Ivan Caiello

Nerve Growth Factor Downregulates Inflammatory Response in Human Monocytes through TrkA

Nerve growth factor (NGF) levels are highly increased in inflamed tissues, but their role is unclear. We show that NGF is part of a regulatory loop in monocytes: inflammatory stimuli, while activating a proinflammatory response through TLRs, upregulate the expression of the NGF receptor TrkA. In turn, NGF, by binding to TrkA, interferes with TLR responses. In TLR-activated monocytes, NGF reduces inflammatory cytokine production (IL-1β, TNF-α, IL-6, and IL-8) while inducing the release of anti-inflammatory mediators (IL-10 and IL-1 receptor antagonist). NGF binding to TrkA affects TLR signaling, favoring pathways that mediate inhibition of inflammatory responses: it increases Akt phosphorylation, inhibits glycogen synthase kinase 3 activity, reduces IκB phosphorylation and p65 NF-κB translocation, and increases nuclear p50 NF-κB binding activity. Use of TrkA inhibitors in TLR-activated monocytes abolishes the effects of NGF on the activation of anti-inflammatory signaling pathways, thus increasing NF-κB pathway activation and inflammatory cytokine production while reducing IL-10 production. PBMC and mononuclear cells obtained from the synovial fluid of patients with juvenile idiopathic arthritis show marked downregulation of TrkA expression. In ex vivo experiments, the addition of NGF to LPS-activated juvenile idiopathic arthritis to both mononuclear cells from synovial fluid and PBMC fails to reduce the production of IL-6 that, in contrast, is observed in healthy donors. This suggests that defective TrkA expression may facilitate proinflammatory mechanisms, contributing to chronic tissue inflammation and damage. In conclusion, this study identifies a novel regulatory mechanism of inflammatory responses through NGF and its receptor TrkA, for which abnormality may have pathogenic implications for chronic inflammatory diseases.

Inhibition of Natural Killer Cell Cytotoxicity by Interleukin-6: Implications for the Pathogenesis of Macrophage Activation Syndrome

Systemic juvenile idiopathic arthritis (JIA) is associated with high levels of interleukin‐6 (IL‐6) in the serum and synovial fluid, and impairment of natural killer (NK) cell function is often observed. This study was undertaken to evaluate a possible link between these 2 biologic findings and whether they may be associated with the development of macrophage activation syndrome, a condition frequently observed in systemic JIA.

Inflammasome Activation by Cystine Crystals: Implications for the Pathogenesis of Cystinosis

Intralysosomal cystine crystal accumulation, due to mutations in the CTNS gene, is a hallmark of nephropathic cystinosis, but the role of these crystals in disease pathogenesis remains unclear. We hypothesized that, similar to other host-derived crystalline moieties, cystine crystals can induce IL-1β production through inflammasome activation. Thus, we investigated the proinflammatory effects of cystine crystals in primary human PBMCs. LPS-primed PBMCs stimulated with cystine crystals secreted IL-1β in a dose-dependent manner. Similarly to IL-1β secretion induced by other crystalline inflammasome activators, cystine crystal-induced IL-1β secretion required activation of caspase-1. Additionally, exogenous cystine crystals were internalized by monocytes, and inhibition of phagocytosis, cathepsin B leakage, generation of reactive oxygen species, and potassium efflux reduced cystine crystal-induced IL-1β secretion. Patients with cystinosis had higher levels of circulating IL-1β and IL-18 compared with controls. Analysis of inflammasome-related gene expression in PBMCs from patients with cystinosis revealed a significant increase in IL-1β and CASP-1 transcript levels compared with controls. Moreover, knockout of cystinosin in mice led to significant increases in serum IL-18 levels and kidney expression of inflammasome-related genes (Casp-1, Pycard, Il-18, Il18r1, Il1r1, and Il1rl2). Taken together, these data demonstrate that cystine crystals are endogenous inflammasome-activating stimuli, suggesting a novel role for cystine crystals in the pathogenesis of nephropathic cystinosis.

