Complement modulation of T cell immune responses during homeostasis and disease

Derivation and transcriptional reprogramming of border-forming wound repair astrocytes after spinal cord injury or stroke in mice

Central nervous system (CNS) lesions become surrounded by neuroprotective borders of newly proliferated reactive astrocytes; however, fundamental features of these cells are poorly understood. Here we show that following spinal cord injury or stroke, 90% and 10% of border-forming astrocytes derive, respectively, from proliferating local astrocytes and oligodendrocyte progenitor cells in adult mice of both sexes. Temporal transcriptome analysis, single-nucleus RNA sequencing and immunohistochemistry show that after focal CNS injury, local mature astrocytes dedifferentiate, proliferate and become transcriptionally reprogrammed to permanently altered new states, with persisting downregulation of molecules associated with astrocyte-neuron interactions and upregulation of molecules associated with wound healing, microbial defense and interactions with stromal and immune cells. These wound repair astrocytes share morphologic and transcriptional features with perimeningeal limitans astrocytes and are the predominant source of neuroprotective borders that re-establish CNS integrity around lesions by separating neural parenchyma from stromal and immune cells as occurs throughout the healthy CNS.

The Interactions of the Complement System with Human Cytomegalovirus

The complement system is an evolutionarily ancient component of innate immunity that serves as an important first line of defense against pathogens, including viruses. In response to infection, the complement system can be activated by three distinct yet converging pathways (classical, lectin, and alternative) capable of engaging multiple antiviral host responses to confront acute, chronic, and recurrent viral infections. Complement can exert profound antiviral effects via multiple mechanisms including the induction of inflammation and chemotaxis to sites of infection, neutralization/opsonization of viruses and virally infected cells, and it can even shape adaptive immune responses. With millions of years of co-evolution and the ability to establish life-long infections, herpesviruses have evolved unique mechanisms to counter complement-mediated antiviral defenses, thus enabling their survival and replication within humans. This review aims to comprehensively summarize how human herpesviruses engage with the complement system and highlight our understanding of the role of complement in human cytomegalovirus (HCMV) infection, immunity, and viral replication. Herein we describe the novel and unorthodox roles of complement proteins beyond their roles in innate immunity and discuss gaps in knowledge and future directions of complement and HCMV research.

Complement, complosome, and complotype: A perspective

Recent rapid progress in key technological advances, including the broader accessibility of single-cell "omic" approaches, have allowed immunologists to gain important novel insights into the contributions of individual immune cells in protective immunity and immunopathologies. These insights also taught us that there is still much to uncover about the (cellular) networks underlying immune responses. For example, in the last decade, studies on a key component of innate immunity, the complement system, have defined intracellularly active complement (the complosome) as a key orchestrator of normal cell physiology. This added an unexpected facet to the biology of complement, which was long considered fully explored. Here, we will summarize succinctly the known activation modes and functions of the complosome and provide a perspective on the origins of intracellular complement. We will also make a case for extending assessments of the complotype, the individual inherited landscape of common variants in complement genes, to the complosome, and for reassessing patients with known serum complement deficiencies for complosome perturbations. Finally, we will discuss where we see current opportunities and hurdles for dissecting the compartmentalization of complement activities toward a better understanding of their contributions to cellular function in health and disease.

Complement System and the Kidney: Its Role in Renal Diseases, Kidney Transplantation and Renal Cell Carcinoma

The crosstalk among the complement system, immune cells, and mediators of inflammation provides an efficient mechanism to protect the organism against infections and support the repair of damaged tissues. Alterations in this complex machinery play a role in the pathogenesis of different diseases. Core complement proteins C3 and C5, their activation fragments, their receptors, and their regulators have been shown to be active intracellularly as the complosome. The kidney is particularly vulnerable to complement-induced damage, and emerging findings have revealed the role of complement system dysregulation in a wide range of kidney disorders, including glomerulopathies and ischemia-reperfusion injury during kidney transplantation. Different studies have shown that activation of the complement system is an important component of tumorigenesis and its elements have been proved to be present in the TME of various human malignancies. The role of the complement system in renal cell carcinoma (RCC) has been recently explored. Clear cell and papillary RCC upregulate most of the complement genes relative to normal kidney tissue. The aim of this narrative review is to provide novel insights into the role of complement in kidney disorders.

Revisiting the role of the complement system in intracerebral hemorrhage and therapeutic prospects

Intracerebral hemorrhage (ICH) is a stroke subtype characterized by non-traumatic rupture of blood vessels in the brain, resulting in blood pooling in the brain parenchyma. Despite its lower incidence than ischemic stroke, ICH remains a significant contributor to stroke-related mortality, and most survivors experience poor outcomes that significantly impact their quality of life. ICH has been accompanied by various complex pathological damage, including mechanical damage of brain tissue, hematoma mass effect, and then leads to inflammatory response, thrombin activation, erythrocyte lysis, excitatory amino acid toxicity, complement activation, and other pathological changes. Accumulating evidence has demonstrated that activation of complement cascade occurs in the early stage of brain injury, and the excessive complement activation after ICH will affect the occurrence of secondary brain injury (SBI) through multiple complex pathological processes, aggravating brain edema, and pathological brain injury. Therefore, the review summarized the pathological mechanisms of brain injury after ICH, specifically the complement role in ICH, and its related pathological mechanisms, to comprehensively understand the specific mechanism of different complements at different stages after ICH. Furthermore, we systematically reviewed the current state of complement-targeted therapies for ICH, providing a reference and basis for future clinical transformation of complement-targeted therapy for ICH.

An overview of complement systems in teleosts

Complement plays an important role in the innate immune system, and it comprises about 35 individual proteins. In mammals, complement is activated via three different pathways, the classical pathway, the alternative pathway, and the lectin pathway. All three activation pathways produce C3-convertase in different forms. C3-convertase cleaves C3 to C3a and C3b and initiates a cascade of cleavage and activation, eventually resulting in the formation of the membrane attack complex. Complement activation results in the generation of activated fragments that are involved in microbial killing, phagocytosis, inflammatory reactions, immune complex clearance, and antibody production. Although the complement system has been studied extensively in mammals, complement is less well understood in teleosts. This review summarizes the current knowledge of the teleost complement components involved in phagocytosis, chemotaxis, and cell lysis. We report the characterized complement components in various teleost species. In addition, we provide a comprehensive compilation of complement regulators, and this information is used to analyze the role of complement regulators in pathogen infection. The influence of complement receptors on the immune responses of teleosts is reviewed. Finally, we propose directions for future study of the molecular evolution, structure, and function of complement components in teleosts. This review provides new insights into the complement system of recognition and defense, and such knowledge is essential for the development of new immune strategies in aquaculture.

The role of the complement system in Multiple Sclerosis: A review

The complement system has been involved in the pathogenesis of multiple neuroinflammatory and neurodegenerative conditions. In this review, we evaluated the possible role of complement activation in multiple sclerosis (MS) with a focus in progressive MS, where the disease pathogenesis remains to be fully elucidated and treatment options are limited. The evidence for the involvement of the complement system in the white matter plaques and gray matter lesions of MS stems from immunohistochemical analysis of post-mortem MS brains, in vivo serum and cerebrospinal fluid biomarker studies, and animal models of Experimental Autoimmune Encephalomyelitis (EAE). Complement knock-out studies in these animal models have revealed that this system may have a “double-edge sword” effect in MS. On the one hand, complement proteins may aid in promoting the clearance of myelin degradation products and other debris through myeloid cell-mediated phagocytosis. On the other, its aberrant activation may lead to demyelination at the rim of progressive MS white matter lesions as well as synapse loss in the gray matter. The complement system may also interact with known risk factors of MS, including as Epstein Barr Virus (EBV) infection, and perpetuate the activation of CNS self-reactive B cell populations. With the mounting evidence for the involvement of complement in MS, the development of complement modulating therapies for this condition is appealing. Herein, we also reviewed the pharmacological complement inhibitors that have been tested in MS animal models as well as in clinical trials for other neurologic diseases. The potential use of these agents, such as the C5-binding antibody eculizumab in MS will require a detailed understanding of the role of the different complement effectors in this disease and the development of better CNS delivery strategies for these compounds.

