Celine A. Beamer

Critical Role of MARCO in Crystalline Silica–Induced Pulmonary Inflammation

Chronic exposure to crystalline silica can lead to the development of silicosis, an irreversible, inflammatory and fibrotic pulmonary disease. Although, previous studies established the macrophage receptor with collagenous structure (MARCO) as an important receptor for binding and uptake of crystalline silica particles in vitro, the role of MARCO in regulating the inflammatory response following silica exposure in vivo remains unknown. Therefore, we determined the role of MARCO in crystalline silica-induced pulmonary pathology using C57Bl/6 wild-type (WT) and MARCO(-/-) mice. Increased numbers of MARCO(+) pulmonary macrophages were observed following crystalline silica, but not phosphate-buffered saline and titanium dioxide (TiO(2)), instillation in WT mice, highlighting a specific role of MARCO in silica-induced pathology. We hypothesized that MARCO(-/-) mice will exhibit diminished clearance of silica leading to enhanced pulmonary inflammation and exacerbation of silicosis. Alveolar macrophages isolated from crystalline silica-exposed mice showed diminished particle uptake in vivo as compared with WT mice, indicating abnormalities in clearance mechanisms. Furthermore, MARCO(-/-) mice exposed to crystalline silica showed enhanced acute inflammation and lung injury marked by increases in early response cytokines and inflammatory cells compared with WT mice. Similarly, histological examination of MARCO(-/-) lungs at 3 months post-crystalline silica exposure showed increased chronic inflammation compared with WT; however, only a small difference was observed with respect to development of fibrosis as measured by hydroxyproline content. Altogether, these results demonstrate that MARCO is important for clearance of crystalline silica in vivo and that the absence of MARCO results in exacerbations in innate pulmonary immune responses.

Innate immune processes are sufficient for driving silicosis in mice

The lung is constantly exposed to potentially pathogenic particles and microorganisms. It has become evident recently that not only innate but also adaptive immune responses to particulates, such as SiO2 entering the respiratory tract, are complex and dynamic events. Although the cellular mechanisms and anatomical consequences involved in the development of silicosis have been studied extensively, they still remain poorly understood. Based on their capacity for immune regulation, lymphocytes may play a key role in the respiratory response to environmental challenge by SiO2. The objective of this study was to characterize the impact of SiO2 exposure on respiratory immune processes, with particular emphasis on evaluating the importance of lymphocytes in the murine silicosis model. Therefore, lymphopenic mice, including NK‐deficient, Rag1−/−, or a combination (Rag1−/− NK‐depleted), were used and demonstrated that SiO2‐induced fibrosis and inflammation can occur independently of T, B, NK T, and NK cells. Studies in Rag1−/− mice suggest further that lymphocytes may participate in the regulation of SiO2‐induced inflammation through modulation of the Nalp3 inflammasome. This observation may have clinical relevance in the treatment of inflammatory and fibrotic lung diseases that are refractory or respond suboptimally to current therapeutics.

IL-33 mediates multi-walled carbon nanotube (MWCNT)-induced airway hyper-reactivity via the mobilization of innate helper cells in the lung

Abstract Allergic asthma is a chronic inflammatory disorder of the airway associated with bronchial obstruction, airway hyper-reactivity (AHR), and mucus production. The epithelium may direct and propagate asthmatic-like responses. Central to this theory is the observation that viruses, air pollution, and allergens promote epithelial damage and trigger the generation of IL-25, IL-33, and TSLP via innate pathways such as TLRs and purinergic receptors. Similarly, engineered nanomaterials promote a Th2-associated pathophysiology. In this study, we tested the hypothesis that instillation of multi-walled carbon nanotubes (MWCNT) impair pulmonary function in C57Bl/6 mice due to the development of IL-33-dependent Th2-associated inflammation. MWCNT exposure resulted in elevated levels of IL-33 in the lavage fluid (likely originating from airway epithelial cells), enhanced AHR, eosinophil recruitment, and production of Th2-associated cytokines and chemokines. Moreover, these events were dependent on IL-13 signaling and the IL-33/ST2 axis, but independent of T and B cells. Finally, MWCNT exposure resulted in the recruitment of innate lymphoid cells. Collectively, our data suggest that MWCNT induce epithelial damage that results in release of IL-33, which in turn promotes innate lymphoid cell recruitment and the development of IL-13-dependent inflammatory response.

