PTX3 is an extrinsic oncosuppressor regulating complement-dependent inflammation in cancer.

PTX3 is an essential component of the humoral arm of innate immunity, playing a nonredundant role in resistance against selected microbes and in the regulation of inflammation. PTX3 activates and regulates the Complement cascade by interacting with C1q and with Factor H. PTX3 deficiency was associated with increased susceptibility to mesenchymal and epithelial carcinogenesis. Increased susceptibility of Ptx3(-/-) mice was associated with enhanced macrophage infiltration, cytokine production, angiogenesis, and Trp53 mutations. Correlative evidence, gene-targeted mice, and pharmacological blocking experiments indicated that PTX3 deficiency resulted in amplification of Complement activation, CCL2 production, and tumor-promoting macrophage recruitment. PTX3 expression was epigenetically regulated in selected human tumors (e.g., leiomyosarcomas and colorectal cancer) by methylation of the promoter region and of a putative enhancer. Thus, PTX3, an effector molecule belonging to the humoral arm of innate immunity, acts as an extrinsic oncosuppressor gene in mouse and man by regulating Complement-dependent, macrophage-sustained, tumor-promoting inflammation.

Cutaneous barrier leakage and gut inflammation drive skin disease in Omenn syndrome.

BACKGROUND: Severe early-onset erythroderma and gut inflammation, with massive tissue infiltration of oligoclonal activated T cells are the hallmark of Omenn syndrome (OS). OBJECTIVE: The impact of altered gut homeostasis in the cutaneous manifestations of OS remains to be clarified. METHODS: We analyzed a cohort of 15 patients with OS and the 129Sv/C57BL/6 knock-in Rag2R229Q/R229Q (Rag2R229Q) mouse model. Homing phenotypes of circulating lymphocytes were analyzed by flow cytometry. Inflammatory cytokines and chemokines were examined in the sera by ELISA and in skin biopsies by immunohistochemistry and in situ RNA hybridization. Experimental colitis was induced in mice by dextran sulfate sodium salt. RESULTS: We show that memory/activated T cells from patients with OS and from the Rag2R229Q mouse model of OS abundantly express the skin homing receptors cutaneous lymphocyte associated antigen and CCR4 (Ccr4), associated with high levels of chemokine C-C motif ligands 17 and 22. Serum levels of LPS are also elevated. A broad Th1/Th2/Th17 inflammatory signature is detected in the periphery and in the skin. Increased Tlr4 expression in the skin of Rag2R229Q mice is associated with enhanced cutaneous inflammation on local and systemic administration of LPS. Likewise, boosting colitis in Rag2R229Q mice results in increased frequency of Ccr4+ splenic T cells and worsening of skin inflammation, as indicated by epidermal thickening, enhanced epithelial cell activation, and dermal infiltration by Th1 effector T cells. CONCLUSIONS: These results support the existence of an interplay between gut and skin that can sustain skin inflammation in OS.

Anti-CD3ε mAb improves thymic architecture and prevents autoimmune manifestations in a mouse model of Omenn syndrome: therapeutic implications.

Omenn syndrome (OS) is an atypical primary immunodeficiency characterized by severe autoimmunity because of activated T cells infiltrating target organs. The impaired recombinase activity in OS severely affects expression of the pre-T-cell receptor complex in immature thymocytes, which is crucial for an efficient development of the thymic epithelial component. Anti-CD3ε monoclonal antibody (mAb) treatment in RAG2(-/-) mice was previously shown to mimic pre-TCR signaling promoting thymic expansion. Here we show the effect of anti-CD3ε mAb administration in the RAG2(R229Q) mouse model, which closely recapitulates human OS. These animals, in spite of the inability to induce the autoimmune regulator, displayed a significant amelioration in thymic epithelial compartment and an important reduction of peripheral T-cell activation and tissue infiltration. Furthermore, by injecting a high number of RAG2(R229Q) progenitors into RAG2(-/-) animals previously conditioned with anti-CD3ε mAb, we detected autoimmune regulator expression together with the absence of peripheral immunopathology. These observations indicate that improving epithelial thymic function might ameliorate the detrimental behavior of the cell-autonomous RAG defect. Our data provide important therapeutic proof of concept for future clinical applications of anti-CD3ε mAb treatment in severe combined immunodeficiency forms characterized by poor thymus function and autoimmunity.