Modulation of C5a-C5aR1 signaling alters the dynamics of AD progression

BACKGROUND

The complement system is part of the innate immune system that clears pathogens and cellular debris. In the healthy brain, complement influences neurodevelopment and neurogenesis, synaptic pruning, clearance of neuronal blebs, recruitment of phagocytes, and protects from pathogens. However, excessive downstream complement activation that leads to generation of C5a, and C5a engagement with its receptor C5aR1, instigates a feed-forward loop of inflammation, injury, and neuronal death, making C5aR1 a potential therapeutic target for neuroinflammatory disorders. C5aR1 ablation in the Arctic (Arc) model of Alzheimer's disease protects against cognitive decline and neuronal injury without altering amyloid plaque accumulation.

METHODS

To elucidate the effects of C5a-C5aR1 signaling on AD pathology, we crossed Arc mice with a C5a-overexpressing mouse (ArcC5a+) and tested hippocampal memory. RNA-seq was performed on hippocampus and cortex from Arc, ArcC5aR1KO, and ArcC5a+ mice at 2.7-10 months and age-matched controls to assess mechanisms involved in each system. Immunohistochemistry was used to probe for protein markers of microglia and astrocytes activation states.

RESULTS

ArcC5a+ mice had accelerated cognitive decline compared to Arc. Deletion of C5ar1 delayed or prevented the expression of some, but not all, AD-associated genes in the hippocampus and a subset of pan-reactive and A1 reactive astrocyte genes, indicating a separation between genes induced by amyloid plaques alone and those influenced by C5a-C5aR1 signaling. Biological processes associated with AD and AD mouse models, including inflammatory signaling, microglial cell activation, and astrocyte migration, were delayed in the ArcC5aR1KO hippocampus. Interestingly, C5a overexpression also delayed the increase of some AD-, complement-, and astrocyte-associated genes, suggesting the possible involvement of neuroprotective C5aR2. However, these pathways were enhanced in older ArcC5a+ mice compared to Arc. Immunohistochemistry confirmed that C5a-C5aR1 modulation in Arc mice delayed the increase in CD11c-positive microglia, while not affecting other pan-reactive microglial or astrocyte markers.

CONCLUSION

C5a-C5aR1 signaling in AD largely exerts its effects by enhancing microglial activation pathways that accelerate disease progression. While C5a may have neuroprotective effects via C5aR2, engagement of C5a with C5aR1 is detrimental in AD models. These data support specific pharmacological inhibition of C5aR1 as a potential therapeutic strategy to treat AD.

Role of the Complement System in the Modulation of T-Cell Responses in Chronic Chagas Disease

Chagas disease, caused by the intracellular pathogen Trypanosoma cruzi, is the parasitic disease with the greatest impact in Latin America and the most common cause of infectious myocarditis in the world. The immune system plays a central role in the control of T. cruzi infection but at the same time needs to be controlled to prevent the development of pathology in the host. It has been shown that persistent infection with T. cruzi induces exhaustion of parasite-specific T cell responses in subjects with chronic Chagas disease. The continuous inflammatory reaction due to parasite persistence in the heart also leads to necrosis and fibrosis. The complement system is a key element of the innate immune system, but recent findings have also shown that the interaction between its components and immune cell receptors might modulate several functions of the adaptive immune system. Moreover, the findings that most of immune cells can produce complement proteins and express their receptors have led to the notion that the complement system also has non canonical functions in the T cell. During human infection by T. cruzi, complement activation might play a dual role in the acute and chronic phases of Chagas disease; it is initially crucial in controlling parasitemia and might later contributes to the development of symptomatic forms of Chagas disease due to its role in T-cell regulation. Herein, we will discuss the putative role of effector complement molecules on T-cell immune exhaustion during chronic human T. cruzi infection.

Tumor Treating Fields dually activate STING and AIM2 inflammasomes to induce adjuvant immunity in glioblastoma

Tumor Treating Fields (TTFields), an approved therapy for glioblastoma (GBM) and malignant mesothelioma, employ noninvasive application of low-intensity, intermediate-frequency, alternating electric fields to disrupt the mitotic spindle, leading to chromosome missegregation and apoptosis. Emerging evidence suggests that TTFields may also induce inflammation. However, the mechanism underlying this property and whether it can be harnessed therapeutically are unclear. Here, we report that TTFields induced focal disruption of the nuclear envelope, leading to cytosolic release of large micronuclei clusters that intensely recruited and activated 2 major DNA sensors - cyclic GMP-AMP synthase (cGAS) and absent in melanoma 2 (AIM2) - and their cognate cGAS/stimulator of interferon genes (STING) and AIM2/caspase 1 inflammasomes to produce proinflammatory cytokines, type 1 interferons (T1IFNs), and T1IFN-responsive genes. In syngeneic murine GBM models, TTFields-treated GBM cells induced antitumor memory immunity and a cure rate of 42% to 66% in a STING- and AIM2-dependent manner. Using single-cell and bulk RNA sequencing of peripheral blood mononuclear cells, we detected robust post-TTFields activation of adaptive immunity in patients with GBM via a T1IFN-based trajectory and identified a gene panel signature of TTFields effects on T cell activation and clonal expansion. Collectively, these studies defined a therapeutic strategy using TTFields as cancer immunotherapy in GBM and potentially other solid tumors.

A clinical approach to children with C3 glomerulopathy

C3 glomerulopathy is a relatively new clinical entity that represents a challenge both to diagnose and to treat. As new therapeutic agents that act as complement inhibitors become available, many with an oral formulation, a better understanding of this disease and of the underlying complement dysregulation driving it has become increasingly useful to optimize patient care. Moreover, recent advances in research have clarified the role of complement in other glomerular diseases in which its role was less established, namely in immune-complex membranoproliferative glomerulonephritis (IC-MPGN), ANCA-vasculitis, IgA nephropathy, and idiopathic membranous nephropathy. Complement inhibitors are being studied in adult and adolescent clinical trials for these indications. This review summarizes current knowledge and future perspectives on every aspect of the diagnosis and management of C3 glomerulopathy and elucidates current understanding of the role of complement in this condition and in other glomerular diseases in children. An overview of ongoing trials involving therapeutic agents targeting complement in glomerular diseases is also provided.

Durability of transgene expression after rAAV gene therapy

Recombinant adeno-associated virus (rAAV) gene therapy has the potential to transform the lives of patients with certain genetic disorders by increasing or restoring function to affected tissues. Following the initial establishment of transgene expression, it is unknown how long the therapeutic effect will last, although animal and emerging human data show that expression can be maintained for more than 10 years. The durability of therapeutic response is key to long-term treatment success, especially since immune responses to rAAV vectors may prevent re-dosing with the same therapy. This review explores the non-immunological and immunological processes that may limit or improve durability and the strategies that can be used to increase the duration of the therapeutic effect.

The pleotropic effects of fluvastatin on complement-mediated T-cell activation in hypercholesterolemia

T-cells orchestrate the inflammatory responses in atherosclerosis, and their function is modified by the lipoprotein milieu and complement activity. We investigated the effects of fluvastatin on the expression of complement decay-accelerating factor (DAF/CD55) antigen, and the levels of transcription factors in circulating T-cells in hypercholesterolemia. The hypercholesterolemic state was associated with the upregulation of DAF expression on circulating T-cells and increased levels nuclear factor kappa B (NF-kB) and interferon regulatory factor 4 (IRF4). Notably, the elevated levels of DAF and NF-kB expression persisted following treatment with fluvastatin. Therefore, the pleiotropic effects of fluvastatin are partially ascribed to its ability to mediate T-cell activation and regulate complement activity. Consequently, enhanced therapeutic interventions that targets complement-induced T-cell activation may be important in mitigating the development of atherosclerosis and major cardiovascular events in individuals with hypercholesterolemia.