IL-6 amplifies TLR mediated cytokine and chemokine production: Implications for the pathogenesis of rheumatic inflammatory diseases

The role of Interleukin(IL)-6 in the pathogenesis of joint and systemic inflammation in rheumatoid arthritis (RA) and systemic juvenile idiopathic arthritis (s-JIA) has been clearly demonstrated. However, the mechanisms by which IL-6 contributes to the pathogenesis are not completely understood. This study investigates whether IL-6 affects, alone or upon toll like receptor (TLR) ligand stimulation, the production of inflammatory cytokines and chemokines in human peripheral blood mononuclear cells (PBMCs), synovial fluid mononuclear cells from JIA patients (SFMCs) and fibroblast-like synoviocytes from rheumatoid arthritis patients (RA synoviocytes) and signalling pathways involved. PBMCs were pre-treated with IL-6 and soluble IL-6 Receptor (sIL-6R). SFMCs and RA synoviocytes were pre-treated with IL-6/sIL-6R or sIL-6R, alone or in combination with Tocilizumab (TCZ). Cells were stimulated with LPS, S100A8-9, poly(I-C), CpG, Pam2CSK4, MDP, IL-1β. Treatment of PBMCs with IL-6 induced production of TNF-α, CXCL8, and CCL2, but not IL-1β. Addition of IL-6 to the same cells after stimulation with poly(I-C), CpG, Pam2CSK4, and MDP induced a significant increase in IL-1β and CXCL8, but not TNF-α production compared with TLR ligands alone. This enhanced production of IL-1β and CXCL8 paralleled increased p65 NF-κB activation. In contrast, addition of IL-6 to PBMCs stimulated with LPS or S100A8-9 (TLR-4 ligands) led to reduction of IL-1β, TNF-α and CXCL8 with reduced p65 NF-κB activation. IL-6/IL-1β co-stimulation increased CXCL8, CCL2 and IL-6 production. Addition of IL-6 to SFMCs stimulated with LPS or S100A8 increased CXCL8, CCL2 and IL-1β production. Treatment of RA synoviocytes with sIL-6R increased IL-6, CXCL8 and CCL2 production, with increased STAT3 and p65 NF-κB phosphorylation. Our results suggest that IL-6 amplifies TLR-induced inflammatory response. This effect may be relevant in the presence of high IL-6 and sIL-6R levels, such as in arthritic joints in the context of stimulation by endogenous TLR ligands.

Reaching the Threshold: A Multilayer Pathogenesis of Macrophage Activation Syndrome

Macrophage activation syndrome (MAS) is a potentially fatal complication of rheumatic diseases. The condition is considered part of secondary hemophagocytic lymphohistiocytoses (HLH). There are similarities in genetic background, pathogenesis, and clinical and laboratory features with primary HLH (p-HLH). We describe findings in mouse models of secondary HLH, comparing them with models of p-HLH and the cellular and molecular mechanisms involved, and relate them to recent findings in patients with secondary HLH. A multilayer model is presented in which background inflammation, infections, and genetics all contribute in different proportions and in several ways. Once the “threshold” has been reached, inflammatory cytokines are the final effectors, independent of the interplay between different upstream pathogenic factors.

Neutralization of IFN-γ reverts clinical and laboratory features in a mouse model of macrophage activation syndrome

