The yin-yang of long pentraxin PTX3 in inflammation and immunity

Pentraxins are a family of multimeric proteins characterized by the presence of a pentraxin signature in their C-terminus region. Based on the primary structure, pentraxins are divided into short and long pentraxin: C-reactive protein (CRP) is the prototype of the short pentraxin subfamily while pentraxin 3 (PTX3) is the prototypic long pentraxin. Despite these two molecules exert similar fundamental actions in the regulation of innate immune and inflammatory responses, several differences exist between CRP and PTX3, including gene organization, protein oligomerization and expression pattern. The pathophysiological roles of PTX3 have been investigated using genetically modified mice since PTX3 gene organization and regulation are well conserved between mouse and human. Such in vivo studies figured out that PTX3 mainly have host-protective effects, even if it could also exert negative effects under certain pathophysiologic conditions. Here we will review the general properties of CRP and PTX3, emphasizing the differences between the two molecules and the regulatory functions exerted by PTX3 in innate immunity and inflammation.     

The long pentraxin PTX3 as a link among innate immunity, inflammation, and female fertility

The long pentraxin 3 (PTX3) is member of a complex superfamily of multifunctional proteins characterized by a cyclic multimeric structure. PTX3 is highly conserved in evolution and is produced by innate-immunity cells in response to proinflammatory signals and Toll-like receptor engagement. PTX3 plays complex, nonredundant functions in vivo, acting as a predecessor of antibodies, recognizing microbes, activating complement, facilitating pathogen recognition by phagocytes, and hence, playing a nonredundant role in resistance against selected pathogens. 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 nonredundant component of the humoral arm of innate immunity and involved in matrix deposition and female fertility.     

The long pentraxin PTX3 at the crossroads between innate immunity and tissue remodelling

Innate immunity represents the first line of defence against pathogens and plays key roles in the activation and orientation of the adaptive immune response. The innate immune system comprises both a cellular and a humoral arm. Components of the humoral arm include soluble pattern recognition molecules that recognize pathogen-associated molecular patterns and initiate the immune response in coordination with the cellular arm, therefore acting as functional ancestors of antibodies. Pentraxins are essential constituents of the humoral arm of innate immunity and represent a superfamily of highly conserved acute phase proteins, traditionally classified into short and long pentraxins. Pentraxin 3 (PTX3) is the prototypic member of the long pentraxins subfamily. As opposed to C-reactive protein, whose sequence and regulation have not been conserved during evolution from mouse to man, the evolutionary conservation of sequence, gene organization and regulation of PTX3 has allowed addressing its pathophysiological roles in genetically modified mice, in diverse conditions, ranging from infections to sterile inflammation, angiogenesis and female fertility. Despite this conservation, a number of predominantly non-coding polymorphisms have been identified in the PTX3 gene which, when associated in particular haplotypes, have been shown to be relevant in clinical conditions including infection and fertility. Here we review the studies on PTX3, with emphasis on pathogen recognition, tissue remodelling and crosstalk with other components of the innate immune system.     

Chorionic gonadotropin up-regulates long pentraxin 3 expression in myeloid cells

Pentraxin 3 (PTX3) is an acute-phase response protein that initiates innate immunity against diverse microorganisms. It is produced in response to proinflammatory stimuli by many cell types including myeloid cells. Increased serum levels of PTX3 are found in pregnancy, a condition characterized by increased serum levels of the pregnancy hormone human chorionic gonadotropin (hCG). As myeloid cells bear the receptor for hCG, we hypothesized that hCG can promote innate immunity by affecting the PTX3 production by myeloid cells. In this paper, we demonstrate that hCG increases PTX3 expression by human monocytes, mouse dendritic cells, and mouse macrophages in vitro. This increased PTX3 expression by hCG is mediated via the protein kinase A signaling pathway. hCG injection in mice also increases the PTX3 serum levels. This serum PTX3 is produced mainly by blood monocytes, which from pregnant women, express more PTX3 compared with nonpregnant controls. The hCG-induced hormones progesterone and estrogen also increase the PTX3 production by human monocytes. In conclusion, hCG increases innate immunity via induction of PTX3 in myeloid cells.     