IL-1R signalling is critical for regulation of multi-walled carbon nanotubes-induced acute lung inflammation in C57Bl/6 mice

Abstract Exposure to certain engineered nanomaterials has been associated with pathological changes in animal models raising concerns about potential human health effects. MWCNT have been reported to activate the NLRP3 inflammasome in vitro, correlating with lung inflammation and pathology, in vivo. In this study, we investigated the role of IL-1 signalling in pulmonary inflammatory responses in WT and IL-1R-/- mice after exposure to MWCNT. The results suggest that MWCNT were effective in inducing acute pulmonary inflammation. Additionally, WT mice demonstrated significant increased airway resistance 24 h post exposure to MWCNT, which was also blocked in the IL-1R-/- mice. In contrast, by 28 days post exposure to MWCNT, the inflammatory response that was initially absent in IL-1R-/- mice was elevated in comparison to the WT mice. These data suggest that IL-1R signalling plays a crucial role in the regulation of MWCNT-induced pulmonary inflammation.

Aryl hydrocarbon receptor (AhR) regulates silica-induced inflammation but not fibrosis.

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is responsible for mediating a variety of pharmacological and toxicological effects caused by halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, recent evidence has revealed that the AhR also has numerous physiological roles aside from xenobiotic metabolism, including regulation of immune and inflammatory signaling as well as normal development and homeostasis of several organs. To investigate the role of the AhR in crystalline silica (SiO(2))-induced inflammation and fibrosis, C57Bl/6 and AhR(-/)(-) mice were exposed to SiO(2) or vehicle. Similarly, C57Bl/6 mice were exposed to SiO(2) and TCDD either simultaneously or sequentially to assess whether AhR activation alters inflammation and fibrosis. SiO(2)-induced acute lung inflammation was more severe in AhR(-)(/-) mice; however, the fibrotic response of AhR(-)(/-) mice was attenuated compared with C57Bl/6 mice. In a model of chronic SiO(2) exposure, AhR activation by TCDD in C57Bl/6 mice resulted in reduced inflammation; however, the fibrotic response was not affected. Bone marrow-derived macrophages (BMM) from AhR(-)(/-) mice also produced higher levels of cytokines and chemokines in response to SiO(2). Analysis of gene expression revealed that BMM derived from AhR(-)(/-) mice exhibit increased levels of pro-interleukin (IL)-1β, IL-6, and Bcl-2, yet decreased levels of signal transducers and activators of transcription (STAT)2, STAT5a, and serpin B2 (Pai-2) in response to SiO(2).

Role of the aryl hydrocarbon receptor (AhR) in lung inflammation

Millions of individuals worldwide are afflicted with acute and chronic respiratory diseases, causing temporary and permanent disabilities and even death. Oftentimes, these diseases occur as a result of altered immune responses. The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, acts as a regulator of mucosal barrier function and may influence immune responsiveness in the lungs through changes in gene expression, cell–cell adhesion, mucin production, and cytokine expression. This review updates the basic immunobiology of the AhR signaling pathway with regards to inflammatory lung diseases such as asthma, chronic obstructive pulmonary disease, and silicosis following data in rodent models and humans. Finally, we address the therapeutic potential of targeting the AhR in regulating inflammation during acute and chronic respiratory diseases.

