Complement factor H binds at two independent sites to C-reactive protein in acute phase concentrations

A tale of two functions: C-reactive protein complement-ary structures and their role in rheumatoid arthritis

C-reactive protein (CRP) is an inflammatory biomarker with associated clinical utility in a wide number of inflammatory disorders, including rheumatoid arthritis (RA). The interaction of CRP with pro-inflammatory cytokines has been explored before, however its role in complement regulation is more subtle, where CRP is capable of both up and downregulating the complement cascade. CRP is produced in a pentameric form and can dissociate to a monomeric form in circulation which has significant implications for its ability to interact with receptors and binding partners. This dichotomy of CRP structure could have relevance in patients with RA who have significant dysfunction in their complement cascade and also widely varying CRP levels including at the time of flare. This review aims to bring together current knowledge of CRP in its various forms, its effects on complement function and how this could influence pathology in the context of RA.

The hypothetical molecular mechanism of the ethnic variations in the manifestation of age-related macular degeneration; focuses on the functions of the most significant susceptibility genes

Age-related macular degeneration (AMD) is the leading sight-threatening disease in developed countries. On the other hand, recent studies indicated an ethnic variation in the phenotype of AMD. For example, several reports demonstrated that the incidence of drusen in AMD patients is less in Asians compared to Caucasians though the reason has not been clarified yet. In the last decades, several genome association studies have disclosed many susceptible genes of AMD and revealed that the association strength of some genes was different among races and AMD phenotypes. In this review article, the essential findings of the clinical studies and genome association studies for the most significant genes CFH and ARMS2/HTRA1 in AMD of different races are summarized, and theoretical hypotheses about the molecular mechanisms underlying the ethnic variation in the AMD manifestation mainly focused on those genes between Caucasians and Asians are discussed.

Anti-complement factor H (CFH) autoantibodies could delay pristane-induced lupus nephritis

PURPOSE

Anti-complement factor H (CFH) autoantibodies could be detected in lupus and its significance remained to be elucidated. Herein, we aimed to explore the roles of anti-CFH autoantibodies based on pristane-induced lupus mice.

METHODS

Twenty-four female Balb/c mice were randomly divided into four groups, with one group injected with pristane (pristane group), one group with pristane and then human CFH (hCFH) (pristane-CFH group) 3 times, and the other two as vertical controls, PBS group and PBS-CFH group. Histopathological analysis was performed six months after pristane administration. Levels of hCFH, anti-CFH autoantibodies and anti-dsDNA antibody were detected. Murine IgG (mIgG) were purified and cross-reactivity, epitopes, subclasses and functional analysis were further evaluated in vitro.

RESULTS

Immunization with hCFH and subsequent development of anti-CFH autoantibodies significantly attenuated nephritis of pristane-induced lupus, including lower levels of urinary protein and serum creatinine, decreased levels of serum anti-dsDNA antibody, greatly ameliorated renal histopathologic damage, decreased IgG, complements (C1q, C3) deposits and lower inflammatory factor (IL-6) expression in glomerulus. Furthermore, the purified mIgG (contained anti-CFH autoantibodies) could recognize both hCFH and murine CFH, and the epitopes were predominantly located in hCFH short consensus repeats (SCRs) 1-4, 7 and 11-14. The IgG subclasses were predominant IgG1. The autoantibodies could enhance the binding between hCFH and C3b, and increase factor I mediated-C3b lysis in vitro.

CONCLUSION

Our results suggested that anti-CFH autoantibodies could attenuate pristane-induced lupus nephritis by increasing bio-functions of CFH on regulating complement activation and controlling inflammation.

The pentraxin family in autoimmune disease

The pentraxins represent a family of multifunctional proteins composed of long and short pentamers. The latter includes serum amyloid P component (SAP) and C-reactive protein (CRP) whereas the former includes neuronal PTX1 and PTX2 (NPTX1 and NPTX2, respectively), PTX3 and PTX4. These serve as a bridge between adaptive immunity and innate immunity and a link between inflammation and immunity. Similarities and differences between long and short pentamers are examined and their roles in autoimmune disease are discussed. Increased CRP and PTX3 could indicate the activity of rheumatoid arthritis, systemic lupus erythematosus or other autoimmune diseases. Mechanistically, CRP and PTX3 may predict target organ injury, regulate bone metabolic immunity and maintain homeostasis as well as participate in vascular endothelial remodeling. Interestingly, PTX3 is pleiotropic, being involved in inflammation and tissue repair. Given the therapeutic potential of PTX3 and CRP, targeting these factors to exert a beneficial effect is the focus of research efforts. Unfortunately, studies on NPTX1, NPTX2, PTX4 and SAP are scarce and more research is clearly needed to elaborate their potential roles in autoimmune disease.

Structural insights into the biological functions of the long pentraxin PTX3

Soluble pattern recognition molecules (PRMs) are a heterogenous group of proteins that recognize pathogen- and danger-associated molecular patterns (PAMPs and DAMPs, respectively), and cooperate with cell-borne receptors in the orchestration of innate and adaptive immune responses to pathogenic insults and tissue damage. Amongst soluble PRMs, pentraxins are a family of highly conserved proteins with distinctive structural features. Originally identified in the early 1990s as an early inflammatory gene, PTX3 is the prototype of long pentraxins. Unlike the short pentraxin C reactive protein (CRP), whose expression is mostly confined to the liver, PTX3 is made by several immune and non-immune cells at sites of infection and inflammation, where it intercepts fundamental aspects of infection immunity, inflammation, and tissue remodeling. Of note, PTX3 cross talks to components of the complement system to control cancer-related inflammation and disposal of pathogens. Also, it is an essential component of inflammatory extracellular matrices (ECMs) through crosslinking of hyaluronic acid and turn-over of provisional fibrin networks that assemble at sites of tissue injury. This functional diversity is mediated by unique structural characteristics whose fine details have been unveiled only recently. Here, we revisit the structure/function relationships of this long pentraxin in light of the most recent advances in its structural biology, with a focus on the interplay with complement and the emerging roles as a component of the ECM. Differences to and similarities with the short pentraxins are highlighted and discussed.

Biomarkers to monitor the prognosis, disease severity, and treatment efficacy in coronary artery disease

INTRODUCTION

Coronary Artery Disease (CAD) is a prevalent condition characterized by the presence of atherosclerotic plaques in the coronary arteries of the heart. The global burden of CAD has increased significantly over the years, resulting in millions of deaths annually and making it the leading health-care expenditure and cause of mortality in developed countries. The lack of cost-effective strategies for monitoring the prognosis of CAD warrants a pressing need for accurate and efficient markers to assess disease severity and progression for both reducing health-care costs and improving patient outcomes.

AREA COVERED

To effectively monitor CAD, prognostic biomarkers and imaging techniques play a vital role in risk-stratified patients during acute treatment and over time. However, with over 1,000 potential markers of interest, it is crucial to identify the key markers with substantial utility in monitoring CAD progression and evaluating therapeutic interventions. This review focuses on identifying and highlighting the most relevant markers for monitoring CAD prognosis and disease severity. We searched for relevant literature using PubMed and Google Scholar.

EXPERT OPINION

By utilizing the markers discussed, health-care providers can improve patient care, optimize treatment plans, and ultimately reduce health-care costs associated with CAD management.

