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Non-invasive mucosal sampling (nasosorption and nasal curettage) was used following nasal allergen challenge with grass pollen in subjects with allergic rhinitis, in order to define the molecular basis of the late allergic reaction (LAR). It was found that the nasal LAR to grass pollen involves parallel changes in pathways of type 2 inflammation (IL-4, IL-5 and IL-13), inflammasome-related (IL-1β), and complement and circadian-associated genes. A grass pollen nasal spray was given to subjects with hay fever followed by serial sampling, in which cytokines and chemokines were measured in absorbed nasal mucosal lining fluid, and global gene expression (transcriptomics) assessed in nasal mucosal curettage samples. Twelve of 19 subjects responded with elevations in interleukin (IL)-5, IL-13, IL-1β and MIP-1β/CCL4 protein levels in the late phase. In addition, in these individuals whole-genome expression profiling showed upregulation of type 2 inflammation involving eosinophils and IL-4, IL-5 and IL-13; neutrophil recruitment with IL-1α and IL-1β; the alternative pathway of complement (factor P and C5aR); and prominent effects on circadian-associated transcription regulators. Baseline IL-33 mRNA strongly correlated with these late-phase responses, whereas a single oral dose of prednisone dose-dependently reversed most nasal allergen challenge-induced cytokine and transcript responses. This study shows that the LAR to grass pollen involves a range of inflammatory pathways and suggests potential new biomarkers and therapeutic targets. Furthermore, the marked variation in mucosal inflammatory events between different patients suggests that in the future precision mucosal sampling may enable rational specific therapy.

ObjectiveTo investigate complement system activation and complement protein levels in relation to radiographic progression in axial spondyloarthritis (axSpA) within a longitudinal randomised controlled trial (RCT) of radiographic axSpA patients initiating tumour necrosis factor inhibitor (TNFi) therapy.MethodsSerum samples from 96 patients with active radiographic axSpA in the multicentre RCT CONSUL were analysed by immunoassays for complement activation, that is, C3dg and complement proteins (MBL, CL-L1, M-, H- and L-ficolin; MASP-1,–2 and −3; and MAp44) before and after 108 weeks of TNF inhibitor therapy with golimumab.ResultsBaseline serum levels of total complement activation, that is, C3dg and lectin pathway activating protease MASP-1 were elevated in patients with new bone formation (new syndesmophytes and/or growth of existing syndesmophytes) after 2 years of follow-up, whereas baseline MASP-3 levels were decreased. Assessed by univariate logistic regression, baseline levels of MASP-1, MASP-3 and C3dg were associated with the development of new bone formation and remained significant in a corresponding multivariate logistic regression analysis. At follow-up, serum levels of C3dg and complement lectin pathway initiator L-ficolin were elevated in patients with new bone formation, and C3dg remained significant in a corresponding multivariate logistic regression analysis.ConclusionsComplement activation marker C3dg, MASP-1 and MASP-3 levels before TNFi therapy predicted new bone formation after 2 years of follow-up among axSpA patients with a high risk of radiographic progression. Furthermore, levels of L-ficolin and C3dg at follow-up were elevated in axSpA patients with new bone formation. Our findings support an association between activation of the complement system and radiographic spinal progression in patients with axSpA.

Deposition of complement factors (opsonization) on nanoparticles may promote clearance from the blood by macrophages and trigger proinflammatory responses, but the mechanisms regulating the efficiency of complement activation are poorly understood. We previously demonstrated that opsonization of superparamagnetic iron oxide (SPIO) nanoworms with the third complement protein (C3) was dependent on the biomolecule corona of the nanoparticles. Here we show that natural antibodies play a critical role in C3 opsonization of SPIO nanoworms and a range of clinically approved nanopharmaceuticals. The dependency of C3 opsonization on immunoglobulin binding is almost universal and is observed regardless of the complement activation pathway. Only a few surface-bound immunoglobulin molecules are needed to trigger complement activation and opsonization. Although the total amount of plasma proteins adsorbed on nanoparticles does not determine C3 deposition efficiency, the biomolecule corona per se enhances immunoglobulin binding to all nanoparticle types. We therefore show that natural antibodies represent a link between biomolecule corona and C3 opsonization, and may determine individual complement responses to nanomedicines.Immunoglobulins mediate deposition of the third complement protein (C3) on the biomolecule corona of nanoparticles, promoting complement activation.

