Autoantibodies are associated with disease progression in idiopathic pulmonary fibrosis.

Several reports have highlighted a potential role of autoreactive B-cells and autoantibodies that correlates with increased disease severity in patients with idiopathic pulmonary fibrosis (IPF). Here we show that patients with IPF have an altered B-cell phenotype and that those subjects who have autoantibodies against the intermediate filament protein periplakin (PPL) have a significantly worse outcome in terms of progression-free survival. Using a mouse model of lung fibrosis, we demonstrate that introducing antibodies targeting the endogenous protein PPL (mimicking naturally occurring autoantibodies seen in patients) directly in the lung increases lung injury, inflammation, collagen and fibronectin expression through direct activation of follicular dendritic cells, which in turn activates and drives proliferation of fibroblasts. This fibrocyte population was also observed in fibrotic foci of patients with IPF and was increased in peripheral blood of IPF patients compared to aged-matched controls. This study reiterates the complex and heterogeneous nature of IPF, identifying new pathways that may prove suitable for therapeutic intervention.

IL-15 suppresses colitis-associated colon carcinogenesis by inducing antitumor immunity.

IL-15 regulates the development, survival, and proliferation of multiple innate and adaptive immune cells and plays a dual role, inducing both tumor cell growth and antitumor immunity. However, the role of IL-15 in inflammation-induced cancer remains unclear. To explore this, we have compared the colon carcinoma burden of Il15-/- and Il15rα -/- mice with wild type (WT) mice after induction of colitis-associated colon carcinogenesis utilizing the AOM/DSS model. Compared to WT mice, Il15-/- but not Il15rα -/- mice showed reduced survival, along with higher tumor incidence, colon weight, and tumor size. This suggests that low affinity IL-15 signaling via the shared IL-2Rß/γc decreases the risk for developing colitis-associated cancer. CD11c-Il15 mice, in which IL-15 expression is reconstituted in Il15-/- mice under the control of the CD11c-promoter, showed that selective reconstitution of IL-15 in antigen-presenting cells restored the CD8+ T and NK cell compartments, serum levels of IFNγ, G-CSF, IL-10, and CXCL1 and reduced tumor burden. After demonstrating IL-15 expression in human colorectal cancer (CRC) cells in situ, we investigated the role of this cytokine in the modulation of key colonic oncogenic pathways in the tumor. While these pathways were found to be unaltered in the absence of IL-15, tumor transcriptome analysis showed that the loss of IL-15 upregulates key inflammatory mediators associated with colon cancer progression, such as IL-1ß, IL-22, IL-23, Cxcl5, and Spp1. These findings provide evidence that IL-15 suppresses colitis-associated colon carcinogenesis through regulation of antitumor cytotoxicity, and modulation of the inflammatory tumor micromilieu.

Listeria monocytogenes alters mast cell phenotype, mediator and osteopontin secretion in a listeriolysin-dependent manner.

Whilst mast cells participate in the immune defence against the intracellular bacterium Listeria monocytogenes, there is conflicting evidence regarding the ability of L. monocytogenes to infect mast cells. It is known that the pore-forming toxin listeriolysin (LLO) is important for mast cell activation, degranulation and the release of pro-inflammatory cytokines. Mast cells, however, are a potential source of a wide range of cytokines, chemokines and other mediators including osteopontin, which contributes to the clearing of L. monocytogenes infections in vivo, although its source is unknown. We therefore aimed to resolve the controversy of mast cell infection by L. monocytogenes and investigated the extent of mediator release in response to the bacterium. In this paper we show that the infection of bone marrow-derived mast cells by L. monocytogenes is inefficient and LLO-independent. LLO, however, is required for calcium-independent mast cell degranulation as well as for the transient and selective downregulation of cell surface CD117 (c-kit) on mast cells. We demonstrate that in addition to the key pro-inflammatory cytokines TNF-α and IL-6, mast cells release a wide range of other mediators in response to L. monocytogenes. Osteopontin, IL-2, IL-4, IL-13 and granulocyte macrophage colony-stimulating factor (GM-CSF), and chemokines including CCL2, CCL3, CCL4 and CCL5 are released in a MyD88-dependent manner. The wide range of mediators released by mast cells in response to L. monocytogenes may play an important role in the recruitment and activation of a variety of immune cells in vivo. The cocktail of mediators, however, is unlikely to skew the immune response to a particular effector response. We propose that mast cells provide a hitherto unreported source of osteopontin, and may provide an important role in co-ordinating the immune response during Listeria infection.