Role of Complement in the Onset of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a progressive degenerative disease of the central retina and the leading cause of severe loss of central vision in people over age 50. Patients gradually lose central visual acuity, compromising their ability to read, write, drive, and recognize faces, all of which greatly impact daily life activities. Quality of life is significantly affected in these patients, and there are worse levels of depression as a result. AMD is a complex, multifactorial disease in which age and genetics, as well as environmental factors, all play a role in its development and progression. The mechanism by which these risk factors interact and converge towards AMD are not fully understood, and therefore, drug discovery is challenging, with no successful therapeutic attempt to prevent the development of this disease. In this review, we describe the pathophysiology of AMD and review the role of complement, which is a major risk factor in the development of AMD.

Modification of the structural stability of human serum albumin in rheumatoid arthritis

Differential scanning calorimetry (DSC) can indicate changes in structure and/or concentration of the most abundant proteins in a biological sample via heat denaturation curves (HDCs). In blood serum for example, HDC changes result from either concentration changes or altered thermal stabilities for 7-10 proteins and has previously been shown capable of differentiating between sick and healthy human subjects. Here, we compare HDCs and proteomic profiles of 50 patients experiencing joint-inflammatory symptoms, 27 of which were clinically diagnosed with rheumatoid arthritis (RA). The HDC of all 50 subjects appeared significantly different from expected healthy curves, but comparison of additional differences between the RA and the non-RA subjects allowed more specific understanding of RA samples. We used mass spectrometry (MS) to investigate the reasons behind the additional HDC changes observed in RA patients. The HDC differences do not appear to be directly related to differences in the concentrations of abundant serum proteins. Rather, the differences can be attributed to modified thermal stability of some fraction of the human serum albumin (HSA) proteins in the sample. By quantifying differences in the frequency of artificially induced post translational modifications (PTMs), we found that HSA in RA subjects had a much lower surface accessibility, indicating potential ligand or protein binding partners in certain regions that could explain the shift in HSA melting temperature in the RA HDCs. Several low abundance proteins were found to have significant changes in concentration in RA subjects and could be involved in or related to binding of HSA. Certain amino acid sites clusters were found to be less accessible in RA subjects, suggesting changes in HSA structure that may be related to changes in protein-protein interactions. These results all support a change in behavior of HSA which may give insight into mechanisms of RA pathology.

A novel phosphocholine-mimetic inhibits a pro-inflammatory conformational change in C-reactive protein

C-reactive protein (CRP) is an early-stage acute phase protein and highly upregulated in response to inflammatory reactions. We recently identified a novel mechanism that leads to a conformational change from the native, functionally relatively inert, pentameric CRP (pCRP) structure to a pentameric CRP intermediate (pCRP*) and ultimately to the monomeric CRP (mCRP) form, both exhibiting highly pro-inflammatory effects. This transition in the inflammatory profile of CRP is mediated by binding of pCRP to activated/damaged cell membranes via exposed phosphocholine lipid head groups. We designed a tool compound as a low molecular weight CRP inhibitor using the structure of phosphocholine as a template. X-ray crystallography revealed specific binding to the phosphocholine binding pockets of pCRP. We provide in vitro and in vivo proof-of-concept data demonstrating that the low molecular weight tool compound inhibits CRP-driven exacerbation of local inflammatory responses, while potentially preserving pathogen-defense functions of CRP. The inhibition of the conformational change generating pro-inflammatory CRP isoforms via phosphocholine-mimicking compounds represents a promising, potentially broadly applicable anti-inflammatory therapy.

Bioengineering approaches for modelling retinal pathologies of the outer blood-retinal barrier

Alterations of the junctional complex of the outer blood-retinal barrier (oBRB), which is integrated by the close interaction of the retinal pigment epithelium, the Bruch's membrane, and the choriocapillaris, contribute to the loss of neuronal signalling and subsequent vision impairment in several retinal inflammatory disorders such as age-related macular degeneration and diabetic retinopathy. Reductionist approaches into the mechanisms that underlie such diseases have been hindered by the absence of adequate in vitro models using human cells to provide the 3D dynamic architecture that enables expression of the in vivo phenotype of the oBRB. Conventional in vitro cell models are based on 2D monolayer cellular cultures, unable to properly recapitulate the complexity of living systems. The main drawbacks of conventional oBRB models also emerge from the cell sourcing, the lack of an appropriate Bruch's membrane analogue, and the lack of choroidal microvasculature with flow. In the last years, the advent of organ-on-a-chip, bioengineering, and stem cell technologies is providing more advanced 3D models with flow, multicellularity, and external control over microenvironmental properties. By incorporating additional biological complexity, organ-on-a-chip devices can mirror physiologically relevant properties of the native tissue while offering additional set ups to model and study disease. In this review we first examine the current understanding of oBRB biology as a functional unit, highlighting the coordinated contribution of the different components to barrier function in health and disease. Then we describe recent advances in the use of pluripotent stem cells-derived retinal cells, Bruch's membrane analogues, and co-culture techniques to recapitulate the oBRB. We finally discuss current advances and challenges of oBRB-on-a-chip technologies for disease modelling.

Cryo-Electron Microscopy and Biochemical Analysis Offer Insights Into the Effects of Acidic pH, Such as Occur During Acidosis, on the Complement Binding Properties of C-Reactive Protein

The pentraxin family of proteins includes C-reactive protein (CRP), a canonical marker for the acute phase inflammatory response. As compared to normal physiological conditions in human serum, under conditions associated with damage and inflammation, such as acidosis and the oxidative burst, CRP exhibits modulated biochemical properties that may have a structural basis. Here, we explore how pH and ligand binding affect the structure and biochemical properties of CRP. Cryo-electron microscopy was used to solve structures of CRP at pH 7.5 or pH 5 and in the presence or absence of the ligand phosphocholine (PCh), which yielded 7 new high-resolution structures of CRP, including pentameric and decameric complexes. Structures previously derived from crystallography were imperfect pentagons, as shown by the variable angles between each subunit, whereas pentameric CRP derived from cryoEM was found to have C5 symmetry, with subunits forming a regular pentagon with equal angles. This discrepancy indicates flexibility at the interfaces of monomers that may relate to activation of the complement system by the C1 complex. CRP also appears to readily decamerise in solution into dimers of pentamers, which obscures the postulated binding sites for C1. Subtle structural rearrangements were observed between the conditions tested, including a putative change in histidine protonation that may prime the disulphide bridges for reduction and enhanced ability to activate the immune system. Enzyme-linked immunosorbent assays showed that CRP had markedly increased association to the C1 complex and immunoglobulins under conditions associated with acidosis, whilst a reduction in the Ca²⁺ concentration lowered this pH-sensitivity for C1q, but not immunoglobulins, suggesting different modes of binding. These data suggest a model whereby a change in the ionic nature of CRP and immunological proteins can make it more adhesive to potential ligands without large structural rearrangements.

