C-reactive protein: structural biology and host defense function

Short-term and residential exposure to air pollution: Associations with inflammatory biomarker levels in adults living in northern France

INTRODUCTION

Air pollution has an impact on health, and low-grade inflammation might be one of the underlying mechanisms. The objective of the present study of adults from northern France was to assess the associations between short-term and residential exposure to air pollution and levels of various inflammatory biomarkers.

METHODS

The cross-sectional Enquête Littoral Souffle Air Biologie Environnement (ELISABET) study was conducted from 2011 to 2013 in the Lille and Dunkirk urban areas of northern France. Here, we evaluated the associations between PM₁₀, NO₂ and O₃ exposure (on the day of the blood sample collection and on the day before, and the mean annual residential level) and levels of the inflammatory biomarkers high-sensitivity C-reactive protein (hsCRP), interleukin (IL)-1β, IL-6, IL-8, IL-10, IL-17A, IL-22, and tumor necrosis factor α.

RESULTS

We assessed 3074 participants for the association with hsCRP and a subsample of 982 non-smokers from Lille for the association with plasma cytokine levels. A 10 μg/m³ increment in PM₁₀ and NO₂ levels on the day of sample collection and on the day before was associated with a higher hsCRP concentration (3.43% [0.68; 6.25] and 1.75% [-1.96; 5.61], respectively, whereas a 10 μg/m³ increment in O₃ was associated with lower hsCRP concentration (-1.2% [-3.95; 1.64]). The associations between mean annual exposure and the hsCRP level were not significant. Likewise, the associations between exposure and plasma cytokine levels were not statistically significant.

CONCLUSION

Short-term exposure to air pollution was associated with higher serum hsCRP levels in adult residents of two urban areas in northern France. Our results suggest that along with other factors, low-grade inflammation might explain the harmful effects of air pollution on health.

Pharmacokinetic study of the novel phosphocholine derivative 3-dibutylaminopropylphosphonic acid by LC-MS coupling

CRP is an important mediator of the inflammatory response. Pro-inflammatory CRP effects are mediated by pCRP* and mCRP, dissociation products of the native pCRP. The concentration of pCRP during inflammation may rise up to concentrations 1000-fold from baseline. By prevention of the conformational change from pCRP to pCRP*, pro-inflammatory immune responses can be inhibited and local tissue damage reduced. 3-(Dibutylamino)propylphosphonic acid (C10m) is a new substance that can suppress ischemic-reperfusion injury by targeting CRP in the complement cascade. It hampers dissociation of pCRP into its monomers, thus preventing exacerbation of tissue inflammation subsequent to reperfusion injury. In this study, the pharmacokinetics and metabolism of the new drug candidate C10m was investigated. A sensitive and selective method for detection of C10m and its metabolites from plasma and urine was developed with LC-MS and LC-MS/MS coupling. The LLOQ is at 0.1 µg mL^-1 and recovery at 87.4% ± 2.8%. Accuracy and precision were within 15% coefficient of variation and nominal concentrations, respectively. Concentration time profile after i.v. bolus injection of C10m was analyzed by LC-MS/MS. Bioavailability has shown to be below 30%. Most likely due to the compounds' very polar chemical properties, no phase-I or phase-II metabolism could be observed. Absence of phase-I metabolism was cross-checked by performing microsomal incubations. Our study revealed that C10m is rapidly eliminated via urine excretion and that half-times appear to be increased with coadministration of the target pCRP.

Complement in Tumourigenesis and the Response to Cancer Therapy

In recent years, our knowledge of the complement system beyond innate immunity has progressed significantly. A modern understanding is that the complement system has a multifaceted role in malignancy, impacting carcinogenesis, the acquisition of a metastatic phenotype and response to therapies. The ability of local immune cells to produce and respond to complement components has provided valuable insights into their regulation, and the subsequent remodeling of the tumour microenvironment. These novel discoveries have advanced our understanding of the immunosuppressive mechanisms supporting tumour growth and uncovered potential therapeutic targets. This review discusses the current understanding of complement in cancer, outlining both direct and immune cell-mediated roles. The role of complement in response to therapies such as chemotherapy, radiation and immunotherapy is also presented. While complement activities are largely context and cancer type-dependent, it is evident that promising therapeutic avenues have been identified, in particular in combination therapies.

C-Reactive Protein Triggers Cell Death in Ischemic Cells

C-reactive protein (CRP) is the best-known acute phase protein. In humans, almost every type of inflammation is accompanied by an increase of CRP concentration. Until recently, the only known physiological function of CRP was the marking of cells to initiate their phagocytosis. This triggers the classical complement pathway up to C4, which helps to eliminate pathogens and dead cells. However, vital cells with reduced energy supply are also marked, which is useful in the case of a classical external wound because an important substrate for pathogens is disposed of, but is counterproductive at internal wounds (e.g., heart attack or stroke). This mechanism negatively affects clinical outcomes since it is established that CRP levels correlate with the prognosis of these indications. Here, we summarize what we can learn from a clinical study in which CRP was adsorbed from the bloodstream by CRP-apheresis. Recently, it was shown that CRP can have a direct effect on blood pressure in rabbits. This is interesting in regard to patients with high inflammation, as they often become tachycardic and need catecholamines. These two physiological effects of CRP apparently also occur in COVID-19. Parts of the lung become ischemic due to intra-alveolar edema and hemorrhage and in parallel CRP increases dramatically, hence it is assumed that CRP is also involved in this ischemic condition. It is meanwhile considered that most of the damage in COVID-19 is caused by the immune system. The high amounts of CRP could have an additional influence on blood pressure in severe COVID-19.

The Multiple Faces of C-Reactive Protein-Physiological and Pathophysiological Implications in Cardiovascular Disease

C-reactive protein (CRP) is an intriguing protein which plays a variety of roles in either physiological or pathophysiological states. For years it has been regarded merely as a useful biomarker of infection, tissue injury and inflammation, and it was only in the early 80s that the modified isoforms (mCRP) of native CRP (nCRP) appeared. It soon became clear that the roles of native CRP should be clearly discriminated from those of the modified form and so the impacts of both isoforms were divided to a certain degree between physiological and pathophysiological states. For decades, CRP has been regarded only as a hallmark of inflammation; however, it has since been recognised as a significant predictor of future episodes of cardiovascular disease, independent of other risk factors. The existence of modified CRP isoforms and their possible relevance to various pathophysiological conditions, suggested over thirty years ago, has prompted the search for structural and functional dissimilarities between the pentameric nCRP and monomeric mCRP isoforms. New attempts to identify the possible relevance between the diversity of structures and their opposing functions have initiated a new era of research on C-reactive protein. This review discusses the biochemical aspects of CRP physiology, emphasizing the supposed relevance between the structural biology of CRP isoforms and their differentiated physiological and pathophysiological roles.