The tissue pentraxin PTX3 limits C1q-mediated complement activation and phagocytosis of apoptotic cells by dendritic cells

Pentraxins (PTX) and complement belong to the humoral arm of the innate immune system and have essential functions in immune defense to microbes and in scavenging cellular debris. The prototypic long PTX, PTX3, and the first component of the classical complement pathway, C1q, are innate opsonins involved in the disposal of dying cells by phagocytes. Whether the interaction between various innate opsonins impacts on their function is not fully understood. We show here that characterized Toll-like receptor (TLR) ligands elicit the production of C1q and PTX3 by immature dendritic cells (DC). Moreover, these molecules bind to dying cells with similar kinetics, although they recognize different domains on the cell membranes. PTX3 binds in the fluid phase to C1q, decreasing C1q deposition and subsequent complement activation on apoptotic cells. C1q increases the phagocytosis of apoptotic cells by DC and the release of interleukin-12 in the presence of TLR4 ligands and apoptotic cells; PTX3 inhibits both events. Moreover, PTX3 inhibited the cross-presentation of the MELAN-A/melanoma antigen-reactive T cell 1 (MART-1) tumor antigen expressed by dying cells, even in the presence of C1q. These results suggest that interaction of C1q and PTX3 influences the clearance of apoptotic cells by DC. The coordinated induction by primary, proinflammatory signals of C1q and PTX3 and their reciprocal regulation during inflammation influences the clearance of apoptotic cells by antigen-presenting cells and possibly plays a role in immune homeostasis.     

Expression and production of the long pentraxin PTX3 in rheumatoid arthritis (RA)

PTX3 is a secreted molecule which consists of a C-terminal domain similar to classical pentraxins (e.g. C-reactive protein (CRP)) and of an unrelated N-terminal domain. Unlike the classical pentraxins, the long pentraxin PTX3 is expressed in response to IL-1beta and tumour necrosis factor-alpha (TNF-alpha), but not to IL-6, in various cell types. The present study was designed to investigate the expression of PTX3 in RA. Dissociated RA and osteoarthritis (OA) type B synoviocytes were cultured in the presence and in the absence of inflammatory cytokines. PTX3 mRNA expression in synoviocytes was evaluated by Northern analysis. PTX3 protein levels in synovial cell cultures and synovial fluid were estimated by ELISA, and PTX3 distribution in synovial tissues by immunohistochemical techniques. OA synoviocytes were induced to express high levels of PTX3 mRNA by TNF-alpha, but not by other cytokines including IL-1beta and IL-6. RA synoviocytes, unlike OA synoviocytes, constitutively expressed high levels of PTX3 in the absence of deliberate stimulation. The constitutive expression of PTX3 in RA synoviocytes was not modified by anti-TNF-alpha antibodies, IL-1 receptor antagonist or a combination of the two agents. In contrast, interferon-gamma and transforming growth factor-beta inhibited PTX3 constitutive expression in RA synoviocytes. The joint fluid from RA patients contained higher levels of immunoreactive PTX3 than controls and the synovial tissue contained endothelial cells and synoviocytes positive for PTX3 by immunohistochemistry. In conclusion, PTX3 may play a role in inflammatory circuits of RA, and its relevance as a marker of disease activity deserves further study.     

The long pentraxin PTX3 as a prototypic humoral pattern recognition receptor: interplay with cellular innate immunity

Summary:  The innate immune system consists of a cellular arm and a humoral arm. Components of humoral immunity include diverse molecular families, which represent functional ancestors of antibodies. They play a key role as effectors and modulators of innate resistance in animals and humans, interacting with cellular innate immunity. The prototypic long pentraxin, pentraxin 3 (PTX3), represents a case in point of this interplay. Gene targeting of this evolutionarily conserved long pentraxin has unequivocally defined its role at the crossroads of innate immunity, inflammation, matrix deposition, and female fertility. Phagocytes represent a key source of this fluid-phase pattern recognition receptor, which, in turn, facilitates microbial recognition by phagocytes acting as an opsonin. Moreover, PTX3 has modulatory functions on innate immunity and inflammation. Here, we review the studies on PTX3 which emphasize the complexity and complementarity of the crosstalk between the cellular and humoral arms of innate immunity.     

Protective effects of long pentraxin PTX3 on lung injury in a severe acute respiratory syndrome model in mice

The outbreak of severe acute respiratory syndrome (SARS) in 2003 reinforces the potential of lethal pandemics of respiratory viral infections. The underlying mechanisms of SARS are still largely undefined. Long pentraxin PTX3, a humoral mediator of innate immunity, has been reported to have anti-viral effects. We examined the role of PTX3 in coronavirus murine hepatitis virus strain 1 (MHV-1)-induced acute lung injury, a previously reported animal model for SARS. PTX3-deficient mice (129/SvEv/C57BL6/J) and their wild-type (WT) littermates were intranasally infected MHV-1. These mice were also treated with recombinant PTX3. Effects of PTX3 on viral binding and infectivity were determined in vitro. Cytokine expression, severity of lung injury, leukocyte infiltration and inflammatory responses were examined in vivo. In PTX3 WT mice, MHV-1 induced PTX3 expression in the lung and serum in a time-dependent manner. MHV-1 infection led to acute lung injury with greater severity in PTX3-deficient mice than that in WT mice. PTX3 deficiency enhanced early infiltration of neutrophils and macrophages in the lung. PTX3 bound to MHV-1 and MHV-3 and reduced MHV-1 infectivity in vitro. Administration of recombinant PTX3 significantly accelerated viral clearance in the lung, attenuated MHV-1-induced lung injury, and reduced early neutrophil influx and elevation of inflammatory mediators in the lung. Results from this study indicate a protective role of PTX3 in coronaviral infection-induced acute lung injury.     