Persistently elevated complement alternative pathway biomarkers in COVID-19 correlate with hypoxemia and predict in-hospital mortality

Mechanisms underlying the SARS-CoV-2-triggered hyperacute thrombo-inflammatory response that causes multi-organ damage in coronavirus disease 2019 (COVID-19) are poorly understood. Several lines of evidence implicate overactivation of complement. To delineate the involvement of complement in COVID-19, we prospectively studied 25 ICU-hospitalized patients for up to 21 days. Complement biomarkers in patient sera and healthy controls were quantified by enzyme-linked immunosorbent assays. Correlations with respiratory function and mortality were analyzed. Activation of complement via the classical/lectin pathways was variably increased. Strikingly, all patients had increased activation of the alternative pathway (AP) with elevated levels of activation fragments, Ba and Bb. This was associated with a reduction of the AP negative regulator, factor (F) H. Correspondingly, terminal pathway biomarkers of complement activation, C5a and sC5b-9, were significantly elevated in all COVID-19 patient sera. C5a and AP constituents Ba and Bb, were significantly associated with hypoxemia. Ba and FD at the time of ICU admission were strong independent predictors of mortality in the following 30 days. Levels of all complement activation markers were sustained throughout the patients’ ICU stays, contrasting with the varying serum levels of IL-6, C-reactive protein, and ferritin. Severely ill COVID-19 patients have increased and persistent activation of complement, mediated strongly via the AP. Complement activation biomarkers may be valuable measures of severity of lung disease and the risk of mortality. Large-scale studies will reveal the relevance of these findings to thrombo-inflammation in acute and post-acute COVID-19.

Interlink between Inflammation and Oxidative Stress in Age-Related Macular Degeneration: Role of Complement Factor H

Age-related macular degeneration (AMD) heads the list of legal blindness among the elderly population in developed countries. Due to the complex nature of the retina and the variety of risk factors and mechanisms involved, the molecular pathways underlying AMD are not yet fully defined. Persistent low-grade inflammation and oxidative stress eventually lead to retinal pigment epithelium dysfunction and outer blood-retinal barrier (oBRB) breakdown. The identification of AMD susceptibility genes encoding complement factors, and the presence of inflammatory mediators in drusen, the hallmark deposits of AMD, supports the notion that immune-mediated processes are major drivers of AMD pathobiology. Complement factor H (FH), the main regulator of the alternative pathway of the complement system, may have a key contribution in the pathogenesis of AMD as it is able to regulate both inflammatory and oxidative stress responses in the oBRB. Indeed, genetic variants in the CFH gene account for the strongest genetic risk factors for AMD. In this review, we focus on the roles of inflammation and oxidative stress and their connection with FH and related proteins as regulators of both phenomena in the context of AMD.

Implications of genetic variation in the complement system in age-related macular degeneration

Age-related macular degeneration (AMD) is the main cause of vision loss among the elderly in the Western world. While AMD is a multifactorial disease, the complement system was identified as one of the main pathways contributing to disease risk. The strong link between the complement system and AMD was demonstrated by genetic associations, and by elevated complement activation in local eye tissue and in the systemic circulation of AMD patients. Several complement inhibitors have been and are being explored in clinical trials, but thus far with limited success, leaving the majority of AMD patients without treatment options to date. This indicates that there is still a gap of knowledge regarding the functional implications of the complement system in AMD pathogenesis and how to bring these towards clinical translation. Many different experimental set-ups and disease models have been used to study complement activation in vivo and in vitro, and recently emerging patient-derived induced pluripotent stem cells and genome-editing techniques open new opportunities to study AMD disease mechanisms and test new therapeutic strategies in the future. In this review we provide an extensive overview of methods employed to understand the molecular processes of complement activation in AMD pathogenesis. We discuss the findings, advantages and challenges of each approach and conclude with an outlook on how recent, exciting developments can fill in current knowledge gaps and can aid in the development of effective complement-targeting therapeutic strategies in AMD.

Anti-Pentraxin Antibodies in Autoimmune Diseases: Bystanders or Pathophysiological Actors?

Pentraxins are soluble innate immunity receptors involved in sensing danger molecules. They are classified as short (CRP, SAP) and long pentraxin subfamilies, including the prototypic long pentraxin PTX3. Pentraxins act mainly as bridging molecules favoring the clearance of microbes and dead cells. They are also involved in many other biological processes, such as regulation of complement activation, inflammation and tissue homeostasis. Autoantibodies directed against pentraxins have been reported in various autoimmune diseases, especially in systemic lupus erythematosus and ANCA-associated vasculitis. In this review, we review the main biological characteristics and functions of pentraxins and summarize data concerning autoantibodies directed against pentraxins in the context of autoimmune diseases and discuss their potential pathological role.

Revisiting the role of factor H in age-related macular degeneration: Insights from complement-mediated renal disease and rare genetic variants

Ophthalmologists are long familiar with the eye showing signs of systemic disease, but the association between age-related macular degeneration and abnormal complement activation, common to several renal disorders, has only recently been elucidated. Although complement activation products were identified in drusen almost three decades ago, it was not until the early 21st century that a single-nucleotide polymorphism in the complement factor H gene was identified as a major heritable determinant of age-related macular degeneration, galvanizing global efforts to unravel the pathogenesis of this common disease. Advances in proteomic analyses and familial aggregation studies have revealed distinctive clinical phenotypes segregated by the functional effects of common and rare genetic variants on the mature protein and its splice variant, factor H-like protein 1. The predominance of loss-of-function, N-terminal mutations implicate age-related macular degeneration as a disease of general complement dysregulation, offering several therapeutic avenues for its modulation. Here, we explore the molecular impact of these mutations/polymorphisms on the ability of variant factor H/factor H-like protein 1 to localize to polyanions, pentraxins, proinflammatory triggers, and cell surfaces across ocular and renal tissues and exert its multimodal regulatory functions and their clinical implications. Finally, we critically evaluate key therapeutic and diagnostic efforts in this rapidly evolving field.

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.

Alternative complement pathway is activated in the brains of scrapie-infected rodents

Activation of complement system in central nervous system (CNS) of the patients suffering from prion diseases or animal models infected with prion agents experimentally is reported repeatedly, but which pathways are involved in the complement system during prion infection is not well documented. Here, we evaluated the level of complement factor B (CFB), which is the key factor that triggers alterative pathway (AP) of complement in the brain tissues of scrapie-infected mice with various methodologies. We found that the levels of mRNA and protein of CFB significantly increased in the brain tissues of scrapie-infected mice. Morphologically, the increased CFB-specific signal overlapped with the elevated C3 signal in brain sections of scrapie-infected mice, meanwhile overlapped with damaged neurons and activated microglia, but not with the proliferative astrocytes. Additionally, the level of complement factor P (CFP), the key positive regulator of AP, also increased remarkably in the brain tissues of infected mice. The transcriptional levels of CD55 and CD46, two negative regulators of AP, decreased without significance in brain tissues of scrapie-infected mice at the terminal stage. However, the mRNA and protein levels of CFH, another negative regulator of AP, increased. Through the dynamic analyses of the expressions of CFB, CFP, and CFH in brain sections of 139A-infected mice, which were collected at different time-points during incubation period, illustrated time-dependent increase levels of each factor during the incubation period of scrapie infection. Taken together, our data here demonstrate that the AP of complement cascade is activated in the CNS microenvironment during prion infection.