Temporal changes in the corpus luteum during early pregnancy reveal regulation of pathways that enhance steroidogenesis and suppress luteolytic mechanisms†

Although rescue of the corpus luteum (CL) is required for pregnancy, luteal function during maternal recognition of pregnancy remains largely unexplored. CL were collected from pregnant cattle on days 14, 17, 20, and 23, to encompass the maternal recognition of pregnancy period. Next-generation sequencing was used to profile mRNA abundance during this time, while tandem mass spectrometry and nanostring technology were used to profile proteins and miRNA, respectively. A total of 1157 mRNA were differentially abundant, while 27 miRNA changed, and 29 proteins tended to change. mRNA that increased were regulators of interferon signaling and DNA repair, while those that decreased were associated with luteolytic processes, such as calcium signaling and matrix metallopeptidase (MMP) signaling, indicating inhibition of these processes. One of these, MMP12, was regulated by prostaglandin F2A in vitro. mRNA that were maximally abundant on day 20 were primarily associated with immune processes. Two of these, C-C motif chemokine ligand 1 and NFKB inhibitor alpha, were regulated by interferon tau in vitro. MiRNA that increased were predicted to inhibit phosphatidylinositol signaling, while those that decreased may be negative regulators of steroidogenesis. One protein that was greater on day 20 than on day 14 was aldehyde dehydrogenase 1 family member A1 (ALDH1A1), which synthesizes retinoic acid. Pharmacological inhibition of this enzyme, or of retinoic acid receptor signaling, led to suppression of progesterone production in vitro. Overall, these data indicate that there are changes in the CL of pregnancy that are important for continued luteal function.

Overcoming innate immune barriers that impede AAV gene therapy vectors

The field of gene therapy has made considerable progress over the past several years. Adeno-associated virus (AAV) vectors have emerged as promising and attractive tools for in vivo gene therapy. Despite the recent clinical successes achieved with recombinant AAVs (rAAVs) for therapeutics, host immune responses against the vector and transgene product have been observed in numerous preclinical and clinical studies. These outcomes have hampered the advancement of AAV gene therapies, preventing them from becoming fully viable and safe medicines. The human immune system is multidimensional and complex. Both the innate and adaptive arms of the immune system seem to play a concerted role in the response against rAAVs. While most efforts have been focused on the role of adaptive immunity and developing ways to overcome it, the innate immune system has also been found to have a critical function. Innate immunity not only mediates the initial response to the vector, but also primes the adaptive immune system to launch a more deleterious attack against the foreign vector. This Review highlights what is known about innate immune responses against rAAVs and discusses potential strategies to circumvent these pathways.

Candida Cell-Surface-Specific Monoclonal Antibodies Protect Mice against Candida auris Invasive Infection

Candida auris is a multidrug-resistant fungal pathogen that can cause disseminated bloodstream infections with up to 60% mortality in susceptible populations. Of the three major classes of antifungal drugs, most C. auris isolates show high resistance to azoles and polyenes, with some clinical isolates showing resistance to all three drug classes. We reported in this study a novel approach to treating C. auris disseminated infections through passive transfer of monoclonal antibodies (mAbs) targeting cell surface antigens with high homology in medically important Candida species. Using an established A/J mouse model of disseminated infection that mimics human candidiasis, we showed that C3.1, a mAb that targets β-1,2-mannotriose (β-Man₃), significantly extended survival and reduced fungal burdens in target organs, compared to control mice. We also demonstrated that two peptide-specific mAbs, 6H1 and 9F2, which target hyphal wall protein 1 (Hwp1) and phosphoglycerate kinase 1 (Pgk1), respectively, also provided significantly enhanced survival and reduction of fungal burdens. Finally, we showed that passive transfer of a 6H1+9F2 cocktail induced significantly enhanced protection, compared to treatment with either mAb individually. Our data demonstrate the utility of β-Man₃- and peptide-specific mAbs as an effective alternative to antifungals against medically important Candida species including multidrug-resistant C. auris.

Shared Molecular Mechanisms between Alzheimer's Disease and Periodontitis Revealed by Transcriptomic Analysis

OBJECTIVE

To investigate the genetic crosstalk mechanisms that link periodontitis and Alzheimer's disease (AD).

BACKGROUND

Periodontitis, a common oral infectious disease, is associated with Alzheimer's disease (AD) and considered a putative contributory factor to its progression. However, a comprehensive investigation of potential shared genetic mechanisms between these diseases has not yet been reported.

METHODS

Gene expression datasets related to periodontitis were downloaded from the Gene Expression Omnibus (GEO) database, and differential expression analysis was performed to identify differentially expressed genes (DEGs). Genes associated with AD were downloaded from the DisGeNET database. Overlapping genes among the DEGs in periodontitis and the AD-related genes were defined as crosstalk genes between periodontitis and AD. The Boruta algorithm was applied to perform feature selection from these crosstalk genes, and representative crosstalk genes were thus obtained. In addition, a support vector machine (SVM) model was constructed by using the scikit-learn algorithm in Python. Next, the crosstalk gene-TF network and crosstalk gene-DEP (differentially expressed pathway) network were each constructed. As a final step, shared genes among the crosstalk genes and periodontitis-related genes in DisGeNET were identified and denoted as the core crosstalk genes.

RESULTS

Four datasets (GSE23586, GSE16134, GSE10334, and GSE79705) pertaining to periodontitis were included in the analysis. A total of 48 representative crosstalk genes were identified by using the Boruta algorithm. Three TFs (FOS, MEF2C, and USF2) and several pathways (i.e., JAK-STAT, MAPK, NF-kappa B, and natural killer cell-mediated cytotoxicity) were identified as regulators of these crosstalk genes. Among these 48 crosstalk genes and the chronic periodontitis-related genes in DisGeNET, C4A, C4B, CXCL12, FCGR3A, IL1B, and MMP3 were shared and identified as the most pivotal candidate links between periodontitis and AD.

CONCLUSIONS

Exploration of available transcriptomic datasets revealed C4A, C4B, CXCL12, FCGR3A, IL1B, and MMP3 as the top candidate molecular linkage genes between periodontitis and AD.

The expression of membrane-bound complement regulatory proteins CD46, CD55 and CD59 in oral lichen planus

OBJECTIVE

To investigate the expression levels of membrane-anchored complement regulatory proteins (mCRPs), CD46, CD55 and CD59 in oral lichen planus (OLP), and evaluate the activation status of complement.

DESIGN

Thirty-seven cases of OLP patients (20 non-erosive OLP and 17 erosive OLP) and twenty healthy controls were recruited in this study. The proteins and mRNA expression levels of CD46, CD55 and CD59 in OLP tissues were detected by western blotting and RT-qPCR respectively, and the expression levels of complement C3 and sC5b-9 in OLP patients' saliva were detected by ELISA to evaluate the activation status of complement. In addition, mucosa tissues of another 3 non-erosive OLP patients and another 3 healthy controls were collected, and the epithelial layer of two groups were separated to culture primary keratinocytes in vitro. Immunofluorescence was used to further detect the expression of mCRPs at the cellular level.

RESULTS

The levels of CD46, CD55 and CD59 in OLP tissues and cells were significantly decreased compared with those of the healthy control group, and the level of complement C3 in the patients' saliva was significantly decreased, while the level of sC5b-9 was increased.

CONCLUSIONS

These results suggest that the reduced expression of mCRPs keeps the complement system in a continuously active state, which may be the reason of the persistent local immune inflammatory state in OLP. This study aimed to provide new insights for the etiology and therapy of OLP.