IL-33 causes selective mast cell tolerance to bacterial cell wall products by inducing IRAK1 degradation.

Mast cells are important cellular constituents of epithelial-mesenchymal interactions, densely located at sites of microbial entry into the host where they are continuously exposed to products from commensals. In order to avoid excessive activation and the associated pathology, mast cell responses to TLR agonists must be tightly regulated. Here, we show that exposure in vitro to subactivating levels of the epithelial cell product, IL-33, renders mast cells insensitive to bacterial cell wall products. Mast cell responsiveness to Ag, cytoplasmic dsDNA, and TLR7/8 agonists is unaffected or enhanced by IL-33. The IL-33-induced mast cell selective tolerance requires the IL-33 receptor ST2 and peritoneal mast cells from St2(-/-) mice display a constitutively activated phenotype, demonstrated by increased expression of activation markers including CD11b and CD28. IL-33 exposure neither affects the levels of TLR4, MyD88, TIRAP, IL-1R associated kinase 2 (IRAK2), or IRAK4, nor induces persistent A20 or Tollip expression, but potently causes ST2-dependent IRAK1 degradation. We show that while IRAK2 is redundant for TLR4 signaling, IRAK1 is essential for TLR4 signaling in mast cells. We suggest that IL-33 produced during homeostasis retains mast cells in an unresponsive state to bacterial cell wall products via IRAK1 degradation, thus preventing chronic inflammation and tissue destruction.

Codon-usage-based inhibition of HIV protein synthesis by human schlafen 11.

In mammals, one of the most pronounced consequences of viral infection is the induction of type I interferons, cytokines with potent antiviral activity. Schlafen (Slfn) genes are a subset of interferon-stimulated early response genes (ISGs) that are also induced directly by pathogens via the interferon regulatory factor 3 (IRF3) pathway. However, many ISGs are of unknown or incompletely understood function. Here we show that human SLFN11 potently and specifically abrogates the production of retroviruses such as human immunodeficiency virus 1 (HIV-1). Our study revealed that SLFN11 has no effect on the early steps of the retroviral infection cycle, including reverse transcription, integration and transcription. Rather, SLFN11 acts at the late stage of virus production by selectively inhibiting the expression of viral proteins in a codon-usage-dependent manner. We further find that SLFN11 binds transfer RNA, and counteracts changes in the tRNA pool elicited by the presence of HIV. Our studies identified a novel antiviral mechanism within the innate immune response, in which SLFN11 selectively inhibits viral protein synthesis in HIV-infected cells by means of codon-bias discrimination.

TLR signaling in mast cells: common and unique features.

In addition to the well known role of mast cells in immunity to multi-cellular parasites and in the pathogenesis of allergy and asthma, the importance of mast cells in the immune defense against bacteria and viruses is increasingly being recognized. Their location in the skin, gut, and airways puts mast cells in an ideal location to encounter and respond to pathogens, and in order to perform this function, these cells express a variety of pattern recognition receptors, including Toll-like receptors (TLRs). Mast cells respond to TLR ligands by secreting cytokines, chemokines, and lipid mediators, and some studies have found that TLR ligands can also cause degranulation, although this finding is contentious. In addition, stimulation via TLR ligands can synergize with signaling via the FcεRI, potentially enhancing the response of the cells to antigen in vivo. A great deal is now known about TLR signaling pathways. Some features of these pathways are cell type-specific, however, and work is under way to fully elucidate the TLR signaling cascades in the mast cell. Already, some interesting differences have been identified. This review aims to address what is known about the responses of mast cells to TLR ligands and the signaling pathways involved. Given the location of mast cells at sites exposed to the environment, the response of these cells to TLR ligands must be carefully regulated. The known mechanisms behind this regulation are also reviewed here.

