C-reactive protein is protective against Streptococcus pneumoniae infection in mice

Severe COVID-19 disease is associated with genetic factors affecting plasma ACE2 receptor and CRP concentrations

A hyperinflammatory state with highly elevated concentrations of inflammatory biomarkers such as C-reactive protein (CRP) is a characteristic feature of severe coronavirus disease 2019 (COVID-19). To examine a potential role of common genetic factors that may influence COVID-19 outcomes, we investigated whether individuals with a polygenic predisposition for a pro-inflammatory response (in the form of Polygenic Scores) are more likely to develop severe COVID-19. The innovative approach of polygenic scores to investigate genetic factors in COVID-19 severity should provide a comprehensive approach beyond single-gene studies. In our cohort of 156 patients of European ancestry, two overlapping Polygenic Scores (PGS) predicting a genetic predisposition to basal CRP concentrations were significantly different between non-severe and severe COVID-19 cases and were associated with less severe COVID-19 outcomes. Furthermore, specific single nucleotide polymorphisms (SNPs) that contribute to either of the two Polygenic Scores predicting basal CRP levels are associated with different traits that represent risk factors for COVID-19 disease initiation (ACE2 receptor, viral replication) and progression (CRP). We suggest that genetically determined enforced CRP formation may contribute to strengthening of innate immune responses and better initial pathogen control thereby reducing the risk of subsequent hyperinflammation and adverse course of COVID-19.

Soluble Human Lectins at the Host-Microbe Interface

Human lectins are integral to maintaining microbial homeostasis on the skin, in the blood, and at mucosal barriers. These proteins can recognize microbial glycans and inform the host about its microbial status. In accordance with their roles, their production can vary with tissue type. They also can have unique structural and biochemical properties, and they can influence microbial colonization at sites proximal and distal to their tissue of origin. In line with their classification as innate immune proteins, soluble lectins have long been studied in the context of acute infectious disease, but only recently have we begun to appreciate their roles in maintaining commensal microbial communities (i.e., the human microbiota). This review provides an overview of soluble lectins that operate at host-microbe interfaces, their glycan recognition properties, and their roles in physiological and pathological mechanisms.

Extra-pulmonary control of respiratory defense

Pneumonia persists as a public health crisis, representing the leading cause of death due to infection. Whether respiratory tract infections progress to pneumonia and its sequelae such as acute respiratory distress syndrome and sepsis depends on numerous underlying conditions related to both the causative agent and host. Regarding the former, pneumonia burden remains staggeringly high, despite the effectiveness of pathogen-targeting strategies such as vaccines and antibiotics. This demands a greater understanding of host features that collaborate to promote immune resistance and tissue resilience in the infected lung. Such features inside the pulmonary compartment have drawn much attention, where major advances have been made related to resident and recruited immune activity. By comparison, extra-pulmonary processes guiding pneumonia susceptibility are relatively elusive, constituting the focus of this review. Here we will highlight examples of when, how, and why tissues outside of the lungs dispatch signals that modulate local immunity in the airspaces. Topics include the liver, gut, bone marrow, brain and more, all of which contribute in direct and indirect ways to pneumonia outcome. When tuned appropriately, it has become clear that these responses can serve protective roles, and this will be considered distinctly from what would otherwise be aberrant responses characteristic of pneumonia-induced organ injury and sepsis. Further advances in this area may reveal novel targetable areas for clinical intervention that are not confined to the intra-pulmonary space.

Epigenomics and the Brain-gut Axis: Impact of Adverse Childhood Experiences and Therapeutic Challenges

The brain-gut axis represents a bidirectional communication network that integrates neural, hormonal, and immunological signaling between the central nervous system and the gastrointestinal tract. Adverse childhood experiences (ACEs) have increasingly been recognized for their profound impact on this axis, with implications for both mental and physical health outcomes. This mini-review explores the emerging field of epigenomics-specifically, how epigenetic modifications incurred by ACEs can influence the brain-gut axis and contribute to the pathophysiology of various disorders. We examine the evidence linking epigenetic mechanisms such as DNA methylation, histone modifications, and non-coding RNAs to the modulation of gene expression involved in stress responses, neurodevelopment, and immune function-all of which intersect at the brain-gut axis. Additionally, we discuss the emerging potential of the gut microbiome as both a target and mediator of epigenetic changes, further influencing brain-gut communication in the context of ACEs. The methodological and therapeutic challenges posed by these insights are significant. The reversibility of epigenetic marks and the long-term consequences of early life stress require innovative and comprehensive approaches to intervention. This underscores the need for comprehensive strategies encompassing psychosocial, pharmacological, neuromodulation, and lifestyle interventions tailored to address ACEs' individualized and persistent effects. Future directions call for a multi-disciplinary approach and longitudinal studies to uncover the full extent of ACEs' impact on epigenetic regulation and the brain-gut axis, with the goal of developing targeted therapies to mitigate the long-lasting effects on health.

Complement-pentraxins synergy: Navigating the immune battlefield and beyond

The complement is a crucial immune defense system that triggers rapid immune responses and offers efficient protection against foreign invaders and unwanted host elements, acting as a sentinel. Activation of the complement system occurs upon the recognition of pathogenic microorganisms or altered self-cells by pattern-recognition molecules (PRMs) such as C1q, collectins, ficolins, and pentraxins. Recent accumulating evidence shows that pentraxins establish a cooperative network with different classes of effector PRMs, resulting in synergistic effects in complement activation. This review describes the complex interaction of pentraxins with the complement system and the implications of this cooperative network for effective host defense during pathogen invasion.

Pentraxins in invertebrates and vertebrates: From structure, function and evolution to clinical applications

The immune system is divided into two broad categories, consisting of innate and adaptive immunity. As recognition and effector factors of innate immunity and regulators of adaptive immune responses, lectins are considered to be important defense chemicals against microbial pathogens, cell trafficking, immune regulation, and prevention of autoimmunity. Pentraxins, important members of animal lectins, play a significant role in protecting the body from pathogen infection and regulating inflammatory reactions. They can recognize and bind to a variety of ligands, including carbohydrates, lipids, proteins, nucleic acids and their complexes, and protect the host from pathogen invasion by activating the complement cascade and Fcγ receptor pathways. Based on the primary structure of the subunit, pentraxins are divided into short and long pentraxins. The short pentraxins are comprised of C-reactive protein (CRP) and serum amyloid P (SAP), and the most important member of the long pentraxins is pentraxin 3 (PTX3). The CRP and SAP exist in both vertebrates and invertebrates, while the PTX3 may be present only in vertebrates. The major ligands and functions of CRP, SAP and PTX3 and three activation pathways involved in the complement system are summarized in this review. Their different characteristics in various animals including humans, and their evolutionary trees are analyzed. The clinical applications of CRP, SAP and PTX3 in human are reviewed. Some questions that remain to be understood are also highlighted.

