Complement protein C1q induces maturation of human dendritic cells

Complement C1q essential for aeroallergen sensitization via CSF1R+ conventional dendritic cells type 2

BACKGROUND

Dendritic cells (DCs) are heterogeneous, comprising multiple subsets with unique functional specifications. Our previous work has demonstrated that the specific conventional type 2 DC subset, CSF1R+cDC2s, plays a critical role in sensing aeroallergens.

OBJECTIVE

It remains to be understood how CSF1R+cDC2s recognize inhaled allergens. We sought to elucidate the transcriptomic programs and receptor-ligand interactions essential for function of this subset in allergen sensitization.

METHODS

We applied single-cell RNA sequencing to mouse lung DCs. Conventional DC-selective knockout mouse models were employed, and mice were subjected to inhaled allergen sensitization with multiple readouts of asthma pathology. Under the clinical arm of this work, human lung transcriptomic data were integrated with mouse data, and bronchoalveolar lavage (BAL) specimens were collected from subjects undergoing allergen provocation, with samples assayed for C1q.

RESULTS

We found that C1q is selectively enriched in lung CSF1R+cDC2s, but not in other lung cDC2 or cDC1 subsets. Depletion of C1q in conventional DCs significantly attenuates allergen sensing and features of asthma. Additionally, we found that C1q binds directly to human dust mite allergen, and the C1q receptor CD91 (LRP1) is required for lung CSF1R+cDC2s to recognize the C1q-allergen complex and induce allergic lung inflammation. Lastly, C1q is enriched in human BAL samples following subsegmental allergen challenge, and human RNA sequencing data demonstrate close homology between lung IGSF21+DCs and mouse CSF1R+cDC2s.

CONCLUSIONS

C1q is secreted from the CSF1R+cDC2 subset among conventional DCs. Our data indicate that the C1q-LRP1 axis represents a candidate for translational therapeutics in the prevention and suppression of allergic lung inflammation.

Immune infiltration associated C1q acts as a novel prognostic biomarker of cutaneous melanoma

C1q (complement C1q A chain, complement C1q B chain, and complement C1q C chain) is a recognized component of the classical complement pathway that influences the prognosis of various cancers. However, the effects of C1q on cutaneous melanoma (SKCM) outcomes and immune infiltration remain unknown. Gene expression profiling interactive analysis 2 and the human protein atlas were used to evaluate differential expression of C1q mRNA and protein. The relationship between C1q expression and clinicopathological features was also examined. The genetic alterations of C1q and their impact on survival were analyzed using the cbioportal database. The Kaplan-Meier approach was used to assess the significance of C1q in individuals with SKCM. The cluster profiler R package and the cancer single-cell state atlas database were used to investigate the function and mechanism of C1q in SKCM. The relationship between C1q and immune cell infiltration was estimated using single-sample gene set enrichment analysis. C1q expression was increased, and predicted a favorable prognosis. High C1q expression correlated with clinicopathological T stage, pathological stage, overall survival, and disease specific survival events. Moreover, C1q genetic alterations range from 2.7% to 4%, with no impact on prognosis. According to the enrichment analysis, C1q and immune-related pathways were closely connected. The link between complement C1q B chain and the functional state of inflammation was determined using the cancer single-cell state atlas database. In particular, C1q expression was significantly associated with infiltration of most immune cells and checkpoints PDCD1, CD274, and HAVCR2. The results of this study suggest that C1q is associated with prognosis and immune cell infiltration, supporting its value as a diagnostic and prognostic biomarker.

Immunometabolic Signature during Respiratory Viral Infection: A Potential Target for Host-Directed Therapies

RNA viruses are known to induce a wide variety of respiratory tract illnesses, from simple colds to the latest coronavirus pandemic, causing effects on public health and the economy worldwide. Influenza virus (IV), parainfluenza virus (PIV), metapneumovirus (MPV), respiratory syncytial virus (RSV), rhinovirus (RhV), and coronavirus (CoV) are some of the most notable RNA viruses. Despite efforts, due to the high mutation rate, there are still no effective and scalable treatments that accompany the rapid emergence of new diseases associated with respiratory RNA viruses. Host-directed therapies have been applied to combat RNA virus infections by interfering with host cell factors that enhance the ability of immune cells to respond against those pathogens. The reprogramming of immune cell metabolism has recently emerged as a central mechanism in orchestrated immunity against respiratory viruses. Therefore, understanding the metabolic signature of immune cells during virus infection may be a promising tool for developing host-directed therapies. In this review, we revisit recent findings on the immunometabolic modulation in response to infection and discuss how these metabolic pathways may be used as targets for new therapies to combat illnesses caused by respiratory RNA viruses.

Identification of Potential Biomarkers of Type 2 Diabetes Mellitus-Related Immune Infiltration Using Weighted Gene Coexpression Network Analysis

Background

Type 2 diabetes mellitus (T2DM) is characterized by chronic low-grade inflammation, showing an increasing trend. The infiltration of immune cells into adipose tissue has been shown to be an important pathogenic cause of T2DM. The purpose of this study is to use the relevant database to identify some abnormally expressed or dysfunctional genes related to diabetes from the perspective of immune infiltration.

Methods

Weighted gene coexpression network analysis (WGCNA) was employed to systematically identify the coexpressed gene modules and hub genes associated with T2DM development based on a microarray dataset (GSE23561) from the Gene Expression Omnibus (GEO) database. The key genes in modules highly related to clinical features were calculated and screened by using R software, and their participation in T2DM was determined by gene enrichment analysis. The mRNA levels of CSF1R, H2AFV, LCK, and TLR9 in pre-T2DM mice and normal wild-type mice were detected by WGCNA screening and real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR).

Results

We constructed 14 coexpressed gene modules, and the brown module was shown to be significantly related to T2DM. Through verification of the protein-protein interaction (PPI) network, four upregulated hub genes, CSF1R, H2AFV, LCK, and TLR9, were screened from the brown module and successfully distinguishedT2DM patients from healthy people. These hub genes may be used as biomarkers and important indicators for patient diagnosis. Enrichment analysis showed that these hub genes were highly associated with IL-6-related inflammatory metabolism, immune regulation, and immune cell infiltration. Finally, we verified the hub genes CSF1R, LCK, and TLR9 in a T2DM animal model and found that their mRNA levels were significantly higher in animals with T2DM than in control group mice (NC).

Conclusions

In summary, our results suggest that these hub genes (CSF1R, LCK, and TLR9) can serve as biomarkers and immunotherapeutic targets for T2DM.