Prevalence and correlates of treatment failure among Kenyan children hospitalised with severe community-acquired pneumonia: a prospective study of the clinical effectiveness of WHO pneumonia case management guidelines.

OBJECTIVE: To determine the extent and pattern of treatment failure (TF) among children hospitalised with community-acquired pneumonia at a large tertiary hospital in Kenya. METHODS: We followed up children aged 2-59 months with WHO-defined severe pneumonia (SP) and very severe pneumonia (VSP) for up to 5 days for TF using two definitions: (i) documentation of pre-defined clinical signs resulting in change of treatment (ii) primary clinician's decision to change treatment with or without documentation of the same pre-defined clinical signs. RESULTS: We enrolled 385 children. The risk of TF varied between 1.8% (95% CI 0.4-5.1) and 12.4% (95% CI 7.9-18.4) for SP and 21.4% (95% CI 15.9-27) and 39.3% (95% CI 32.5-46.4) for VSP depending on the definition applied. Higher rates were associated with early changes in therapy by clinician in the absence of an obvious clinical rationale. Non-adherence to treatment guidelines was observed for 70/169 (41.4%) and 67/201 (33.3%) of children with SP and VSP, respectively. Among children with SP, adherence to treatment guidelines was associated with the presence of wheeze on initial assessment (P = 0.02), while clinician non-adherence to guideline-recommended treatments for VSP tended to occur in children with altered consciousness (P < 0.001). Using propensity score matching to account for imbalance in the distribution of baseline clinical characteristics among children with VSP revealed no difference in TF between those treated with the guideline-recommended regimen vs. more costly broad-spectrum alternatives [risk difference 0.37 (95% CI -0.84 to 0.51)]. CONCLUSION: Before revising current pneumonia case management guidelines, standardised definitions of TF and appropriate studies of treatment effectiveness of alternative regimens are required.

Bias in macrophage activation pattern influences non-alcoholic steatohepatitis (NASH) in mice.

In humans, there is large inter-individual variability in the evolution of NAFLD (non-alcoholic fatty liver disease) to NASH (non-alcoholic steatohepatitis). To investigate this issue, NASH was induced with an MCD (methionine-choline-deficient) diet in C57BL/6 and Balb/c mice that are characterized by different biases in Th1/Th2 and macrophage (M1/M2) responses. Following 4 weeks on the MCD diet, steatosis and lobular inflammation were prevalent in C57BL/6 (Th1, M1 oriented) than in Balb/c (Th2, M2 oriented) mice. Consistently, hepatic TNFα (tumour necrosis factor α) mRNA expression and circulating TNFα levels were higher in MCD-fed C57BL/6 than in MCD-fed Balb/c mice. The Th1/Th2 bias did not account for the increased NASH severity, as in both strains MCD feeding did not significantly modify the liver mRNA expression of the Th1 markers IFNγ (interferon γ) and T-bet or that of the Th2 markers IL-4 (interleukin 4) and GATA-3. Conversely, MCD-fed C57BL/6 mice displayed higher liver mRNAs for the macrophage M1 activation markers iNOS (inducible NO synthase), IL-12p40 and CXCL10 (CXC chemokine ligand 10) than similarly treated Balb/c mice, without effects on the M2 polarization markers IL-10 and MGL-1 (macrophage galactose-type C-type lectin-1). Circulating IL-12 was also higher in MCD-fed C57BL/6 than in MCD-fed Balb/c mice. The analysis of macrophages isolated from the livers of MCD-fed animals confirmed an enhanced expression of M1 markers in C57BL/6 mice. Among all of the MCD-treated mice, liver iNOS, IL-12p40 and CXCL10 mRNA levels positively correlated with the frequency of hepatic necro-inflammatory foci. We concluded that the macrophage M1 bias in C57BL/6 mice may account for the increased severity of NASH in this strain, suggesting macrophage responses as important contributors to NAFLD progression.