Silica suppresses Toll-like receptor ligand-induced dendritic cell activation

Inhalation of silica, without evidence of silicosis, is believed to predispose individuals to bacterial infections and impair respiratory immune functions. Silica may alter the sensitivity of antigen‐presenting cells (APCs), such as macrophages and dendritic cells (DCs), to other types of infection;however, the exact nature of these exchanges remains uncertain. The purpose of the present study is to characterize the effect of silica exposure on innate pulmonary defensemechanisms following Toll‐like receptor (TLR) ligand‐ induced activation using DCs as a model APC and determine whether these signals act in synergy or opposition to one another. Using C57Bl/6 mice, pattern recognition receptor expression on DCs was examined in vitro and in vivo using flow cytometry, and the activation state of pulmonary and granulocyte‐macrophage colony‐stimulating factor‐derived DCs was assessed in response to silica in combination with TLR ligands (lipopolysaccharide, cytosine‐phosphate‐guanine, or polyinosinic:polycytidylic acid) using flow cytometry and measurement of cytokine production. In this study, silica attenuated TLR ligand‐dependent DC activation with regards to accessory molecule expression as well as nitric oxide and inflammatory cytokine production. Furthermore, silicas ability to modulate TLR ligand‐dependent DC activation did not appear to be dependent on the class A scavenger receptors. Taken together, silicas ability to alter susceptibility to infection may be due to impaired inflammatory re sponses and reduced antibacterial activity.— Beamer, C. A., Holian, A. Silica suppresses Toll‐like receptor ligand‐induced dendritic cell activation. FASEB J. 22, 2053–2063 (2008)

Motheaten (me/me) mice deficient in SHP-1 are less susceptible to focal cerebral ischemia

We have demonstrated previously that the protein tyrosine phosphatase SHP‐1 seems to play a role in glial development and is upregulated in non‐dividing astrocytes after injury. The present study examines the effect of loss of SHP‐1 on the CNS response to permanent focal ischemia. SHP‐1 deficient (me/me) mice and wild‐type littermates received a permanent middle cerebral artery occlusion (MCAO). At 1, 3, and 7 days after MCAO, infarct volume, neuronal survival and cell death, gliosis, and inflammatory cytokine levels were quantified. SHP‐1 deficient me/me mice display smaller infarct volumes at 7 days post‐MCAO, increased neuronal survival within the ischemic penumbra, and decreased numbers of cleaved caspase 3+ cells within the ischemic core compared with wild‐type mice. In addition, me/me mice exhibit increases in GFAP+ reactive astrocytes, F4‐80+ microglia, and a concomitant increase in the level of interleukin 12 (IL‐12) over baseline compared with wild‐type. Taken together, these results demonstrate that loss of SHP‐1 results in greater healing of the infarct due to less apoptosis and more neuronal survival in the ischemic core and suggests that pharmacologic inactivation of SHP‐1 may have potential therapeutic value in limiting CNS degeneration after ischemic stroke.

Inhibition of TLR Ligand- and Interferon Gamma-Induced Murine Microglial Activation by Panax Notoginseng

Among the many products which influence microglial activation and resulting neuroinflammation, herbal medicine has recently drawn much attention due to its immunomodulatory and neuroprotective activities. The purpose of the current study was to investigate the effects of an extract of Panax notoginseng (NotoG™) on TLR ligand- and IFNγ-induced activation in N9 and EOC20 microglial cells lines. NotoG suppressed microglial activation as measured by reduced expression of accessory molecules (CD40 and CD86), decreased production of inflammatory mediators (IL-6 and TNFα), and diminished release of antibacterial products (nitric oxide). Furthermore, this immunosuppressive activity was neither dependent on the glucocorticoid receptor, nor the result of a single ginsenosides (Rb1, Rg1, or Re), which are the major active constituents of the whole extract. NotoG and select ginsenosides may therefore be of therapeutic benefit in treating or preventing neurodegenerative diseases such as multiple sclerosis and parkinson’s disease.

Environmental Immunology: Lessons Learned from Exposure to a Select Panel of Immunotoxicants

Exposure to environmental contaminants can produce profound effects on the immune system. Many classes of xenobiotics can significantly suppress or enhance immune responsiveness depending on the levels (i.e., dose) and context (i.e., timing, route) of exposure. Although defining the effects that toxicants can have on the immune system is a valuable component to improving public health, environmental immunology has greatly enhanced our understanding of how the immune system functions and has provided innovative avenues to explore new immunotherapies. This Brief Review focuses on three examples of how immunotoxicology has benefitted the field of immunology, presenting information on the aryl hydrocarbon receptor signaling pathway, the immunomodulatory effects of nanomaterials, and the impact of xenobiotic exposure on the developing immune system. Collectively, contributions from immunotoxicology have significantly enhanced public health and spurred seminal advances in both basic and applied immunology.