Structure-Function Relationships of C-Reactive Protein in Bacterial Infection

One host defense function of C-reactive protein (CRP) is to protect against Streptococcus pneumoniae infection as shown by experiments employing murine models of pneumococcal infection. The protective effect of CRP is due to reduction in bacteremia. There is a distinct relationship between the structure of CRP and its anti-pneumococcal function. CRP is functional in both native and non-native pentameric structural conformations. In the native conformation, CRP binds to pneumococci through the phosphocholine molecules present on the C-polysaccharide of the pneumococcus and the anti-pneumococcal function probably involves the known ability of ligand-complexed CRP to activate the complement system. In the native structure-function relationship, CRP is protective only when given to mice within a few hours of the administration of pneumococci. The non-native pentameric conformation of CRP is created when CRP is exposed to conditions mimicking inflammatory microenvironments, such as acidic pH and redox conditions. In the non-native conformation, CRP binds to immobilized complement inhibitor factor H in addition to being able to bind to phosphocholine. Recent data using CRP mutants suggest that the factor H-binding function of non-native CRP is beneficial: in the non-native structure-function relationship, CRP can be given to mice any time after the administration of pneumococci irrespective of whether the pneumococci became complement-resistant or not. In conclusion, while native CRP is protective only against early stage infection, non-native CRP is protective against both early stage and late stage infections. Because non-native CRP displays phosphocholine-independent anti-pneumococcal activity, it is quite possible that CRP functions as a general anti-bacterial molecule.

Pentraxins in Complement Activation and Regulation

The complement is the first line of immune defense system involved in elimination of invading pathogens and dying host cells. Its activation is mainly triggered by immune complexes or pattern recognition molecules (PRMs) upon recognition against non-self or altered self-cells, such as C1q, collectins, ficolins, and properdin. Recent findings have interestingly shown that the pentraxins (C-reactive protein, CRP; serum-amyloid P component, SAP; long pentraxin 3, PTX3) are involved in complement activation and amplification via communication with complement initiation PRMs, but also complement regulation via recruitment of complement regulators, for instance C4b binding protein (C4BP) and factor H (fH). This review addresses the potential roles of the pentraxins in the complement system during infection and inflammation, and emphasizes the underlining implications of the pentraxins in the context of complement activation and regulation both under physiological and pathological conditions.

Two distinct conformations of factor H regulate discrete complement-binding functions in the fluid phase and at cell surfaces

Factor H (FH) is the major regulator of C3b in the alternative pathway of the complement system in immunity. FH comprises 20 short complement regulator (SCR) domains, including eight glycans, and its Y402H polymorphism predisposes those who carry it to age-related macular degeneration. To better understand FH complement binding and self-association, we have studied the solution structures of both the His-402 and Tyr-402 FH allotypes. Analytical ultracentrifugation revealed that up to 12% of both FH allotypes self-associate, and this was confirmed by small-angle X-ray scattering (SAXS), MS, and surface plasmon resonance analyses. SAXS showed that monomeric FH has a radius of gyration (Rg ) of 7.2-7.8 nm and a length of 25 nm. Starting from known structures for the SCR domains and glycans, the SAXS data were fitted using Monte Carlo methods to determine atomistic structures of monomeric FH. The analysis of 29,715 physically realistic but randomized FH conformations resulted in 100 similar best-fit FH structures for each allotype. Two distinct molecular structures resulted that showed either an extended N-terminal domain arrangement with a folded-back C terminus or an extended C terminus and a folded-back N terminus. These two structures are the most accurate to date for glycosylated full-length FH. To clarify FH functional roles in host protection, crystal structures for the FH complexes with C3b and C3dg revealed that the extended N-terminal conformation accounted for C3b fluid-phase regulation, the extended C-terminal conformation accounted for C3d binding, and both conformations accounted for bivalent FH binding to glycosaminoglycans on the target cell surface.

PTX3, a Humoral Pattern Recognition Molecule, in Innate Immunity, Tissue Repair, and Cancer

Innate immunity includes a cellular and a humoral arm. PTX3 is a fluid-phase pattern recognition molecule conserved in evolution which acts as a key component of humoral innate immunity in infections of fungal, bacterial, and viral origin. PTX3 binds conserved microbial structures and self-components under conditions of inflammation and activates effector functions (complement, phagocytosis). Moreover, it has a complex regulatory role in inflammation, such as ischemia/reperfusion injury and cancer-related inflammation, as well as in extracellular matrix organization and remodeling, with profound implications in physiology and pathology. Finally, PTX3 acts as an extrinsic oncosuppressor gene by taming tumor-promoting inflammation in murine and selected human tumors. Thus evidence suggests that PTX3 is a key homeostatic component at the crossroad of innate immunity, inflammation, tissue repair, and cancer. Dissecting the complexity of PTX3 pathophysiology and human genetics paves the way to diagnostic and therapeutic exploitation.

Self-Damage Caused by Dysregulation of the Complement Alternative Pathway: Relevance of the Factor H Protein Family

The alternative pathway is a continuously active surveillance arm of the complement system, and it can also enhance complement activation initiated by the classical and the lectin pathways. Various membrane-bound and plasma regulatory proteins control the activation of the potentially deleterious complement system. Among the regulators, the plasma glycoprotein factor H (FH) is the main inhibitor of the alternative pathway and its powerful amplification loop. FH belongs to a protein family that also includes FH-like protein 1 and five factor H-related (FHR-1 to FHR-5) proteins. Genetic variants and abnormal rearrangements involving the FH protein family have been linked to numerous systemic and organ-specific diseases, including age-related macular degeneration, and the renal pathologies atypical hemolytic uremic syndrome, C3 glomerulopathies, and IgA nephropathy. This review covers the known and recently emerged ligands and interactions of the human FH family proteins associated with disease and discuss the very recent experimental data that suggest FH-antagonistic and complement-activating functions for the FHR proteins.

Common and rare genetic variants of complement components in human disease

Genetic variability in the complement system and its association with disease has been known for more than 50 years, but only during the last decade have we begun to understand how this complement genetic variability contributes to the development of diseases. A number of reports have described important genotype-phenotype correlations that associate particular diseases with genetic variants altering specific aspects of the activation and regulation of the complement system. The detailed functional characterization of some of these genetic variants provided key insights into the pathogenic mechanisms underlying these pathologies, which is facilitating the design of specific anti-complement therapies. Importantly, these analyses have sometimes revealed unknown features of the complement proteins. As a whole, these advances have delineated the functional implications of genetic variability in the complement system, which supports the implementation of a precision medicine approach based on the complement genetic makeup of the patients. Here we provide an overview of rare complement variants and common polymorphisms associated with disease and discuss what we have learned from them.

Characterization of Retinal Pigment Epithelial Melanin and Degraded Synthetic Melanin Using Mass Spectrometry and In Vitro Biochemical Diagnostics

With increasing age, there is an observable loss of melanin in retinal pigment epithelial (RPE) cells. It is possible that degradation of the pigment contributes to the pathogenesis of retinal disease, as the cellular antioxidant material is depleted. Functionally, intact melanin maintains protective qualities, while oxidative degradation of melanin promotes reactive oxygen species (ROS) generation and formation of metabolic byproducts, such as melanolipofuscin. Understanding the structural and functional changes to RPE melanin with increasing age may contribute to a better understanding of disease progression and risk factors for conditions such as age-related macular degeneration (AMD). In this study, human donor RPE melanin is characterized using MALDI mass spectrometry to follow melanin degradation trends. In vitro models using ARPE-19 cells are used to assess photo-reactivity in repigmented cells. Significant protection against intracellular ROS produced by blue light is observed in calf melanin-pigmented cells versus unpigmented and black latex bead controls (P < 0.0001). UV-B exposure to aged human melanin-pigmented cells results in a significant increase in nitric oxide production versus control cells (P < 0.001). Peroxide-treated synthetic melanin is characterized to elucidate degradation products that may contribute to RPE cell damage.