Cardioprotective function of the long pentraxin PTX3 in acute myocardial infarction.

BACKGROUND: Despite widespread clinical use as a prognostic marker in ischemic heart disorders, the actual pathogenetic role of the short pentraxin, C-reactive protein, has not undergone stringent genetic testing because of evolutionary divergence between mouse and humans. The long pentraxin PTX3 is conserved in evolution, is expressed in the heart under inflammatory conditions, and is a candidate prognostic marker in acute myocardial infarction. It was therefore important to assess whether PTX3 plays a pathogenetic role in acute myocardial infarction. METHODS AND RESULTS: In a model of acute myocardial infarction caused by coronary artery ligation and reperfusion, tissue mRNA expression and circulating levels of PTX3 increased. The interleukin-1R-MyD88 pathway plays a pivotal role in the induction of PTX3 transcript after ischemia. ptx3-deficient mice showed exacerbated heart damage (33% larger infarcts in null mice; P=0.0047). Increased myocardial damage in ptx3-deficient mice was associated with a greater no-reflow area, increased neutrophil infiltration, decreased number of capillaries, and increased number of apoptotic cardiomyocytes. In addition, ptx3-deficient mice with acute myocardial infarction showed higher circulating levels of interleukin-6 and increased C3 deposition in lesional tissue. The phenotype was reversed by exogenous PTX3. CONCLUSIONS: Thus, PTX3 plays a nonredundant, regulatory, cardioprotective role in acute myocardial infarction in mice. Our results suggest that modulation of the complement cascade contributes to the cardioprotective function of PTX3.

Long pentraxin 3, a key component of innate immunity, is modulated by high-density lipoproteins in endothelial cells.

OBJECTIVE: High-density lipoproteins (HDL) are endowed with cardiovascular protective activities. In addition to their role in reverse cholesterol transport, HDL exert several beneficial effects on endothelial cells, including the induction of endothelial nitric oxide synthase and prostacyclin release, and the control of the immune and inflammatory response. METHODS AND RESULTS: To identify possible mechanisms involved in these effects we investigated the modulation of the expression of acute phase proteins of the pentraxin superfamily, such as C-reactive protein (CRP), serum amyloid P component protein (SAP), and the long pentraxin 3 (PTX3) by HDL in human endothelial cells. HDL induced PTX3 mRNA expression and protein release, whereas no effect was observed on CRP and SAP expression. This effect was mainly dependent on the activation of the lysosphingolipids receptors-PI3K/Akt axis and was mimicked by sphingosine 1 phosphate and other S1P mimetics. This observation was confirmed in vivo; indeed an increased expression of PTX3 mRNA was detected in the aorta of transgenic mice overexpressing human apoA-I, compared to apoA-I knock-out mice. Furthermore, plasma levels of PTX3 significantly increased in C57BL/6 mice injected with HDL. CONCLUSIONS: These data suggest that part of the atheroprotective effects of HDL could result from the modulation of molecules that act as sensors of the immunoinflammatory balance in the vascular wall.

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.

First trimester PTX3 levels in women who subsequently develop preeclampsia and fetal growth restriction.

Pentraxin 3 (PTX3) and C-reactive protein (CRP) levels were measured in the first trimester of pregnancy in women who subsequently developed preeclampsia (PE, n=16) and fetal growth restriction (FGR, n=12) requiring iatrogenic delivery before 37 weeks, and those who had uncomplicated pregnancies delivering at term (n=60). Mean PTX3 levels were significantly higher in women who subsequently developed PE (7.31 ng/ml, SD = 4.12) when compared to those with normal pregnancy outcome (4.92 ng/ml, SD = 1.94, p=0.0046). There were no significant differences between PTX3 levels in women with FGR (4.82 ng/ml, SD = 2.35) compared to normal pregnancy outcome (p=0.88). The median CRP levels did not vary significantly between the three groups (p=0.26). PTX3 levels in women who subsequently develop PE are already elevated in the first trimester, but not in those that develop FGR. This supports the hypothesis of an excessive maternal inflammatory response to pregnancy in the etiology of PE.