Role of ADCC, CDC, and CDCC in Vaccine-Mediated Protection against Her2 Mammary Carcinogenesis

Amplification or mutation of the Her2 oncoantigen in human mammary glands leads to the development of an aggressive breast carcinoma. Several features of this breast carcinoma are reproduced in mammary carcinomas that spontaneously arise in female transgenic mice bearing the activated rat Her2 oncogene under transcriptional control of the mouse mammary tumor virus promoter-BALB-neuT (neuT) mice. We previously demonstrated that carcinoma progression in neuT mice can be prevented by DNA vaccination with RHuT, a plasmid coding for a chimeric rat/human Her2 protein. RHuT vaccination exerts an antitumor effect, mostly mediated by the induction of a strong anti-rat Her2 antibody response. IgG induced by RHuT vaccine mainly acts by blocking Her2 signaling, thus impairing cell cycle progression and inducing apoptosis of cancer cells, but other indirect effector mechanisms could be involved in the antibody-mediated protection. The recruitment of cells with perforin-dependent cytotoxic activity, able to perform antibody-dependent cellular cytotoxicity, has already been investigated. Less is known about the role of the complement system in sustaining antitumor response through complement-dependent cytotoxicity and cellular cytotoxicity in vaccinated mice. This work highlights that the weight of such mechanisms in RHuT-induced cancer protection is different in transplantable versus autochthonous Her2⁺ tumor models. These results may shed new light on the effector mechanisms involved in antibody-dependent anti-cancer responses, which might be exploited to ameliorate the therapy of Her2⁺ breast cancer.

Renal diseases and the role of complement: Linking complement to immune effector pathways and therapeutics

The complement system is an ancient and phylogenetically conserved key danger sensing system that is critical for host defense against pathogens. Activation of the complement system is a vital component of innate immunity required for the detection and removal of pathogens. It is also a central orchestrator of adaptive immune responses and a constituent of normal tissue homeostasis. Once complement activation occurs, this system deposits indiscriminately on any cell surface in the vicinity and has the potential to cause unwanted and excessive tissue injury. Deposition of complement components is recognized as a hallmark of a variety of kidney diseases, where it is indeed associated with damage to the self. The provenance and the pathophysiological role(s) played by complement in each kidney disease is not fully understood. However, in recent years there has been a renaissance in the study of complement, with greater appreciation of its intracellular roles as a cell-intrinsic system and its interplay with immune effector pathways. This has been paired with a profusion of novel therapeutic agents antagonizing complement components, including approved inhibitors against complement components (C)1, C3, C5 and C5aR1. A number of clinical trials have investigated the use of these more targeted approaches for the management of kidney diseases. In this review we present and summarize the evidence for the roles of complement in kidney diseases and discuss the available clinical evidence for complement inhibition.

Heat-Inactivation of Human Serum Destroys C1 Inhibitor, Pro-motes Immune Complex Formation, and Improves Human T Cell Function

Heat-inactivation of sera is used to reduce possible disturbing effects of complement factors in cell-culture experiments, but it is controversially discussed whether this procedure is appropriate or could be neglected. Here, we report a strong impact of heat-inactivation of human sera on the activation and effector functions of human CD4+ T cells. While T cells cultured with native sera were characterized by a higher proliferation rate and higher expression of CD28, heat-inactivated sera shaped T cells towards on-blast formation, higher cytokine secretion (interferon γ, tumor necrosis factor, and interleukin-17), stronger CD69 and PD-1 expression, and increased metabolic activity. Heat-inactivated sera contained reduced amounts of complement factors and regulators like C1 inhibitor, but increased concentrations of circulating immune complexes. Substitution of C1 inhibitor reduced the beneficial effect of heat-inactivation in terms of cytokine release, whereas surface-molecule expression was affected by the addition of complex forming anti-C1q antibody. Our data clearly demonstrate a beneficial effect of heat-inactivation of human sera for T cell experiments but indicate that beside complement regulators and immune complexes other components might be relevant. Beyond that, this study further underpins the strong impact of the complement system on T cell function.

Complement system network in cell physiology and in human diseases

The complement system is a multi-functional system representing the first line host defense against pathogens in innate immune response, through three different pathways. Impairment of its function, consisting in deficiency or excessive deregulated activation, may lead to severe systemic infections or autoimmune disorders. These diseases may be inherited or acquired. Despite many diagnostic tools are currently available, ranging from traditional, such as hemolytic or ELISA based assays, to innovative ones, like next generation sequencing techniques, these diseases are often not recognized. As for therapeutic aspects, strategies based on the use of targeted drugs are now widespread. The aim of this review is to present an updated overview of complement system pathophysiology, clinical implications of its dysfunction and to summarize diagnostic and therapeutic approaches.

SLE: Novel Postulates for Therapeutic Options

Genetic deficiency in C1q is a strong susceptibility factor for systemic lupus erythematosus (SLE). There are two major hypotheses that potentially explain the role of C1q in SLE. The first postulates that C1q deficiency abrogates apoptotic cell clearance, leading to persistently high loads of potentially immunogenic self-antigens that trigger autoimmune responses. While C1q undoubtedly plays an important role in apoptotic clearance, an essential biological process such as removal of self- waste is so critical for host survival that multiple ligand-receptor combinations do fortunately exist to ensure that proper disposal of apoptotic debris is accomplished even in the absence of C1q. The second hypothesis is based on the observation that locally synthesized C1q plays a critical role in regulating the earliest stages of monocyte to dendritic cell (DC) differentiation and function. Indeed, circulating C1q has been shown to keep monocytes in a pre-dendritic state by silencing key molecular players and ensuring that unwarranted DC-driven immune responses do not occur. Monocytes are also able to display macromolecular C1 on their surface, representing a novel mechanism for the recognition of circulating "danger." Translation of this danger signal in turn, provides the requisite "license" to trigger a differentiation pathway that leads to adaptive immune response. Based on this evidence, the second hypothesis proposes that deficiency in C1q dysregulates monocyte-to-DC differentiation and causes inefficient or defective maintenance of self-tolerance. The fact that C1q receptors (cC1qR and gC1qR) are also expressed on the surface of both monocytes and DCs, suggests that C1q/C1qR may regulate DC differentiation and function through specific cell-signaling pathways. While their primary ligand is C1q, C1qRs can also independently recognize a vast array of plasma proteins as well as pathogen-associated molecular ligands, indicating that these molecules may collaborate in antigen recognition and processing, and thus regulate DC-differentiation. This review will therefore focus on the role of C1q and C1qRs in SLE and explore the gC1qR/C1q axis as a potential target for therapy.

Essential Role of Complement in Pregnancy: From Implantation to Parturition and Beyond

The complement cascade was identified over 100 years ago, yet investigation of its role in pregnancy remains an area of intense research. Complement inhibitors at the maternal-fetal interface prevent inappropriate complement activation to protect the fetus. However, this versatile proteolytic cascade also favorably influences numerous stages of pregnancy, including implantation, fetal development, and labor. Inappropriate complement activation in pregnancy can have adverse lifelong sequelae for both mother and child. This review summarizes the current understanding of complement activation during all stages of pregnancy. In addition, consequences of complement dysregulation during adverse pregnancy outcomes from miscarriage, preeclampsia, and pre-term birth are examined. Finally, future research directions into complement activation during pregnancy are considered.