A biofunctional review of C-reactive protein (CRP) as a mediator of inflammatory and immune responses: differentiating pentameric and modified CRP isoform effects

C-reactive protein (CRP) is an acute phase, predominantly hepatically synthesized protein, secreted in response to cytokine signaling at sites of tissue injury or infection with the physiological function of acute pro-inflammatory response. Historically, CRP has been classified as a mediator of the innate immune system, acting as a pattern recognition receptor for phosphocholine-containing ligands. For decades, CRP was envisioned as a single, non-glycosylated, multi-subunit protein arranged non-covalently in cyclic symmetry around a central void. Over the past few years, however, CRP has been shown to exist in at least three distinct isoforms: 1.) a pentamer of five identical globular subunits (pCRP), 2.) a modified monomer (mCRP) resulting from a conformational change when subunits are dissociated from the pentamer, and 3.) a transitional isoform where the pentamer remains intact but is partially changed to express mCRP structural characteristics (referred to as pCRP* or mCRPm). The conversion of pCRP into mCRP can occur spontaneously and is observed under commonly used experimental conditions. In careful consideration of experimental design used in published reports of in vitro pro- and anti-inflammatory CRP bioactivities, we herein provide an interpretation of how distinctive CRP isoforms may have affected reported results. We argue that pro-inflammatory amplification mechanisms are consistent with the biofunction of mCRP, while weak anti-inflammatory mechanisms are consistent with pCRP. The interplay of each CRP isoform with specific immune cells (platelets, neutrophils, monocytes, endothelial cells, natural killer cells) and mechanisms of the innate immune system (complement), as well as differences in mCRP and pCRP ligand recognition and effector functions are discussed. This review will serve as a revised understanding of the structure-function relationship between CRP isoforms as related to inflammation and innate immunity mechanisms.

C-reactive protein - My perspective on its first half century, 1930-1982

C-reactive protein (CRP) was discovered in 1930 in the sera of patients during the acute phase of pneumococcal pneumonia and was so named because it bound to the C-polysaccharide of the pneumococcal cell wall. During the next half century many questions raised by this discovery were answered. Phosphorylcholine was found to be the moiety of the C-polysaccharide to which CRP bound. The molecular structure of CRP was elucidated: five identical subunits arranged in cyclic symmetry, giving rise to the term pentraxin. Initially felt to be not normally present in the blood, CRP was found to be a component of normal serum in trace amounts. Its site of origin was determined to be the hepatocyte. It became clear that the presumed humoral mediator responsible for CRP induction was of leukocytic origin. Binding of CRP to its ligand activated the complement system, one of the important effector mechanisms of innate immunity. CRP was found to stimulate phagocytosis of some bacterial species via binding to Fc receptors and was found to be protective in vivo against the pneumococcus in mice. It appeared likely that a related function of CRP was clearance of necrotic tissue. CRP was recognized as being a highly evolutionary conserved molecule. Its discovery during the acute phase of pneumococcal pneumonia led to its being dubbed an acute phase protein. What we today call "the acute phase response", refers to the large number of behavioral, physiologic, biochemical, and nutritional changes that occur during inflammatory states.

Characterization of the innate immune response to Streptococcus pneumoniae infection in zebrafish

Streptococcus pneumoniae (pneumococcus) is one of the most frequent causes of pneumonia, sepsis and meningitis in humans, and an important cause of mortality among children and the elderly. We have previously reported the suitability of the zebrafish (Danio rerio) larval model for the study of the host-pathogen interactions in pneumococcal infection. In the present study, we characterized the zebrafish innate immune response to pneumococcus in detail through a whole-genome level transcriptome analysis and revealed a well-conserved response to this human pathogen in challenged larvae. In addition, to gain understanding of the genetic factors associated with the increased risk for severe pneumococcal infection in humans, we carried out a medium-scale forward genetic screen in zebrafish. In the screen, we identified a mutant fish line which showed compromised resistance to pneumococcus in the septic larval infection model. The transcriptome analysis of the mutant zebrafish larvae revealed deficient expression of a gene homologous for human C-reactive protein (CRP). Furthermore, knockout of one of the six zebrafish crp genes by CRISPR-Cas9 mutagenesis predisposed zebrafish larvae to a more severe pneumococcal infection, and the phenotype was further augmented by concomitant knockdown of a gene for another Crp isoform. This suggests a conserved function of C-reactive protein in anti-pneumococcal immunity in zebrafish. Altogether, this study highlights the similarity of the host response to pneumococcus in zebrafish and humans, gives evidence of the conserved role of C-reactive protein in the defense against pneumococcus, and suggests novel host genes associated with pneumococcal infection.

C-Reactive Protein Controls IL-23 Production by Human Monocytes

C-reactive protein (CRP) is an acute-phase protein in humans that is produced in high quantities by the liver upon infection and under inflammatory conditions. Although CRP is commonly used as a marker of inflammation, CRP can also directly contribute to inflammation by eliciting pro-inflammatory cytokine production by immune cells. Since CRP is highly elevated in serum under inflammatory conditions, we have studied the CRP-induced cytokine profile of human monocytes, one of the main innate immune cell populations in blood. We identified that CRP is relatively unique in its capacity to induce production of the pro-inflammatory cytokine IL-23, which was in stark contrast to a wide panel of pattern recognition receptor (PRR) ligands. We show that CRP-induced IL-23 production was mediated at the level of gene transcription, since CRP particularly promoted gene transcription of IL23A (encoding IL-23p19) instead of IL12A (encoding IL-12p35), while PRR ligands induce the opposite response. Interestingly, when CRP stimulation was combined with PRR ligand stimulation, as for example, occurs in the context of sepsis, IL-23 production by monocytes was strongly reduced. Combined, these data identify CRP as a unique individual ligand to induce IL-23 production by monocytes, which may contribute to shaping systemic immune responses under inflammatory conditions.

A Single-Center Retrospective Observational Study Evaluating the Favorable Predictive Factors for the Disease Control Time of Treatment with Tocilizumab in Patients of Rheumatoid Arthritis

Background

Tocilizumab (TCZ) is humanized monoclonal antibody against the interleukin-6 (IL-6) and receptor that has prominent efficacy for the treatment of rheumatoid arthritis (RA). We conducted a retrospective observational study to determine how long TCZ controls RA.

Patients and Methods

We retrospectively reviewed the medical records of RA patients treated with TCZ. The aim of this study was to evaluate the contribution of clinical parameters to disease control time (DCT) in RA patients.

Results

Overall, 144 patients were enrolled in the study. The median age of patients was 66 years (range: 34–85 years). In univariate analysis, DCT was significantly increased in patients who had never received previous biologic disease-modifying anti-rheumatic drugs treatment (P = 0.0064). We also analyzed the contribution of the base line value of C-reactive protein (CRP) to DCT. We divided the patients with RA into two groups according to a cutoff value of 1.000 mg/dl. The median control times were 77.5 months (95% confidence interval [CI]: 44.8–not reached to median) and 34.5 months (95% CI: 17.0–79.3) for patients with high and low CRP value, respectively. In univariate analysis, DCT was significantly increased in patients with a high CRP value (P = 0.0283). Multivariate analysis clearly revealed that a high baseline CRP value was an independent favorable predictive factor for longer DCT (hazard ratio, 0.608, 95% CI: 0.378–0.981, P = 0.0416).

Conclusion

These data clearly demonstrate that the baseline value of CRP was closely associated with long time DCT in patients of RA treated with TCZ.