Fibronectin is a TH1-specific molecule in human subjects.

BACKGROUND: T(H)1 cell-mediated immunity is essential for host defense against a variety of intracellular pathogens, such as mycobacteria, salmonella, and Leishmania species. A major T(H)1-mediated effector mechanism involves the IFN-gamma-induced killing of the pathogen by infected macrophages. OBJECTIVES: The range of known T(H)1-specific effector molecules is limited, especially in human subjects. We sought to identify novel effector molecules that might be involved in T(H)1-mediated pathogen clearance. METHODS: We performed microarray-based analysis of human T(H)1 and T(H)2 cells to identify T(H)1-specific molecules. These analyses identified the extracellular matrix molecule fibronectin as a highly expressed T(H)1-specific molecule. We examined the expression of fibronectin in a variety of human cell types by using real-time RT-PCR, ELISA, and Western blotting. We also studied the role of fibronectin in modulating monocyte phenotype using in vitro culture. RESULTS: We show that human T(H)1 cells constitutively express and secrete fibronectin after in vitro differentiation from naive precursors. Furthermore, we demonstrate that ex vivo human T(H)1 cells selectively express fibronectin when compared with T(H)2 cells. The predominant isoform of fibronectin expressed by T(H)1 cells contains additional domains of the protein responsible for alpha4beta1 integrin binding and activation of Toll-like receptor 4. We show that treatment of monocytes with T(H)1 cell-derived fibronectin induces expression of the proinflammatory cytokine IL-6 while inhibiting IL-10 expression. CONCLUSIONS: Because fibronectin also plays a major role in the attachment and opsonization of numerous intracellular pathogens, we propose that it might be a critical molecule produced by T(H)1 cells involved in pathogen eradication.

Human Th2 cells selectively express the orexigenic peptide, pro-melanin-concentrating hormone.

Th1 and Th2 cells represent the two main functional subsets of CD4(+) T helper cell, and are defined by their cytokine expression. Human Th1 cells express IFNgamma, whilst Th2 cells express IL-4, IL-5, and IL-13. Th1 and Th2 cells have distinct immunological functions, and can drive different immunopathologies. Here, we show that in vitro-differentiated human Th2 cells highly selectively express the gene for pro-melanin-concentrating hormone (PMCH), using real-time RT-PCR, enzyme immunoassay, and Western blot analysis. PMCH encodes the prohormone, promelanin-concentrating hormone (PMCH), which is proteolytically processed to produce several peptides, including the orexigenic hormone melanin-concentrating hormone (MCH). PMCH expression by Th2 cells was activation responsive and increased throughout the 28-day differentiation in parallel with the expression of the Th2 cytokine genes. MCH immunoreactivity was detected in the differentiated Th2 but not Th1 cell culture supernatants after activation, and contained the entire PMCH protein, in addition to several smaller peptides. Human Th1 and Th2 cells were isolated by their expression of IFNgamma and CRTH2, respectively, and the ex vivo Th2 cells expressed PMCH upon activation, in contrast to the Th1 cells. Because Th2 cells are central to the pathogenesis of allergic diseases including asthma, expression of PMCH by activated Th2 cells in vivo may directly link allergic inflammation to energy homeostasis and may contribute to the association between asthma and obesity.

Contrary prostaglandins: the opposing roles of PGD2 and its metabolites in leukocyte function.