Complement: Bridging the innate and adaptive immune systems in sterile inflammation

The complement system is a collection of soluble and membrane-bound proteins that together act as a powerful amplifier of the innate and adaptive immune systems. Although its role in infection is well established, complement is becoming increasingly recognized as a key contributor to sterile inflammation, a chronic inflammatory process often associated with noncommunicable diseases. In this context, damaged tissues release danger signals and trigger complement, which acts on a range of leukocytes to augment and bridge the innate and adaptive immune systems. Given the detrimental effect of chronic inflammation, the complement system is therefore well placed as an anti-inflammatory drug target. In this review, we provide a general outline of the sterile activators, effectors, and targets of the complement system and a series of examples (i.e., hypertension, cancer, allograft transplant rejection, and neuroinflammation) that highlight complement's ability to bridge the 2 arms of the immune system.

The complement system in Aspergillus fumigatus infections and its crosstalk with pentraxins

Aspergillosis is a life-threatening infection mostly affecting immunocompromised individuals and primarily caused by the saprophytic fungus Aspergillus fumigatus. At the host-pathogen interface, both cellular and humoral components of the innate immune system are increasingly acknowledged as essential players in the recognition and disposal of this opportunistic mold. Fundamental hereof is the contribution of the complement system, which deploys all three activation pathways in the battle against A. fumigatus, and functionally cooperates with other soluble pattern recognition molecules, including pentraxins. In particular, preclinical and clinical observations point to the long pentraxin PTX3 as a nonredundant and complement-dependent effector with protective functions against A. fumigatus. Based on past and current literature, here we discuss how the complement participates in the immune response to this fungal pathogen, and illustrate its crosstalk with the pentraxins, with a focus on PTX3. Emphasis is placed on the molecular mechanisms underlying such processes, the genetic evidence from human epidemiology, and the translational potential of the currently available knowledge.

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.

Expressions of HLA Class II Genes in Cutaneous Melanoma Were Associated with Clinical Outcome: Bioinformatics Approaches and Systematic Analysis of Public Microarray and RNA-Seq Datasets

Major histocompatibility complex (MHC) class II molecules, encoded by human leukocyte antigen (HLA) class II genes, play important roles in antigen presentation and initiation of immune responses. However, the correlation between HLA class II gene expression level and patient survival and disease progression in cutaneous melanoma is still under investigation. In the present study, we analyzed microarray and RNA-Seq data of cutaneous melanoma from The Cancer Genome Atlas (TCGA) using different bioinformatics tools. Survival analysis revealed higher expression level of HLA class II genes in cutaneous melanoma, especially HLA-DP and -DR, was significantly associated with better overall survival. Furthermore, the expressions of HLA class II genes were most closely associated with survival in cutaneous melanoma as compared with other cancer types. The expression of HLA class II co-expressed genes, which were found to associate with antigen processing, immune response, and inflammatory response, was also positively associated with overall survival in cutaneous melanoma. Therefore, the results indicated that increased HLA class II expression may contribute to enhanced anti-tumor immunity and related inflammatory response via presenting tumor antigens to the immune system. The expression pattern of HLA class II genes may serve as a prognostic biomarker and therapeutic targets in cutaneous melanoma.

Formation of Immune Complexes with a Tetanus-Derived B Cell Epitope Boosts Human T Cell Responses to Covalently Linked Peptides in an Ex Vivo Blood Loop System

Enhancing T cell responses against both viral and tumor Ags requires efficient costimulation and directed delivery of peptide Ags into APCs. Long peptide vaccines are considered favorable vaccine moieties from a clinical perspective, as they can harbor more than one immunogenic epitope enabling treatment of a broader target population. In addition, longer peptides are not extracellularly loaded on MHC class I; rather, they require intracellular processing and will thereby be presented to T cells mainly by professional APCs, thereby avoiding the risk of tolerance induction. The drawback of peptide vaccines regardless of peptide length is that naked peptides are not actively targeted to and taken up by APCs, and the standard nonconjugated adjuvant-peptide mixtures do not ensure cotargeting of the two to the same APC. We have identified a tetanus toxin-derived B cell epitope that can mediate the formation of immune complexes in the presence of circulating Abs. In this study, we show that these immune complexes improve both Ag uptake by APCs (blood monocytes and CD1c⁺ dendritic cells) and consequently improve CD8⁺ T cell recall responses in a human ex vivo blood loop system. The uptake of the peptide conjugate by blood monocytes is dependent on Abs and the complement component C1q. We envision that this strategy can be used to facilitate active uptake of Ags into APCs to improve T cell responses against pathogens or cancer.

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.

Complement as a regulator of adaptive immunity

The complement system is an ancient and evolutionarily conserved effector system comprising in mammals over 50 circulating and membrane bound proteins. Complement has long been described as belonging to the innate immune system; however, a number of recent studies have demonstrated its key role in the modulation of the adaptive immune response. This review does not set out to be an exhaustive list of the numerous interactions of the many complement components with adaptive immunity; rather, we will focus more precisely on the role of some complement molecules in the regulation of antigen presenting cells, as well as on their direct effect on the activation of the core adaptive immune cells, B and T lymphocytes. Recent reports on the local production and activation of complement proteins also suggest a major role in the control of effector responses. The crucial role of complement in adaptive immunity is further highlighted by several examples of dysregulation of these pathways in human diseases.

The "ins and outs" of complement-driven immune responses

The complement system represents an evolutionary old and critical component of innate immunity where it forms the first line of defense against invading pathogens. Originally described as a heat-labile fraction of the serum responsible for the opsonization and subsequent lytic killing of bacteria, work over the last century firmly established complement as a key mediator of the general inflammatory response but also as an acknowledged vital bridge between innate and adaptive immunity. However, recent studies particularly spanning the last decade have provided new insights into the novel modes and locations of complement activation and highlighted unexpected additional biological functions for this ancient system, for example, in regulating basic processes of the cell. In this review, we will cover the current knowledge about complement's established and novel roles in innate and adaptive immunity with a focus on the functional differences between serum circulating and intracellularly active complement and will describe and discuss the newly discovered cross-talks of complement with other cell effector systems particularly during T-cell induction and contraction.

Quantitative and multiplexed detection for blood typing based on quantum dot-magnetic bead assay

Background

Accurate and reliable blood grouping is essential for safe blood transfusion. However, conventional methods are qualitative and use only single-antigen detection. We overcame these limitations by developing a simple, quantitative, and multiplexed detection method for blood grouping using quantum dots (QDs) and magnetic beads.

Methods

In the QD fluorescence assay (QFA), blood group A and B antigens were quantified using QD labeling and magnetic beads, and the blood groups were identified according to the R value (the value was calculated with the fluorescence intensity from dual QD labeling) of A and B antigens. The optimized performance of QFA was established by blood typing 791 clinical samples.

Results

Quantitative and multiplexed detection for blood group antigens can be completed within 35 min with more than 10⁵ red blood cells. When conditions are optimized, the assay performance is satisfactory for weak samples. The coefficients of variation between and within days were less than 10% and the reproducibility was good. The ABO blood groups of 791 clinical samples were identified by QFA, and the accuracy obtained was 100% compared with the tube test. Receiver-operating characteristic curves revealed that the QFA has high sensitivity and specificity toward clinical samples, and the cutoff points of the R value of A and B antigens were 1.483 and 1.576, respectively.