The long pentraxin PTX3: A prototypical sensor of tissue injury and a regulator of homeostasis

Tissue damage frequently occurs. The immune system senses it and enforces homeostatic responses that lead to regeneration and repair. The synthesis of acute phase molecules is emerging as a crucial event in this program. The prototypic long pentraxin PTX3 orchestrates the recruitment of leukocytes, stabilizes the provisional matrix in order to facilitate leukocyte and stem progenitor cells trafficking, promotes swift and safe clearance of dying cells and of autoantigens, limiting autoimmunity and protecting the vasculature. These non-redundant actions of PTX3 are necessary for the resolution of inflammation. Recent studies have highlighted the mechanisms by which PTX3 adapts the functions of innate immune cells, orchestrates tissue repair and contributes to select the appropriate acquired immune response in various tissues. Conversely, PTX3 continues to be produced in diseases where the inflammatory response does not resolve. It is therefore a valuable biomarker for more precise and personalized stratification of patients, often independently predicting clinical evolution and outcome. There is strong promise for novel therapies based on understanding the mechanisms with which PTX3 plays its homeostatic role, especially in regulating leukocyte migration and the resolution of inflammatory processes.

C-Reactive Protein as a Therapeutic Target in Age-Related Macular Degeneration

Age-related macular degeneration (AMD), a retinal degenerative disease, is the leading cause of central vision loss among the elderly population in developed countries and an increasing global burden. The major risk is aging, compounded by other environmental factors and association with genetic variants for risk of progression. Although the etiology of AMD is not yet clearly understood, several pathogenic pathways have been proposed, including dysfunction of the retinal pigment epithelium, inflammation, and oxidative stress. The identification of AMD susceptibility genes encoding complement factors and the presence of complement and other inflammatory mediators in drusen, the hallmark deposits of AMD, support the concept that local inflammation and immune-mediated processes play a key role in AMD pathogenesis that may be accelerated through systemic immune activation. In this regard, increased levels of circulating C-reactive protein (CRP) have been associated with higher risk of AMD. Besides being a risk marker for AMD, CRP may also play a role in the progression of the disease as it has been identified in drusen, and we have recently found that its monomeric form (mCRP) induces blood retinal barrier disruption in vitro. In this review, we will address recent evidence that links CRP and AMD pathogenesis, which may open new therapeutic opportunities to prevent the progression of AMD.

C-Reactive Protein As a Mediator of Complement Activation and Inflammatory Signaling in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a devastating neurodegenerative disease affecting millions worldwide. Complement activation, inflammation, and the loss of choroidal endothelial cells have been established as key factors in both normal aging and AMD; however, the exact mechanisms for these events have yet to be fully uncovered. Herein, we provide evidence that the prototypic acute phase reactant, C-reactive protein (CRP), contributes to AMD pathogenesis. We discuss serum CRP levels as a risk factor for disease, immunolocalization of distinct forms of CRP in the at-risk and diseased retina, and direct effects of CRP on ocular tissue. Furthermore, we discuss the complement system as it relates to AMD pathophysiology, provide a model for the role of CRP in this disease, and outline current therapies being developed and tested to treat AMD patients.

C-reactive protein and pentraxin-3 binding of factor H-like protein 1 differs from complement factor H: implications for retinal inflammation

Retinal inflammation plays a key role in the progression of age-related macular degeneration (AMD), a condition that leads to loss of central vision. The deposition of the acute phase pentraxin C-reactive protein (CRP) in the macula activates the complement system, thereby contributing to dysregulated inflammation. The complement protein factor H (FH) can bind CRP and down-regulate an inflammatory response. However, it is not known whether a truncated form of FH, called factor H-like protein 1 (FHL-1), which plays a significant regulatory role in the eye, also interacts with CRP. Here, we compare the binding properties of FHL-1 and FH to both CRP and the related protein pentraxin-3 (PTX3). We find that, unlike FH, FHL-1 can bind pro-inflammatory monomeric CRP (mCRP) as well as the circulating pentameric form. Furthermore, the four-amino acid C-terminal tail of FHL-1 (not present in FH) plays a role in mediating its binding to mCRP. PTX3 was found to be present in the macula of donor eyes and the AMD-associated Y402H polymorphism altered the binding of FHL-1 to PTX3. Our findings reveal that the binding characteristics of FHL-1 differ from those of FH, likely underpinning independent immune regulatory functions in the context of the human retina.

The Complement System in Dialysis: A Forgotten Story?

Significant advances have lead to a greater understanding of the role of the complement system within nephrology. The success of the first clinically approved complement inhibitor has created renewed appreciation of complement-targeting therapeutics. Several clinical trials are currently underway to evaluate the therapeutic potential of complement inhibition in renal diseases and kidney transplantation. Although, complement has been known to be activated during dialysis for over four decades, this area of research has been neglected in recent years. Despite significant progress in biocompatibility of hemodialysis (HD) membranes and peritoneal dialysis (PD) fluids, complement activation remains an undesired effect and relevant issue. Short-term effects of complement activation include promoting inflammation and coagulation. In addition, long-term complications of dialysis, such as infection, fibrosis and cardiovascular events, are linked to the complement system. These results suggest that interventions targeting the complement system in dialysis could improve biocompatibility, dialysis efficacy, and long-term outcome. Combined with the clinical availability to safely target complement in patients, the question is not if we should inhibit complement in dialysis, but when and how. The purpose of this review is to summarize previous findings and provide a comprehensive overview of the role of the complement system in both HD and PD.

Complement factor H in AMD: Bridging genetic associations and pathobiology

Age-Related Macular Degeneration (AMD) is a complex multifactorial disease characterized in its early stages by lipoprotein accumulations in Bruch's Membrane (BrM), seen on fundoscopic exam as drusen, and in its late forms by neovascularization ("wet") or geographic atrophy of the Retinal Pigmented Epithelial (RPE) cell layer ("dry"). Genetic studies have strongly supported a relationship between the alternative complement cascade, in particular the common H402 variant in Complement Factor H (CFH) and development of AMD. However, the functional significance of the CFH Y402H polymorphism remains elusive. In this article, we critically review the literature surrounding the functional significance of this polymorphism. Furthermore, based on our group's studies we propose a model in which CFH H402 affects CFH binding to heparan sulfate proteoglycans leading to accelerated lipoprotein accumulation in BrM and drusen progression. We also review the literature on the role of other complement components in AMD pathobiologies, including C3a, C5a and the membrane attack complex (MAC), and on transgenic mouse models developed to interrogate in vivo the effects of the CFH Y402H polymorphism.