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.

Intestinal microbiota sustains inflammation and autoimmunity induced by hypomorphic RAG defects.

Omenn syndrome (OS) is caused by hypomorphic Rag mutations and characterized by a profound immunodeficiency associated with autoimmune-like manifestations. Both in humans and mice, OS is mediated by oligoclonal activated T and B cells. The role of microbial signals in disease pathogenesis is debated. Here, we show that Rag2(R229Q) knock-in mice developed an inflammatory bowel disease affecting both the small bowel and colon. Lymphocytes were sufficient for disease induction, as intestinal CD4 T cells with a Th1/Th17 phenotype reproduced the pathological picture when transplanted into immunocompromised hosts. Moreover, oral tolerance was impaired in Rag2(R229Q) mice, and transfer of wild-type (WT) regulatory T cells ameliorated bowel inflammation. Mucosal immunoglobulin A (IgA) deficiency in the gut resulted in enhanced absorption of microbial products and altered composition of commensal communities. The Rag2(R229Q) microbiota further contributed to the immunopathology because its transplant into WT recipients promoted Th1/Th17 immune response. Consistently, long-term dosing of broad-spectrum antibiotics (ABXs) in Rag2(R229Q) mice ameliorated intestinal and systemic autoimmunity by diminishing the frequency of mucosal and circulating gut-tropic CCR9(+) Th1 and Th17 T cells. Remarkably, serum hyper-IgE, a hallmark of the disease, was also normalized by ABX treatment. These results indicate that intestinal microbes may play a critical role in the distinctive immune dysregulation of OS.

An acidic microenvironment sets the humoral pattern recognition molecule PTX3 in a tissue repair mode.

Pentraxin 3 (PTX3) is a fluid-phase pattern recognition molecule and a key component of the humoral arm of innate immunity. In four different models of tissue damage in mice, PTX3 deficiency was associated with increased fibrin deposition and persistence, and thicker clots, followed by increased collagen deposition, when compared with controls. Ptx3-deficient macrophages showed defective pericellular fibrinolysis in vitro. PTX3-bound fibrinogen/fibrin and plasminogen at acidic pH and increased plasmin-mediated fibrinolysis. The second exon-encoded N-terminal domain of PTX3 recapitulated the activity of the intact molecule. Thus, a prototypic component of humoral innate immunity, PTX3, plays a nonredundant role in the orchestration of tissue repair and remodeling. Tissue acidification resulting from metabolic adaptation during tissue repair sets PTX3 in a tissue remodeling and repair mode, suggesting that matrix and microbial recognition are common, ancestral features of the humoral arm of innate immunity.

Hypomorphic mutation in the RAG2 gene affects dendritic cell distribution and migration.

OS is a severe combined immunodeficiency characterized by erythrodermia and protracted diarrhea as a result of infiltration of oligoclonal-activated T cells, caused by hypomorphic mutations in RAGs. The RAG2(R229Q) mouse model fully recapitulates the clinical OS phenotype. We evaluated whether T and B cell defects, together with the abnormal lymphoid structure, could affect DC homeostasis and function. High density of LCs was observed in skin biopsies of Omenn patients and in the derma of RAG2(R229Q) mice, correlating with the presence of erythrodermia. In vivo models of cutaneous skin painting and CHS demonstrated a decreased migration of RAG2(R229Q) DCs-in particular, LCs-into draining LNs. Interestingly, at steady state, RAG2(R229Q) mice showed a reduction in DC number in all hematopoietic organs except LNs. Analysis of the MHCII marker revealed a diminished expression also upon the LPS-driven inflammatory condition. Despite the decreased number of peripheral DCs, BM pre-cDCs were present in normal number compared with RAG2(+/+) controls, whereas pDCs and monocytes were reduced significantly. Overall, these results point to a secondary defect in the DC compartment, which contributes to clinical manifestations and autoimmunity in OS.