Endometriosis (EMS) is a disease that shows immune dysfunction and chronic inflammation characteristics, suggesting a role of complement system in its pathophysiology. To find out the hub genes and pathways involved in the pathogenesis of EMs, three raw microarray datasets were recruited from the Gene Expression Omnibus database (GEO). Then, a series of bioinformatics technologies including gene ontology (GO), Hallmark pathway enrichment, protein–protein interaction (PPI) network and gene co-expression correlation analysis were performed to identify hub genes. The hub genes were further verified by the Real-time quantitative polymerase chain reaction (RT-PCR) and Western Blot (WB). We identified 129 differentially expressed genes (DEGs) in EMs, of which 78 were up-regulated and 51 were down-regulated. Through GO functional enrichment analysis, we found that the DEGs are mainly enriched in cell adhesion, extracellular matrix remodeling, chemokine regulation, angiogenesis regulation, epithelial cell proliferation, et al. In Hallmark pathway enrichment analysis, coagulation pathway showed great significance and the terms in which included the central complement factors. Moreover, the genes were dominating in PPI network. Combined co-expression analysis with experimental verification, we found that the up-regulated expression of complement (C1S, C1QA, C1R, and C3) was positively related to tissue factor (TF) in EMs. In this study, we discovered the over expression complement and the positive correlation between complement and TF in EMs, which suggested that interaction of complement and coagulation system may play a role within the pathophysiology of EMS.

Oxidative stress and enhanced lipid peroxidation are linked to many chronic inflammatory diseases, including age-related macular degeneration (AMD). AMD is the leading cause of blindness in Western societies, but its aetiology remains largely unknown. Malondialdehyde (MDA) is a common lipid peroxidation product that accumulates in many pathophysiological processes, including AMD. Here we identify complement factor H (CFH) as a major MDA-binding protein that can block both the uptake of MDA-modified proteins by macrophages and MDA-induced proinflammatory effects in vivo in mice. The CFH polymorphism H402, which is strongly associated with AMD, markedly reduces the ability of CFH to bind MDA, indicating a causal link to disease aetiology. Our findings provide important mechanistic insights into innate immune responses to oxidative stress, which may be exploited in the prevention of and therapy for AMD and other chronic inflammatory diseases. Causes of age-related macular degeneration Age-related macular degeneration (AMD) is a leading cause of blindness in older people. A polymorphism in complement factor H (CFH) has been strongly associated with the disease, but the mechanism of the association has been unclear. Here it is shown that CFH binds specifically to the lipid peroxidation product, malondialdehyde, which builds up in AMD as a result of oxidative stress. Malondialdehyde and malondialdehyde-modified proteins induce inflammatory responses; CFH neutralizes this inflammatory potential both in vitro and in the mouse retina. A common CFH polymorphism associated with AMD leads to impaired binding to malondialdehyde, potentially explaining why homozygous individuals with this polymorphism have a 6–7-fold increased risk of developing the condition.

Injury is a key driver of inflammation, a critical yet necessary response involving several mediators that is aimed at restoring tissue homeostasis. Inflammation in the central nervous system can be triggered by a variety of stimuli, some intrinsic to the brain and others arising from peripheral signals. Fine-tuned regulation of this response is crucial in a system that is vulnerable due to, for example, aging and ongoing neurodegeneration. In this context, seemingly harmless interventions like a common surgery to repair a broken limb can overwhelm the immune system and become the driver of further complications such as delirium and other perioperative neurocognitive disorders. Here, we discuss potential mechanisms by which the immune system affects the central nervous system after surgical trauma. Together, these neuroimmune interactions are becoming hallmarks of and potential therapeutic targets for multiple neurologic conditions, including those affecting the perioperative space. Terrando and colleagues review key mechanisms related to postoperative inflammation and the implications for developing perioperative neurocognitive disorders, with a focus on neuroinflammation and key cellular targets affected by surgical trauma.