Pentraxins in the activation and regulation of innate immunity

Humoral fluid phase pattern recognition molecules (PRMs) are a key component of the activation and regulation of innate immunity. Humoral PRMs are diverse. We focused on the long pentraxin PTX3 as a paradigmatic example of fluid phase PRMs. PTX3 acts as a functional ancestor of antibodies and plays a non-redundant role in resistance against selected microbes in mouse and man and in the regulation of inflammation. This molecule interacts with complement components, thus modulating complement activation. In particular, PTX3 regulates complement-driven macrophage-mediated tumor progression, acting as an extrinsic oncosuppressor in preclinical models and selected human tumors. Evidence collected over the years suggests that PTX3 is a biomarker and potential therapeutic agent in humans, and pave the way to translation of this molecule into the clinic.

FHR-1 Binds to C-Reactive Protein and Enhances Rather than Inhibits Complement Activation

Factor H-related protein (FHR) 1 is one of the five human FHRs that share sequence and structural homology with the alternative pathway complement inhibitor FH. Genetic studies on disease associations and functional analyses indicate that FHR-1 enhances complement activation by competitive inhibition of FH binding to some surfaces and immune proteins. We have recently shown that FHR-1 binds to pentraxin 3. In this study, our aim was to investigate whether FHR-1 binds to another pentraxin, C-reactive protein (CRP), analyze the functional relevance of this interaction, and study the role of FHR-1 in complement activation and regulation. FHR-1 did not bind to native, pentameric CRP, but it bound strongly to monomeric CRP via its C-terminal domains. FHR-1 at high concentration competed with FH for CRP binding, indicating possible complement deregulation also on this ligand. FHR-1 did not inhibit regulation of solid-phase C3 convertase by FH and did not inhibit terminal complement complex formation induced by zymosan. On the contrary, by binding C3b, FHR-1 allowed C3 convertase formation and thereby enhanced complement activation. FHR-1/CRP interactions increased complement activation via the classical and alternative pathways on surfaces such as the extracellular matrix and necrotic cells. Altogether, these results identify CRP as a ligand for FHR-1 and suggest that FHR-1 enhances, rather than inhibits, complement activation, which may explain the protective effect of FHR-1 deficiency in age-related macular degeneration.

Complement factor H in host defense and immune evasion

Complement is the major humoral component of the innate immune system. It recognizes pathogen- and damage-associated molecular patterns, and initiates the immune response in coordination with innate and adaptive immunity. When activated, the complement system unleashes powerful cytotoxic and inflammatory mechanisms, and thus its tight control is crucial to prevent damage to host tissues and allow restoration of immune homeostasis. Factor H is the major soluble inhibitor of complement, where its binding to self markers (i.e., particular glycan structures) prevents complement activation and amplification on host surfaces. Not surprisingly, mutations and polymorphisms that affect recognition of self by factor H are associated with diseases of complement dysregulation, such as age-related macular degeneration and atypical haemolytic uremic syndrome. In addition, pathogens (i.e., non-self) and cancer cells (i.e., altered-self) can hijack factor H to evade the immune response. Here we review recent (and not so recent) literature on the structure and function of factor H, including the emerging roles of this protein in the pathophysiology of infectious diseases and cancer.

Presence of multimeric isoforms of human C-reactive protein in tissues and blood

The baseline concentration of C-reactive protein (CRP) has been associated with a wide array of human diseases. In epidemiological studies and in the clinic, CRP is typically measured as a pentamer, composed of 5 identical CRP subunits. The present study aimed to determine whether other isoforms were present in the blood by examining CRP conformations. Transgenic rats expressing human CRP under the mouse albumin promoter were generated and genotyped. Non-reducing western blotting was performed using the blood and tissues of transgenic rats and human patients. CRP concentrations in human blood were examined by enzyme-linked immunosorbent assay. In addition to the pentameric isoform, CRP was detected as a trimer and tetramer in the blood of human CRP transgenic rats. Furthermore, trimeric and tetrameric CRP was observed in various tissues, including aorta, liver, kidney, pancreas, heart and skeletal muscle. Notably, these two isoforms appeared to be age-associated, as they were detected only in the blood and tissues of older transgenic rats. The existence of additional CRP isoforms was confirmed in the blood of human patients by non-reducing western blotting. Clinical and epidemiological studies typically focus on CRP concentration. However, the results of the present study suggest that, in addition to concentration, CRP conformation may require analysis.

Self-nonself discrimination by the complement system

The alternative pathway (AP) of complement can recognize nonself structures by only two molecules, C3b and factor H. The AP deposits C3b covalently on nonself structures via an amplification system. The actual discrimination is performed by factor H, which has binding sites for polyanions (sialic acids, glycosaminoglycans, phospholipids). This robust recognition of 'self' protects our own intact viable cells and tissues, while activating structures are recognized by default. Foreign targets are opsonized for phagocytosis or killed. Mutations in factor H predispose to severe diseases. In hemolytic uremic syndrome, they promote complement attack against blood cells and vascular endothelial cells and lead, for example, to kidney and brain damage. Even pathogens can exploit factor H. In fact, the ability to bind factor H discriminates most pathogenic microbes from nonpathogenic ones.

The Treponema denticola FhbB Protein Is a Dominant Early Antigen That Elicits FhbB Variant-Specific Antibodies That Block Factor H Binding and Cleavage by Dentilisin

The Treponema denticola FhbB protein contributes to immune evasion by binding factor H (FH). Cleavage of FH by the T. denticola protease, dentilisin, may contribute to the local immune dysregulation that is characteristic of periodontal disease (PD). Although three FhbB phyletic types have been defined (FhbB1, FhbB2, and FhbB3), the in vivo expression patterns and antigenic heterogeneity of FhbB have not been assessed. Here, we demonstrate that FhbB is a dominant early antigen that elicits FhbB type-specific antibody (Ab) responses. Using the murine skin abscess model, we demonstrate that the presence or absence of FhbB or dentilisin significantly influences Ab responses to infection and skin abscess formation. Competitive binding analyses revealed that α-FhbB Ab can compete with FH for binding to T. denticola and block dentilisin-mediated FH cleavage. Lastly, we demonstrate that dentilisin cleavage sites reside within critical functional domains of FH, including the complement regulatory domain formed by CCPs 1 to 4. Analysis of the FH cleavage products revealed that they lack cofactor activity. The data presented here provide insight into the in vivo significance of dentilisin, FhbB and its antigenic diversity, and the potential impact of FH cleavage on the regulation of complement activation.

The pentraxins PTX3 and SAP in innate immunity, regulation of inflammation and tissue remodelling

Pentraxins are a superfamily of fluid phase pattern recognition molecules conserved in evolution and characterized by a cyclic multimeric structure. C-reactive protein (CRP) and serum amyloid P component (SAP) constitute the short pentraxin arm of the superfamily. CRP and SAP are produced in the liver in response to IL-6 and are acute phase reactants in humans and mice respectively. In addition SAP has been shown to affect tissue remodelling and fibrosis by stabilizing all types of amyloid fibrils and by regulating monocyte to fibrocyte differentiation. Pentraxin 3 (PTX3) is the prototype of the long pentraxin arm. Gene targeted mice and genetic and epigenetic studies in humans suggest that PTX3 plays essential non-redundant roles in innate immunity and inflammation as well as in tissue remodelling. Recent studies have revealed the role of PTX3 as extrinsic oncosuppressor, able to tune cancer-related inflammation. In addition, at acidic pH PTX3 can interact with provisional matrix components promoting inflammatory matrix remodelling. Thus acidification during tissue repair sets PTX3 in a tissue remodelling and repair mode, suggesting that matrix and microbial recognition are common, ancestral features of the humoral arm of innate immunity.