Osteopetrosis rescue upon RANKL administration to Rankl(-/-) mice: a new therapy for human RANKL-dependent ARO.

In the last decades the molecular basis of monogenic diseases has been largely unraveled, although their treatment has often remained unsatisfactory. Autosomal recessive osteopetrosis (ARO) belongs to the small group of genetic diseases that are usually treated with hematopoietic stem cell transplantation (HSCT). However, this approach is not effective in the recently identified form carrying mutations in the receptor activator of NF-κB ligand (RANKL) gene. In this subset, therapy replacement approach based on RANKL delivery has a strong rationale. Here we demonstrate that the systematic administration of RANKL for 1 month to Rankl(-/-) mice, which closely resemble the human disease, significantly improves the bone phenotype and has beneficial effects on bone marrow, spleen and thymus; major adverse effects arise only when mice are clearly overtreated. Overall, we provide evidence that the pharmacological administration of RANKL represents the appropriate treatment option for RANKL-deficient ARO patients, to be validated in a pilot clinical trial.

Omenn syndrome does not live by V(D)J recombination alone.

PURPOSE OF REVIEW: During the past decade, easy access to sequence analyses has allowed us to increase our understanding of the pathogenesis of severe combined immunodeficiencies. Here, we describe the expanding clinical and immunological spectrum associated with Omenn syndrome phenotype. In particular, we review the cellular and molecular mechanisms involved in the pathophysiology of 'classical' Omenn syndrome due to the recombination activating gene (RAG) defects and of a new subgroup of Omenn-like disorders. RECENT FINDINGS: Different types of mutations are associated with the Omenn phenotype characterized by skin erythroderma, oligoclonal-activated T cells and elevated IgE in the absence of circulating B cells. Extensive studies conducted over the last few years have allowed the definition of the 'classical form' of Omenn syndrome due to hypomorphic defects in genes involved in V(D)J recombination, mainly RAG genes, and 'Omenn-like' features associated with mutations in genes involved in the maturation steps of lymphoid cells other than V(D)J recombination. Moreover, an increasing number of diseases other than those due to V(D)J recombination defects develop Omenn signs. SUMMARY: Impaired but not abolished V(D)J recombination process leads to the generation of a few T cells which expand in the periphery, infiltrate target organs such as skin and gut, resulting in severe erythroderma and colitis, both typical signs of Omenn syndrome. Extensive molecular studies now demonstrate that genes other than V(D)J molecules have a role in the pathogenesis of this disease, supporting the evidence that 'Omenn' defines an inflammatory condition associated with various genetic defects.

Oxidative stress parameters in paediatric non-alcoholic fatty liver disease.

We have investigated the presence and the possible clinical implications of oxidative stress in children with non-alcoholic fatty liver disease (NAFLD). The present study was an observational study of oxidative stress parameters in the progression of paediatric NAFLD. We observed the role of oxidative stress in children diagnosed with NAFLD by evaluating: serum protein carbonyls, hepatic expression of 8-hydroxy-2-deoxyguanosine (8-OHG), and circulating antibody against malondialdehyde adducted human serum albumin (MDA-HSA). Forty consecutive children with biopsy-proven NAFLD (27 male; 13 female) referred to Bambino Gesù Children's Hospital, Rome, Italy, from January 2007 to April 2008 were included in the study. Serum variations of protein carbonyls, 8-OHG, and circulating antibody against MDA-HSA were evaluated. Elevated protein carbonyls were evident in 33 subjects (83%) irrespective of obesity and insulin resistance. Moreover, liver biopsies of NAFLD patients positive for circulating protein carbonyls also showed a significant increase in the nuclear staining for 8-OHG (p=0.006; 95% CI 3.1-17.7). Anti-MDA-HSA IgG above control threshold was detected in 25 (63%) children. Although protein carbonyl levels were unrelated with disease severity, patients with elevated anti-MDA-HSA IgG had scores for lobular inflammation significantly higher (p=0.019) than subjects with antibodies within the control range, while steatosis, hepatocyte ballooning and fibrosis were similar. High anti-MDA-HSA reactivity was also associated with a 13-fold increased risk (OR=12.9; 95= CI 1.5-113.8; p=0.013) of a NAFLD activity score (NAS) >or=5. These results demonstrate that oxidative stress has an high prevalence in children with NAFLD and is associated with an increased severity of steatohepatitis.