The Effect of Tocilizumab on Inflammatory Markers in Patients Hospitalized with Serious Infections. Case Series and Review of Literature

Background: The human anti-IL-6 receptor antibody tocilizumab (TCZ) has been approved for the treatment of rheumatoid arthritis (RA) and giant cell arteritis (GCA). It is observed that CRP levels drop quickly after starting TCZ treatment. This may lead to misinterpretation of laboratory results when accessing the patient with infectious disease while on TCZ. We conducted this study to report cases treated with tocilizumab who developed serious infections with special reference to levels of CRP and to review the literature on the effect of tocilizumab on acute phase response (APR) during infections. Methods: The files of RA and GCA patients hospitalized in the Tel Aviv medical center between 2009–2019 were reviewed. Cases of patients with RA and GCA treated with tocilizumab who were hospitalized due to severe infections were reviewed with special emphasis on the duration of treatment, type of infection, and APR. Results: We identified nine admissions. Seven patients were treated with tocilizumab for RA, two for GCA. The diagnosis was pneumonia in three cases, osteomyelitis in one, cellulitis in one, endocarditis due to Whipple disease in one, abscess of cervix uteri in one, meningitis in one, and perforated diverticulitis in one. The mean CRP levels on admission were 4.75 mg/L (normal range, up to 5 mg/L). All cases were diagnosed correctly on admission. Conclusions: CRP levels may not correctly reflect the severity of infectious diseases during tocilizumab treatment. Increased awareness of the masking effect of tocilizumab on the APR during infection is needed in order to avoid a delay in the diagnosis.

Therapeutic Lowering of C-Reactive Protein

In the blood of healthy individuals C-reactive protein (CRP) is typically quite scarce, whereas its blood concentration can rise robustly and rapidly in response to tissue damage and inflammation associated with trauma and infectious and non-infectious diseases. Consequently, CRP plasma or serum levels are routinely monitored in inpatients to gauge the severity of their initial illness and injury and their subsequent response to therapy and return to health. Its clinical utility as a faithful barometer of inflammation notwithstanding, it is often wrongly concluded that the biological actions of CRP (whatever they may be) are manifested only when blood CRP is elevated. In fact over the last decades, studies done in humans and animals (e.g. human CRP transgenic and CRP knockout mice) have shown that CRP is an important mediator of biological activities even in the absence of significant blood elevation, i.e. even at baseline levels. In this review we briefly recap the history of CRP, including a description of its discovery, early clinical use, and biosynthesis at baseline and during the acute phase response. Next we overview evidence that we and others have generated using animal models of arthritis, neointimal hyperplasia, and acute kidney injury that baseline CRP exerts important biological effects. In closing we discuss the possibility that therapeutic lowering of baseline CRP might be a useful way to treat certain diseases, including cancer.

C-Reactive Protein-Based Strategy to Reduce Antibiotic Dosing for the Treatment of Pneumococcal Infection

C-reactive protein (CRP) is a component of innate immunity. The concentration of CRP in serum increases in microbial infections including Streptococcus pneumoniae infection. Employing a mouse model of pneumococcal infection, it has been shown that passively administered human wild-type CRP protects mice against infection, provided that CRP is injected into mice within two hours of administering pneumococci. Engineered CRP (E-CRP) molecules have been reported recently; unlike wild-type CRP, passively administered E-CRP protected mice against infection even when E-CRP was injected into mice after twelve hours of administering pneumococci. The current study was aimed at comparing the protective capacity of E-CRP with that of an antibiotic clarithromycin. We established a mouse model of pneumococcal infection in which both E-CRP and clarithromycin, when used alone, provided minimal but equal protection against infection. In this model, the combination of E-CRP and clarithromycin drastically reduced bacteremia and increased survival of mice when compared to the protective effects of either E-CRP or clarithromycin alone. E-CRP was more effective in reducing bacteremia in mice treated with clarithromycin than in untreated mice. Also, there was 90% reduction in antibiotic dosing by including E-CRP in the antibiotic-treatment for maximal protection of infected mice. These findings provide an example of cooperation between the innate immune system and molecules that prevent multiplication of bacteria, and that should be exploited to develop novel combination therapies for infections against multidrug-resistant pneumococci. The reduction in antibiotic dosing by including E-CRP in the combination therapy might also resolve the problem of developing antibiotic resistance.

Treatment of Pneumococcal Infection by Using Engineered Human C-Reactive Protein in a Mouse Model

C-reactive protein (CRP) binds to several species of bacterial pathogens including Streptococcus pneumoniae. Experiments in mice have revealed that one of the functions of CRP is to protect against pneumococcal infection by binding to pneumococci and activating the complement system. For protection, however, CRP must be injected into mice within a few hours of administering pneumococci, that is, CRP is protective against early-stage infection but not against late-stage infection. It is assumed that CRP cannot protect if pneumococci got time to recruit complement inhibitor factor H on their surface to become complement attack-resistant. Since the conformation of CRP is altered under inflammatory conditions and altered CRP binds to immobilized factor H also, we hypothesized that in order to protect against late-stage infection, CRP needed to change its structure and that was not happening in mice. Accordingly, we engineered CRP molecules (E-CRP) which bind to factor H on pneumococci but do not bind to factor H on any host cell in the blood. We found that E-CRP, in cooperation with wild-type CRP, was protective regardless of the timing of administering E-CRP into mice. We conclude that CRP acts via two different conformations to execute its anti-pneumococcal function and a model for the mechanism of action of CRP is proposed. These results suggest that pre-modified CRP, such as E-CRP, is therapeutically beneficial to decrease bacteremia in pneumococcal infection. Our findings may also have implications for infections with antibiotic-resistant pneumococcal strains and for infections with other bacterial species that use host proteins to evade complement-mediated killing.

Complement Activation by C-Reactive Protein Is Critical for Protection of Mice Against Pneumococcal Infection

C-reactive protein (CRP), a component of the innate immune system, is an antipneumococcal plasma protein. Human CRP has been shown to protect mice against infection with lethal doses of Streptococcus pneumoniae by decreasing bacteremia. in vitro, CRP binds to phosphocholine-containing substances, such as pneumococcal C-polysaccharide, in a Ca²⁺-dependent manner. Phosphocholine-complexed human CRP activates the complement system in both human and murine sera. The mechanism of antipneumococcal action of CRP in vivo, however, has not been defined yet. In this study, we tested a decades-old hypothesis that the complement-activating property of phosphocholine-complexed CRP contributes to protection of mice against pneumococcal infection. Our approach was to investigate a CRP mutant, incapable of activating murine complement, in mouse protection experiments. We employed site-directed mutagenesis of CRP, guided by its three-dimensional structure, and identified a mutant H38R which, unlike wild-type CRP, did not activate complement in murine serum. Substitution of His³⁸ with Arg in CRP did not affect the pentameric structure of CRP, did not affect the binding of CRP to pneumococci, and did not decrease the stability of CRP in mouse circulation. Employing a murine model of pneumococcal infection, we found that passively administered H38R CRP failed to protect mice against infection. Infected mice injected with H38R CRP showed no reduction in bacteremia and did not survive longer, as opposed to infected mice treated with wild-type CRP. Thus, the hypothesis that complement activation by phosphocholine-complexed CRP is an antipneumococcal effector function was supported. We can conclude now that complement activation by phosphocholine-complexed CRP is indeed essential for CRP-mediated protection of mice against pneumococcal infection.

Predicting bacteria causing acute bacterial rhinosinusitis by clinical features

Introduction

Clinicians rely on clinical presentations to select therapeutic agents for acute bacterial rhinosinusitis. Streptococcus pneumoniae and Haemophilus influenzae are common in acute bacterial rhinosinusitis. Drug resistant Streptococcus pneumoniae and Haemophilus influenzae require different antibiotics.