Granzymes are a family of serine proteases that are mainly expressed by CD8 + T cells, natural killer cells and innate-like lymphocytes 1 . Although their primary function is thought to be the induction of cell death in virally infected cells and tumours, accumulating evidence indicates that some granzymes can elicit inflammation by acting on extracellular substrates 1 . We previously found that most tissue CD8 + T cells in rheumatoid arthritis synovium, and in inflamed organs for some other diseases, express granzyme K (GZMK) 2 , a tryptase-like protease with poorly defined function. Here, we show that GZMK can activate the complement cascade by cleaving the C2 and C4 proteins. The nascent C4b and C2b fragments form a C3 convertase that cleaves C3, enabling the assembly of a C5 convertase that cleaves C5. The resulting convertases generate all the effector molecules of the complement cascade: the anaphylatoxins C3a and C5a, the opsonins C4b and C3b, and the membrane attack complex. In rheumatoid arthritis synovium, GZMK is enriched in regions with abundant complement activation, and fibroblasts are the main producers of complement proteins that serve as substrates for GZMK-mediated complement activation. Furthermore, Gzmk -deficient mice are significantly protected from inflammatory disease, exhibiting reduced arthritis and dermatitis, with concomitant decreases in complement activation. Our findings describe the discovery of a previously unidentified mechanism of complement activation that is driven entirely by lymphocyte-derived GZMK. Given the widespread abundance of GZMK -expressing T cells in tissues in chronic inflammatory diseases, GZMK-mediated complement activation is likely to be an important contributor to tissue inflammation in multiple disease contexts. A study finds that a protease called granzyme K can activate the entire complement cascade, explaining how it can drive destructive inflammation in inflammatory diseases such as rheumatoid arthritis.

The complement system consists of a network of plasma and membrane proteins that modulate tissue homeostasis and contribute to immune surveillance by interacting with the innate and adaptive immune systems. Dysregulation, impairment or inadvertent activation of complement components contribute to the pathogenesis of some autoimmune neurological disorders and could even contribute to neurodegenerative diseases. In this Review, we summarize current knowledge about the main functions of the complement pathways and the involvement of complement in neurological disorders. We describe the complex network of complement proteins that target muscle, the neuromuscular junction, peripheral nerves, the spinal cord or the brain and discuss the autoimmune mechanisms of complement-mediated myopathies, myasthenia, peripheral neuropathies, neuromyelitis and other CNS disorders. We also consider the emerging role of complement in some neurodegenerative diseases, such as Alzheimer disease, amyotrophic lateral sclerosis and even schizophrenia. Finally, we provide an overview of the latest complement-targeted immunotherapies including monoclonal antibodies, fusion proteins and peptidomimetics that have been approved, that are undergoing phase I–III clinical trials or that show promise for the treatment of neurological conditions that respond poorly to existing immunotherapies.In this Review, Dalakas et al. discuss the complement system, the role it plays in autoimmune neurological disease and neurodegenerative disease, and provide an overview of the latest therapeutics that target complement and that can be used for or have potential in neurological disorders.

Lambris and colleagues discuss new and previously unanticipated functions of complement and how these affect immunity and disease pathogenesis. Progress at the beginning of the 21st century transformed the perception of complement from that of a blood-based antimicrobial system to that of a global regulator of immunity and tissue homeostasis. More recent years have witnessed remarkable advances in structure–function insights and understanding of the mechanisms and locations of complement activation, which have added new layers of complexity to the biology of complement. This complexity is readily reflected by the multifaceted and contextual involvement of complement-driven networks in a wide range of inflammatory and neurodegenerative disorders and cancer. This Review provides an updated view of new and previously unanticipated functions of complement and how these affect immunity and disease pathogenesis.

Glioblastoma (GBM) is the most prevalent and malignant primary brain tumor in adults. While immune evasion is a well-recognized driver of GBM progression and a major obstacle for efficient immunotherapy, the role of the complement system remains underexplored. C1-inhibitor (C1-INH), a regulator of complement activation, was recently found overexpressed in GBM. We therefore hypothesized that GBM overexpresses additional complement regulators beyond C1-INH and the present work aimed to identify these. Gene expression of complement inhibitors, the complement regulator pentraxin-3 (PTX3), and complement proteins was analyzed across nine publicly available transcriptomic datasets. Within each dataset, statistical comparisons were performed between sample groups for each gene. Differentially expressed complement inhibitors were validated at the protein level by immunostaining in the rat GBM cell line NS1 and patient derived GBM tissue. CFI, encoding factor I, was significantly overexpressed in GBM compared to non-tumoral brain, while THBD and CFH, encoding thrombomodulin and factor H, displayed moderate overexpression. SERPING1, encoding C1-INH, was also upregulated, confirming previous findings. Immunostaining confirmed the expression of these inhibitors in vitro as well as in human glioblastoma tissue. Additionally, PTX3 and early complement proteins were significantly overexpressed in GBM, while levels of C5 and downstream components were comparable to normal brain. Our findings indicate that the GBM tumor overexpresses a specific set of complement regulators and components of the complement cascade, possibly inhibiting an efficient anti-tumoral immune response. Further investigations of these regulators as potential therapeutical targets in GBM are therefore highly warranted.