The soluble pattern recognition receptor pentraxin-3 in innate immunity, inflammation and fertility.

The innate immune system consists of a cellular and a humoral arm. Components of humoral immunity include diverse molecular families, which represent functional ancestors of antibodies. They play key roles as effectors and modulators of innate resistance and inflammation. The long pentraxin PTX3 represents a prototype humoral effector molecule. 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. Here, we will review the studies on PTX3, which emphasize its role as a multifunctional soluble pattern recognition receptor acting as a non-redundant component of the humoral arm of innate immunity involved in fine-tuning inflammation, matrix deposition, angiogenesis and, in particular, in female fertility.

Coregulation in human leukocytes of the long pentraxin PTX3 and TSG-6.

The prototypic long PTX3 is a multifunctional protein involved in innate resistance to pathogens and in controlling inflammation. TSG-6 is a hyaluronan-binding protein that is involved in ECM remodeling and has anti-inflammatory and chondroprotective functions. PTX3 and TSG-6 are coregulated by growth differentiation factor-9 in granulosa cells, where they are produced during the periovulatory period and play essential roles in the incorporation of hyaluronan into the ECM during cumulus expansion. The present study was designed to assess whether PTX3 and TSG-6 are coregulated in leukocytes, in particular, in phagocytes and DC. Monocytes, macrophages, and myeloid DC were found to produce high levels of TSG-6 and PTX3 in response to proinflammatory mediators (LPS or cytokines). Unstimulated neutrophil polymorphonuclear granulocytes expressed high levels of TSG-6 mRNA, but not PTX3 transcript, and stored both proteins in granules. In contrast, endothelial cells expressed substantial amounts of PTX3 mRNA and low levels of TSG-6 transcript under the conditions tested. Anti-inflammatory cytokines, such as IL-4, dampened LPS-induced TSG-6 and PTX3 expression. Divergent effects were observed with IL-10, which synergizes with TLR-mediated PTX3 induction but inhibits LPS-induced TSG-6 transcription. Immunohistochemical analysis confirms the colocalization of the two proteins in inflammatory infiltrates and in endothelial cells of inflamed tissues. Thus, here we show that myelomonocytic cells and MoDC are a major source of TSG-6 and that PTX3 and TSG-6 are coregulated under most of the conditions tested. The coordinated expression of PTX3 and TSG-6 may play a role in ECM remodeling at sites of inflammation.

Complement dependent amplification of the innate response to a cognate microbial ligand by the long pentraxin PTX3.

The long pentraxin PTX3 is a fluid-phase pattern recognition receptor, which plays a nonredundant role in resistance against selected pathogens. PTX3 has properties similar to Abs; its production is induced by pathogen recognition, it recognizes microbial moieties, activates complement, and facilitates cellular recognition by phagocytes. The mechanisms responsible for the effector function of PTX3 in vivo have not been elucidated. OmpA, a major outer membrane protein of Gram-negative Enterobacteriaceae, is a microbial moiety recognized by PTX3. In the air pouch model, KpOmpA induces an inflammatory response, which is amplified by coadministration of PTX3 in terms of leukocyte recruitment and proinflammatory cytokine production. PTX3 did not affect the inflammatory response to LPS, a microbial moiety not recognized by PTX3. As PTX3 binds to C1q and modulates the activation of the complement cascade, we assessed the involvement of complement in the amplification of the response elicited by KpOmpA and PTX3. Experiments performed using cobra venom factor, C1-esterase inhibitor, and soluble complement receptor 1 indicate that PTX3 amplifies the inflammatory response to KpOmpA through complement activation. The results reported here demonstrate that PTX3 activates a complement-dependent humoral amplification loop of the innate response to a microbial ligand.

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.