Conclusion

In this study, we reported a novel quantitative and multiplexed method for the identification of ABO blood groups and presented an effective alternative for quantitative blood typing. This method can be used as an effective tool to improve blood typing and further guarantee clinical transfusion safety.

Old game, new players: Linking classical theories to new trends in transplant immunology

The evolutionary emergence of an efficient immune system has a fundamental role in our survival against pathogenic attacks. Nevertheless, this same protective mechanism may also establish a negative consequence in the setting of disorders such as autoimmunity and transplant rejection. In light of the latter, although research has long uncovered main concepts of allogeneic recognition, immune rejection is still the main obstacle to long-term graft survival. Therefore, in order to define effective therapies that prolong graft viability, it is essential that we understand the underlying mediators and mechanisms that participate in transplant rejection. This multifaceted process is characterized by diverse cellular and humoral participants with innate and adaptive functions that can determine the type of rejection or promote graft acceptance. Although a number of mediators of graft recognition have been described in traditional immunology, recent studies indicate that defining rigid roles for certain immune cells and factors may be more complicated than originally conceived. Current research has also targeted specific cells and drugs that regulate immune activation and induce tolerance. This review will give a broad view of the most recent understanding of the allogeneic inflammatory/tolerogenic response and current insights into cellular and drug therapies that modulate immune activation that may prove to be useful in the induction of tolerance in the clinical setting.

Alternative functions of the complement protein C1q at embryo implantation site

Complement component C1q is one of the recognition molecules of the complement system which can serve several functions unrelated to complement activation. This molecule is produced at foeto-maternal interface by macrophages as wells as by decidual endothelial cells and invading trophoblast. Foetal trophoblast cells migrating through the decidua in the early stages of pregnancy synthesize and express C1q on their surface, which is actively involved in promoting trophoblast endovascular and interstitial invasion of the decidua. These functions are mediated by two cell surface receptors, gC1qR and α4β1 integrin, which promote trophoblast adhesion and migration through the activation of ERK1/2 MAPKs. C1q^-/- mice manifest increased frequency of foetal resorption, reduced foetal weight, and smaller litter size when compared to their wild-type counterparts, suggesting that defective local production of C1q may be involved in pregnancy disorders, such as pre-eclampsia. C1q acts also as a strong angiogenic factor and promotes neovascularization. These studies suggest novel and unexpected roles of this complement component in physiological and pathological pregnancies.

Breakdown of Immune Tolerance in Systemic Lupus Erythematosus by Dendritic Cells

Dendritic cells (DC) play an important role in the pathogenesis of systemic lupus erythematosus (SLE), an autoimmune disease with multiple tissue manifestations. In this review, we summarize recent studies on the roles of conventional DC and plasmacytoid DC in the development of both murine lupus and human SLE. In the past decade, studies using selective DC depletions have demonstrated critical roles of DC in lupus progression. Comprehensive in vitro and in vivo studies suggest activation of DC by self-antigens in lupus pathogenesis, followed by breakdown of immune tolerance to self. Potential treatment strategies targeting DC have been developed. However, many questions remain regarding the mechanisms by which DC modulate lupus pathogenesis that require further investigations.

Anti-C1q Autoantibodies from Systemic Lupus Erythematosus Patients Induce a Proinflammatory Phenotype in Macrophages

Anti-C1q autoantibodies (anti-C1q) are frequently found in patients with systemic lupus erythematosus (SLE) and correlate with the occurrence of proliferative lupus nephritis. A previous study of anti-C1q in experimental lupus nephritis demonstrated an important role for FcγRs in the pathogenesis of lupus nephritis, suggesting a direct effect on phagocytes. Therefore, we developed an in vitro model to study the effect of SLE patient-derived anti-C1q bound to immobilized C1q (imC1q) on human monocyte-derived macrophages (HMDMs) obtained from healthy donors and SLE patients. HMDMs were investigated by analyzing the cell morphology, LPS-induced cytokine profile, surface marker expression, and phagocytosis rate of apoptotic Jurkat cells. Morphologically, bound anti-C1q induced cell aggregations of HMDMs compared with imC1q or IgG alone. In addition, anti-C1q reversed the effect of imC1q alone, shifting the LPS-induced cytokine release toward a proinflammatory response. FcγR-blocking experiments revealed that the secretion of proinflammatory cytokines was mediated via FcγRII. The anti-C1q-induced inflammatory cytokine profile was accompanied by a downregulation of CD163 and an upregulation of LPS-induced CD80, CD274, and MHC class II. Finally, HMDMs primed on bound anti-C1q versus imC1q alone displayed a significantly lower phagocytosis rate of early and late apoptotic cells accompanied by a reduced Mer tyrosine kinase expression. Interestingly, anti-C1q-dependent secretion of proinflammatory cytokines was similar in SLE patient-derived cells, with the exception that IL-10 was slightly increased. In conclusion, anti-C1q induced a proinflammatory phenotype in HMDMs reversing the effects of imC1q alone. This effect might exacerbate underlying pathogenic mechanisms in lupus nephritis.

Emerging and Novel Functions of Complement Protein C1q

Complement protein C1q, the recognition molecule of the classical pathway, performs a diverse range of complement and non-complement functions. It can bind various ligands derived from self, non-self, and altered self and modulate the functions of immune and non-immune cells including dendritic cells and microglia. C1q involvement in the clearance of apoptotic cells and subsequent B cell tolerance is more established now. Recent evidence appears to suggest that C1q plays an important role in pregnancy where its deficiency and dysregulation can have adverse effects, leading to preeclampsia, missed abortion, miscarriage or spontaneous loss, and various infections. C1q is also produced locally in the central nervous system, and has a protective role against pathogens and possible inflammatory functions while interacting with aggregated proteins leading to neurodegenerative diseases. C1q role in synaptic pruning, and thus CNS development, its anti-cancer effects as an immune surveillance molecule, and possibly in aging are currently areas of extensive research.

The paradoxical roles of C1q and C3 in autoimmunity

In this review we will focus on the links between complement and autoimmune diseases and will highlight how animal models have provided insights into the manner by which C1q and C3 act to modulate both adaptive and innate immune responses. In particular we will highlight how C1q may not only act as initiator of the classical complement pathway, but can also mediate multiple immune responses in a complement activation independent manner.