Single cell sequencing reveals cell populations that predict primary resistance to imatinib in chronic myeloid leukemia

The treatment of chronic myeloid leukemia (CML), a disease caused by t(9;22)(q34;q11) reciprocal translocation, has advanced largely through the use of targeted tyrosine kinase inhibitors (TKIs). To identify molecular differences that might distinguish TKI responders from non-responders, we performed single cell RNA sequencing on cells (n = 41,723 cells) obtained from the peripheral blood of four CML patients at different stages of treatment to generate single cell expression profiles. Analysis of our single cell expression profiles in conjunction with those previously obtained from the bone marrow of additional CML patients and healthy donors (total = 69,263 cells) demonstrated that imatinib treatment significantly altered leukocyte population compositions in both responders and non-responders, and affected the expression profiles of multiple cell populations, including non-neoplastic cell types. Notably, in imatinib poor-responders, patient-specific pre-treatment unique stem/progenitor cells became enriched in peripheral blood compared to the responders. These results indicate that resistance to TKIs might be intrinsic in some CML patients rather than acquired, and that non-neoplastic immune cell types may also play vital roles in dispersing the responsiveness of patients to TKIs. Furthermore, these results demonstrated the potential utility of peripheral blood as a diagnostic tool in the TKI sensitivity of CML patients.

How Does Complement Affect Hematological Malignancies: From Basic Mechanisms to Clinical Application

Complement, as a central immune surveillance system, can be activated within seconds upon stimulation, thereby displaying multiple immune effector functions. However, in pathologic scenarios (like in tumor progression), activated complement can both display protective effects to control tumor development and passively promotes the tumor growth. Clinical investigations show that patients with several hematological malignancies often display abnormal level of specific complement components, which in turn modulates complement activation or deregulated cascade. In the past decades, complement-dependent cytotoxicity and complement-dependent cell-mediated phagocytosis were fully approved to display vital roles in monoclonal antibody-based immunotherapies, especially in therapies against hematological malignancies. However, tumor-mediated complement evasion presents a big challenge for such a therapy. This review aims to provide an integrative overview on the roles of the complement in tumor promotion, highlights complement mediated effects on antibody-based immunotherapy against distinct hematological tumors, hopefully provides a theoretical basis for the development of complement-based cancer targeted therapies.

Inverse correlation between serum complement component C1q levels and whole blood type-1 interferon signature in active tuberculosis and QuantiFERON-positive uveitis: implications for diagnosis

Objectives

To examine the relation between serum C1q levels and blood type‐1 interferon signature (type‐1 IFN signature) in active pulmonary tuberculosis (APTB) and to determine whether combined measurement of serum C1q and type‐1 IFN signature may add to the diagnosis of QuantiFERON‐positive (QFT⁺) patients with uveitis of unknown cause.

Methods

C1q was determined (ELISA) in serum from two distinct Indonesian cohorts, and in total, APTB (n = 72), QFT⁺ uveitis of unknown aetiology (n = 58), QFT⁻ uveitis (n = 51) patients and healthy controls (HC; n = 73) were included. The type‐1 IFN signature scores were previously determined.

Results

Serum C1q was higher in APTB than HC (P < 0.001). APTB patients with uveitis had higher serum C1q than APTB patients without uveitis (P = 0.0207). Serum C1q correlated inversely with type‐1 IFN signature scores in APTB (P = 0.0036, r² = 0.3526), revealing that these biomarkers for active TB disease can be mutually exclusive. Stratification of QFT⁺ patients with uveitis of unknown cause, by serum C1q and type‐1 IFN signature, yielded four groups with different likelihood of suffering from active TB uveitis.

Conclusion

Serum C1q is elevated in APTB, especially in those cases with uveitis. We propose that combined measurement of blood type‐1 IFN signature and serum C1q may provide added value in the diagnosis of active TB disease. Combined measurement of type‐1 IFN signature and serum C1q in QFT⁺ patients without signs of active TB disease, but suffering from uveitis of unknown cause, may be of help to identify cases with low or high likelihood of having active TB uveitis, which may facilitate clinical management decisions.

Complement component C1q plays a critical role in VLRA/VLRC-mediated immune response

In jawless vertebrates, the lamprey complement component C1q (LC1q) acts as a lectin and activates lamprey complement component C3 (LC3) in association with mannose-binding lectin (MBL)-associated serine protease (MASP) via the lectin pathway. Furthermore, LC1q may interact with variable lymphocyte receptor B (VLRB) in a complex with antigens and mediate the activation of LC3, leading to cytolysis. In the present study, we found, for the first time, that LC1q plays a critical role in VLRA/VLRC-mediated immune response. Escherichia coli, Shigella flexneri, Aeromonas hydrophila, Pseudomonas plecoglossicida, Aeromonas allosaccharophila, P. luteola, Brevundimonas diminuta, and Bacillus cereus were isolated from infected Lampetra morii in our laboratory and identified using the 16s rRNA method. A. hydrophila was confirmed as a rapidly spreading lethal pathogen in the larvae of L. morii and was used in subsequent immune stimulation experiments. The results of real-time quantitative polymerase chain reaction (Q-PCR) and immunofluorescence analyses indicated that the RNA and protein expression levels of LC1q were upregulated following exposure to 10⁷ cfu/mL of A. hydrophila, compared to the levels of the naïve group. We obtained LC1q morphants (LC1q MO) of lamprey larvae by morpholino-mediated knockdowns. We found that LC1q played key roles in the embryonic development of lamprey. The median lethal time (LT50) of LC1q MO larvae was 2 d after being exposed to the pathogens, whereas the LT50 of control MO was 5 d. The drastic decrease in LT50 values after LC1q knockdown implies that LC1q plays a critical role in lamprey immune response. Gene expression profiles of LC1q-deficient A. hydrophila, control MO A. hydrophila, wild type A. hydrophila, and naive 1-month-old ammocoetes larvae were compared by examining the expression levels of a selected panel of orthologous genes. It is worth mentioning that LC1q MO affected the VLRA+/VLRC + population genes but did not affect the VLRB + populations. Immunohistochemical data indicated that LC1q deficiency also affected VLRA and VLRC but not VLRB. Thus, LC1q plays a critical role in VLRA/VLRC-mediated immune response in lamprey.

Complement-dependent synapse loss and microgliosis in a mouse model of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory, neurodegenerative disease of the CNS characterized by both grey and white matter injury. Microglial activation and a reduction in synaptic density are key features of grey matter pathology that can be modeled with MOG_35-55 experimental autoimmune encephalomyelitis (EAE). Complement deposition combined with microglial engulfment has been shown during normal development and in disease as a mechanism for pruning synapses. We tested whether there is excess complement production in the EAE hippocampus and whether complement-dependent synapse loss is a source of degeneration in EAE using C1qa and C3 knockout mice. We found that C1q and C3 protein and mRNA levels were elevated in EAE mice. Genetic loss of C3 protected mice from EAE-induced synapse loss, reduced microglial activation, decreased the severity of the EAE clinical score, and protected memory/freezing behavior after contextual fear conditioning. C1qa KO mice with EAE showed little to no change on these measurements compared to WT EAE mice. Thus, pathologic expression and activation of the early complement pathway, specifically at the level of C3, contributes to hippocampal grey matter pathology in the EAE.

Systemic and pulmonary C1q as biomarker of progressive disease in experimental non-human primate tuberculosis

Tuberculosis (TB) causes 1.6 million deaths annually. Early differential diagnosis of active TB infection is essential in optimizing treatment and reducing TB mortality, but is hampered by a lack of accurate and accessible diagnostics. Previously, we reported on complement component C1q, measured in serum by ELISA, as a candidate biomarker for active tuberculosis. In this work we further examine the dynamics of C1q as a marker of progressive TB disease in non-human primates (NHP). We assessed systemic and pulmonary C1q levels after experimental infection using high or low single dose as well as repeated limiting dose Mycobacterium tuberculosis (Mtb) challenge of macaques. We show that increasing C1q levels, either peripherally or locally, correlate with progressive TB disease, assessed by PET-CT imaging or post-mortem evaluation. Upregulation of C1q did not precede detection of Mtb infection by a conventional interferon-gamma release assay, confirming its association with disease progression. Finally, pulmonary vaccination with Bacillus Calmette Guérin also increased local production of C1q, which might contribute to the generation of pulmonary protective immunity. Our data demonstrate that NHP modelling of TB can be utilized to study the role of C1q as a liquid biomarker in TB protection and disease, complementing findings in TB patients.

