normal binding to MBL. This variant was also not able to autoactivate in the presence of MBL and mannan. We find the R439H variant is common in Sub-Saharan Africans with a gene frequency of 10%. Our results indicate that individuals with different types of MASP-2 defects may be identified through genotyping.

Correlation between Animal and Mathematical Models for Prostate Cancer Progression

This work demonstrates that prostate tumour progressionin vivocan be analysed by using solutions of a mathematical model supplemented by initial conditions chosen according to growth rates of cell linesin vitro. The mathematical model is investigated and solved numerically. Its numerical solutions are compared with experimental data from animal models. The numerical results confirm the experimental results with the growth ratesin vivo.

Existence of different but overlapping IgG- and IgM-binding sites on the globular domain of human C1q

C1q is the first subcomponent of the classical complement pathway that binds antigen-bound IgG or IgM and initiates complement activation via association of serine proteases C1r and C1s. The globular domain of C1q (gC1q), which is the ligand-recognition domain, is a heterotrimeric structure composed of the C-terminal regions of A (ghA), B (ghB), and C (ghC) chains. The expression and functional characterization of ghA, ghB, and ghC modules have revealed that each chain has some structural and functional autonomy. Although a number of studies have tried to identify IgG-binding sites on the gC1q domain, no such attempt has been made to localize IgM-binding site. On the basis of the information available via the gC1q crystal structure, molecular modeling, mutational studies, and bioinformatics, we have generated a series of substitution mutants of ghA, ghB, and ghC and examined their interactions with IgM. The comparative analysis of IgM- and IgG-binding abilities of the mutants suggests that the IgG- and IgM-binding sites within the gC1q domain are different but may overlap. Whereas Arg(B108), Arg (B109), and Tyr(B175) mainly constitute the IgM-binding site, the residues Arg(B114), Arg(B129), Arg(B163), and His(B117) that have been shown to be central to IgG binding are not important for the C1q-IgM interaction. Given the location of Arg(B108), Arg (B109), and Tyr(B175) in the gC1q crystal structure, it is likely that C1q interacts with IgM via the top of the gC1q domain.

Interaction of C1q with IgG1, C-reactive protein and pentraxin 3: mutational studies using recombinant globular head modules of human C1q A, B, and C chains

C1q is the first subcomponent of the classical complement pathway that can interact with a range of biochemically and structurally diverse self and nonself ligands. The globular domain of C1q (gC1q), which is the ligand-recognition domain, is a heterotrimeric structure composed of the C-terminal regions of A (ghA), B (ghB), and C (ghC) chains. The expression and functional characterization of ghA, ghB, and ghC modules have revealed that each chain has specific and differential binding properties toward C1q ligands. It is largely considered that C1q-ligand interactions are ionic in nature; however, the complementary ligand-binding sites on C1q and the mechanisms of interactions are still unclear. To identify the residues on the gC1q domain that are likely to be involved in ligand recognition, we have generated a number of substitution mutants of ghA, ghB, and ghC modules and examined their interactions with three selected ligands: IgG1, C-reactive protein (CRP), and pentraxin 3 (PTX3). Our results suggest that charged residues belonging to the apex of the gC1q heterotrimer (with participation of all three chains) as well as the side of the ghB are crucial for C1q binding to these ligands, and their contribution to each interaction is different. It is likely that a set of charged residues from the gC1q surface participate via different ionic and hydrogen bonds with corresponding residues from the ligand, instead of forming separate binding sites. Thus, a recently proposed model suggesting the rotation of the gC1q domain upon ligand recognition may be extended to C1q interaction with CRP and PTX3 in addition to IgG1.