Monocyte Expressed Macromolecular C1 and C1q Receptors as Molecular Sensors of Danger: Implications in SLE

The ability of circulating blood monocytes to express C1q receptors (cC1qR and gC1qR) as well as to synthesize and secrete the classical pathway proteins C1q, C1r, and C1s and their regulator, C1-INH is very well established. What is intriguing, however, is that, in addition to secretion of the individual C1 proteins monocytes are also able to display macromolecular C1 on their surface in a manner that is stable and functional. The cell surface C1 complex is presumably formed by a Ca²⁺-dependent association of the C1r₂⋅C1s₂ tetramer to C1q, which in turn is anchored via a membrane-binding domain located in the N-terminus of its A-chain as shown previously. Monocytes, which circulate in the blood for 1–3 days before they move into tissues throughout the body, not only serve as precursors of macrophages and dendritic cells (DCs), but also fulfill three main functions in the immune system: phagocytosis, antigen presentation, and cytokine production. Since the globular heads of C1q within the membrane associated C1 are displayed outwardly, we hypothesize that their main function – especially in circulating monocytes – is to recognize and capture circulating immune complexes or pathogen-associated molecular patterns in the blood. This in turn may give crucial signal, which drives the monocytes to migrate into tissues, differentiate into macrophages or DCs, and initiate the process of antigen elimination. Unoccupied C1q on the other hand may serve to keep monocytes in a pre-dendritic phenotype by silencing key molecular players thus ensuring that unwarranted DC-driven immune response does not occur. In this paper, we will discuss the role of monocyte/DC-associated C1q receptors, macromolecular C1 as well as secreted C1q in both innate and acquired immune responses.

Aggregation of human recombinant monoclonal antibodies influences the capacity of dendritic cells to stimulate adaptive T-cell responses in vitro

Subvisible proteinaceous particles which are present in all therapeutic protein formulations are in the focus of intense discussions between health authorities, academics and biopharmaceutical companies in the context of concerns that such particles could promote unwanted immunogenicity via anti-drug antibody formation. In order to provide further understanding of the subject, this study closely examines the specific biological effects proteinaceous particles may exert on dendritic cells (DCs) as the most efficient antigen-presenting cell population crucial for the initiation of the adaptive immune response. Two different model IgG antibodies were subjected to three different types of exaggerated physical stress to generate subvisible particles in far greater concentrations than the ones typical for the currently marketed biotherapeutical antibodies. The aggregated samples were used in in vitro biological assays in order to interrogate the early DC-driven events that initiate CD4 T-cell dependent humoral adaptive immune responses – peptide presentation capacity and co-stimulatory activity of DCs. Most importantly, antigen presentation was addressed with a unique approach called MHC-associated Peptide Proteomics (MAPPs), which allows for identifying the sequences of HLA-DR associated peptides directly from human dendritic cells.

The experiments demonstrated that highly aggregated solutions of two model mAbs generated under controlled conditions can induce activation of human monocyte-derived DCs as indicated by upregulation of typical maturation markers including co-stimulatory molecules necessary for CD4 T-cell activation. Additional data suggest that highly aggregated proteins could induce in vitro T-cell responses. Intriguingly, strong aggregation-mediated changes in the pattern and quantity of antigen-derived HLA-DR associated peptides presented on DCs were observed, indicating a change in protein processing and presentation. Increasing the amounts of subvisible proteinaceous particles correlated very well with the pronounced increase in the peptide number and clusters presented in the context of class II HLA-DR molecules, suggesting a major involvement of a mass-action mechanism of altering the presentation.

Phenotypic and functional maturation of murine dendritic cells induced by 18 alpha- and beta-glycyrrhetinic acid

Various studies have described glycyrrhizin (GL), an active triterpenoic saponin extract of licorice roots, as an anti-inflammatory, antiviral, antimicrobial, anti-tumor and immunomodulating agent. The activity of GL has been mainly attributed to its metabolites, 18-alpha (GA) and 18-beta-glycyrrhetinic acid (GB), which their mechanism of action on the immune system cells is not clearly known. In this study, we have investigated the effects of GA and GB on the immune system by targeting dendritic cells and analyzing phenotypic and functional maturity of murine dendritic cells (DCs) after treatment with these components. Stimulation of DCs with GA and GB resulted in up-regulation of CD40, CD86 and MHC-II molecules indicating their effects on the maturation of DCs. These components induced the allogenic immunostimulatory capacity of DCs by stimulating the proliferation of T cells and production of the T helper (h)1-promoting cytokine, IL-12. They also increased the production of IFN-γ by T cells in mixed-lymphocyte reaction. In conclusion, these results indicate that GA and GB may insert their immunomodulatory effects by enhancing DC maturation and modulating Th1/Th2 response through an increase in Th1 responses, implying their beneficial in host defense against infectious diseases.

Anti-DNA antibodies cross-react with C1q

Systemic lupus erythematosus (SLE) is an autoimmune disorder that involves multiple organ systems and typically presents as a chronic inflammatory disease. Antibodies to double-stranded (ds) DNA are present in approximately 70% of patients and form nucleic acid containing immune complexes which activate dendritic cells through engagement of toll-like receptors, leading to a pro-inflammatory, pro-immunogenic milieu. In addition, anti-dsDNA antibodies deposit in kidneys to initiate glomerulonephritis. Antibodies to C1q have also been implicated in lupus nephritis and are found in 30-50% of patients. C1q is a known suppressor of immune activation and C1q deficiency is the strongest risk factor for SLE. We previously identified a subset of anti-DNA antibodies that binds the N-methyl-D-aspartate receptor. We now show that both mouse and human anti-DNA antibodies with this specificity bind C1q. These antibodies bind to Clq in glomeruli and exhibit decreased glomerular deposition in the absence of C1q. We propose that this subset of anti-DNA antibodies participates in lupus pathogenesis through direct targeting of C1q on glomeruli and also through removal of soluble C1q thereby limiting the ability of C1q to mediate immune homeostasis.

The α7β0 isoform of the complement regulator C4b-binding protein induces a semimature, anti-inflammatory state in dendritic cells

The classical pathway complement regulator C4b-binding protein (C4BP) is composed of two polypeptides (α- and β-chains), which form three plasma oligomers with different subunit compositions (α7β1, α7β0, and α6β1). We show in this article that the C4BP α7β0 isoform (hereafter called C4BP[β(-)] [C4BP lacking the β-chain]), overexpressed under acute-phase conditions, induces a semimature, tolerogenic state on human monocyte-derived dendritic cells (DCs) activated by a proinflammatory stimulus. C4BP isoforms containing β-chain (α7β1 and α6β1; C4BP[β(+)]) neither interfered with the normal maturation of DCs nor competed with C4BP(β(-)) activity on these cells. Immature DCs (iDCs) treated with C4BP(β(-)) retained high endocytic activity, but, upon LPS treatment, they did not upregulate surface expression of CD83, CD80, and CD86. Transcriptional profiling of these semimature DCs revealed that treatment with C4BP(β(-)) prevented the induction of IDO and BIC-1, whereas TGF-β1 expression was maintained to the level of iDCs. C4BP(β(-))-treated DCs were also unable to release proinflammatory Th1 cytokines (IL-12, TNF-α, IFN-γ, IL-6, IL-8) and, conversely, increased IL-10 secretion. They prevented surface CCR7 overexpression and, accordingly, displayed reduced chemotaxis, being morphologically indistinguishable from iDCs. Moreover, C4BP(β(-))-treated DCs failed to enhance allogeneic T cell proliferation, impairing IFN-γ production in these cells and, conversely, promoting CD4(+)CD127(low/neg)CD25(high)Foxp3(+) T cells. Deletion mutant analysis revealed that the complement control protein-6 domain of the α-chain is necessary for the tolerogenic activity of C4BP(β(-)). Our data demonstrate a novel anti-inflammatory and immunomodulatory function of the complement regulator C4BP, suggesting a relevant role of the acute-phase C4BP(β(-)) isoform in a number of pathophysiological conditions and potential applications in autoimmunity and transplantation.