正五聚蛋白 3在炎症及自身免疫中的作用

 PTX3(Pentraxin 3)作为一种可溶性模式识别受体,参与了免疫防御、炎症反应、细胞凋亡、血管重塑、女性生殖生育及血管内皮损伤等多种生理及病理效应。并可作为临床检测自身免疫性疾病中组织损伤,炎症状态严重性和活动性的一项敏感的生物学标记。其具体的作用机制仍然不明。PTX3在多数情况下,限制炎症及自身免疫的发生发展,而起到保护性效应。     

Dynamic induction of the long pentraxin PTX3 in the CNS after limbic seizures: evidence for a protective role in seizure-induced neurodegeneration

Pentraxin 3, a prototypic long pentraxin, is induced by proinflammatory signals in the brain. Inflammatory cytokines are rapidly induced in glia by epileptic activity. We show that pentraxin 3 immunoreactivity and mRNA are enhanced in the rat forebrain above undetectable control levels by limbic seizures with a dual pattern of induction. Within 6 h from seizure onset, pentraxin 3 immunoreactivity was increased in astrocytes. Eighteen to 48 h later, specific neuronal populations and leucocytes were strongly immunoreactive only in areas of neurodegeneration. This staining was abolished when neuronal cell loss, but not seizures, was prevented by blocking N-methyl-D-aspartate receptors. Pentraxin 3 -/- mice had a more widespread seizure-related neuronal damage in the forebrain than their wild-type littermates although both groups had similar epileptic activity. Our results provide evidence that pentraxin 3 is synthesized in brain after seizures and may exert a protective role in seizure-induced neurodegeneration.     

Macrophage migration inhibitory factor: a probable link between inflammation and cancer

The pleiotropic effects of macrophage migration inhibitory factor (MIF) place it in a central position in the immunopathogenesis of many diseases. Here we discuss the current understanding of MIF's role and highlight it as a potential link between inflammatory activation and malignant progression.     

Long pentraxin 3 (PTX3) expression and release by neutrophils in vitro and in ulcerative colitis

Pentraxin 3 (PTX3) is the first identified long pentraxin, and it is rapidly produced and released by several cell types in response to proinflammatory signals. The aim of this study was to investigate the behavior of neutrophils to produce PTX3 protein in response to proinflammatory cytokine IL-8 in vitro, as well as identify the expression pattern of PTX3 in human ulcerative colitis lesions. Pentraxin 3 protein was found to be present following release upon IL-8 stimulation in cultured neutrophils together with lactoferrin(+)-specific granules localized in neutrophil extracellular traps (NETs) formed by extruded DNA. Neutrophils in colonic mucosal tissue of patients with ulcerative colitis were the main cellular source of PTX3 protein, the expression of which is correlated well with the histological grades of inflammation. Immunofluorescence analysis against anti-lactoferrin antibody revealed the formation of NETs released from neutrophils within crypt abscess lesions, which were found to be activated through the expression of IL-8 receptor B (CXCR2). Of interest, neutrophils depleted of PTX3 protein were displayed, supporting the release of PTX3 from neutrophils in crypt abscess. We suspected that PTX3 protein may contribute to cell-mediated immune defense in inflamed colon tissue, and in particular in crypt abscess lesions, of patients with ulcerative colitis.     

Innate immunity,hemostasis and matrix remodeling: PTX3 as a link

Innate immunity is evolutionarily connected with hemostasis. PTX3 is an essential fluid-phase pattern recognition molecule of the innate immune system that acts as a functional ancestor of antibodies. PTX3 by interacting with defense collagens and fibrinogens amplifies effector functions of the innate immune system. At wound sites, PTX3 regulates the injury-induced thrombotic response and promotes wound healing by favoring timely fibrinolysis. Therefore, PTX3 interacts with ancestral domains conserved in innate immunity, hemostasis and extracellular matrix and exerts functions related to both antimicrobial resistance and tissue repair. These findings strengthen the connection between innate immune system and hemostasis, and suggest that recognition of microbes and extracellular matrix are evolutionarily conserved and integrated functions of the innate immune system.     