Impacts of event-specific air quality improvements on total hospital admissions and reduced systemic inflammation in COPD patients

There is limited evidence linking the impacts of reduced air pollution on hospital admissions. The potential biological mechanisms are still not completely understood. This study examined the effects of mitigated ambient pollution on hospital admissions and inflammatory biomarker levels in chronic obstructive pulmonary disease (COPD) COPD patients. Daily hospital admissions were compared over 51 days associated with the Asian Games period (Nov 1-Dec 21, 2010) with the identical calendar dates of baseline years (2004–2009 and 2011–2013). A three-year cohort study was conducted with 36 COPD patient participants. The daily particulate matter (PM₁₀) decreased from 65.86 μg/m³ during the baseline period to 62.63 μg/m³ during the Asian Games period; the daily NO₂ level decreased from 51.33 μg/m³ to 42.63 μg/m³. Between the baseline period and the Asian Games, daily hospital admissions from non-accidental diseases decreased from 116 to 93, respectively; respiratory diseases decreased from 20 to 17, respectively; and cardiovascular diseases decreased from 11 to 9 during the Asian Games period, respectively. No statistically significant reductions were seen in the remaining months of 2010 in Guangzhou, during the the Asian Games period in the control city, and two other control diseases. Furthermore, we identified significant improvement in CRP and fibrinogen by -20.4% and -15.4% from a pre-Asian game period to a during-Asian game period, respectively. For CRP, we found significant increases in NO₂ at lag1-3 days after-Asian game period and significant increases in PM₁₀ at lag1-2 days. Similar effects were also seen with fibrinogen. This discovery provides support for efforts to diminish air pollution and improve public health through human air pollutants intervention. Improved air pollution during the 2010 Asian games was correlated with decreases in biomarkers associated with systemic inflammation in COPD patient participants.

Peptidylarginine deiminase and deiminated proteins are detected throughout early halibut ontogeny - Complement components C3 and C4 are post-translationally deiminated in halibut (Hippoglossus hippoglossus L.)

Post-translational protein deimination is mediated by peptidylarginine deiminases (PADs), which are calcium dependent enzymes conserved throughout phylogeny with physiological and pathophysiological roles. Protein deimination occurs via the conversion of protein arginine into citrulline, leading to structural and functional changes in target proteins. In a continuous series of early halibut development from 37 to 1050° d, PAD, total deiminated proteins and deiminated histone H3 showed variation in temporal and spatial detection in various organs including yolksac, muscle, skin, liver, brain, eye, spinal cord, chondrocytes, heart, intestines, kidney and pancreas throughout early ontogeny. For the first time in any species, deimination of complement components C3 and C4 is shown in halibut serum, indicating a novel mechanism of complement regulation in immune responses and homeostasis. Proteomic analysis of deiminated target proteins in halibut serum further identified complement components C5, C7, C8 C9 and C1 inhibitor, as well as various other immunogenic, metabolic, cytoskeletal and nuclear proteins. Post-translational deimination may facilitate protein moonlighting, an evolutionary conserved phenomenon, allowing one polypeptide chain to carry out various functions to meet functional requirements for diverse roles in immune defences and tissue remodelling.

Factors Predicting Bacterial Infection in Out-of-Hospital Cardiac Arrest Patients Undergoing Targeted Temperature Management

The objective of this study was to determine a risk factor for predicting bacterial infection in patients, who survived out-of-hospital cardiac arrest (OHCA), during targeted temperature management (TTM). This prospective registry-based retrospective observational study was conducted from November 2010 to October 2017. We measured several biomarkers such as whole blood cell counts, and levels of C-reactive protein and procalcitonin daily during TTM. The primary outcome was bacterial growth in initial blood or sputum cultures. A total of 116 patients were analyzed in this study. The bacterial growth rate was 32.8% and the procalcitonin levels measured at 24 h from cardiac arrest was significantly higher in the culture-positive group than the culture-negative group (10.6 vs. 2.5 ng/mL, p = 0.017). Area under the receiver operating characteristic curve for procalcitonin obtained after 24 h was 0.727 and the cutoff value was 6.5 ng/mL (odds ratio 9.58 [95% confidential interval, CI 2.21-41.55], p = 0.003). Sensitivity was 71.4% [95% CI 41.9-91.6] and specificity was 79.3% [95% CI 60.3-92.0]. Procalcitonin measured at 24 h from cardiac arrest was associated with bacterial infection in OHCA patients undergoing TTM. Further prospective interventional studies are needed to validate these results.

C-reactive protein (CRP) but not the related pentraxins serum amyloid P and PTX3 inhibits the proliferation and induces apoptosis of the leukemia cell line Mono Mac 6

Background

Pentraxins are a family of highly conserved secreted proteins that regulate the innate immune system, including monocytes and macrophages. C-reactive protein (CRP) is a plasma protein whose levels can rise to 1000 μg/ml from the normal <3 μg/ ml during inflammation.

Results

We find that CRP inhibits proliferation of the human myeloid leukemia cell line Mono Mac 6 with an IC50 of 75 μg/ ml by inducing apoptosis of these cells. The related proteins serum amyloid P (SAP) and pentraxin 3 (PTX3) do not inhibit Mono Mac 6 proliferation. CRP has no significant effect on the proliferation of other leukemia cell lines such as HL-60, Mono Mac 1, K562, U937, or THP-1, or the survival of normal peripheral blood cells. The effect of CRP appears to be dependent on the CRP receptor FcγRI, and is negatively regulated by a phosphatidylinositol −3-kinase pathway.

Conclusion

These data reveal differential signaling by pentraxins on immune cells, and suggest that CRP can regulate the proliferation of some myeloid leukemia cells.

Overview of Laboratory Testing and Clinical Presentations of Complement Deficiencies and Dysregulation

Historically, complement disorders have been attributed to immunodeficiency associated with severe or frequent infection. More recently, however, complement has been recognized for its role in inflammation, autoimmune disorders, and vision loss. This paradigm shift requires a fundamental change in how complement testing is performed and interpreted. Here, we provide an overview of the complement pathways and summarize recent literature related to hereditary and acquired angioedema, infectious diseases, autoimmunity, and age-related macular degeneration. The impact of complement dysregulation in atypical hemolytic uremic syndrome, paroxysmal nocturnal hemoglobinuria, and C3 glomerulopathies is also described. The advent of therapeutics such as eculizumab and other complement inhibitors has driven the need to more fully understand complement to facilitate diagnosis and monitoring. In this report, we review analytical methods and discuss challenges for the clinical laboratory in measuring this complex biochemical system.