Objective

This study aimed to evaluate the associations between clinical features of acute bacterial rhinosinusitis and pathogenic bacteria.

Methods

Sixty-four patients with acute bacterial rhinosinusitis were enrolled. Clinical features including nasal obstruction, discolored discharge, facial pain, smell disturbance, fever and laboratory findings of patients with acute bacterial rhinosinusitis were collected. The bacterial cultures of endoscopic middle meatal swabs were used as a reference.

Results

Serum C-reactive protein level elevation correlated with the bacterial species (p = 0.03), by which was increased in 80.0% of Haemophilus influenzae rhinosinusitis and 57.1% of Streptococcus pneumoniae rhinosinusitis. The elevated C-reactive protein was the significant predictor for Haemophilus influenzae rhinosinusitis with the Odds Ratio of 18.06 (95% CI 2.36–138.20). The sensitivity of serum C-reactive protein level elevation for diagnosing Haemophilus influenzae rhinosinusitis was 0.80 (95% CI 0.49–0.94).

Conclusion

Elevation of serum C-reactive protein level was associated with and predicted acute bacterial rhinosinusitis caused by Haemophilus influenzae.

Phase Variation of Streptococcus pneumoniae

Streptococcus pneumoniae undergoes phase variation or spontaneous, reversible phenotypic variation in colony opacity, encapsulation, and pilus expression. The variation in colony opacity appears to occur in all strains, whereas the switches in the production of the capsule and pilus have been observed in several strains. This chapter elaborates on the variation in colony opacity since this phenomenon has been extensively characterized. S. pneumoniae produces opaque and transparent colonies on the translucent agar medium. The different colony phases are fundamentally distinct phenotypes in their metabolism and multiple characteristics, as exemplified by cell surface features and phenotypes in colonization and virulence. Opaque variants, which express more capsular polysaccharides and fewer teichoic acids, are more virulent in animal models of sepsis but colonize the nasopharynx poorly. In contrast, transparent variants, with fewer capsular polysaccharides and more teichoic acid, colonize the nasopharynx in animal models more efficiently but are relatively avirulent. Lastly, pneumococcal opacity variants are generated by differential methylation of the genome DNA variation. The reversible switch in the methylation pattern is caused by DNA inversions in three homologous hsdS genes of the colony opacity determinant (cod) or SpnD39III locus, a conserved type I restriction-modification (RM) system. The hsdS gene encodes the sequence recognition subunit of the type I RM DNA methyltransferase. The combination of DNA inversion and differential methylation, a complex mechanism of phase variation, generates a mixed population that may allow for the selection of organisms in vivo with characteristics permissive for either carriage or systemic infection.

Pentraxins and Fc Receptor-Mediated Immune Responses

C-reactive protein (CRP) is a member of the pentraxin family of proteins. These proteins are highly conserved over the course of evolution being present as far back as 250 million years ago. Mammalian pentraxins are characterized by the presence of five identical non-covalently linked subunits. Each subunit has a structurally conserved site for calcium-dependent ligand binding. The biological activities of the pentraxins established over many years include the ability to mediate opsonization for phagocytosis and complement activation. Pentraxins have an important role in protection from infection from pathogenic bacteria, and regulation of the inflammatory response. It was recognized early on that some of these functions are mediated by activation of the classical complement pathway through C1q. However, experimental evidence suggested that cellular receptors for pentraxins also play a role in phagocytosis. More recent experimental evidence indicates a direct link between pentraxins and Fc receptors. The Fc receptors were first identified as the major receptors for immunoglobulins. The avidity of the interaction between IgG complexes and Fc receptors is greatly enhanced when multivalent ligands interact with the IgG binding sites and activation of signaling pathways requires Fc receptor crosslinking. Human pentraxins bind and activate human and mouse IgG receptors, FcγRI and FcγRII, and the human IgA receptor, FcαRI. The affinities of the interactions between Fc receptors and pentraxins in solution and on cell surfaces are similar to antibody binding to low affinity Fc receptors. Crystallographic and mutagenesis studies have defined the structural features of these interactions and determined the stoichiometry of binding as one-to-one. Pentraxin aggregation or binding to multivalent ligands increases the avidity of binding and results in activation of these receptors for phagocytosis and cytokine synthesis. This review will discuss the structural and functional characteristics of pentraxin Fc receptor interactions and their implications for host defense and inflammation.

The Pentraxins 1975-2018: Serendipity, Diagnostics and Drugs

The phylogenetically ancient, pentraxin family of plasma proteins, comprises C-reactive protein (CRP) and serum amyloid P component (SAP) in humans and the homologous proteins in other species. They are composed of five, identical, non-covalently associated protomers arranged with cyclic pentameric symmetry in a disc-like configuration. Each protomer has a calcium dependent site that mediates the particular specific ligand binding responsible for all the rigorously established functional properties of these proteins. No genetic deficiency of either human CRP or SAP has been reported, nor even any sequence polymorphism in the proteins themselves. Although their actual functions in humans are therefore unknown, gene deletion studies in mice demonstrate that both proteins can contribute to innate immunity. CRP is the classical human acute phase protein, routinely measured in clinical practice worldwide to monitor disease activity. Human SAP, which is not an acute phase protein, is a universal constituent of all human amyloid deposits as a result of its avid specific binding to amyloid fibrils of all types. SAP thereby contributes to amyloid formation and persistence in vivo. Whole body radiolabelled SAP scintigraphy safely and non-invasively localizes and quantifies systemic amyloid deposits, and has transformed understanding of the natural history of amyloidosis and its response to treatment. Human SAP is also a therapeutic target, both in amyloidosis and Alzheimer's disease. Our drug, miridesap, depletes SAP from the blood and the brain and is currently being tested in the DESPIAD clinical trial in Alzheimer's disease. Meanwhile, the obligate therapeutic partnership of miridesap, to deplete circulating SAP, and dezamizumab, a humanized monoclonal anti-SAP antibody that targets residual SAP in amyloid deposits, produces unprecedented removal of amyloid from the tissues and improves organ function. Human CRP binds to dead and damaged cells in vivo and activates complement and this can exacerbate pre-existing tissue damage. The adverse effects of CRP are completely abrogated by compounds that block its binding to autologous ligands and we are developing CRP inhibitor drugs. The present personal and critical perspective on the pentraxins reports, for the first time, the key role of serendipity in our work since 1975. (345 words).