Distinct phases of blood gene expression pattern through tuberculosis treatment reflect modulation of the humoral immune response

BACKGROUND

Accurate assessment of treatment efficacy would facilitate clinical trials of new antituberculosis drugs. We hypothesized that early alterations in peripheral immunity could be measured by gene expression profiling in tuberculosis patients undergoing successful conventional combination treatment.

METHODS

Ex vivo blood samples from 27 pulmonary tuberculosis patients were assayed at diagnosis and during treatment. RNA was processed and hybridized to Affymetrix GeneChips, to determine expression of over 47,000 transcripts.

RESULTS

There were significant ≥ 2-fold changes in expression of >4000 genes during treatment. Rapid, large-scale changes were detected, with down-regulated expression of 1261 genes within the first week, including inflammatory markers such as complement components C1q and C2. This was followed by slower changes in expression of different networks of genes, including a later increase in expression of B-cell markers, transcription factors, and signaling molecules.

CONCLUSIONS

The fast initial down-regulation of expression of inflammatory mediators coincided with rapid killing of actively dividing bacilli, whereas slower delayed changes occurred as drugs acted on dormant bacilli and coincided with lung pathology resolution. Measurement of biosignatures during clinical trials of new drugs could be useful predictors of rapid bactericidal or sterilizing drug activity, and would expedite the licensing of new treatment regimens.

DC-SIGN, C1q, and gC1qR form a trimolecular receptor complex on the surface of monocyte-derived immature dendritic cells

C1q modulates the differentiation and function of cells committed to the monocyte-derived dendritic cell (DC) lineage. Because the 2 C1q receptors found on the DC surface-gC1qR and cC1qR-lack a direct conduit into intracellular elements, we postulated that the receptors must form complexes with transmembrane partners. In the present study, we show that DC-SIGN, a C-type lectin expressed on DCs, binds directly to C1q, as assessed by ELISA, flow cytometry, and immunoprecipitation experiments. Surface plasmon resonance analysis revealed that the interaction was specific, and both intact C1q and the globular portion of C1q bound to DC-SIGN. Whereas IgG reduced this binding significantly, the Arg residues (162-163) of the C1q-A chain, which are thought to contribute to the C1q-IgG interaction, were not required for C1q binding to DC-SIGN. Binding was reduced significantly in the absence of Ca(2+) and by preincubation of DC-SIGN with mannan, suggesting that C1q binds to DC-SIGN at its principal Ca(2+)-binding pocket, which has increased affinity for mannose residues. Antigen-capture ELISA and immunofluorescence microscopy revealed that C1q and gC1qR associate with DC-SIGN on blood DC precursors and immature DCs. The results of the present study suggest that C1q/gC1qR may regulate DC differentiation and function through the DC-SIGN-mediated induction of cell-signaling pathways.

The immunological contribution of NF-κB within the tumor microenvironment: a potential protective role of zinc as an anti-tumor agent

Over decades, cancer treatment has been mainly focused on targeting cancer cells and not much attention to host tumor microenvironment. Recent advances suggest that the tumor microenvironment requires in-depth investigation for understanding the interactions between tumor cell biology and immunobiology in order to optimize therapeutic approaches. Tumor microenvironment consists of cancer cells and tumor associated reactive fibroblasts, infiltrating non-cancer cells, secreted soluble factors or molecules, and non-cellular support materials. Tumor associated host immune cells such as Th(1), Th(2), Th17, regulatory cells, dendritic cells, macrophages, and myeloid-derived suppressor cells are major components of the tumor microenvironment. Accumulating evidence suggests that these tumor associated immune cells may play important roles in cancer development and progression. However, the exact functions of these cells in the tumor microenvironment are poorly understood. In the tumor microenvironment, NF-κB plays an important role in cancer development and progression because this is a major transcription factor which regulates immune functions within the tumor microenvironment. In this review, we will focus our discussion on the immunological contribution of NF-κB in tumor associated host immune cells within the tumor microenvironment. We will also discuss the potential protective role of zinc, a well-known immune response mediator, in the regulation of these immune cells and cancer cells in the tumor microenvironment especially because zinc could be useful for conditioning the tumor microenvironment toward innovative cancer therapy.

Nucleic acid adjuvants: toward an educated vaccine

Two striking facts surround the practice of vaccination: It is the sole medical approach to have fully annihilated a disease, yet the development of most effective vaccines took place without considering the intricate cellular processes they wish to effectuate. While extremely potent vaccines have been developed that can protect practically a lifetime after a single dose, numerous other vaccines have utterly failed or provide only marginal protection. Here, we aim to illustrate why this difference in efficacy exists, and underline why specific cytotoxic T cell-inducing vaccines could combat persistent major diseases. Moreover, we discuss how the combinatorial use of nucleic acid adjuvants in vaccines could aid the development of the latter and move vaccine design from the empirical stage into an era of "educated design."

Barriers of the Human Organism and Their Achilles’ Heels

The human body is covered by barriers separating it from the external and internal surroundings. The “milieu enterieur” has to be stabilised in spite of the variable external and internal conditions of toxic, osmotic, microbial and climatic environmental circumstances. This first line of barriers is composed of skin and mucous membranes of complicated structures.

A second line of barrier system is present in our organisms. Certain organs have to be separated from the immune system and other parts of the body because of evolutionary reasons (eye-bulb and testicles) because of unique proteins “unknown” for the acquired immune system. The blood-brain barrier (BBB) is providing enhanced safety circumstances for the central nervous system. The second line of barriers is represented by the special properties of the capillary endothelial system.

The maternal-fetal barrier is the most complex. At the maternal fetal interface two individuals of two different haplotypes has to be live 9 months separated by a very complicated dynamic barrier.

The placenta is the organ, which is separating the maternal and fetal tissues. Similar to others the bidirectional transport of gasses, metabolites, cells, proteins, regulatory substances, are transported by active or passive transcellular and intercellular mechanisms.

The fetal immune system develops immunotolerance to all maternal cells and antigens transferred transplacentally. The problem is to mitigate the maternal immune system to tolerate the paternal haplotype of the fetus. In the case of normal pregnancy a complex series of physiological modifications can solve the problem without harmful consequences to the mother and fetus.

The outermost contact cells of trophoblasts express instead of HLA-class Ia and class II antigens non-variable HLA-C, HLA-E, HLA-F and HLA-G antigens. The first consequence of this is reduction of the activity of maternal natural killer cells and maternal dendritic cells;

Progesteron, micro-RNA and mediators influence the development of T effector-cells. The production of soluble HLA-G(5 and 6) and IL-10 supports the differentiation of Th-2 CD4⁺ helper cells, reducing the ability of maternal cells to kill fetal cells.