Early second-trimester plasma protein profiling using multiplexed isobaric tandem mass tag (TMT) labeling predicts gestational diabetes mellitus

AIMS

Gestational diabetes mellitus (GDM) is associated with an increased risk of serious complications for mother and child during pregnancy. The main option for diagnosis of GDM is 75 g oral glucose tolerance test (OGTT) at 24-28 gestation weeks, when harms to both mother and child have already potentially occurred. The aim of this study was to investigate new biomarkers for earlier detection and assessment of GDM at early second trimester (16-18 gestation weeks).

METHODS

We systematically used multiplexed isobaric tandem mass tag labeling combined with liquid chromatography mass spectrometry (LC-MS/MS) to screen differentially expressed proteins in plasma collected at 16-18 gestational weeks between pregnant women with and without GDM outcome.

RESULTS

A total of 828 proteins were identified, of which 36 proteins implicated in immune response, inflammation, transport, platelet aggregation, catalyze and defense response were identified as differentially regulated proteins in GDM. To assess the validity of the results, four selected proteins including C-reactive protein, sex hormone-binding globulin, Ficolin 3 and pregnancy-specific beta-1-glycoprotein 4 were selected for subsequent Western blot analysis.

CONCLUSIONS

This is the first comprehensive study that integrates multiple state-of-the-art proteomic technologies to discover the earlier potential plasma biomarkers for GDM.

Complement activation, regulation, and molecular basis for complement-related diseases

The complement system is an essential element of the innate immune response that becomes activated upon recognition of molecular patterns associated with microorganisms, abnormal host cells, and modified molecules in the extracellular environment. The resulting proteolytic cascade tags the complement activator for elimination and elicits a pro-inflammatory response leading to recruitment and activation of immune cells from both the innate and adaptive branches of the immune system. Through these activities, complement functions in the first line of defense against pathogens but also contributes significantly to the maintenance of homeostasis and prevention of autoimmunity. Activation of complement and the subsequent biological responses occur primarily in the extracellular environment. However, recent studies have demonstrated autocrine signaling by complement activation in intracellular vesicles, while the presence of a cytoplasmic receptor serves to detect complement-opsonized intracellular pathogens. Furthermore, breakthroughs in both functional and structural studies now make it possible to describe many of the intricate molecular mechanisms underlying complement activation and the subsequent downstream events, as well as its cross talk with, for example, signaling pathways, the coagulation system, and adaptive immunity. We present an integrated and updated view of complement based on structural and functional data and describe the new roles attributed to complement. Finally, we discuss how the structural and mechanistic understanding of the complement system rationalizes the genetic defects conferring uncontrolled activation or other undesirable effects of complement.

Crystal structures for short-chain pentraxin from zebrafish demonstrate a cyclic trimer with new recognition and effector faces

Short-chain pentraxins (PTXs), including CRP and SAP, are innate pattern recognition receptors that play vital roles in the recognition and elimination of various pathogenic bacteria by triggering the classical complement pathway through C1q. Similar to antibodies, pentraxins can also activate opsonisation and phagocytosis by interacting with Fc receptors (FcRs). Various structural studies on human PTXs have been performed, but there are no reports about the crystal structure of bony fish pentraxins. Here, the crystal structures of zebrafish PTX (Dare-PTX-Ca and Dare-PTX) are presented. Both Dare-PTX-Ca and Dare-PTX are cyclic trimers, which are new forms of crystallised pentraxins. The structures reveal that the ligand-binding pocket (LBP) in the recognition face of Dare-PTX is deep and narrow. Homology modelling shows that LBPs from different Dare-PTX loci differ in shape, reflecting their specific recognition abilities. Furthermore, in comparison with the structure of hCPR, a new C1q binding mode was identified in Dare-PTX. In addition, the FcR-binding sites of hSAP are partially conserved in Dare-PTX. These results will shed light on the understanding of a primitive PTX in bony fish, which evolved approximately 450 million years ago.

C-reactive protein and lung diseases

C-reactive protein (CRP), a member of the pentraxin family of plasma proteins, is one of the most distinctive acute phase reactants. In response to inflammation, cell damage or tissue injury, plasma level of CRP rapidly and dramatically increases up to 1000-fold, a phenomenon that has been used for years to monitor infections and many destructive/inflammatory conditions. The magnitude of CRP increase usually correlates with the severity of injury or inflammation and reflects an important physiological role of this interesting but still under-investigated protein. It is now generally accepted that CRP is involved in host defense and inflammation. However, the exact function of this protein in health and disease remains unclear. Many studies have demonstrated that in different pathophysiological conditions CRP might be involved in the regulation of lung function and may participate in the pathogenesis of various pulmonary disorders. The fluctuation of CRP concentrations in both alveolar fluid and serum associated with different pulmonary diseases suggests its important role in lung biology. Discussion of the still controversial functions of CRP in lung physiology and diseases is the main focus of this review.

Pentraxins in nephrology: C-reactive protein, serum amyloid P and pentraxin-3

Every clinician uses C-reactive protein (CRP) levels as a biomarker for systemic inflammation in acute disorders. Nephrologists also consider CRP levels as a predictor for overall mortality in patients with chronic kidney disease or end-stage renal disease. But what is the biological function of CRP? CRP is a member of the family of pentraxins, which are small pentameric innate immunity effector proteins. Pentraxins are absent or weakly expressed during homeostasis. However, the pro-inflammatory cytokines interleukin (IL)-1, IL-6 and tumour necrosis factor induce CRP and serum amyloid P (SAP) in hepatocytes, whereas the long pentraxins, such as pentraxin (PTX)-3, are produced in peripheral tissues and monocytic phagocytes. Pentraxins opsonize pathogens or other particles such as dead cells, for their phagocytic clearance or induce pathogen killing in extracellular compartments. In this review, we discuss the immunoregulatory properties of the different members of the pentraxin family. We discuss the evolving evidence demonstrating their roles in acute and chronic forms of kidney disease and the significance of SAP and PTX3 as additional biomarkers of innate immune activation and systemic inflammation.

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.

Molecular characterization and expression analysis of two new C-reactive protein genes from common carp (Cyprinus carpio)

C-Reactive protein (CRP) plays an important role in the acute phase response. Transcripts encoding two new CRP-like molecules (ccCRP1 and ccCRP2) from European common carp have been characterized which has enabled seven CRP-like genes to be identified in zebrafish. 79.3% (ccCRP1) and 74.5% (ccCRP2) identity to CRP from East-Asian common carp occurs and fish CRP genes form a distinct clade. ccCRP2 gene organization comprises four exons and three introns, in contrast to the two exons/one intron organization of mammalian CRP genes. Gene expression assays showed both ccCRP-like molecules are constitutively expressed in liver, skin, gill, gut, muscle, kidney, spleen and blood. Protein levels of ccCRP in serum and spleen were significantly different from other organs analyzed, and levels were greatest in the liver. It is proposed that the two carp CRP genes defined differ in their expression profiles which may suggest differences in their biological activities.