Role of C-Reactive Protein at Sites of Inflammation and Infection

C-reactive protein (CRP) is an acute inflammatory protein that increases up to 1,000-fold at sites of infection or inflammation. CRP is produced as a homopentameric protein, termed native CRP (nCRP), which can irreversibly dissociate at sites of inflammation and infection into five separate monomers, termed monomeric CRP (mCRP). CRP is synthesized primarily in liver hepatocytes but also by smooth muscle cells, macrophages, endothelial cells, lymphocytes, and adipocytes. Evidence suggests that estrogen in the form of hormone replacement therapy influences CRP levels in the elderly. Having been traditionally utilized as a marker of infection and cardiovascular events, there is now growing evidence that CRP plays important roles in inflammatory processes and host responses to infection including the complement pathway, apoptosis, phagocytosis, nitric oxide (NO) release, and the production of cytokines, particularly interleukin-6 and tumor necrosis factor-α. Unlike more recent publications, the findings of early work on CRP can seem somewhat unclear and at times conflicting since it was often not specified which particular CRP isoform was measured or utilized in experiments and whether responses attributed to nCRP were in fact possibly due to dissociation into mCRP or lipopolysaccharide contamination. In addition, since antibodies for mCRP are not commercially available, few laboratories are able to conduct studies investigating the mCRP isoform. Despite these issues and the fact that most CRP research to date has focused on vascular disorders, there is mounting evidence that CRP isoforms have distinct biological properties, with nCRP often exhibiting more anti-inflammatory activities compared to mCRP. The nCRP isoform activates the classical complement pathway, induces phagocytosis, and promotes apoptosis. On the other hand, mCRP promotes the chemotaxis and recruitment of circulating leukocytes to areas of inflammation and can delay apoptosis. The nCRP and mCRP isoforms work in opposing directions to inhibit and induce NO production, respectively. In terms of pro-inflammatory cytokine production, mCRP increases interleukin-8 and monocyte chemoattractant protein-1 production, whereas nCRP has no detectable effect on their levels. Further studies are needed to expand on these emerging findings and to fully characterize the differential roles that each CRP isoform plays at sites of local inflammation and infection.

Bacterial-Host Interactions: Physiology and Pathophysiology of Respiratory Infection

It has long been thought that respiratory infections are the direct result of acquisition of pathogenic viruses or bacteria, followed by their overgrowth, dissemination, and in some instances tissue invasion. In the last decades, it has become apparent that in contrast to this classical view, the majority of microorganisms associated with respiratory infections and inflammation are actually common members of the respiratory ecosystem and only in rare circumstances do they cause disease. This suggests that a complex interplay between host, environment, and properties of colonizing microorganisms together determines disease development and its severity. To understand the pathophysiological processes that underlie respiratory infectious diseases, it is therefore necessary to understand the host-bacterial interactions occurring at mucosal surfaces, along with the microbes inhabiting them, during symbiosis. Current knowledge regarding host-bacterial interactions during asymptomatic colonization will be discussed, including a plausible role for the human microbiome in maintaining a healthy state. With this as a starting point, we will discuss possible disruptive factors contributing to dysbiosis, which is likely to be a key trigger for pathobionts in the development and pathophysiology of respiratory diseases. Finally, from this renewed perspective, we will reflect on current and potential new approaches for treatment in the future.

Article Commentary: Serum C-Reactive Protein (CRP), Target for Therapy or Trouble?

High sensitivity serum C-reactive protein (hs-CRP) has come into clinical use as a marker of risk for cardiovascular disease (CVD). In addition to a role as a marker of disease, CRP has also been implicated in the pathogenesis of CVD. Specific small-molecule inhibitors of CRP have recently been developed with the intent of mitigating cardiac damage during acute myocardial infarction. However, the use of CRP, both as a risk marker and a disease target are controversial for several reasons. Serum hs-CRP concentrations can be elevated on the basis of genetics, female gender, and non-Caucasian ethnicity. It is not clear, in these contexts, that elevations of hs-CRP have any pathological significance. As a non-specific indicator of inflammation, CRP is also not a specific indicator of a single disease state such as cardiovascular disease but elevated concentrations can be seen in association with other comorbidities including obesity and pulmonary disease. In sharp contrast to the proposed inhibition of CRP for cardiovascular disease treatment, the infusion of CRP has been shown to have profound therapeutic benefits for autoimmune disease and septic shock. The balance between the risks and benefits of these competing views of the role of CRP in disease and disease therapy is reminiscent of the ongoing controversy regarding the use of non-steroidal anti-inflammatory drugs (NSAIDs) for musculoskeletal disease and their cardiovascular side effects. Soon, NSAIDs may not be the only agents about which Rheumatologists and Cardiologists may spar.

An overview of the synergy and crosstalk between pentraxins and collectins/ficolins: their functional relevance in complement activation

The complement system is an innate immune defense machinery comprising components that deploy rapid immune responses and provide efficient protection against foreign invaders and unwanted host elements. The complement system is activated upon recognition of pathogenic microorganisms or altered self-cells by exclusive pattern recognition molecules (PRMs), such as collectins, ficolins and pentraxins. Recent accumulating evidence shows that the different classes of effector PRMs build up a co-operative network and exert synergistic effects on complement activation. In this review, we describe our updated view of the crosstalk between previously unlinked PRMs in complement activation and the potential pathogenic effects during infection and inflammation.

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.

The Elements Steering Pathogenesis in IgG-Mediated Alloimmune Diseases

Alloimmune diseases can occur in pregnancy and after blood transfusions, where antibodies are formed, targeting foreign cells and tissues for destruction by myeloid cells through IgG Fc-receptors (FcγR). In pregnancy, antibodies against human blood group or platelet antigens (e.g. HPA1-a) cause life-threatening anemia or thrombocytopenia in the developing fetus or newborn. Here we discuss how both the induction of those IgG antibodies as well as the proinflammatory status of the fetus affects the effector functions through FcγR. Recent studies have found IgG-glycosylation to be important with low IgG-Fc-core fucosylation resulting in increased affinity to FcγRIIIa and FcγRIIIb and enhanced antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis. The importance of these and other features, including oxidative stress and acute phase responses (C-reactive protein, CRP), will be discussed and how these features may collectively synergize resulting in elevated disease pathology in these allo-, but also autoimmune mediated diseases.

C-reactive protein enhances IgG-mediated phagocyte responses and thrombocytopenia

CRP enhances IgG-mediated respiratory burst and phagocytosis of platelets in vitro and their clearance in vivo. CRP levels are increased in ITP patients and correlate with platelet counts and bleeding severity and predict time to recovery.

C-reactive protein protects mice against pneumococcal infection via both phosphocholine-dependent and phosphocholine-independent mechanisms

The mechanism of action of C-reactive protein (CRP) in protecting mice against lethal Streptococcus pneumoniae infection is unknown. The involvement of the phosphocholine (PCh)-binding property of CRP in its antipneumococcal function previously has been explored twice, with conflicting results. In this study, using three different intravenous sepsis mouse models, we investigated the role of the PCh-binding property of CRP by employing a CRP mutant incapable of binding to PCh. The ability of wild-type CRP to protect mice against infection was found to differ in the three models; the protective ability of wild-type CRP decreased when the severity of infection was increased, as determined by measuring mortality and bacteremia. In the first animal model, in which we used 25 μg of CRP and 10(7) CFU of pneumococci, both wild-type and mutant CRP protected mice against infection, suggesting that the protection was independent of the PCh-binding activity of CRP. In the second model, in which we used 25 μg of CRP and 5 × 10(7) CFU of pneumococci, mutant CRP was not protective while wild-type CRP was, suggesting that the protection was dependent on the PCh-binding activity of CRP. In the third model, in which we used 150 μg of CRP and 10(7) CFU of pneumococci, mutant CRP was as protective as wild-type CRP, again indicating that the protection was independent of the PCh-binding activity of CRP. We conclude that both PCh-dependent and PCh-independent mechanisms are involved in the CRP-mediated decrease in bacteremia and the resulting protection of mice against pneumococcal infection.