Inflammation and its role in age-related macular degeneration

Inflammation is a cellular response to factors that challenge the homeostasis of cells and tissues. Cell-associated and soluble pattern-recognition receptors, e.g. Toll-like receptors, inflammasome receptors, and complement components initiate complex cellular cascades by recognizing or sensing different pathogen and damage-associated molecular patterns, respectively. Cytokines and chemokines represent alarm messages for leukocytes and once activated, these cells travel long distances to targeted inflamed tissues. Although it is a crucial survival mechanism, prolonged inflammation is detrimental and participates in numerous chronic age-related diseases. This article will review the onset of inflammation and link its functions to the pathogenesis of age-related macular degeneration (AMD), which is the leading cause of severe vision loss in aged individuals in the developed countries. In this progressive disease, degeneration of the retinal pigment epithelium (RPE) results in the death of photoreceptors, leading to a loss of central vision. The RPE is prone to oxidative stress, a factor that together with deteriorating functionality, e.g. decreased intracellular recycling and degradation due to attenuated heterophagy/autophagy, induces inflammation. In the early phases, accumulation of intracellular lipofuscin in the RPE and extracellular drusen between RPE cells and Bruch's membrane can be clinically detected. Subsequently, in dry (atrophic) AMD there is geographic atrophy with discrete areas of RPE loss whereas in the wet (exudative) form there is neovascularization penetrating from the choroid to retinal layers. Elevations in levels of local and systemic biomarkers indicate that chronic inflammation is involved in the pathogenesis of both disease forms.

Probing the solution structure of Factor H using hydroxyl radical protein footprinting and cross-linking

The control protein Factor H (FH) is a crucial regulator of the innate immune complement system, where it is active on host cell membranes and in the fluid phase. Mutations impairing the binding capacity of FH lead to severe autoimmune diseases. Here, we studied the solution structure of full-length FH, in its free state and bound to the C3b complement protein. To do so, we used two powerful techniques, hydroxyl radical protein footprinting (HRPF) and chemical cross-linking coupled with mass spectrometry (MS), to probe the structural rearrangements and to identify protein interfaces. The footprint of C3b on the FH surface matches existing crystal structures of C3b complexed with the N- and C-terminal fragments of FH. In addition, we revealed the position of the central portion of FH in the protein complex. Moreover, cross-linking studies confirmed the involvement of the C-terminus in the dimerization of FH.

The dysfunctions of complement factor H in lupus nephritis

OBJECTIVE

Our previous study showed that plasma levels of factor H (FH) were significantly decreased in patients with lupus nephritis and reflected lupus nephritis activity. The aim of this study was to further investigate in vitro biofunctions of plasma FH in patients with lupus nephritis.

METHODS

FH was purified from the first run of plasma exchange in four active lupus nephritis patients and two non-renal involvement systemic lupus erythematosus (SLE) patients, and plasma from two healthy controls. Then, the biofunctions of the purified FH were analyzed. In addition, FH exons sequencing analysis was performed.

RESULTS

Homogeneous FH was purified from the plasma fractions and the purity of the purified FH was comparable to the commercial FH. The abilities of FH binding with C3b and mCRP, and its protecting abilities from the lysis of sheep erythrocytes, from No. 3 and No. 4 lupus nephritis patients, decreased significantly compared with those in normal controls. The purified FH from lupus nephritis patients Nos. 2-4 could not induce the phagocytosis of late apoptotic cells significantly compared with normal controls. All four lupus nephritis patients had the known SNP rs1061147 (SCR5, A307A), rs1061170 (SCR7, Y402H), CM050194 (SCR20, S1191W) and CM010322 (SCR20, V1197A), which might be associated with the above dysfunctions.

CONCLUSIONS

Dysfunctions of FH, including the regulations of complement alternative pathway and the clearance of apoptotic cells, were found in some active lupus nephritis patients, which were associated with their clinical phenotypes. The FH SNPs might contribute to the dysfunctions of FH in patients with lupus nephritis.

The Carbohydrate-linked Phosphorylcholine of the Parasitic Nematode Product ES-62 Modulates Complement Activation

Parasitic nematodes manufacture various carbohydrate-linked phosphorylcholine (PCh)-containing molecules, including ES-62, a protein with an N-linked glycan terminally substituted with PCh. The PCh component is biologically important because it is required for immunomodulatory effects. We showed that most ES-62 was bound to a single protein, C-reactive protein (CRP), in normal human serum, displaying a calcium-dependent, high-avidity interaction and ability to form large complexes. Unexpectedly, CRP binding to ES-62 failed to efficiently activate complement as far as the C3 convertase stage in comparison with PCh-BSA and PCh-containing Streptococcus pneumoniae cell wall polysaccharide. C1q capture assays demonstrated an ES-62-CRP-C1q interaction in serum. The three ligands all activated C1 and generated C4b to similar extents. However, a C2a active site was not generated following ES-62 binding to CRP, demonstrating that C2 cleavage was far less efficient for ES-62-containing complexes. We proposed that failure of C2 cleavage was due to the flexible nature of carbohydrate-bound PCh and that reduced proximity of the C1 complex was the reason that C2 was poorly cleaved. This was confirmed using synthetic analogues that were similar to ES-62 only in respect of having a flexible PCh. Furthermore, ES-62 was shown to deplete early complement components, such as the rate-limiting C4, following CRP interaction and thereby inhibit classical pathway activation. Thus, flexible PCh-glycan represents a novel mechanism for subversion of complement activation. These data illustrate the importance of the rate-limiting C4/C2 stage of complement activation and reveal a new addition to the repertoire of ES-62 immunomodulatory mechanisms with possible therapeutic applications.

Complement factor H binding of monomeric C-reactive protein downregulates proinflammatory activity and is impaired with at risk polymorphic CFH variants

Inflammation and immune-mediated processes are pivotal to the pathogenic progression of age-related macular degeneration (AMD). Although plasma levels of C-reactive protein (CRP) have been shown to be associated with an increased risk for AMD, the pathophysiological importance of the prototypical acute-phase reactant in the etiology of the disease is unknown, and data regarding the exact role of CRP in ocular inflammation are limited. In this study, we provide mechanistic insight into how CRP contributes to the development of AMD. In particular, we show that monomeric CRP (mCRP) but not the pentameric form (pCRP) upregulates IL-8 and CCL2 levels in retinal pigment epithelial cells. Further, we show that complement factor H (FH) binds mCRP to dampen its proinflammatory activity. FH from AMD patients carrying the “risk” His402 polymorphism displays impaired binding to mCRP, and therefore proinflammatory effects of mCRP remain unrestrained.

Fibulin-1 purification from human plasma using affinity chromatography on Factor H-Sepharose

A method is reported to purify Fibulin-1 from human plasma resulting in a 36% recovery. The steps involve removal of the cryoglobulin and the vitamin K dependent proteins followed by polyethylene glycol and ammonium sulfate precipitations, DEAE-Sephadex column chromatography and finally Factor H-Sepharose affinity purification. The procedure is designed to be integrated into an overall scheme for the isolation of over 30 plasma proteins from a single batch of human plasma. Results from mass spectroscopy, SDS-PAGE, and Western blotting indicate that human plasma Fibulin-1 is a single chain of the largest isotype. Functional binding assays demonstrated calcium ion dependent interaction of Fibulin-1 for fibrinogen, fibronectin, and Factor H. The procedure described is the first to our knowledge that enables a large scale purification of Fibulin-1 from human plasma.