Infections and inflammatory diseases as risk factors for venous thrombosis. A systematic review

Inflammation and venous thrombosis are intertwined. Only in the recent 15 years clinical epidemiological studies have focussed on inflammatory or infectious diseases as risk factors for venous thrombosis. Although a few reviews and many case reports or studies on these topic has been written, a review reporting relative or absolute risks for venous thrombosis has not been published yet. We performed a systematic review using Medline, Pubmed and Embase and found 31 eligible articles. Inflammatory bowel disease, ANCA-associated vasculitis, infections in general and more specifically, human immunodeficiency virus, pneumonia and urinary tract infections are associated with an increased risk of venous thrombosis.

The human c1q globular domain: structure and recognition of non-immune self ligands

C1q, the ligand-binding unit of the C1 complex of complement, is a pattern recognition molecule with the unique ability to sense an amazing variety of targets, including a number of altered structures from self, such as apoptotic cells. The three-dimensional structure of its C-terminal globular domain, responsible for its recognition function, has been solved by X-ray crystallography, revealing a tightly packed heterotrimeric assembly with marked differences in the surface patterns of the subunits, and yielding insights into its versatile binding properties. In conjunction with other approaches, this same technique has been used recently to decipher the mechanisms that allow this domain to interact with various non-immune self ligands, including molecules known to provide eat-me signals on apoptotic cells, such as phosphatidylserine and DNA. These investigations provide evidence for a common binding area for these ligands located in subunit C of the C1q globular domain, and suggest that ligand recognition through this area down-regulates C1 activation, hence contributing to the control of the inflammatory reaction. The purpose of this article is to give an overview of these advances which represent a first step toward understanding the recognition mechanisms of C1q and their biological implications.

Pentraxin 3 in maternal circulation: an association with preterm labor and preterm PROM, but not with intra-amniotic infection/inflammation

OBJECTIVE

Pentraxin 3 (PTX3) is an acute-phase protein that has an important role in the regulation of the innate immune response. The aim of this study was to determine if maternal plasma PTX3 concentration changes in the presence of intra-amniotic infection and/or inflammation (IAI) in women with preterm labor (PTL) and intact membranes, as well as those with preterm prelabor rupture of membranes (preterm PROM).

STUDY DESIGN

This cross-sectional study included women in the following groups: (1) nonpregnant (n=40); (2) uncomplicated pregnancies in the first (n=22), second (n=22) or third trimester (n=71, including 50 women at term not in labor); (3) uncomplicated pregnancies at term with spontaneous labor (n=49); (4) PTL and intact membranes who delivered at term (n=49); (5) PTL without IAI who delivered preterm (n=26); (6) PTL with IAI (n=65); (7) preterm PROM without IAI (n=25); and (8) preterm PROM with IAI (n=77). Maternal plasma PTX3 concentrations were determined by ELISA.

RESULTS

(1) Maternal plasma PTX3 concentrations increased with advancing gestational age (r=0.62, p<0.001); (2) women at term with spontaneous labor had a higher median plasma PTX3 concentration than those at term not in labor (8.29 ng/ml vs. 5.98  ng/ml, p=0.013); (3) patients with an episode of PTL, regardless of the presence or absence of IAI and whether these patients delivered preterm or at term had a higher median plasma PTX3 concentration than normal pregnant women (p<0.001 for all comparisons); (4) similarly, patients with preterm PROM, with or without IAI had a higher median plasma PTX3 concentration than normal pregnant women (p<0.001 for both comparisons); and (5) among patients with PTL and those with preterm PROM, IAI was not associated with significant changes in the median maternal plasma PTX3 concentrations.

CONCLUSIONS

The maternal plasma PTX3 concentration increases with advancing gestational age and is significantly elevated during labor at term and in the presence of spontaneous preterm labor or preterm PROM. These findings could not be explained by the presence of IAI, suggesting that the increased PTX3 concentration is part of the physiologic or pathologic activation of the pro-inflammatory response in the maternal circulation during the process of labor at term or preterm.

C-reactive protein and venous thromboembolism: causal or casual association?

The plasma concentration of C-reactive protein (CRP), the first acute-phase protein to be identified, increases dramatically following tissue injury or inflammation. Although the physiological role of CRP is still not fully known, it has been suggested that concentrations might increase as part of the acute-phase response for facilitating non-specific immune functions, defense against bacterial pathogens, clearance of apoptotic and necrotic cells to prevent immunization against autoantigens and acceleration of the repair process. In agreement with the evidence that inflammation plays a pivotal role in the pathogenesis of atherosclerosis, CRP concentrations have been associated with cardiovascular disease, and measurement of CRP has therefore been proposed as a valuable aid to predict and stratify the risk of myocardial infarction and stroke. Recently, some clinical and biological evidence in support of the hypothesis that CRP might be also involved in the onset of venous thrombosis have emerged. Native and monomeric CRP exert several prothrombotic activities, including activation of blood coagulation, impairment of the endogenous fibrinolytic capacity, and stimulation or enhancement of platelet adhesiveness and responsiveness. Epidemiological investigations have also shown that CRP concentrations are associated with increased risk of venous thromboembolism and, even more interestingly, that statins might be effective in reducing the risk of this pathology. Although there is increasing emphasis that CRP might not only be a marker but also an active player in the development of venous thrombosis, further evidence is needed to establish which event comes first--thrombosis or inflammation.

Cutting edge: C1q binds deoxyribose and heparan sulfate through neighboring sites of its recognition domain

C1q, the recognition subunit of the C1 complex of complement, is an archetypal pattern recognition molecule with the striking ability to sense a wide variety of targets, including a number of altered self-motifs. The recognition properties of its globular domain were further deciphered by means of x-ray crystallography using deoxy-D-ribose and heparan sulfate as ligands. Highly specific recognition of deoxy-D-ribose, involving interactions with Arg C98, Arg C111, and Asn C113, was observed at 1.2 A resolution. Heparin-derived tetrasaccharide interacted more loosely through Lys C129, Tyr C155, and Trp C190. These data together with previous findings define a unique binding area exhibiting both polyanion and deoxy-D-ribose recognition properties, located on the inner face of C1q. DNA and heparin compete for C1q binding but are poor C1 activators compared with immune complexes. How the location of this binding area in C1q may regulate the level of C1 activation is discussed.

Pentraxin 3 in amniotic fluid: a novel association with intra-amniotic infection and inflammation

OBJECTIVE

Pentraxin 3 (PTX3) is a soluble pattern recognition receptor (PRR) that has an important role in immunoregulation and vascular integrity. The aim of this study was to determine if PTX3 is present in amniotic fluid (AF) and whether its concentration changes with gestational age (GA), in the presence of preterm or term labor, and in cases of intra-amniotic infection/inflammation (IAI) associated with spontaneous preterm labor (PTL) or preterm prelabor rupture of membranes (PROM).