Long pentraxin 3: a marker of inflammation in untreated psoriatic patients

Psoriasis is a common cutaneous disorder characterized by abnormal epidermal differentiation, proliferation and inflammation mediated by dermal infiltrates, such as T cells, neutrophils, dendritic cells and macrophages. There are renewed interest in the role of components of the innate immune system. Cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin (IL)-6, and -1beta involved in pathogenic phenomena in psoriasis are known as inducers of the acute phase response. Among the large group of acute phase reactants, C-reactive protein (CRP) and fibrinogen are of special interest in psoriasis. The PTX-3, a long pentraxin sharing similarities with the classical short proteins. Thus, considering the numerous biological roles of inflammatory cytokines and their relationship with inflammatory markers, such as CRP and fibrinogen we have investigated the role of PTX3 in psoriasis. To this aim PTX3, TNF-alpha, IL-6 and IL-1beta in plasma and in monocytic cultures by enzyme linked immunosorbent assay (ELISA) in 44 patients including severe and mild psoriasis were measured. An increased production of PTX3, both in supernatant of purified monocytes and in plasma from patients with severe psoriasis, was found. The significant correlation, between cellular production and plasma levels of PTX3 in psoriasis was found as a sign of cellular activation by monocytes/macrophages that first infiltrate the psoriatic lesion. In severe psoriasis, a significant correlation between psoriasis area and severity index (PASI) score and TNF-alpha and IL-6 levels in both supernatant of monocytes and plasma was found. In contrast, no correlation was found for IL-1beta. By immunohistochemistry and immunofluorescence, a strong PTX3 staining in fibroblasts, endothelial cells and monocytes/macrophages in severe psoriatic lesional skin was detected. Finally, a positive correlation between PTX3 and disease activity of psoriasis was observed as PASI score was elevated. These findings suggest that PTX3 could be used as a further marker of disease activity of psoriasis.     

Angiopoietins: a link between angiogenesis and inflammation

The angiopoietin (Ang)-Tie ligand-receptor system has a key regulatory role in regulating vascular integrity and quiescence. Besides its role in angiogenesis, it is an important regulator in numerous diseases including inflammation. Ang-1-mediated Tie2 activation is required to maintain the quiescent resting state of the endothelium. Agonistic Ang-1 functions are antagonized by Ang-2, which is believed to inhibit Ang-1-Tie2 signaling. Ang-2 destabilizes the quiescent endothelium and primes it to respond to exogenous stimuli, thereby facilitating the activities of inflammatory (tumor necrosis factor and interleukin-1) and angiogenic (vascular endothelial growth factor) cytokines. Intriguingly, Ang-2 is expressed weakly by the resting endothelium but becomes strongly upregulated following endothelial activation. Moreover, endothelial cells store Ang-2 in Weibel-Palade bodies from where it can be made available quickly following stimulation, suggesting a role of Ang-2 in controlling rapid vascular adaptive processes. This suggests that Ang-2 is the dynamic regulator of the Ang-Tie2 axis, thereby functioning as a built-in switch controlling the transition of the resting quiescent endothelium towards the activated responsive endothelium.     

Relation between the plasma levels of LDL-cholesterol and the expression of the early marker of inflammation long pentraxin PTX3 and the stress response gene p66<Superscript>(ShcA)</Superscript> in pacemaker-implanted patients

Abstract Our goal was to set up a pilot study to explore the possible relation between the expression of p66^(ShcA) and PTX3, two emerging regulators of stress response and inflammation processes, respectively, and the circulating levels of LDL-cholesterol (LDL), a factor implicated in the development of inflammation and oxidative-stress associated diseases such as atherosclerosis. p66^(ShcA) and PTX3 mRNA contents were determined locally, in subcutaneous adipose specimens of non-diabetic pacemakerimplanted patients, and systemically in the circulating white blood cells (WBC) obtained from the same patients. The mean of the circulating LDL levels (125 mg/dl) was chosen as a threshold to identify two groups here considered to have high (>125 mg/dl) and low (<125 mg/dl) LDL plasma levels. Our data show that PTX3 and p66^(ShcA) mRNA levels are significantly more elevated in WBCs and in adipose tissue samples of patients with high levels of LDL compared to those with low levels. Additionally, a multiple regression analysis indicates that among LDL, TG, HDL, total cholesterol, CRP, creatinine and glucose levels, the only variable significantly affecting p66^(ShcA) and PTX3 mRNA expressions either in adipose tissue or in WBCs is represented by the circulating amount of LDL. In conclusion, our results suggest a potential link between the level of LDL and the expression of two genes involved in inflammation/oxidative stress pathways, i.e., p66^(ShcA) and PTX3, thus contributing to further understand the mechanism through which LDL may mediate the pathogenesis of inflammation and oxidative-stress associated diseases such as atherosclerosis. *These two authors contributed equally to this paper