Series of receptors and costimulators are expressed by the different lines of semi-allogenic trophoblast cells to bind HLA-G and mitigate maternal immune response;

The maternal immunotolerance is further facilitated by the activation of CD4⁺CD25^brightFoxp3⁺ regulatory T (T_REG) cells.

Infections have to be prevented during pregnancy. The cells of placenta express 10 Toll-like receptors a group of pattern recognition receptors responsible for innate immunity. The interferon level is also higher in the placental tissues than in the somatic fetal or maternal cells.

The complement system is also adapted to the requirements of the pregnancy and fetal damage is inhibited by the production of “assymmetric IgG antibodies” under hormonal and placental-regulation. These modifications prevent the activation of complement, cytotoxic activity, opsonising ability, antigen clearance and precipitating activity of the molecules.

The Achilles’ heels of the different barriers are regularly found by virus infections. Lamina cribrosa of the blood-brain barrier, optical nerve of the eyes, etc. the risk factors of the maternal-fetal barrier has been summarised in Table 1.1.

Complement and non-complement activating functions of C1q: A prototypical innate immune molecule

C1q is a versatile innate immune molecule that serves as the initiation subcomponent of the classical complement pathway. In addition, it is also a potent pattern recognition molecule, the versatility of which has fuelled its functional flexibility. C1q recognises an array of self, non-self and altered-self ligands. The broad-spectrum ligand-binding potential of C1q is facilitated by the modular organisation of the heterotrimeric globular head region, its ability to change its conformation in a very subtle way, and the manner in which this ancient molecule appears to have evolved to deal with the different types of ligands. Over recent years, molecules that resemble C1q have been put together to form the C1q family. In this review, we briefly summarise complement-dependent and complement-independent functions of C1q, its cognate receptors and key members of the rapidly growing C1q family.

Expression of complement components, receptors and regulators by human dendritic cells

Integration of innate and adaptive arms of the immune response at a cellular and molecular level appears to be fundamental to the development of powerful effector functions in host defence and aberrant immune responses. Here we provide evidence that the functions of human complement activation and antigen presentation converge on dendritic cells (DCs). We show that several subsets of human DCs [i.e., monocyte derived (CD1a(+)CD14(-)), dermal (CD1a(+)DC-SIGN(+)), Langerhans (CD1a(+)Langerin(+)), myeloid (CD1c(+)CD19(-)), plamacytoid (CD45RA(+)CD123(+))] express many of the components of the classical and alternative and terminal pathways of complement. Moreover human DCs have receptors known to detect the biologically active peptides C3a and C5a (C3aR, C5aR) and the covalently bound fragments C3b and metabolites iC3b and C3d which serve in immune adhesion (i.e., CR3, CR4, CRIg). We also show that the human DC surface is characterised by membrane bound regulators of complement activation, which are also known to participate in intracellular signalling (i.e., CD46, CD55, CD59). This work provides an extensive description of complement components relevant to the integrated actions of complement and DC, illuminated by animal studies. It acts as a resource that allows further understanding and exploitation of role of complement in human health and immune mediated diseases.

C1q regulation of dendritic cell development from monocytes with distinct cytokine production and T cell stimulation

The causative association of complement C1q deficiency with systemic lupus erythematosus (SLE), which inevitably involves the breakdown of tolerance, remains poorly explained. Its non-hepatic, macrophage and dendritic cell (DC) origin may be highly relevant. In tissues, C1q is produced by DCs and macrophages which deposits around these cells and we ask whether this pericellular form of C1q regulates DC development from monocytes. DCs cultured on immobilized C1q (C1q-DCs) show similar MHC, CD40, CD80, CD86, CD83 and CCR7 expression as normal DCs, but these cells exhibit increased phagocytosis of apoptotic cells and elevated IL-10 but reduced IL-12 and IL-23 production. Intracellularly, C1q-DCs exhibit increased ERK, p38 and p70S6 kinase activity. By mixed leukocyte reaction, C1q-DCs show reduced Th1 and Th17 induction from allogeneic CD4(+) T cells. LPS and IFNγ, which cause normal DCs to induce increased CD25 expression on CD4(+) T cells, attenuate C1q-DC induction of CD25. These imply that the DC pericellular C1q may induce tolerogenic properties in developing DCs.

Investigations on the C1q-calreticulin-phosphatidylserine interactions yield new insights into apoptotic cell recognition

Both C1q and calreticulin (CRT) are involved in the recognition of apoptotic cells. CRT was initially characterized as a receptor for the C1q collagen-like fragment (CLF), whereas C1q was shown to bind apoptotic cells through its globular region (GR). Using purified CRT and recombinant CRT domains, we now provide unambiguous experimental evidence that, in addition to its CLF, the C1q GR also binds CRT and that both types of interactions are mediated by the CRT globular domain. Surface plasmon resonance analyses revealed that the C1q CLF and GR domains each bind individually to immobilized CRT and its globular domain with K(D) values of (2.6-8.3) × 10(-7) M. Further evidence that CRT binds to the C1q GR was obtained by electron microscopy. The role of CRT in the recognition of apoptotic HeLa cells by C1q was analyzed. The C1q GR partially colocalized with CRT on the surface of early apoptotic cells, and siRNA (small interfering RNA)-induced CRT deficiency resulted in increased apoptotic cell binding to C1q. The interaction between CRT and phosphatidylserine (PS), a known C1q ligand on apoptotic cells, was also investigated. The polar head of PS was shown to bind to CRT with a 10-fold higher affinity (K(D)=1.5 × 10(-5) M) than that determined for C1q, and, accordingly, the C1q GR-PS interaction was impaired in the presence of CRT. Together, these observations indicate that CRT, C1q, and PS are all closely involved in the uptake of apoptotic cells and strongly suggest a combinatorial role of these three molecules in the recognition step.

Mannan-binding lectin regulates dendritic cell maturation and cytokine production induced by lipopolysaccharide

Background

Mannan-binding lectin (MBL) is a pattern-recognition molecule present in serum, which is involved in the innate immune defense by activating complement and promoting opsonophagocytosis. Dendritic cells (DCs) are professional antigen presenting cells (APCs) that are crucial for the initiation of adaptive immunity. Lipopolysaccharide (LPS) has been shown to be a strong activator of the inflammatory response and immune regulation. We first examined whether MBL modulated LPS-induced cellular responses, then investigated possible mechanisms of its inhibitory effect.

Results

MBL at higher concentrations (10-20 μg/ml) significantly attenuated LPS-induced maturation of monocyte-derived DCs (MDCs) and production of proinflammatory cytokines (e.g., IL-12 and TNF-α), and inhibited their ability to activate allogeneic T lymphocytes. It bound to immature MDCs at physiological calcium concentrations, and was optimal at supraphysiological calcium concentrations. MBL also bound directly to immature MDCs and attenuated the binding of LPS to the cell surfaces, resulting in decreased LPS-induced nuclear factor-κB (NF-κB) activity in these cells.

Conclusion

All these data suggest that MBL could affect the functions of DCs by modifying LPS-induced cellular responses. This study supports an important role for MBL in the regulation of adaptive immune responses and inflammatory responses.