STUDY DESIGN

This cross-sectional study included the following groups: 1) mid-trimester (n=45); 2) uncomplicated pregnancies at term with (n=48) and without (n=40) spontaneous labor; 3) women with PTL and intact membranes who: a) delivered at term (n=44); b) delivered preterm without IAI (n=40); or c) delivered preterm with IAI (n=62); 4) women with preterm PROM with (n=63) and without (n=36) IAI. PTX3 concentration in AF was determined by ELISA. Non-parametric statistics were used for analyses.

RESULTS

1) Among women with PTL and intact membranes, the median AF PTX3 concentration was significantly higher in women with IAI than in those without IAI (7.95 ng/mL vs. 0.38 ng/mL; P<0.001) and than in those who delivered at term (0.55 ng/mL; P<0.001); 2) women with preterm PROM and IAI had a higher median AF PTX3 concentration than those without IAI (9.12 ng/mL vs. 0.76 ng/mL; P<0.001); 3) the median AF PTX3 concentration did not change with GA (mid-trimester: 0.79 ng/mL vs. term not in labor: 0.58 ng/mL; P=0.09); and 4) labor at term was not associated with a significant change of AF PTX 3 concentration (in labor: 0.54 ng/mL vs. not in labor: 0.58 ng/mL, P=0.9).

CONCLUSIONS

PTX3 is a physiologic constituent of the AF, and its median concentration is elevated in the presence of IAI, suggesting that PTX3 may play a role in the innate immune response against IAI.

Evaluation of a quick test for C‐reactive protein in a pediatric emergency department

OBJECTIVE

C-reactive protein (CRP) is a reliable laboratory test that is useful in distinguishing between viral and bacterial infection. Although widely used, blood sampling and the need for a well-organized laboratory are limiting factors. Recently, a rapid test for serum CRP (QuickRead CRP) has been developed that can use both venous and capillary blood. The aim of this study was to use QuickRead CRP in our Pediatric Emergency Department and to compare this method with the standard laboratory determination (CRP-lab).

MATERIAL AND METHODS

All children with fever were given a quick CRP test simultaneously with venous (CRP-V) and capillary blood samples (CRP-C). A total of 127 children were included in the study (median age 2.5 years).

RESULTS

The QuickRead CRP test had an excellent correlation with the standard biochemical determination (CRP-lab). More importantly, there was no difference in determination of CRP in the venous and capillary blood samples. Finally, there was no significant intra-assay variability.

CONCLUSIONS

The QuickRead CRP test is easy to use, provides reliable results and reduces the need for antibacterial therapy.

Pentraxins in innate immunity: from C-reactive protein to the long pentraxin PTX3

Pentraxins are a family of multimeric pattern-recognition proteins highly conserved in evolution. Based on the primary structure of the subunit, the pentraxins are divided into two groups: short pentraxins and long pentraxins. C-reactive protein and serum amyloid P-component are classic short pentraxins produced in the liver, whereas the prototype of the long pentraxin family is PTX3. Innate immunity cells and vascular cells produce PTX3 in response to proinflammatory signals and Toll-like receptor engagement. PTX3 interacts with several ligands, including growth factors, extracellular matrix components, and selected pathogens, playing a role in complement activation, facilitating pathogen recognition, and acting as a predecessor of antibodies. In addition, PTX3 is essential in female fertility acting on the assembly of the cumulus oophorus extracellular matrix. Thus, PTX3 is a multifunctional soluble pattern recognition receptor acting as a nonredundant component of the humoral arm of innate immunity and involved in tuning inflammation, in matrix deposition and female fertility. Evidence suggests that PTX3 is a useful new serological marker, rapidly reflecting tissue inflammation and damage under diverse clinical conditions.

The humoral pattern recognition receptor PTX3 is stored in neutrophil granules and localizes in extracellular traps

The long pentraxin (PTX) 3 is produced by macrophages and myeloid dendritic cells in response to Toll-like receptor agonists and represents a nonredundant component of humoral innate immunity against selected pathogens. We report that, unexpectedly, PTX3 is stored in specific granules and undergoes release in response to microbial recognition and inflammatory signals. Released PTX3 can partially localize in neutrophil extracellular traps formed by extruded DNA. Eosinophils and basophils do not contain preformed PTX3. PTX3-deficient neutrophils have defective microbial recognition and phagocytosis, and PTX3 is nonredundant for neutrophil-mediated resistance against Aspergillus fumigatus. Thus, neutrophils serve as a reservoir, ready for rapid release, of the long PTX3, a key component of humoral innate immunity with opsonic activity.

Polymorphism of the C-reactive protein gene is associated with mortality in bacteraemia

C-reactive protein (CRP) is an important molecule in the defence against bacterial infections. To discover if variation in the CRP gene is associated with clinical outcome of bacteraemia, we investigated 147 microbiologically verified bacteraemia patients (mean age 59 y, range 19-93 y) and determined whether CRP -717A>G, +1059G>C or +1444C>T single nucleotide polymorphisms (SNPs) were associated with clinical outcome of bacteraemia and/or CRP concentration caused by Staphylococcus aureus, Streptococcus pneumoniae, beta-haemolytic streptococci or Escherichia coli. The patients were genotyped for CRP gene polymorphisms, CRP was measured and clinical outcomes were recorded. The CRP -717A>G, a promoter region polymorphism was strongly associated with mortality from Streptococcus pneumoniae but did not correlate with plasma CRP concentration. These results suggest that mortality from Streptococcus pneumoniae may be associated with polymorphism of the promoter region of the CRP gene.

The long pentraxin PTX3 in vascular pathology

Pentraxins are a family of evolutionarily conserved multifunctional pattern-recognition proteins characterized by a cyclic multimeric structure. Based on the primary structure of the subunit, the pentraxins are divided into two groups: short pentraxins and long pentraxins. C-reactive protein (CRP) and serum amyloid P-component (SAP) are the two short pentraxins. The prototype protein of the long pentraxin group is pentraxin 3 (PTX3). CRP and SAP are produced primarily in the liver in response to IL-6, while PTX3 is produced by a variety of tissues and cells and in particular by innate immunity cells in response to proinflammatory signals and Toll-like receptor (TLR) engagement. PTX3 interacts with several ligands, including growth factors, extracellular matrix components and selected pathogens, playing a role in complement activation and facilitating pathogen recognition by phagocytes, acting as a predecessor of antibodies. In addition, PTX3 is essential in female fertility by acting as a nodal point for the assembly of the cumulus oophorus hyaluronan-rich extracellular matrix. Thus, the prototypic long pentraxin PTX3 is a multifunctional soluble pattern recognition receptor acting as a non-redundant component of the humoral arm of innate immunity and involved in tuning inflammation, in matrix deposition and female fertility.