Revisiting the complement system in systemic lupus erythematosus

Introduction: Systemic lupus erythematosus (SLE) is a multi-system autoimmune disease, characterized by the production of autoantibodies. Numerous mechanisms contribute to the pathogenesis and autoimmunity in SLE. One of the most important mechanisms is the defective function of the early complement components that are involved in clearing the immune-complexes and apoptotic debris. Major evidence supporting this hypothesis is the development of severe lupus in individuals with monogenic defects in any one of the early complement components such as C1q, C1 s, C1 r, C2, or C4.Areas covered: In this review, we discuss hereditary defects in classical complement components and their clinical manifestations, acquired defects of complements in lupus, the role of complements in the pathogenesis of antiphospholipid antibody syndrome and lupus nephritis, and laboratory assessment of complement components and their functions. Articles from the last 20 years were retrieved from PubMed for this purpose.Expert opinion: Complements have a dual role in the pathogenesis of SLE. On one hand, deficiency of complement components predisposes to lupus, while, on the other, excess complement activation plays a role in the organ damage. Understanding the intricacies of the role of complements in SLE can pave way for the development of targeted therapies.

Complement-Mediated Events in Alzheimer's Disease: Mechanisms and Potential Therapeutic Targets

An estimated 5.7 million Americans suffer from Alzheimer's disease in the United States, with no disease-modifying treatments to prevent or treat cognitive deficits associated with the disease. Genome-wide association studies suggest that an enhancement of clearance mechanisms and/or promotion of an anti-inflammatory response may slow or prevent disease progression. Increasing awareness of distinct roles of complement components in normal brain development and function and in neurodegenerative disorders align with complement-mediated responses, and thus, thorough understanding of these molecular pathways is needed to facilitate successful therapeutic design. Both beneficial and detrimental effects of C1q as well as contributions to local inflammation by C5a-C5aR1 signaling in brain highlight the need for precision of therapeutic design. The potential benefit of β-amyloid clearance from the circulation via CR1-mediated mechanisms is also reviewed. Therapies that suppress inflammation while preserving protective effects of complement could be tested now to slow the progression of this debilitating disease.

Role of the Complement Pathway in Inflammatory Skin Diseases: A Focus on Hidradenitis Suppurativa

Although the role of immune dysregulation in hidradenitis suppurativa (HS) has yet to be elucidated, recent studies identified several complement abnormalities in patients with HS. The complement system serves a critical role in the modulation of immune response and regulation of cutaneous commensal bacteria. Complement is implicated in several inflammatory skin diseases including systemic lupus erythematosus, angioedema, pemphigus, bullous pemphigoid, and HS. A model of HS pathogenesis is proposed, integrating the role of commensal bacteria, cutaneous immune responses, and complement dysregulation. The role of complement in disease pathogenesis has led to the development of novel anticomplement agents and clinical trials investigating the efficacy of such treatments in HS.

Mucosal Immunity and the FOXO1 Transcription Factors

FOXO1 transcription factors affect a number of cell types that are important in the host response. Cell types whose functions are modulated by FOXO1 include keratinocytes in the skin and mucosal dermis, neutrophils and macrophages, dendritic cells, Tregs and B-cells. FOXO1 is activated by bacterial or cytokine stimulation. Its translocation to the nucleus and binding to promoter regions of genes that have FOXO response elements is stimulated by the MAP kinase pathway and inhibited by the PI3 kinase/AKT pathway. Downstream gene targets of FOXO1 include pro-inflammatory signaling molecules (TLR2, TLR4, IL-1β, and TNF-α), wound healing factors (TGF-β, VEGF, and CTGF) adhesion molecules (integrins-β1, -β3, -β6, α_vβ₃, CD11b, CD18, and ICAM-1), chemokine receptors (CCR7 and CXCR2), B cell regulators (APRIL and BLYS), T-regulatory modulators (Foxp3 and CTLA-4), antioxidants (GPX-2 and cytoglobin), and DNA repair enzymes (GADD45α). Each of the above cell types are found in oral mucosa and modulated by bacteria or an inflammatory microenvironment. FOXO1 contributes to the regulation of these cells, which collectively maintain and repair the epithelial barrier, formation and activation of Tregs that are needed to resolve inflammation, mobilization, infiltration, and activation of anti-bacterial defenses in neutrophils, and the homing of dendritic cells to lymph nodes to induce T-cell and B-cell responses. The goal of the manuscript is to review how the transcription factor, FOXO1, contributes to the activation and regulation of key leukocytes needed to maintain homeostasis and respond to bacterial challenge in oral mucosal tissues. Examples are given with an emphasis on lineage specific deletion of Foxo1 to explore the impact of FOXO1 on cell behavior, inflammation and susceptibility to infection.

Multi-omics study in monozygotic twins confirm the contribution of de novo mutation to psoriasis

BACKGROUND

Genome-wide association studies have identified over 120 risk loci for psoriasis. However, most of the variations are located in non-coding region with high frequency and small effect size. Pathogenetic variants are rarely reported except HLA-C*0602 with the odds ratio being approximately 4.0 in Chinese population. Although rare variations still account for a small proportion of phenotypic variances in complex diseases, their effect on phenotypes is large. Recently, more and more studies focus on the low-frequency functional variants and have achieved a certain amount of success.

METHOD

Whole genome sequencing and sanger sequencing was performed on 8 MZ twin pairs discordant for psoriasis to scan and verified the de novo mutations (DNMs). Additionally, 665 individuals with about 20 years' medical history versus 2054 healthy controls and two published large population studies which had about 8 years' medical history (including 10,727 cases versus 10,582 controls) were applied to validate the enrichment of rare damaging mutations in two DNMs genes. Besides, to verify the pathogenicity of candidate DNM in C3, RNA-sequencing for CD4⁺, CD8⁺ T cells of twins and lesion, non-lesion skin of psoriasis patients were carried out. Meanwhile, the enzyme-linked immunosorbent assay kit was used to detect the level of C3, C3b in the supernatant of peripheral blood.

RESULT

A total of 27 DNMs between co-twins were identified. We found six of eight twins carry HLA-C∗0602 allele which have large effects on psoriasis. And it is interesting that a missense mutation in SPRED1 and a splice region mutation in C3 are found in the psoriasis individuals in the other two MZ twin pairs without carrying HLA-C*0602 allele. In the replication stage, we found 2 loss-of-function (LOF) variants of C3 only in 665 cases with about 20 years' medical history and gene-wise analysis in 665 cases and 2054 controls showed that the rare missense mutations in C3 were enriched in cases (OR = 1.91, P = 0.0028). We further scanned the LOF mutations of C3 in two published studies (about 8 years' medical history), and found one LOF mutation in the case without carrying HLA-C*0602. In the individual with DNM in C3, RNA sequencing showed the expression level of C3 in skin was significant higher than healthy samples in public database (TPM fold change = 1.40, P = 0.000181) and ELISA showed protein C3 in peripheral blood was higher (~2.2-fold difference) than the other samples of twins without DNM in C3.

CONCLUSION

To the best of our knowledge, this is the first report that DNM in C3 is the likely pathological mutations, and it provided a better understanding of the genetic etiology of psoriasis and additional treatments for this disease.

Immunotoxicity Considerations for Next Generation Cancer Nanomedicines

Although interest and funding in nanotechnology for oncological applications is thriving, translating these novel therapeutics through the earliest stages of preclinical assessment remains challenging. Upon intravenous administration, nanomaterials interact with constituents of the blood inducing a wide range of associated immunotoxic effects. The literature on the immunological interactions of nanomaterials is vast and complicated. A small change in a particular characteristic of a nanomaterial (e.g., size, shape, or charge) can have a significant effect on its immunological profile in vivo, and poor selection of specific assays for establishing these undesirable effects can overlook this issue until the latest stages of preclinical assessment. This work describes the current literature on unintentional immunological effects associated with promising cancer nanomaterials (liposomes, dendrimers, mesoporous silica, iron oxide, gold, and quantum dots) and puts focus on what is missing in current preclinical evaluations. Opportunities for avoiding or limiting immunotoxicity through efficient preclinical assessment are discussed, with an emphasis placed on current regulatory views and requirements. Careful consideration of these issues will ensure a more efficient preclinical assessment of cancer nanomedicines, enabling a smoother clinical translation with less failures in the future.