C-reactive protein is essential for innate resistance to pneumococcal infection

No deficiency of human C-reactive protein (CRP), or even structural polymorphism of the protein, has yet been reported so its physiological role is not known. Here we show for the first time that CRP-deficient mice are remarkably susceptible to Streptococcus pneumoniae infection and are protected by reconstitution with isolated pure human CRP, or by anti-pneumococcal antibodies. Autologous mouse CRP is evidently essential for innate resistance to pneumococcal infection before antibodies are produced. Our findings are consistent with the significant association between clinical pneumococcal infection and non-coding human CRP gene polymorphisms which affect CRP expression. Deficiency or loss of function variation in CRP may therefore be lethal at the first early-life encounter with this ubiquitous virulent pathogen, explaining the invariant presence and structure of CRP in human adults.

Role of C-reactive protein in schizophrenia: an overview

Over the years, schizophrenia is speculated to be associated with immune or inflammatory reactions mediated by cytokines. It is proposed that chronic inflammation might damage the micro-vascular system of brain and hamper cerebral blood flow. Scientific evidence suggests that an increase of stress hormone like norepinephrine may activate the inflammatory arm of the immune system and trigger the expression of genes that cause chronic, low-grade inflammation. Thus, studies were conducted to decipher the potentiality of CRP as a marker for inflammation in schizophrenia. This article reviews the findings of CRP in schizophrenia, and the limitations of the previous studies have been discussed. The importance of simultaneous study of CRP modulating cytokines and CRP gene polymorphism in the study of serum or plasma level of CRP has been emphasized.

Community acquired pneumonia: genetic variants influencing systemic inflammation

The inflammatory response depends on several factors, including pathogenicity and duration of the stimulus, and also on the balance between inflammatory and antiinflammatory response. Several studies have presented evidence of the importance of genetic factors in severe infections. The innate immune response prevents the invasion and spread of pathogens during the first hours after infection. Each of the different processes involved in innate immunity may be affected by genetic polymorphisms, which can result in susceptibility or resistance to infection. The results obtained in the different studies do not irrefutably prove the role or function of a gene in the pathogenesis of respiratory infections. However, they can generate new hypotheses, suggest new candidate genes based on their role in the inflammatory response, and constitute a first step in understanding the underlying genetic factors.

Pentraxins: structure, function, and role in inflammation

The pentraxins are an ancient family of proteins with a unique architecture found as far back in evolution as the Horseshoe crab. In humans the two members of this family are C-reactive protein and serum amyloid P. Pentraxins are defined by their sequence homology, their pentameric structure and their calcium-dependent binding to their ligands. Pentraxins function as soluble pattern recognition molecules and one of the earliest and most important roles for these proteins is host defense primarily against pathogenic bacteria. They function as opsonins for pathogens through activation of the complement pathway and through binding to Fc gamma receptors. Pentraxins also recognize membrane phospholipids and nuclear components exposed on or released by damaged cells. CRP has a specific interaction with small nuclear ribonucleoproteins whereas SAP is a major recognition molecule for DNA, two nuclear autoantigens. Studies in autoimmune and inflammatory disease models suggest that pentraxins interact with macrophage Fc receptors to regulate the inflammatory response. Because CRP is a strong acute phase reactant it is widely used as a marker of inflammation and infection.

Human CRP defends against the toxicity of circulating histones

C-reactive protein (CRP) is an acute-phase protein that plays an important defensive role in innate immunity against bacterial infection, but it is also upregulated in many noninfectious diseases. The generic function of this highly conserved molecule in diseases that range from infection, inflammation, trauma, and malignancy is not well understood. In this article, we demonstrate that CRP defends the human body against the toxicity of histones released into the circulation after extensive cell death. In vitro, CRP significantly alleviates histone-induced endothelial cell damage, permeability increase, and platelet aggregation. In vivo, CRP rescues mice challenged with lethal doses of histones by inhibiting endothelial damage, vascular permeability, and coagulation activation, as reflected by significant reductions in lung edema, hemorrhage, and thrombosis. In patients, elevation of CRP significantly increases the capacity to neutralize extracellular histones in the circulation. We have also confirmed that CRP interacts with individual histones in vitro and forms CRP-histone complexes in serum from patients with both elevated CRP and histones. CRP is able to compete with phospholipid-containing liposomes for the binding to histones. This explains how CRP prevents histones from integrating into cell membranes, which would otherwise induce calcium influx as the major mechanism of cytotoxicity caused by extracellular histones. Because histone elevation occurs in the acute phase of numerous critical illnesses associated with extensive cell death, CRP detoxification of circulating histones would be a generic host defense mechanism in humans.

Pneumococcal surface protein A inhibits complement deposition on the pneumococcal surface by competing with the binding of C-reactive protein to cell-surface phosphocholine

In the presence of normal serum, complement component C3 is deposited on pneumococci primarily via the classical pathway. Pneumococcal surface protein A (PspA), a major virulence factor of pneumococci, effectively inhibits C3 deposition. PspA's C terminus has a choline-binding domain that anchors PspA to the phosphocholine (PC) moieties on the pneumococcal surface. C-reactive protein (CRP), another important host defense molecule, also binds to PC, and CRP binding to pneumococci enhances complement C3 deposition through the classical pathway. Using flow cytometry of PspA(+) and PspA(-) strains, we observed that the absence of PspA led to exposure of PC, enhanced the surface binding of CRP, and increased the deposition of C3. Moreover, when the PspA(-) mutant was incubated with a pneumococcal eluate containing native PspA, there was decreased deposition of CRP and C3 on the pneumococcal surface compared with incubation with an eluate from a PspA(-) strain. This inhibition was not observed when a recombinant PspA fragment, which lacks the choline-binding region of PspA, was added to the PspA(-) mutant. Also, there was much greater C3 deposition onto the PspA(-) pneumococcus when exposed to normal mouse serum from wild-type mice as compared with that from CRP knockout mice. Furthermore, when CRP knockout mouse serum was replenished with CRP, there was a dose-dependent increase in C3 deposition. The combined data reveal a novel mechanism of complement inhibition by a bacterial protein: inhibition of CRP surface binding and, thus, diminution of CRP-mediated complement deposition.

The phosphocholine-binding pocket on C-reactive protein is necessary for initial protection of mice against pneumococcal infection

Human C-reactive protein (CRP) protects mice from lethal Streptococcus pneumoniae infection when injected into mice within the range of 6 h before to 2 h after the administration of pneumococci. Because CRP binds to phosphocholine-containing substances and subsequently activates the complement system, it has been proposed that the antipneumococcal function of CRP requires the binding of CRP to phosphocholine moieties present in pneumococcal cell wall C-polysaccharide. To test this proposal experimentally, in this study, we utilized a new CRP mutant incapable of binding to phosphocholine. Based on the structure of CRP-phosphocholine complexes, which showed that Phe(66), Thr(76), and Glu(81) formed the phosphocholine-binding pocket, we constructed a CRP mutant F66A/T76Y/E81A in which the pocket was blocked by substituting Tyr for Thr(76). When compared with wild-type CRP, mutant CRP bound more avidly to phosphoethanolamine and could be purified by affinity chromatography using phosphoethanolamine-conjugated Sepharose. Mutant CRP did not bind to phosphocholine, C-polysaccharide, or pneumococci. Mutant CRP was free in the mouse serum, and its rate of clearance in vivo was not faster than that of wild-type CRP. When either 25 μg or 150 μg of CRP was administered into mice, unlike wild-type CRP, mutant CRP did not protect mice from lethal pneumococcal infection. Mice injected with mutant CRP had higher mortality rates than mice that received wild-type CRP. Decreased survival was due to the increased bacteremia in mice treated with mutant CRP. We conclude that the phosphocholine-binding pocket on CRP is necessary for CRP-mediated initial protection of mice against lethal pneumococcal infection.