Mass spectrometric quantitation of C-reactive protein using labeled tryptic peptides

Given the extensive efforts applied toward proteomics and research in biomarkers, methods for the simultaneous measurement of proteins, peptides, metabolic intermediates, hormones, etc. in a complex sample may be required in the foreseeable future. Assays based on mass spectrometric detection may be suitable for meeting the demands of such complex samples with sensitivity and specificity. An analytical method for the quantitation of C-reactive protein (CRP), a well-known marker of inflammation, is described. Exact quantities of two synthetic (13)C-labeled CRP tryptic peptides were added as internal standards directly to the sample prior to chemical treatment, trypsinization, and liquid chromatography/mass spectrometry quantitation. C-reactive protein levels based on isotopic response ratios were measured. Intact C-reactive protein was spiked into blank rat urine for chemical and enzymatic treatment, producing linear response ratios of labeled to unlabeled peptides. For rigorous quantitation, standard curves, and quality control samples were prepared in rat urine with highly purified labeled and unlabeled peptides over the 50 pg-5 ng/muL concentration range. Using the same chemical and enzymatic treatment used for digestion of intact CRP, data from these samples demonstrated excellent analytical performance. The method was successfully applied toward the quantitation of urinary C-reactive protein from a study of drug-induced nephrotoxicity.

High-sensitivity C-reactive protein as cardiovascular risk marker in patients with diabetes mellitus

C-reactive protein (CRP) is a liver-derived pattern recognition molecule that is increased in inflammatory states. It rapidly increases within hours after tissue injury, and it is suggested that it is part of the innate immune system and contributes to host defense. Since cardiovascular disease is at least in part an inflammatory process, CRP has been investigated in the context of arteriosclerosis and subsequent vascular disorders. Based on multiple epidemiological and intervention studies, minor CRP elevation [high-sensitivity CRP (hsCRP)] has been shown to be associated with future major cardiovascular risk (hsCRP:<1 mg/L=low risk; 1-3 mg/L=intermediate risk; 3-10 mg/L=high risk; >10 mg/L=unspecific elevation). It is recommended by the American Heart Association that patients at intermediate or high risk of coronary heart disease may benefit from measurement of hsCRP with regard to their individual risk prediction. Elevation of hsCRP is associated with increased risk of type 2 diabetes development in patients with all levels of metabolic syndrome. In type 1 and type 2 diabetes mellitus, hemoglobin A1c significantly correlates with hsCRP levels and future cardiovascular risk. Also, hsCRP levels increase with the stage of beta-cell dysfunction and insulin resistance. Non-diabetes drugs that have been shown to reduce hsCRP concentrations include aspirin, statins, cyclooxygenase-2 inhibitors, and fibrates. Recent intervention studies have also demonstrated the distinct efficacy of different anti-diabetes treatments on a variety of cardiovascular risk markers. Intensive insulin therapy may reduce inflammation, but this effect may be influenced by the degree of weight gain. Treatment with peroxisome proliferator-activated receptor gamma has lead to substantial reduction of hsCRP and other cardiovascular risk markers in several comparator studies. Since this effect was shown to be independent of the degree of glycemic improvement, it can be regarded as a classspecific effect. Whether these findings translate into a reduction of overall cardiovascular mortality will soon be shown by the currently running thiazolidinedione outcome studies. Positive results in these trials will further strengthen the value and acceptance of hsCRP, which is recommended as a predictive laboratory marker for cardiovascular disease risk also in patients with diabetes mellitus.

Pentraxins at the crossroads between innate immunity, inflammation, matrix deposition, and female fertility

C reactive protein, the first innate immunity receptor identified, and serum amyloid P component are classic short pentraxins produced in the liver. Long pentraxins, including the prototype PTX3, are expressed in a variety of tissues. Some long pentraxins are expressed in the brain and some are involved in neuronal plasticity and degeneration. PTX3 is produced by a variety of cells and tissues, most notably dendritic cells and macrophages, in response to Toll-like receptor (TLR) engagement and inflammatory cytokines. PTX3 acts as a functional ancestor of antibodies, recognizing microbes, activating complement, and facilitating pathogen recognition by phagocytes, hence playing a nonredundant role in resistance against selected pathogens. In addition, PTX3 is essential in female fertility because it acts as a nodal point for the assembly of the cumulus oophorus hyaluronan-rich extracellular matrix. Thus, the prototypic long pentraxin PTX3 is a multifunctional soluble pattern recognition receptor at the crossroads between innate immunity, inflammation, matrix deposition, and female fertility.

Complexity and complementarity of outer membrane protein A recognition by cellular and humoral innate immunity receptors

Outer membrane protein A (OmpA) is a conserved major component of the outer membrane of Enterobacteriaceae. Here, we report that OmpA from Klebsiella pneumoniae (KpOmpA) activates macrophages and dendritic cells (DCs) in a TLR2-dependent way. However, TLR2 does not account for binding of KpOmpA to innate immune cells. KpOmpA binds the scavenger receptors (SRs) LOX-1 and SREC-I, but not other members of the same family. LOX-1 colocalizes and cooperates with TLR2 in triggering cellular responses. The TLR2-activated functional program includes production of the long pentraxin PTX3, a soluble pattern recognition receptor involved in resistance against diverse pathogens. PTX3, in turn, binds KpOmpA but does not affect recognition of this microbial moiety by cellular receptors. KpOmpA-elicited in vivo inflammation is abrogated in TLR2(-/-) mice and significantly reduced in PTX3(-/-) mice. Thus, SR-mediated KpOmpA recognition and TLR2-dependent cellular activation set in motion a nonredundant PTX3-mediated humoral amplification loop of innate immunity.

C-reactive protein and end-stage renal disease

The significance of CRP and inflammation has increased over time, especially in the end-stage renal disease (ESRD) population. From a simple marker it now appears that CRP is an active participant in pro-atherosclerotic phenomenon including local pro-inflammatory and thrombotic events. Studies in the general population indicate the usefulness of CRP in prognostication and in monitoring response to therapy. The clinical usefulness of CRP monitoring in chronic kidney disease (CKD) and especially in ESRD deserves closer study. In the meantime, the utility of CRP measurements for monitoring and treatment is on a case-by-case basis. Management of traditional cardiovascular risk factors should be considered. In the interest of optimizing therapy it is prudent to use biocompatible membranes and ultrapure water. A careful search for infectious processes in dialysis patients is recommended, with special attention to vascular access sites, periodontitis, gastritis, and other potentially chronic or covert infections. ACE-inhibitor use should be maximized in all eligible CKD patients. The data on the use of statins in ESRD have been generally positive but await further validation. Individualized use for selected patients is probably beneficial.