Background: The pathogenesis of macrophage activation syndrome (MAS) is not clearly understood: a large body of evidence supports the involvement of mechanisms similar to those implicated in the setting of primary hemophagocytic lymphohistiocytosis. Objective: We sought to investigate the pathogenic role of IFN‐&ggr; and the therapeutic efficacy of IFN‐&ggr; neutralization in an animal model of MAS. Methods: We used an MAS model established in mice transgenic for human IL‐6 (IL‐6TG mice) challenged with LPS (MAS mice). Levels of IFN‐&ggr; and IFN‐&ggr;–inducible chemokines were evaluated by using real‐time PCR in the liver and spleen and by means of ELISA in plasma. IFN‐&ggr; neutralization was achieved by using the anti–IFN‐&ggr; antibody XMG1.2 in vivo. Results: Mice with MAS showed a significant upregulation of the IFN‐&ggr; pathway, as demonstrated by increased mRNA levels of Ifng and higher levels of phospho–signal transducer and activator of transcription 1 in the liver and spleen and increased expression of the IFN‐&ggr;–inducible chemokines Cxcl9 and Cxcl10 in the liver and spleen, as well as in plasma. A marked increase in Il12a and Il12b expression was also found in livers and spleens of mice with MAS. In addition, mice with MAS had a significant increase in numbers of liver CD68+ macrophages. Mice with MAS treated with an anti–IFN‐&ggr; antibody showed a significant improvement in survival and body weight recovery associated with a significant amelioration of ferritin, fibrinogen, and alanine aminotransferase levels. In mice with MAS, treatment with the anti–IFN‐&ggr; antibody significantly decreased circulating levels of CXCL9, CXCL10, and downstream proinflammatory cytokines. The decrease in CXCL9 and CXCL10 levels paralleled the decrease in serum levels of proinflammatory cytokines and ferritin. Conclusion: These results provide evidence for a pathogenic role of IFN‐&ggr; in the setting of MAS.

Interferon-gamma (IFNy) in macrophage activation syndrome (MAS) associated with systemic juvenile idiopathic arthritis (sJIA). High levels in patients and a role in a murine mas model

Interferon-gamma (IFNg) in macrophage activation syndrome (MAS) associated with systemic juvenile idiopathic arthritis (sJIA). High levels in patients and a role in a murine mas model Claudia Bracaglia, Ivan Caiello, Kathy De Graaf, Giovanni D’Ario, Florence Guilhot, Walter Ferlin, Lidia Melli, Giusi Prencipe, Sergio Davi, Grant Schulert, Angelo Ravelli, Alexei Grom, Cristina De Min, Fabrizio De Benedetti

Switched Memory B Cells Are Increased in Oligoarticular and Polyarticular Juvenile Idiopathic Arthritis and Their Change Over Time Is Related to Response to Tumor Necrosis Factor Inhibitors

To investigate whether abnormalities in B cell subsets in patients with juvenile idiopathic arthritis (JIA) correlate with clinical features and response to treatment.

High levels of interferon-gamma (IFNγ) in macrophage activation syndrome (MAS) and CXCL9 levels as a biomarker for IFNγ production in MAS

Objectives Given the similarities between primary and secondary HLH (sec-HLH), including MAS, we measured levels of IFNg, IFNg-related chemokines (CXCL9, CXCL10, CXLC11), and IL-6 in patients with sec-HLH, and in patients with systemic Juvenile Idiopathic Arthritis (sJIA) with or without MAS at sampling and evaluated their relation to disease activity. In addition, we evaluated the correlation between serum levels of IFNg and of the three IFNg related chemokines with themselves and with laboratory parameters of disease activity in patients with active MAS.

Neutralization of Interferon-gamma is efficacious in a mouse model of HLH secondary to chronic inflammation

Macrophage activation syndrome is a term used to identify hemophagocytic lymphohistiocytosis secondary to rheumatic diseases (rheuHLH). It is a severe, potentially fatal condition that occurs in the context of rheumatic diseases, particularly systemic juvenile idiopathic arthritis. It is part of secondary HLH forms, that are clinically and biochemically similar to primary HLH (pHLH), with generalized hypercytokinemia as a major feature. While the triggering mechanism behind pHLH is the defect in cytotoxicity, caused by mutations in genes encoding proteins required for lymphocyte and natural killer cell activity, the rheuHLH pathogenesis is not clearly understood.