Cefditoren and ceftriaxone enhance complement-mediated immunity in the presence of specific antibodies against antibiotic-resistant pneumococcal strains

Background

Specific antibodies mediate humoral and cellular protection against invading pathogens such as Streptococcus pneumoniae by activating complement mediated immunity, promoting phagocytosis and stimulating bacterial clearance. The emergence of pneumococcal strains with high levels of antibiotic resistance is of great concern worldwide and a serious threat for public health.

Methodology/Principal Findings

Flow cytometry was used to determine whether complement-mediated immunity against three antibiotic-resistant S. pneumoniae clinical isolates is enhanced in the presence of sub-inhibitory concentrations of cefditoren and ceftriaxone. The binding of acute phase proteins such as C-reactive protein and serum amyloid P component, and of complement component C1q, to pneumococci was enhanced in the presence of serum plus either of these antibiotics. Both antibiotics therefore trigger the activation of the classical complement pathway against S. pneumoniae. C3b deposition was also increased in the presence of specific anti-pneumococcal antibodies and sub-inhibitory concentrations of cefditoren and ceftriaxone confirming that the presence of these antibiotics enhances complement-mediated immunity to S. pneumoniae.

Conclusions/Significance

Using cefditoren and ceftriaxone to promote the binding of acute phase proteins and C1q to pneumococci, and to increase C3b deposition, when anti-pneumococcal antibodies are present, might help reduce the impact of antibiotic resistance in S. pneumoniae infections.

The innate immune response to products of phospholipid peroxidation

Lipid peroxidation occurs in the context of many physiological processes but is greatly increased in various pathological situations. A consequence of phospholipid peroxidation is the generation of oxidation-specific epitopes, such as phosphocholine of oxidized phospholipids and malondialdehyde, which form neo-self determinants on dying cells and oxidized low-density lipoproteins. In this review we discuss evidence demonstrating that pattern recognition receptors of the innate immune system recognize oxidation-specific epitopes as endogenous damage-associated molecular patterns, allowing the host to identify dangerous biological waste. Oxidation-specific epitopes are important targets of both cellular and soluble pattern recognition receptors, including toll-like and scavenger receptors, C-reactive protein, complement factor H, and innate natural IgM antibodies. This recognition allows the innate immune system to mediate important physiological house keeping functions, for example by promoting the removal of dying cells and oxidized molecules. Once this system is malfunctional or overwhelmed the development of diseases, such as atherosclerosis and age-related macular degeneration is favored. Understanding the molecular components and mechanisms involved in this process, will help the identification of individuals with increased risk of developing chronic inflammation, and indicate novel points for therapeutic intervention. This article is part of a Special Issue entitled: Oxidized phospholipids—their properties and interactions with proteins.

Identifying host genetic risk factors in the context of public health surveillance for invasive pneumococcal disease

Host genetic factors that modify risk of pneumococcal disease may help target future public health interventions to individuals at highest risk of disease. We linked data from population-based surveillance for invasive pneumococcal disease (IPD) with state-based newborn dried bloodspot repositories to identify biological samples from individuals who developed invasive pneumococcal disease. Genomic DNA was extracted from 366 case and 732 anonymous control samples. TagSNPs were selected in 34 candidate genes thought to be associated with host response to invasive pneumococcal disease, and a total of 326 variants were successfully genotyped. Among 543 European Americans (EA) (182 cases and 361 controls), and 166 African Americans (AA) (53 cases and 113 controls), common variants in surfactant protein D (SFTPD) are consistently underrepresented in IPD. SFTPD variants with the strongest association for IPD are intronic rs17886286 (allelic OR 0.45, 95% confidence interval (CI) [0.25, 0.82], with p = 0.007) in EA and 5' flanking rs12219080 (allelic OR 0.32, 95%CI [0.13, 0.78], with p = 0.009) in AA. Variants in CD46 and IL1R1 are also associated with IPD in both EA and AA, but with effects in different directions; FAS, IL1B, IL4, IL10, IL12B, SFTPA1, SFTPB, and PTAFR variants are associated (p≤0.05) with IPD in EA or AA. We conclude that variants in SFTPD may protect against IPD in EA and AA and genetic variation in other host response pathways may also contribute to risk of IPD. While our associations are not corrected for multiple comparisons and therefore must be replicated in additional cohorts, this pilot study underscores the feasibility of integrating public health surveillance with existing, prospectively collected, newborn dried blood spot repositories to identify host genetic factors associated with infectious diseases.

The Fcγ receptor IIA-H/H131 genotype is associated with bacteremia in pneumococcal community-acquired pneumonia

OBJECTIVE

To assess the potential association of the functional polymorphism rs1801274 in the receptor IIa for the Fc portion of immunoglobin G (FcγRIIa) gene (FCGR2A-H131R) with the susceptibility to and the severity of community-acquired pneumonia (CAP).

DESIGN

Multicenter prospective and observational study.

SETTING

Four university hospitals in Spain.

PATIENTS

FCGR2A-H131R polymorphism was determined in 1,262 patients with CAP and in 1,224 in the subject control group.

MEASUREMENTS AND MAIN RESULTS

Severe sepsis was recorded in 366 patients. No significant differences in genotype or allele frequencies were seen among patients with CAP or pneumococcal CAP (PCAP) and controls. Patients with bacteremic PCAP (B-PCAP) had significantly higher frequencies of FCGR2A-H/H131 genotypes than those with nonbacteremic PCAP (p = .00016, odds ratio = 2.9, 95% confidence interval 1.58-5.3). The differences remained significant when adjusting for pneumonia severity index, hospital of origin, and intensive care unit admission (p = .0012, odds ratio = 2.83, 95% confidence interval 1.51-5.32). B-PCAP was associated with a significantly higher severity of the disease, evaluated as sepsis severity (p = .000007, odds ratio = 4.40, 95% confidence interval 2.31-8.39), multiorgan dysfunction syndrome (0.00048, odds ratio = 3.29, 95% confidence interval 1.69-6.41), intensive care unit admission, acute renal failure, and acute respiratory distress syndrome.

CONCLUSIONS

Our results do not support a role of FCGR2A-H131R polymorphism in susceptibility to CAP or PCAP. However, we provide the insight that homozygosity for FCGR2A-H131 predisposes B-PCAP, which was associated with higher severity in our study.

A computational and experimental study of the regulatory mechanisms of the complement system

The complement system is key to innate immunity and its activation is necessary for the clearance of bacteria and apoptotic cells. However, insufficient or excessive complement activation will lead to immune-related diseases. It is so far unknown how the complement activity is up- or down- regulated and what the associated pathophysiological mechanisms are. To quantitatively understand the modulatory mechanisms of the complement system, we built a computational model involving the enhancement and suppression mechanisms that regulate complement activity. Our model consists of a large system of Ordinary Differential Equations (ODEs) accompanied by a dynamic Bayesian network as a probabilistic approximation of the ODE dynamics. Applying Bayesian inference techniques, this approximation was used to perform parameter estimation and sensitivity analysis. Our combined computational and experimental study showed that the antimicrobial response is sensitive to changes in pH and calcium levels, which determines the strength of the crosstalk between CRP and L-ficolin. Our study also revealed differential regulatory effects of C4BP. While C4BP delays but does not decrease the classical complement activation, it attenuates but does not significantly delay the lectin pathway activation. We also found that the major inhibitory role of C4BP is to facilitate the decay of C3 convertase. In summary, the present work elucidates the regulatory mechanisms of the complement system and demonstrates how the bio-pathway machinery maintains the balance between activation and inhibition. The insights we have gained could contribute to the development of therapies targeting the complement system.