Measurement of C-reactive protein: two high sensitivity methods compared

C-reactive protein (CRP) is an acute phase marker and a predictor of the risk of developing atherosclerotic complications. However, as a predictor of this risk, high sensitivity measurements are needed, and high sensitive CRP (hsCRP) assays have been developed. In this study, we experimentally compared two hsCRP assays, based on nephelometry and turbidimetry, both implemented on automated analyzers. Linearity, imprecision, turbidity interference, and results in the assay of 96 samples have been compared. Method comparison of the same two analytical systems in the assay of CRP was also performed on the basis of results in an interlaboratory external quality assessment scheme (EQAS). The two systems were found to perform substantially equally, both in hsCRP and in CRP measurement, but in the hsCRP assay the precision of nephelometry (CV% in the interval 3.0-5.8) was lower than that of turbidimetry (CV% in the interval 1.8-2.3). The classification of results by the two methods into three predefined relative risk classes gave 18% rate of discordance, in any case by one class only. The two methods proved reliable and comparable in the measurement of hsCRP, but precision should be improved.

Assessment of Acute Phase Proteins in Acute Ischemic Stroke

Acute phase proteins (APPs) have been implicated to play important roles during both acute and chronic inflammatory processes in different diseases including ischemic stroke. Though there are several studies showing the importance of APPs as inflammation markers in acute ischemic stroke (AIS), the time course of these proteins during acute phase of AIS is not well known. Thus, the aim of this study was to show the changes in plasma levels of six APPs (i.e., haptoglobin [Hp], ceruloplasmin [Cp], high-sensitive C-reactive protein [h-CRP], fibrinogen, complement 3 [C3] and complement 4 [C4]) during the first 10 days after acute stroke. The study group consisted of 34 female and 19 male patients (n = 53; mean age 65 +/- 12 years), who had first acute ischemic stroke (AIS). An age-matched control group (n = 53; 32 female and 21 male subjects, mean age 62 +/- 6 years) was also included. To evaluate the plasma levels of six APPs, the blood samples of patients with AIS were withdrawn on admission (day 1), and after 3, 5 and 10 days, whereas only one measurement was performed in the control group. In addition, several cerebrovascular risk factors were determined. The peak levels of APPs were higher in the AIS group than the control group (p < 0.0001). In serial measurements, the levels of h-CRP, Hp, C3 and C4 showed alterations during 10 days after AIS (p < 0.0001, p < 0.05, p < 0.0001, p < 0.0001, respectively). The alterations in levels of fibrinogen and Cp were not statistically significant (p > 0.05). After stroke, h-CRP, C3 and fibrinogen reached their highest values on the third day, Cp and C4 on the fifth day, and Hp on the tenth day. The plasma levels of h-CRP correlated positively with other five APPs studied (p < 0.05). These findings support the importance of inflammation processes after stroke. We suggest that the differences in levels of APPs could be used in predicting the outcome of stroke patients.

C-reactive protein as a risk factor versus risk marker

PURPOSE OF REVIEW

C-reactive protein (CRP) is consistently associated with cardiovascular disease in prospective and cross-sectional clinical and epidemiological studies. Inflammation is an important mechanism in cardiovascular disease, and the plasma level of CRP is considered to reflect the inflammatory condition of the patient and/or the vessel wall. In addition, there are also a number of indications for a causal role of CRP in cardiovascular disease.

RECENT FINDINGS

A number of new publications show potential causal effects of CRP on cardiovascular disease, and evidence from human-CRP transgenic animals also indicates a causal contribution of CRP to cardiovascular disease. On the other hand, a new large prospective study and an updated meta-analysis indicate that the contribution of CRP to cardiovascular disease is less impressive than reported earlier (odds ratio, 1.58; 95% confidence interval, 1.48-1.68).

SUMMARY

We review here the most recent evidence on mechanisms by which CRP is involved as a causal factor in the precipitation of cardiovascular disease. Evidence for such a role is accumulating.

C-reactive Protein

C-reactive protein (CRP) is a phylogenetically highly conserved plasma protein, with homologs in vertebrates and many invertebrates, that participates in the systemic response to inflammation. Its plasma concentration increases during inflammatory states, a characteristic that has long been employed for clinical purposes. CRP is a pattern recognition molecule, binding to specific molecular configurations that are typically exposed during cell death or found on the surfaces of pathogens. Its rapid increase in synthesis within hours after tissue injury or infection suggests that it contributes to host defense and that it is part of the innate immune response. Recently, an association between minor CRP elevation and future major cardiovascular events has been recognized, leading to the recommendation by the Centers for Disease Control and the American Heart Association that patients at intermediate risk of coronary heart disease might benefit from measurement of CRP. This review will largely focus on our current understanding of the structure of CRP, its ligands, the effector molecules with which it interacts, and its apparent functions.

Thermodynamic, conformational and functional properties of the human C1q globular heads in the intact C1q molecule in solution

Thermodynamic. conformational and functional properties of the human C1q globular heads (hgC1q) were studied with the experimental approaches, which allow investigating these properties in the intact hC1q molecule in solution. Surprisingly, the scanning calorimetry data reveal a low level of cooperativity of interactions between the hgC1q A, B and C domains even at a neutral pH area. Ionization of His residues due to acidification of the medium at the pH range from 6 to 5 or the chemical modification of His residues completely abolishes the cooperative interactions between the domains without significant effect on their conformation. The thermodynamic data provide evidence that the hgC1q module is composed of three structurally independent A, B and C globular domains characterized by the practically identical thermal stability and very similar enthalpy of melting. The spectroscopic studies and modification with 2-oxy-5-nitrobenzylbromide (ONBB) indicate that Trp residues in the hgC1q A and C domains are accessible to the solvent that has been confirmed by the hgC1q crystal structure solved and refined to 1.9 A. The modification of Trp residues significantly affects the complement-dependent cytotoxicity without noticeable effect on the hC1q conformation. These data provide evidence that Trp residues are the components of immunoglobulin-binding sites both in the hgC1q A and C domains.

The crystal structure of the globular head of complement protein C1q provides a basis for its versatile recognition properties

C1q is a versatile recognition protein that binds to an amazing variety of immune and non-immune ligands and triggers activation of the classical pathway of complement. The crystal structure of the C1q globular domain responsible for its recognition properties has now been solved and refined to 1.9 A of resolution. The structure reveals a compact, almost spherical heterotrimeric assembly held together mainly by non-polar interactions, with a Ca2+ ion bound at the top. The heterotrimeric assembly of the C1q globular domain appears to be a key factor of the versatile recognition properties of this protein. Plausible three-dimensional models of the C1q globular domain in complex with two of its physiological ligands, C-reactive protein and IgG, are proposed, highlighting two of the possible recognition modes of C1q. The C1q/human IgG1 model suggests a critical role for the hinge region of IgG and for the relative orientation of its Fab domain in C1q binding.