Complement factor H polymorphism rs1061170 and the effect of cigarette smoking on the risk of lung cancer

Aim of the study

Complement factor H (CFH) has been known to inhibit the complement pathway and to contribute to tumour growth by suppressing the anti-tumour cell mediated response in cell lines from several malignancies. We examined the association of Try402His single nucleotide polymorphism in CFH gene with lung cancer and the interaction with cigarette smoking.

Material and methods

This case-control study included 80 primary lung cancer patients and 106 control subjects who were genotyped for Try402His (rs1061170) by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis.

Results

Variant genotypes (Tyr/His and His/His) were overpresented among patients compared to controls (p = 0.03, OR = 2.510, 95% CI: 1.068–5.899), and the frequency of variant H allele was significantly overexpressed in cases compared to controls (p = 0.021). Tyr/His genotype was identified in 100% of small cell lung cancer (SCLC) patients vs. 34.5% of non-SCLC (NSCLC), while 20.7% of NSCLC patients were homozygous for the variant allele (His/His) (p = 0.001). Binary logistic regression analysis revealed a 2.5 times greater estimated risk for NSCLC than for SCLC among variant allele carriers, and a 7.3-fold increased risk of lung cancer among variant allele smoking carriers vs. 1.3-fold increased risk among wild allele smoking carriers. Moreover, the stage of cancer positively correlated with smoking and pack-years in allele H carriers, and the correlation was stronger among those who were homozygous for it (His/His) than those who were heterozygous (Tyr/His).

Conclusions

CFH 402H variant is a smoking-related risk factor for lung cancer, particularly the NSCLC.

Complement pathway biomarkers and age-related macular degeneration

In the age-related macular degeneration (AMD) 'inflammation model', local inflammation plus complement activation contributes to the pathogenesis and progression of the disease. Multiple genetic associations have now been established correlating the risk of development or progression of AMD. Stratifying patients by their AMD genetic profile may facilitate future AMD therapeutic trials resulting in meaningful clinical trial end points with smaller sample sizes and study duration.

A chimeric Cfh transgene leads to increased retinal oxidative stress, inflammation, and accumulation of activated subretinal microglia in mice

PURPOSE

Variants of complement factor H (Cfh) affecting short consensus repeats (SCRs) 6 to 8 increase the risk of age-related macular degeneration. Our aim was to explore the effect of expressing a Cfh variant on the in vivo susceptibility of the retina and RPE to oxidative stress and inflammation, using chimeric Cfh transgenic mice (chCfhTg).

METHODS

The chCfhTg and age-matched C57BL/6J (B6) mice were subjected to oxidative stress by either normal aging, or by exposure to a combination of oral hydroquinone (0.8% HQ) and increased light. Eyes were collected for immunohistochemistry of RPE-choroid flat mounts and of retinal sections, ELISA, electron microscopy, and RPE/microglia gene expression analysis.

RESULTS

Aging mice to 2 years led to an increased accumulation of basal laminar deposits, subretinal microglia/macrophages (MG/MΦ) staining for CD16 and for malondialdehyde (MDA), and MDA-modified proteins in the retina in chCfhTg compared to B6 mice. The chCfhTg mice maintained on HQ diet and increased light showed greater deposition of basal laminar deposits, more accumulation of fundus spots suggestive of MG/MΦ, and increased deposition of C3d in the sub-RPE space, compared to controls. In addition, chCfhTg mice demonstrated upregulation of NLRP3, IP-10, CD68, and TREM-2 in the RNA isolates from RPE/MG/MΦ.

CONCLUSIONS

Expression of a Cfh transgene introducing a variant in SCRs 6 to 8 was sufficient to lead to increased retinal/RPE susceptibility to oxidative stress, a proinflammatory MG/MΦ phenotype, and a proinflammatory RPE/MG/MΦ gene expression profile in a transgenic mouse model. Our data suggest that altered interactions of Cfh with MDA-modified proteins may be relevant in explaining the effects of the Cfh variant.

Systemic and Ocular Long Pentraxin 3 in Patients with Age-Related Macular Degeneration

Age-related macular degeneration (AMD) has been associated with both systemic and ocular alterations of the immune system. In particular dysfunction of complement factor H (CFH), a soluble regulator of the alternative pathway of the complement system, has been implicated in AMD pathogenesis. One of the ligands for CFH is long pentraxin 3 (PTX3), which is produced locally in the retinal pigment epithelium (RPE). To test the hypothesis that PTX3 is relevant to retinal immunohomeostasis and may be associated with AMD pathogenesis, we measured plasma PTX3 protein concentration and analyzed the RPE/choroid PTX3 gene expression in patients with AMD. To measure the ability of RPE cells to secrete PTX3 in vitro, polarized ARPE-19 cells were treated with activated T cells or cytokines (interferon (IFN)-gamma and/or tumor necrosis factor (TNF)-alpha) from the basolateral side; then PTX3 protein concentration in supernatants and PTX3 gene expression in tissue lysates were quantified. Plasma levels of PTX3 were generally low and did not significantly differ between patients and controls (P=0.307). No statistically significant difference was observed between dry and exudative AMD nor was there any correlation with hsCRP or CFH genotype. The gene expression of PTX3 increased in RPE/choroid with age (P=0.0098 macular; P=0.003 extramacular), but did not differ between aged controls and AMD patients. In vitro, ARPE-19 cells increased expression of the PTX3 gene as well PTX3 apical secretions after stimulation with TNF-alpha or activated T cells (P<0.01). These findings indicate that PTX3 expressed in the eye cannot be detected systemically and systemic PTX3 may have little or no impact on disease progression, but our findings do not exclude that locally produced PTX3 produced in the posterior segment of the eye may be part of the AMD immunopathogenesis.

Phagocytes as Corrupted Policemen in Cancer-Related Inflammation

Inflammation is a key component of the tumor microenvironment. Tumor-associated macrophages (TAMs) and tumor-associated neutrophils (TANs) are prototypic inflammatory cells in cancer-related inflammation. Macrophages provide a first line of resistance against infectious agents but in the ecological niche of cancer behave as corrupted policemen. TAMs promote tumor growth and metastasis by direct interactions with cancer cells, including cancer stem cells, as well as by promoting angiogenesis and tissue remodeling and suppressing effective adaptive immunity. In addition, the efficacy of chemotherapy, radiotherapy, and checkpoint blockade inhibitors is profoundly affected by regulation of TAMs. In particular, TAMs can protect and rescue tumor cells from cytotoxic therapy by orchestrating a misguided tissue repair response. Following extensive preclinical studies, there is now proof of concept that targeting tumor-promoting macrophages by diverse strategies (e.g., Trabectedin, anti-colony-stimulating factor-1 receptor antibodies) can result in antitumor activity in human cancer and further studies are ongoing. Neutrophils have long been overlooked as a minor component of the tumor microenvironment, but there is evidence for an important role of TANs in tumor progression. Targeting phagocytes (TAMs and TANs) as corrupted policemen in cancer may pave the way to innovative therapeutic strategies complementing cytoreductive therapies and immunotherapy.