The complement system, which is the frontline immune defense, constitutes proteins that flow freely in the blood. It quickly detects invading microbes and alerts the host by sending signals into immune responsive cells to eliminate the hostile substances. Inadequate or excessive complement activities harm the host and may lead to immune-related diseases. Thus, it is crucial to understand how the host boosts the complement activity to protect itself and simultaneously establishes tight surveillance to attain homeostasis. Towards this goal, we developed a detailed computational model of the human complement system. To overcome the challenges resulting from the large model size, we applied probabilistic approximation and inference techniques to train the model on experimental data and explored the key network features of the model. Our model-based study highlights the importance of infection-mediated microenvironmental perturbations, which alter the pH and calcium levels. It also reveals that the inhibitor, C4BP induces differential inhibition on the classical and lectin complement pathways and acts mainly by facilitating the decay of the C3 convertase. These predictions were validated empirically. Thus, our results help to elucidate the regulatory mechanisms of the complement system and potentially contribute to the development of complement-based immunomodulation therapies.

Identification of acidic pH-dependent ligands of pentameric C-reactive protein

C-reactive protein (CRP) is a phylogenetically conserved protein; in humans, it is present in the plasma and at sites of inflammation. At physiological pH, native pentameric CRP exhibits calcium-dependent binding specificity for phosphocholine. In this study, we determined the binding specificities of CRP at acidic pH, a characteristic of inflammatory sites. We investigated the binding of fluid-phase CRP to six immobilized proteins: complement factor H, oxidized low-density lipoprotein, complement C3b, IgG, amyloid β, and BSA immobilized on microtiter plates. At pH 7.0, CRP did not bind to any of these proteins, but, at pH ranging from 5.2 to 4.6, CRP bound to all six proteins. Acidic pH did not monomerize CRP but modified the pentameric structure, as determined by gel filtration, 1-anilinonaphthalene-8-sulfonic acid-binding fluorescence, and phosphocholine-binding assays. Some modifications in CRP were reversible at pH 7.0, for example, the phosphocholine-binding activity of CRP, which was reduced at acidic pH, was restored after pH neutralization. For efficient binding of acidic pH-treated CRP to immobilized proteins, it was necessary that the immobilized proteins, except factor H, were also exposed to acidic pH. Because immobilization of proteins on microtiter plates and exposure of immobilized proteins to acidic pH alter the conformation of immobilized proteins, our findings suggest that conformationally altered proteins form a CRP-ligand in acidic environment, regardless of the identity of the protein. This ligand binding specificity of CRP in its acidic pH-induced pentameric state has implications for toxic conditions involving protein misfolding in acidic environments and favors the conservation of CRP throughout evolution.

C-reactive protein is a strong predictor for anaemia in renal cell carcinoma: role of IL-6 in overall survival

OBJECTIVE

• To elucidate the association of progression of advanced renal cell carcinoma with anaemia and investigate factors influencing tumor-associated anaemia.

PATIENTS AND METHODS

• We analyzed different clinical variables to study associations with anaemia in 86 metastatic renal cell carcinoma patients. • 45 (52%) of patients had already developed anaemia prior to therapy.

RESULTS

• Anaemic patients had an increase in the serum markers C-reactive protein (CRP), IL-6 and erythropoietin (EPO). In addition we observed substantial correlation between IL-6 and CRP serum levels (R = 0.639, P < 0.0001). • Univariate logistic regression analysis revealed that patients with IL-6 >10 pg/mL had a considerable increase in risk for anaemia (odds ratio 3.86, P= 0.003). • In addition, patients with CRP >0.7 mg/dL had a very strong increase in risk for anaemia (OR = 14.08, P < 0.0001). • Stepwise multivariate logistic regression analysis confirmed CRP >0.7 mg/mL as the only independent predictor for anaemia. Cox-regression modeling selected serum IL-6 as the strongest independent prognostic indicator (hazard ratio 3.58, P < 0.0001).

CONCLUSION

• Anaemia depends on serum IL-6, which is a strong inductor of CRP and regulator of the iron-transport. Serum IL-6 may be considered as a target to treat cancer-related anaemia.

NF-κB and STAT3 signaling hubs for lung innate immunity

Innate immune responses to lung pathogens involve the coordinated expression of myriad affector and effector molecules of innate immunity, which must be induced and appropriately regulated in response to diverse stimuli generated by microbes or the infected host. Many intercellular and intracellular signaling pathways are involved, but we propose NF-κB and STAT3 transcription factors to be especially important signaling hubs for integrating these pathways to orchestrate effective host defense without excessive inflammatory injury.

C-reactive protein at the interface between innate immunity and inflammation

C-reactive protein (CRP), the prototypic acute-phase protein, increases rapidly in response to infection and inflammation. Although CRP was thought to be a passive, nonspecific marker of inflammation, recent studies indicate that CRP plays a key role in the innate immune system by recognizing pathogens and altered self determinants. Activation of complement and interaction with Fcgamma receptors by CRP provides a link between the innate and adaptive immune systems. Recent evidence suggests that CRP is a marker of atherosclerotic disease and may play a role in its induction. However, CRP has an anti-inflammatory role in autoimmune diseases, such as systemic lupus erythematosus. In this article, we review the biological mechanisms by which CRP exerts its effects on the immune system and discuss its role in infection, cardiovascular disease, malignancy and systemic lupus erythematosus.

Neuroimmune regulation in immunocompetence, acute illness, and healing

Adaptive immunocompetence is maintained by growth hormone (GH), prolactin (PRL), and vasopressin (VP). Innate or natural immunocompetence depends on cytokines, hormones (especially of the hypothalamus-pituitary-adrenal axis), and catecholamines. The acute phase response (APR, or acute febrile illness) is an emergency defense reaction whereby the adaptive, T cell-dependent, immune reactions are suppressed and the innate immune function is dramatically amplified. Infection and various forms of injury induce APR. Cytokines [interleukin (IL)-1beta, tumor necrosis factor-alpha, and IL-6] stimulate corticotropin-releasing hormone (CRH) and VP secretion and cause a "sympathetic outflow." Colony-stimulating factors activate leukocytes. CRH is a powerful activator of the pituitary adrenocortical axis and elevates glucocorticoid (GC) levels. Cytokines, GCs, and catecholamines play fundamental roles in the amplification of natural immune defense mechanisms. VP supports the APR at this stage. However, VP remains active and is elevated for a longer period than is CRH. VP, but not CRH, is elevated during chronic inflammatory diseases. VP controls adaptive immune function and stimulates adrenocorticotropic hormone (ACTH) and PRL secretion. PRL maintains the function of the thymus and of the T cell-dependent adaptive immune system. The ACTH-adrenal axis stimulates natural immunity and of suppressor/regulatory T cells, which suppress the adaptive immune system. VP also has a direct effect on lymphoid cells, the significance of which remains to be elucidated. It is suggested that VP regulates the process of recovery from acute illness.