Surfactant strengthens the inhibitory effect of C-reactive protein on human lung macrophage cytokine release

In this study we investigated the effect of acute-phase levels of C-reactive protein (CRP) on cytokine production by pulmonary macrophages in the presence or absence of pulmonary surfactant. Both human alveolar and interstitial macrophages as well as human surfactant were obtained from multiple organ donor lungs. Precultured macrophages were stimulated with LPS alone or together with IFN-gamma in the presence or absence of CRP, surfactant, and combinations. Releases of TNF-alpha and of IL-1beta to the medium were determined. We found that CRP could modulate lung inflammation in humans by decreasing the production of proinflammatory cytokines by both alveolar and interstitial macrophages stimulated with LPS alone or together with IFN-gamma. The potential interaction between CRP and surfactant phospholipids did not overcome the effect of either CRP or surfactant on TNF-alpha and IL-1beta release by lung macrophages. On the contrary, CRP and pulmonary surfactant together had a greater inhibitory effect than either alone on the release of proinflammatory cytokines by lung macrophages.

Experimental allergic encephalomyelitis is inhibited in transgenic mice expressing human C-reactive protein

We show here using a transgenic model that human C-reactive protein (CRP) protects against experimental allergic encephalomyelitis (EAE) in C57BL/6 mice. In transgenic compared with wild-type females, the duration of the human CRP acute phase response that accompanies the inductive phase of active EAE correlates with a delay in disease onset. In transgenic males, which have higher human CRP expression than females do, EAE is delayed, and its severity is reduced relative to same-sex controls. Furthermore, in male transgenics, there is little or no infiltration of the spinal cord by CD3(+) T cells and CD11b(+) monocytes and macrophages, and EAE is sometimes prevented altogether. CRP transgenics also resist EAE induced passively by transfer of encephalitogenic T cells from wild-type donors. Human CRP has three effects on cultured encephalitogenic cells that could contribute to the protective effect observed in vivo: 1) CRP inhibits encephalitogenic peptide-induced proliferation of T cells; 2) CRP inhibits production of inflammatory cytokines (TNF-alpha, IFN-gamma) and chemokines (macrophage-inflammatory protein-1alpha, RANTES, monocyte chemoattractant protein-1); and 3) CRP increases IL-10 production. All three of these actions are realized in vitro only in the presence of high concentrations of human CRP. The combined data suggest that during the acute phase of inflammation accompanying EAE, the high level of circulating human CRP that is achieved in CRP-transgenic mice inhibits the damaging action of inflammatory cells and/or T cells that otherwise support onset and development of EAE.

Complete cDNA sequence of SAP-like pentraxin from Limulus polyphemus: implications for pentraxin evolution

The serum amyloid P component (SAP)-like pentraxin Limulus polyphemus SAP is a recently discovered, distinct pentraxin species, of known structure, which does not bind phosphocholine and whose N-terminal sequence has been shown to differ markedly from the highly conserved N terminus of all other known horseshoe crab pentraxins. The complete cDNA sequence of Limulus SAP, and the derived amino acid sequence, the first invertebrate SAP-like pentraxin sequence, have been determined. Two sequences were identified that differed only in the length of the 3' untranslated region. Limulus SAP is synthesised as a precursor protein of 234 amino acid residues, the first 17 residues encoding a signal peptide that is absent from the mature protein. Phylogenetic analysis clusters Limulus SAP pentraxin with the horseshoe crab C-reactive proteins (CRPs) rather than the mammalian SAPs, which are clustered with mammalian CRPs. The deduced amino acid sequence shares 22% identity with both human SAP and CRP, which are 51% identical, and 31-35% with horseshoe crab CRPs. These analyses indicate that gene duplication of CRP (or SAP), followed by sequence divergence and the evolution of CRP and/or SAP function, occurred independently along the chordate and arthropod evolutionary lines rather than in a common ancestor. They further indicate that the CRP/SAP gene duplication event in Limulus occurred before both the emergence of the Limulus CRP variants and the mammalian CRP/SAP gene duplication. Limulus SAP, which does not exhibit the CRP characteristic of calcium-dependent binding to phosphocholine, is established as a pentraxin species distinct from all other known horseshoe crab pentraxins that exist in many variant forms sharing a high level of sequence homology.

C-reactive protein induces signaling through Fc gamma RIIa on HL-60 granulocytes

Human C-reactive protein (CRP) at acute phase levels of 10-200 microg/ml triggered the phosphorylation of FcgammaRIIa, Syk kinase, and phospholipase Cgamma2 in granulocytic HL-60 cells. CRP also stimulated translocation to the membrane of both phospholipase Cgamma2 and phosphatidylinositol-3-kinase. The signaling response triggered by CRP was a rapid, early event with kinetics similar to the response elicited by human IgG. Both soluble-aggregated CRP and monomeric CRP cross-linked FcgammaRII to generate a signal of the same intensity. The results are consistent with signaling through the intrinsic immunoreceptor tyrosine-based activation motif of the cytoplasmic domain of FcgammaRIIa, the major CRP-receptor on monocytes and neutrophils that is responsible for CRP-mediated phagocytosis. The signaling events driven by CRP have the potential to regulate infiltrating neutrophil activities.

Lack of specific receptors for C-reactive protein on white blood cells

The classic acute-phase reactant C-reactive protein (CRP) plays an important role in innate immunity. Specific CRP receptors have been described on white blood cells and were further characterized as Fcgamma receptors I and II. Here, we used biotinylated, highly purified natural CRP and recombinant human CRP from E. coli to investigate binding to white blood cells. The structural integrity of recombinant CRP was demonstrated by proof of pentamer assembly using non-denaturing gel electrophoresis. Furthermore, the functional capability was confirmed by calcium-dependent ligand binding (phosphorylcholine-coupled BSA and nuclear constituents), and by complement activation (C3 deposition). The monocytic cell line U937 expresses FcgammaRI and FcgammaRII--the proposed CRP receptors--in high density. Binding of biotinylated CRP was only detected by flow cytometry using a partially purified CRP preparation, that contained additional proteins, e.g. IgG as demonstrated by immunoblotting. Highly purified and recombinant CRP, free of IgG, were not bound. To exclude blocking of binding epitopes by labeling on recombinant CRP, biotinylation was performed at various biotin to protein ratios. In addition, competition assays demonstrated that binding of biotinylated, partially purified CRP was only inhibited by partially purified CRP and IgG, but not by highly purified and recombinant CRP. Recombinant CRP bound to U937 cells only after contamination with 0.5 microg IgG per 100 microg CRP before biotinylation. Therefore, we conclude that CRP itself is not bound to white blood cells and strongly suggest a reassessment of previous data.