Cell culture plastics with immobilized interleukin-4 for monocyte differentiation

Standard cell culture plastic was surface modified by passive adsorption or covalent attachment of interleukin (IL)-4 and investigated for its ability to induce differentiation of human monocytes into mature dendritic cells, a process dose-dependently regulated by IL-4. Covalent attachment of IL-4 proceeded via anthraquinone photochemistry to introduce amine functionalities at the surface followed by coupling of IL-4 through a bifunctional amine-reactive linker. X-ray photoelectron spectroscopy showed that undesirable multilayer formation of the photoactive compound could be avoided by reaction in water instead of phosphate-buffered saline. Passively adsorbed IL-4 was observed to induce differentiation to dendritic cells, but analysis of cell culture supernatants revealed that leakage of IL-4 into solution could account for the differentiation observed. Covalent attachment resulted in bound IL-4 at similar concentrations to the passive adsorption process, as measured by enzyme-linked immunosorbent assays, and the bound IL-4 did not leak into solution to any measurable extent during cell culture. However, covalently bound IL-4 was incapable of inducing monocyte differentiation. This may be caused by IL-4 denaturation or improper epitope presentation induced by the immobilization process, or by biological irresponsiveness of monocytes to IL-4 in immobilized formats.

Complement in organ transplantation

PURPOSE OF REVIEW

The aim of this review is to bring to attention the most recent advances made in understanding the role of complement components in both innate and adaptive immune responses in solid organ transplantation with emphasis on the kidney.

RECENT FINDINGS

Alongside recent findings related to the role of anaphylatoxins in modulating adaptive immune responses, there has been a genomic study to assess the expression of inflammatory markers in kidney transplantation, showing significant involvement of some complement molecules in predicting graft function. Modulators of complement pathway activity such as decay accelerating factor (CD55) and CD59 have also been shown to have a role in graft rejection. Potential new therapeutic targets related to complement proteins are being investigated.

SUMMARY

The mechanism of rejection in solid organ transplantation is influenced by the initial inflammatory response and subsequent adaptive allo-immune response, both of which have been shown to be affected by various complement components. Due to limitations of existing treatments, new approaches are needed to better control these responses to improve graft survival. Built on an expanding knowledge of complement involvement, targeted blocking of the effector complement molecules and modulating the expression of complement inhibitors has suggested potentially useful approaches for reducing the effect of inflammatory damage from cold ischaemia as well as reducing the activation of the adaptive immune system related to complement.

Serum antibodies critically affect virus-specific CD4+/CD8+ T cell balance during respiratory syncytial virus infections

Following infection with respiratory syncytial virus (RSV), reinfection in healthy individuals is common and presumably due to ineffective memory T cell responses. In peripheral blood of healthy adults, a higher CD4(+)/CD8(+) memory T cell ratio was observed compared with the ratio of virus-specific effector CD4(+)/CD8(+) T cells that we had found in earlier work during primary RSV infections. In mice, we show that an enhanced ratio of RSV-specific neutralizing to nonneutralizing Abs profoundly enhanced the CD4(+) T cell response during RSV infection. Moreover, FcγRs and complement factor C1q contributed to this Ab-mediated enhancement. Therefore, the increase in CD4(+) memory T cell response likely occurs through enhanced endosomal Ag processing dependent on FcγRs. The resulting shift in memory T cell response was likely amplified by suppressed T cell proliferation caused by RSV infection of APCs, a route important for Ag presentation via MHC class I molecules leading to CD8(+) T cell activation. Decreasing memory CD8(+) T cell numbers could explain the inadequate immunity during repeated RSV infections. Understanding this interplay of Ab-mediated CD4(+) memory T cell response enhancement and infection mediated CD8(+) memory T cell suppression is likely critical for development of effective RSV vaccines.

Role and mechanism of action of complement in regulating T cell immunity

Complement is a part of the innate immune system that contributes to first-line host defense. It is also implicated in a number of human inflammatory conditions and has attracted interest as a potential therapeutic target. Understanding the basic biology of complement and its mechanism(s) of action is imperative for developing complement-based treatments for infectious and autoimmune diseases. One of the exciting new developments in this regard is the revelation that complement plays an important role in T cell immunity. In this review, we highlight recent published studies implicating complement in models of CD4+ and CD8+ T cell immune responses, and discuss its potential mechanism(s) action in these processes. We also comment on issues that may impact data interpretation and draw attention to their consideration in future studies.

Dendritic cell function in lupus: Independent contributors or victims of aberrant immune regulation

Dendritic cells (DCs) represent an important component of the immune system connecting the innate and adaptive immune responses. They are able to trigger strong immunity as well as tolerance against certain antigens, and therefore it is obvious that they have a central role in the expression of immunological diseases. However, because DCs are sparse, heterogeneous and plastic, their exact role in complex autoimmune diseases, such as systemic lupus erythematosus (SLE) remains not well defined. In this review, we make an attempt to summarize critically recent knowledge on the role of conventional DCs in the expression of autoimmunity and pathology in SLE.

The non-classical functions of the classical complement pathway recognition subcomponent C1q

C1q, the ligand recognition subcomponent of the classical complement pathway has steadily been gaining recognition as a bridge between innate and adaptive immunity. C1q has been shown to be involved in the modulation of various immune cells (such as dendritic cells, platelets, microglia cells and lymphocytes), clearance of apoptotic cells, a range of cell processes such as differentiation, chemotaxis, aggregation and adhesion, and pathogenesis of neurodegenerative diseases and systemic lupus erythematosus. Recent studies have highlighted the importance of C1q during pregnancy, coagulation process and embryonic development including neurological synapse function. It is intriguing to note that a prototypical defence molecule has so many diverse functions that probably have its origin in its versatility as a potent charge pattern recognition molecule, modularity within the ligand-recognising globular domain, and the redundancy of putative C1q receptors. The range of function that C1q has been shown to perform also provides clues for the undiscovered functions of a number of C1q family members.

Oncostatin M induces dendritic cell maturation and Th1 polarization

Oncostatin M (OSM) is a pleiotropic cytokine and a member of the gp130/IL-6 cytokine family that has been found to be involved in both pro- and anti-inflammatory responses in cell-mediated immunity. Maturation of dendritic cells (DCs) is crucial for initiation of primary immune responses and is regulated by several stimuli. In this study, the role of OSM in the phenotypic and functional maturation of DCs was evaluated in vitro. Stimulation with OSM upregulated the expression of CD80, CD86, MHC class I and MHC class II and reduced the endocytic capacity of immature DCs. Moreover, OSM induced the allogeneic immunostimulatory capacity of DCs by stimulating the production of the Th1-promoting cytokine IL-12. OSM also increased the production of IFN-gamma by T cells in mixed-lymphocyte reactions, which would be expected to contribute to the Th1 polarization of the immune response. The expression of surface markers and cytokine production in DCs was mediated by both the MAPK and NF-kappaB pathways. Taken together, these results indicate that OSM may play a role in innate immunity and in acquired immunity by enhancing DCs maturation and promoting Th1 immune responses.