Traditionally, PGD(2) has been considered to be a pro-inflammatory mediator, acting via classical PG receptors, such as the PGD(2) receptor (DP). PGD(2) is degraded rapidly in vitro and in vivo to a variety of metabolites, the majority of which were thought, until recently, to be physiologically inactive. Several "inactive" metabolites, particularly 15d-PGJ(2), have been shown to have wide-ranging effects on leukocytes and other cell types, however, and a potentially important anti-inflammatory role for PGD(2) has now been recognized, and the complexity of PGD(2) signaling is beginning to be elucidated. PGD(2) and its metabolites are biologically active over a broad concentration range, and, intriquingly, it appears that there are marked concentration-dependent variations in the consequences of signaling by these eicosanoids, which have the potential to exert pro- and anti-inflammatory effects. For example, the actions of PGD(2) can influence multiple stages in the life of the mature eosinophil, from causing its release from the bone marrow to inducing its recruitment and activation and, ultimately, regulating its apoptosis. This review is concerned with the diverse responses induced in leukocytes by PGD(2) and its metabolites and the signaling mechanisms which are thought to be responsible for them.

9alpha,11beta-PGF2 and its stereoisomer PGF2alpha are novel agonists of the chemoattractant receptor, CRTH2.

CRTH2 is a recently described chemoattractant receptor for the prostaglandin, PGD(2), expressed by Th2 cells, eosinophils and basophils, and believed to play a role in allergic inflammation. Here we describe the potency of several PGD(2) metabolites at the receptor to induce cell migration and activation. We report for the first time that the PGD(2) metabolite, 9alpha,11beta-PGF(2), and its stereoisomer, PGF(2alpha), are CRTH2 agonists. 9alpha,11beta-PGF(2) is a major metabolite produced in vivo following allergen challenge, whilst PGF(2alpha) is generated independently of PGD synthetase, with implications for CRTH2 signalling in the presence or absence of PGD(2) production.

11-Dehydro-thromboxane B2, a stable thromboxane metabolite, is a full agonist of chemoattractant receptor-homologous molecule expressed on TH2 cells (CRTH2) in human eosinophils and basophils.

Thromboxane (TX) A(2), a cyclooxygenase-derived mediator involved in allergic responses, is rapidly converted in vivo to a stable metabolite, 11-dehydro-TXB(2), which is considered to be biologically inactive. In this study, we found that 11-dehydro-TXB(2), but not the TXA(2) analogue U46,619 or TXB(2), activated eosinophils and basophils, as assayed by flow cytometric shape change. 11-Dehydro-TXB(2) was also chemotactic for eosinophils but did not induce, nor inhibit, platelet aggregation. Chemoattractant receptor-homologous molecule expressed on TH2 cells (CRTH2) is an important chemoattractant receptor expressed by eosinophils, basophils, and TH2 lymphocytes, and prostaglandin (PG)D(2) has been shown to be its principal ligand. 11-Dehydro-TXB(2) induced calcium flux mainly from intracellular stores in eosinophils, and this response was desensitized after stimulation with PGD(2) but not other eosinophil chemoattractants. Shape change responses of eosinophils and basophils to 11-dehydro-TXB(2) were inhibited by the thromboxane (TP)/CRTH2 receptor antagonist ramatroban, but not the selective TP antagonist SQ29,548, and were insensitive to pertussis toxin. The phospholipase C inhibitor U73,122 attenuated both 11-dehydro-TXB(2)- and PGD(2)-induced shape change. 11-Dehydro-TXB(2) also induced the chemotaxis of BaF/3 cells transfected with hCRTH2 but not naive BaF/3 cells. At a threshold concentration, 11-dehydro-TXB(2) had no antagonistic effect on CRTH2-mediated responses as induced by PGD2. These data show that 11-dehydro-TXB(2) is a full agonist of the CRTH2 receptor and hence might cause CRTH2 activation in cellular contexts where PGD-synthase is not present. Given its production in the allergic lung, antagonism of the 11-dehydro-TXB(2)/CRTH2axis may be of therapeutic relevance.