Complement in Human Pre-implantation Embryos: Attack and Defense

It is essential for early human life that mucosal immunological responses to developing embryos are tightly regulated. An imbalance of the complement system is a common feature of pregnancy complications. We hereby present the first full analysis of the expression and deposition of complement molecules in human pre-implantation embryos. Thus, far, immunological imbalance has been considered in stages of pregnancy following implantation. We here show that complement activation against developing human embryos takes place already at the pre-implantation stage. Using confocal microscopy, we observed deposition of activation products on healthy developing embryos, which highlights the need for strict complement regulation. We show that embryos express complement membrane inhibitors and bind soluble regulators. These findings show that mucosal complement targets human embryos, and indicate potential adverse pregnancy outcomes, if regulation of activation fails. In addition, single-cell RNA sequencing revealed cellular expression of complement activators. This shows that the embryonic cells themselves have the capacity to express and activate C3 and C5. The specific local embryonic expression of complement components, regulators, and deposition of activation products on the surface of embryos suggests that complement has immunoregulatory functions and furthermore may impact cellular homeostasis and differentiation at the earliest stages of life.

Hematological and biochemical parameters for Chinese rhesus macaque

Rhesus macaque is an important animal model in biomedical research, especially human disease, developmental, translational, and pre-clinical research. Blood physiological and biochemical parameters are important markers for physiology, pathology, and toxicology research. However, these parameters have not been systematically reported for Chinese rhesus macaques. To characterize the reference for these parameters, this study collected 1805 Chinese rhesus macaques living in Southwestern China. A total of 24 blood physiological indexes and 27 biochemical parameters were determined. Sex and age were found to affect these parameters. In conclusion, a comprehensive and systematic reference of hematological and biochemical parameters for Chinese rhesus macaque was established in this work on the basis of a large cohort. Such reference will benefit biomedical research employing rhesus macaques as animal models.

Complement and CD4+ T cells drive context-specific corneal sensory neuropathy

Whether complement dysregulation directly contributes to the pathogenesis of peripheral nervous system diseases, including sensory neuropathies, is unclear. We addressed this important question in a mouse model of ocular HSV-1 infection, where sensory nerve damage is a common clinical problem. Through genetic and pharmacologic targeting, we uncovered a central role for C3 in sensory nerve damage at the morphological and functional levels. Interestingly, CD4 T cells were central in facilitating this complement-mediated damage. This same C3/CD4 T cell axis triggered corneal sensory nerve damage in a mouse model of ocular graft-versus-host disease (GVHD). However, this was not the case in a T-dependent allergic eye disease (AED) model, suggesting that this inflammatory neuroimmune pathology is specific to certain disease etiologies. Collectively, these findings uncover a central role for complement in CD4 T cell-dependent corneal nerve damage in multiple disease settings and indicate the possibility for complement-targeted therapeutics to mitigate sensory neuropathies.

The Role of Forkhead Box 1 (FOXO1) in the Immune System: Dendritic Cells, T Cells, B Cells, and Hematopoietic Stem Cells

Forkhead box-O (FOXO) transcription factors have a fundamental role in the development and differentiation of immune cells. FOXO1 and FOXO3 are FOXO members that are structurally similar and bind to the same conserved consensus DNA sequences to induce transcription. FOXO1 has been studied in detail in the activation of dendritic cells (DCs), where it plays an important role through the regulation of target genes such as ICAM-1, CCR7, and the integrin αvβ3. FOXO1 is activated by bacteria challenge in DCs and promotes DC bacterial phagocytosis, migration, homing to lymph nodes, DC stimulation of CD4+ T cells and resting B cells, and antibody production. Deletion of FOXO1 in DCs enhances susceptibility to bacteria-induced periodontal disease. FOXO1 and FOXO3 maintain naive T cell quiescence and survival. FOXO1 and FOXO3 enhance the formation of regulatory T cells and inhibit the formation of T-helper 1 (Th1) and Th17 cells. FOXO1 promotes differentiation, proliferation, survival, immunoglobulin gene rearrangement, and class switching in B cells, but FOXO3 has little effect. Both FOXO1 and FOXO3 are important in the maintenance of hematopoietic stem cells by protecting them from oxidative stress. This review examines FOXO1/FOXO3 in the adaptive immune response, key target genes, and FOXO inhibition by the phosphoinositide 3-kinase/AKT pathway.

Expression of complement receptor 3 (CR3) and regulatory protein CD46 on dendritic cells of antiretroviral naïve and treated HIV-1 infected individuals: Correlation with immune activation status

During infection and budding, human immunodeficiency virus-1 (HIV-1) acquires regulators of Complement Activation (RCAs) along with the host cell membrane on the viral envelope. Activation of host complement system results in opsonization of virus by complement fragments, however the virus evades complement mediated lysis (CoML) by virtue of the RCAs on the viral envelope. The RCAs on HIV-1 envelope process complement protein C3 into various fragments that promote viral entry and infection of cells through different complement receptors. Complement opsonized HIV-1 has been shown in vitro to infect dendritic cells (DCs) in a CR3 dependent manner, although the role of CR3 and CD46 in natural HIV-1 infection is not clear. Surface expression of CR3 and CD46 on DC subsets of 30 antiretroviral naïve, 31 treated (cART) HIV-1 infected individuals and 30 seronegative controls was measured by flow cytometry and plasma levels of cytokines and complement activity (C3c levels) were quantitated by sandwich ELISA. Significantly lower surface expression of CR3 and CD46 was observed on DC subsets in naïve and treated HIV-1 infected individuals compared to controls. Significantly higher complement activation and plasma levels of IL-4, IL-8, IL-10 and IFN-γ were observed in treatment naïve HIV-1 infected individuals than controls. Significantly lower plasma levels of IL-4, IL-6, IL-8 and IL-10 were observed in treated vs. naïve HIV-1 infected individuals. Our findings suggest that alterations in expression of CR3 and CD46 on DCs along with complement activity could be factors that influence viral persistence and HIV-1 disease progression and need to be further evaluated.

Comparative Transcriptomic Analysis Identifies a Range of Immunologically Related Functional Elaborations of Lymph Node Associated Lymphatic and Blood Endothelial Cells

Lymphatic and blood vessels are formed by specialized lymphatic endothelial cells (LEC) and blood endothelial cells (BEC), respectively. These endothelial populations not only form peripheral tissue vessels, but also critical supporting structures in secondary lymphoid organs, particularly the lymph node (LN). Lymph node LEC (LN-LEC) also have been shown to have important immunological functions that are not observed in LEC from tissue lymphatics. LN-LEC can maintain peripheral tolerance through direct presentation of self-antigen via MHC-I, leading to CD8 T cell deletion; and through transfer of self-antigen to dendritic cells for presentation via MHC-II, resulting in CD4 T cell anergy. LN-LEC also can capture and archive foreign antigens, transferring them to dendritic cells for maintenance of memory CD8 T cells. The molecular basis for these functional elaborations in LN-LEC remain largely unexplored, and it is also unclear whether blood endothelial cells in LN (LN-BEC) might express similar enhanced immunologic functionality. Here, we used RNA-Seq to compare the transcriptomic profiles of freshly isolated murine LEC and BEC from LN with one another and with freshly isolated LEC from the periphery (diaphragm). We show that LN-LEC, LN-BEC, and diaphragm LEC (D-LEC) are transcriptionally distinct from one another, demonstrating both lineage and tissue-specific functional specializations. Surprisingly, tissue microenvironment differences in gene expression profiles were more numerous than those determined by endothelial cell lineage specification. In this regard, both LN-localized endothelial cell populations show a variety of functional elaborations that suggest how they may function as antigen presenting cells, and also point to as yet unexplored roles in both positive and negative regulation of innate and adaptive immune responses. The present work has defined in depth gene expression differences that point to functional specializations of endothelial cell populations in different anatomical locations, but especially the LN. Beyond the analyses provided here, these data are a resource for future work to uncover mechanisms of endothelial cell functionality.

Complement factor and T-cell interactions during alloimmune inflammation in transplantation

Complement factor and T-cell signaling during an effective alloimmune response plays a key role in transplant-associated injury, which leads to the progression of chronic rejection (CR). During an alloimmune response, activated complement factors (C3a and C5a) bind to their corresponding receptors (C3aR and C5aR) on a number of lymphocytes, including T-regulatory cells (Tregs), and these cell-molecular interactions have been vital to modulate an effective immune response to/from Th1-effector cell and Treg activities, which result in massive inflammation, microvascular impairments, and fibrotic remodeling. Involvement of the complement-mediated cell signaling during transplantation signifies a crucial role of complement components as a key therapeutic switch to regulate ongoing inflammatory state, and further to avoid the progression of CR of the transplanted organ. This review highlights the role of complement-T cell interactions, and how these interactions shunt the effector immune response during alloimmune inflammation in transplantation, which could be a novel therapeutic tool to protect a transplanted organ and avoid progression of CR.

TAILS proteomics reveals dynamic changes in airway proteolysis controlling protease activity and innate immunity during COPD exacerbations

Dysregulated protease activity is thought to cause parenchymal and airway damage in chronic obstructive pulmonary disease (COPD). Multiple proteases have been implicated in COPD, and identifying their substrates may reveal new disease mechanisms and treatments. However, as proteases interact with many substrates that may be protease inhibitors or proteases themselves, these webs of protease interactions make the wider consequences of therapeutically targeting proteases difficult to predict. We therefore used a systems approach to determine protease substrates and protease activity in COPD airways. Protease substrates were determined by proteomics using the terminal amine isotopic labeling of substrates (TAILS) methodology in paired sputum samples during stable COPD and exacerbations. Protease activity and specific protein degradation in airway samples were assessed using Western blotting, substrate assays, and ex vivo cleavage assays. Two hundred ninety-nine proteins were identified in human COPD sputum, 125 of which were proteolytically processed, including proteases, protease inhibitors, mucins, defensins, and complement and other innate immune proteins. During exacerbations, airway neutrophils and neutrophil proteases increased and more proteins were cleaved, particularly at multiple sites, consistent with degradation and inactivation. During exacerbations, different substrates were processed, including protease inhibitors, mucins, and complement proteins. Exacerbations were associated with increasing airway elastase activity and increased processing of specific elastase substrates, including secretory leukocyte protease inhibitor. Proteolysis regulates multiple processes including elastase activity and innate immune proteins in COPD airways and differs during stable disease and exacerbations. The complexity of protease, inhibitor, and substrate networks makes the effect of protease inhibitors hard to predict which should be used cautiously.

Complement After Trauma: Suturing Innate and Adaptive Immunity

The overpowering effect of trauma on the immune system is undisputed. Severe trauma is characterized by systemic cytokine generation, activation and dysregulation of systemic inflammatory response complementopathy and coagulopathy, has been immensely instrumental in understanding the underlying mechanisms of the innate immune system during systemic inflammation. The compartmentalized functions of the innate and adaptive immune systems are being gradually recognized as an overlapping, interactive and dynamic system of responsive elements. Nonetheless the current knowledge of the complement cascade and its interaction with adaptive immune response mediators and cells, including T- and B-cells, is limited. In this review, we discuss what is known about the bridging effects of the complement system on the adaptive immune system and which unexplored areas could be crucial in understanding how the complement and adaptive immune systems interact following trauma.

Immunoregulatory Effects of Myeloid-Derived Suppressor Cell Exosomes in Mouse Model of Autoimmune Alopecia Areata

The treatment of autoimmune diseases still poses a major challenge, frequently relying on non-specific immunosuppressive drugs. Current efforts aim at reestablishing self tolerance using immune cells with suppressive activity like the regulatory T cells (Treg) or the myeloid-derived suppressor cells (MDSC). We have demonstrated therapeutic efficacy of MDSC in mouse Alopecia Areata (AA). In the same AA model, we now asked whether MDSC exosomes (MDSC-Exo) can replace MDSC. MDSC-Exo from bone marrow cells (BMC) cultures of healthy donors could substantially facilitate treatment. With knowledge on MDSC-Exo being limited, their suitability needs to be verified in advance. Protein marker profiles suggest comparability of BMC- to ex vivo collected inflammatory MDSC/MDSC-Exo in mice with a chronic contact dermatitis, which is a therapeutic option in AA. Proteome analyses substantiated a large overlap of function-relevant molecules in MDSC and MDSC-Exo. Furthermore, MDSC-Exo are taken up by T cells, macrophages, NK, and most avidly by Treg and MDSC-Exo uptake exceeds binding of MDSC themselves. In AA mice, MDSC-Exo preferentially target skin-draining lymph nodes and cells in the vicinity of remnant hair follicles. MDSC-Exo uptake is accompanied by a strong increase in Treg, reduced T helper proliferation, mitigated cytotoxic activity, and a slight increase in lymphocyte apoptosis. Repeated MDSC-Exo application in florid AA prevented progression and sufficed for partial hair regrowth. Deep sequencing of lymphocyte mRNA from these mice revealed a significant increase in immunoregulatory mRNA, including FoxP3 and arginase 1. Downregulated mRNA was preferentially engaged in prohibiting T cell hyperreactivity. Taken together, proteome analysis provided important insights into potential MDSC-Exo activities, these Exo preferentially homing into AA-affected organs. Most importantly, changes in leukocyte mRNA seen after treatment of AA mice with MDSC-Exo sustainably supports the strong impact on the adaptive and the non-adaptive immune system, with Treg expansion being a dominant feature. Thus, MDSC-Exo could potentially serve as therapeutic agents in treating AA and other autoimmune diseases.

Under control: The innate immunity of fish from the inhibitors' perspective

The innate immune response involves a concerted network of induced gene products, preformed immune effectors, biochemical signalling cascades and specialised cells. However, the multifaceted activation of these defensive measures can derail or overshoot and, if left unchecked, overwhelm the host. A plenty of regulatory devices therefore mediate the fragile equilibrium between pathogen defence and pathophysiological manifestations. Over the past decade in particular, an almost complete set of teleostean sequences orthologous to mammalian immunoregulatory factors has been identified in various fish species, which prove the remarkable conservation of innate immune-control concepts among vertebrates. This review will present the current knowledge on more than 50 teleostean regulatory factors (plus additional fish-specific paralogs) that are of paramount importance for controlling the clotting cascade, the complement system, pattern-recognition pathways and cytokine-signalling networks. A special focus lies on those immunoregulatory features that have emerged as potential biomarker genes in transcriptome-wide research studies. Moreover, we report on the latest progress in elucidating control elements that act directly with immune-gene-encoding nucleic acids, such as transcription factors, hormone receptors and micro- and long noncoding RNAs. Investigations into the function of teleostean inhibitory factors are still mainly based on gene-expression profiling or overexpression studies. However, in support of structural and in-vitro analyses, evidence from in-vivo trials is also available and revealed many biochemical details on piscine immune regulation. The presence of multiple gene copies in fish adds a degree of complexity, as it is so far hardly understood if they might play distinct roles during inflammation. The present review addresses this and other open questions that should be tackled by fish immunologists in future.

The Classical Complement Pathway Is Required to Control Borrelia burgdorferi Levels During Experimental Infection

Activation of the classical complement pathway occurs to varying degrees within strains of the Borrelia burgdorferi sensu lato complex, which contain a group of pathogenic spirochetes that cause tick-borne Lyme borreliosis, including the agent of Lyme disease in the United States, B. burgdorferi. Despite this information, details related to the control of B. burgdorferi by the classical pathway are not clear. To address this question, we infected C1qα^-/- mice, which cannot assemble the C1 complex and thus fail to activate the classical pathway, with B. burgdorferi sensu stricto strain B31. Using bioluminescent in vivo imaging, we found that C1qα^-/- mice harbored more B. burgdorferi following 10 days of infection relative to their isogenic C57BL/6 parent. Quantitative PCR (qPCR) demonstrated that C1qα^-/- mice harbored significantly more B. burgdorferi than parent mice did within lymph nodes, skin, heart, and joints. The increased B. burgdorferi load in C1qα^-/- mice was observed at 21 and 28 days of infection, consistent with the classical pathway promoting complement-dependent, antibody-mediated killing following the development of a B. burgdorferi-specific humoral immune response. In addition, circulating borrelial-specific IgM was higher in C1qα^-/- mice relative to their parent mouse strain and did not decrease at 21 and 28 days post-infection, indicating that IgG class switching was delayed in C1qα^-/- mice. At day 28, both Borrelia-specific IgG1 and IgG3 levels were higher in infected C1qα^-/- mice, but that these antibodies were not sufficient to control borrelial infection in the absence of the classical pathway. Furthermore, the lack of C1q also altered the balance of the Th1/Th2 response, as both circulating Th1 (MIP-1α, IL-2, IL-12, and TNFα), Th2 (IL-4, IL-10, and MCP-1), and Th17 (IL-17) cytokines were elevated in infected C1qα^-/- mice. These data imply that C1q and the classical pathway play important roles in controlling borrelial infection via antibody and complement-dependent killing, as well as altering both antibody maturation processes and the T cell response following exposure to infectious B. burgdorferi.

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.

Unexpected Roles for Intracellular Complement in the Regulation of Th1 Responses

The complement system is generally recognized as an evolutionarily ancient and critical part of innate immunity required for the removal of pathogens that have breached the protective host barriers. It was originally defined as a liver-derived serum surveillance system that induces the opsonization and killing of invading microbes and amplifies the general inflammatory reactions. However, studies spanning the last four decades have established complement also as a vital bridge between innate and adaptive immunity. Furthermore, recent work on complement, and in particular its impact on human T helper 1 (Th1) responses, has led to the unexpected findings that the complement system also functions within cells and that it participates in the regulation of basic processes of the cell, including metabolism. These recent new insights into the unanticipated noncanonical activities of this ancient system suggest that the functions of complement extend well beyond mere host protection and into cellular physiology.

The C3aR promotes macrophage infiltration and regulates ANCA production but does not affect glomerular injury in experimental anti-myeloperoxidase glomerulonephritis

The anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitides are autoimmune diseases associated with significant morbidity and mortality. They often affect the kidney causing rapidly progressive glomerulonephritis. While signalling by complement anaphylatoxin C5a though the C5a receptor is important in this disease, the role of the anaphylatoxin C3a signalling via the C3a receptor (C3aR) is not known. Using two different murine models of anti-myeloperoxidase (MPO) glomerulonephritis, one mediated by passive transfer of anti-MPO antibodies, the other by cell-mediated immunity, we found that the C3aR did not alter histological disease severity. However, it promoted macrophage recruitment to the inflamed glomerulus and inhibited the generation of MPO-ANCA whilst not influencing T cell autoimmunity. Thus, whilst the C3aR modulates some elements of disease pathogenesis, overall it is not critical in effector responses and glomerular injury caused by autoimmunity to MPO.

Complementing T-cell Function: An Inhibitory Role of the Complement System in T-cell-Mediated Antitumor Immunity

New data from Wang and colleagues show that complement C3 suppresses the function of CD8(+) tumor-infiltrating T cells by inhibiting IL10 production, and targeting the complement receptors C3aR and C5aR enhances the antitumor activity of immune checkpoint blockade. Their results not only define a new role of complement receptors as T-cell coinhibitory receptors, but also are useful in the development of novel strategies to improve the effectiveness of cancer immunotherapy. Cancer Discov; 6(9); 953-5. ©2016 AACR.See related article by Wang et al., p. 1022.

Complement component C3aR constitutes a novel regulator for chick eye morphogenesis

Complement components have been implicated in a wide variety of functions including neurogenesis, proliferation, cell migration, differentiation, cancer, and more recently early development and regeneration. Following our initial observations indicating that C3a/C3aR signaling induces chick retina regeneration, we analyzed its role in chick eye morphogenesis. During eye development, the optic vesicle (OV) invaginates to generate a bilayer optic cup (OC) that gives rise to the retinal pigmented epithelium (RPE) and neural retina. We show by immunofluorescence staining that C3 and the receptor for C3a (the cleaved and active form of C3), C3aR, are present in chick embryos during eye morphogenesis in the OV and OC. Interestingly, C3aR is mainly localized in the nuclear compartment at the OC stage. Loss of function studies at the OV stage using morpholinos or a blocking antibody targeting the C3aR (anti-C3aR Ab), causes eye defects such as microphthalmia and defects in the ventral portion of the eye that result in coloboma. Such defects were not observed when C3aR was disrupted at the OC stage. Histological analysis demonstrated that microphthalmic eyes were unable to generate a normal optic stalk or a closed OC. The dorsal/ventral patterning defects were accompanied by an expansion of the ventral markers Pax2, cVax and retinoic acid synthesizing enzyme raldh-3 (aldh1a3) domains, an absence of the dorsal expression of Tbx5 and raldh-1 (aldh1a1) and a re-specification of the ventral RPE to neuroepithelium. In addition, the eyes showed overall decreased expression of Gli1 and a change in distribution of nuclear β-catenin, suggesting that Shh and Wnt pathways have been affected. Finally, we observed prominent cell death along with a decrease in proliferating cells, indicating that both processes contribute to the microphthalmic phenotype. Together our results show that C3aR is necessary for the proper morphogenesis of the OC. This is the first report implicating C3aR in eye development, revealing an unsuspected hitherto regulator for proper chick eye morphogenesis.

C1q: A fresh look upon an old molecule

Originally discovered as part of C1, the initiation component of the classical complement pathway, it is now appreciated that C1q regulates a variety of cellular processes independent of complement activation. C1q is a complex glycoprotein assembled from 18 polypeptide chains, with a C-terminal globular head region that mediates recognition of diverse molecular structures, and an N-terminal collagen-like tail that mediates immune effector mechanisms. C1q mediates a variety of immunoregulatory functions considered important in the prevention of autoimmunity such as the enhancement of phagocytosis, regulation of cytokine production by antigen presenting cells, and subsequent alteration in T-lymphocyte maturation. Furthermore, recent advances indicate additional roles for C1q in diverse physiologic and pathologic processes including pregnancy, tissue repair, and cancer. Finally, C1q is emerging as a critical component of neuronal network refinement and homeostatic regulation within the central nervous system. This review summarizes the classical functions of C1q and reviews novel discoveries within the field.

Preconditioned mesenchymal stem cells treat myasthenia gravis in a humanized preclinical model

Myasthenia gravis (MG) with anti-acetylcholine receptor (AChR) Abs is an autoimmune disease characterized by severe defects in immune regulation and thymic inflammation. Because mesenchymal stem cells (MSCs) display immunomodulatory features, we investigated whether and how in vitro-preconditioned human MSCs (cMSCs) could treat MG disease. We developed a new humanized preclinical model by subcutaneously grafting thymic MG fragments into immunodeficient NSG mice (NSG-MG model). Ninety percent of the animals displayed human anti-AChR Abs in the serum, and 50% of the animals displayed MG-like symptoms that correlated with the loss of AChR at the muscle endplates. Interestingly, each mouse experiment recapitulated the MG features of each patient. We next demonstrated that cMSCs markedly improved MG, reducing the level of anti-AChR Abs in the serum and restoring AChR expression at the muscle endplate. Resting MSCs had a smaller effect. Finally, we showed that the underlying mechanisms involved (a) the inhibition of cell proliferation, (b) the inhibition of B cell-related and costimulatory molecules, and (c) the activation of the complement regulator DAF/CD55. In conclusion, this study shows that a preconditioning step promotes the therapeutic effects of MSCs via combined mechanisms, making cMSCs a promising strategy for treating MG and potentially other autoimmune diseases.