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Key Event Title
Increased, recruitment of inflammatory cells
Key Event Components
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP||Point of Contact||Author Status||OECD Status|
|Substance interaction with the lung cell membrane leading to lung fibrosis||KeyEvent||Sabina Halappanavar (send email)||Under development: Not open for comment. Do not cite||EAGMST Under Review|
|Frustrated phagocytosis-induced lung cancer||KeyEvent||Carole Seidel (send email)||Under development: Not open for comment. Do not cite||Under Development|
Key Event Description
Increased, recruitment of pro-inflammatory cells
How it works
Pro-inflammatory cells originate in bone marrow and are recruited to the site of infection or injury via circulation following specific pro-inflammatory mediator (cytokine and chemokine) signalling. Pro-inflammatory cells are recruited to lungs to clear the invading pathogen or the toxic substance. Monocytes (dendritic cells, macrophages, and neutrophils) are subsets of circulating white blood cells that are involved in the immune responses to pathogen or toxicant stimuli. They are derived from the bone marrow. They can differentiate into different macrophage types and dendritic cells. They can be categorised based on their size, the type of cell surface receptors and their ability to differentiate following external or internal stimulus such as increased expression of cytokines. Monocytes participate in tissue healing, clearance of toxic substance or pathogens, and in the initiation of adaptive immunity. Recruited monocytes can also influence pathogenesis (Ingersoll MA et al., 2011). Sensing or recognition of pathogens and harmful substances results in the recruitment of monocytes to lungs (Shi C and Pamer EG, 2011). Activated immune cells secrete a variety of pro-inflammatory mediators, the purpose of which is to propagate the immune signalling and response, which when not controlled, leads to chronic inflammation, cell death and tissue injury. Thus, KE1 and KE2 act in a positive feedback loop mechanism and propagate the pro-inflammatory environment. All pro-fibrotic agents induce leukocyte infiltration in a dose and time-dependent manner.
Evidence for its perturbation
Macrophages acuumulate in bronchoalveolar fluid (BALF) post-exposure to fibrogenic bleomycin (Phan, 1980; Smith, 1995). NM-induced inflammation is predominantly neutrophilic (Shevedova, 2005; Rahman L, 2017; Rahman, 2017; Poulsen 2015). Increased number of pro-inflammatory cells (Zuo, 2002), neutrophils (Reynolds 1997) is observed in the BALF of IPF patients. Eosinophils are a type of white blood cells and a type of granulocytes (contain granules and enzymes) that are recruited following exposure to allergens, during allergic reactions such as asthma or during fibrosis (Reynolds, 1997). MWCNTs induce increased eosinophil count in lungs (Købler C, 2015). MWCNTs act as allergens and induce lung infiltration of eosinophils and cause airway hypersensitivity (Beamer, 2013).
It is important to note that the stressor-induced MIE, KE1 and KE2 are part of the functional changes that we collectively consider as inflammation, and together, they mark the initiation of acute inflammatory phase. MIE and KE1 occur at the cellular level. KE2 occurs at the tissue level.
How It Is Measured or Detected
How it is measured or detected
In vivo, recruitment of pro-inflammatory cells is measured using BALF cellularity assay.
The fluid lining the lung epithelium (BALF) is lavaged and its composition is assessed as marker of lung immune response to the toxic substances or pathogens. BALF is assessed quantitatively for types of infiltrating cells, levels and types of cytokines and chemokines. Thus, BALF assessment can aid in developing dose-response of a substance, to rank a substances’ potency and to set up no effect level of exposure for the regulatory decision making. For NMs, in vivo BALF assessment is recommended as a mandatory test (discussed in ENV/JM/MONO(2012)40 and also in OECD inhalation TG for NMs). Temporal changes in the BALF composition can be prognostic of initiation and progression of lung immune disease (Cho et al., 2010).
In vitro, it is difficult to assess the recruitment of pro-inflammatory cells. Thus, a suit of pro-inflammatory mediators specific to cell types are assessed using the same techniques mentioned above (qRT-PCR, ELISA, immunohistochemistry) in cell culture models, as indicative of recruitment of cells into the lungs. Details of in vitro methods are described under KE2.
Domain of Applicability
- Cho, W., Duffin, R., Poland, C., Howie, S., MacNee, W., Bradley, M., Megson, I. and Donaldson, K. (2010). Metal Oxide Nanoparticles Induce Unique Inflammatory Footprints in the Lung: Important Implications for Nanoparticle Testing. Environmental Health Perspectives, 118(12), pp.1699-1706.
- Ingersoll, M., Platt, A., Potteaux, S. and Randolph, G. (2011). Monocyte trafficking in acute and chronic inflammation. Trends in Immunology, 32(10), pp.470-477.
- Købler, C., Poulsen, S., Saber, A., Jacobsen, N., Wallin, H., Yauk, C., Halappanavar, S., Vogel, U., Qvortrup, K. and Mølhave, K. (2015). Time-Dependent Subcellular Distribution and Effects of Carbon Nanotubes in Lungs of Mice. PLOS ONE, 10(1), p.e0116481.
- Kolaczkowska, E. and Kubes, P. (2013). Neutrophil recruitment and function in health and inflammation. Nature Reviews Immunology, 13(3), pp.159-175.
- Kopf, M., Schneider, C. and Nobs, S. (2014). The development and function of lung-resident macrophages and dendritic cells. Nature Immunology, 16(1), pp.36-44.
- Phan, S., Thrall, R. and Ward, P. (1980). Bleomycin-induced Pulmonary Fibrosis in Rats: Biochemical Demonstration of Increased Rate of Collagen Synthesis1,2. American Review of Respiratory Disease, 121(3), pp.501-506.
- Poulsen, S., Saber, A., Williams, A., Andersen, O., Købler, C., Atluri, R., Pozzebon, M., Mucelli, S., Simion, M., Rickerby, D., Mortensen, A., Jackson, P., Kyjovska, Z., Mølhave, K., Jacobsen, N., Jensen, K., Yauk, C., Wallin, H., Halappanavar, S. and Vogel, U. (2015). MWCNTs of different physicochemical properties cause similar inflammatory responses, but differences in transcriptional and histological markers of fibrosis in mouse lungs. Toxicology and Applied Pharmacology, 284(1), pp.16-32.
- Rahman, L., Jacobsen, N., Aziz, S., Wu, D., Williams, A., Yauk, C., White, P., Wallin, H., Vogel, U. and Halappanavar, S. (2017). Multi-walled carbon nanotube-induced genotoxic, inflammatory and pro-fibrotic responses in mice: Investigating the mechanisms of pulmonary carcinogenesis. Mutation Research/Genetic Toxicology and Environmental Mutagenesis, 823, pp.28-44.
- Rahman, L., Wu, D., Johnston, M., Williams, A. and Halappanavar, S. (2016). Toxicogenomics analysis of mouse lung responses following exposure to titanium dioxide nanomaterials reveal their disease potential at high doses. Mutagenesis, 32(1), pp.59-76.
- Reynolds, H., Fulmer, J., Kazmierowski, J., Roberts, W., Frank, M. and Crystal, R. (1977). Analysis of cellular and protein content of broncho-alveolar lavage fluid from patients with idiopathic pulmonary fibrosis and chronic hypersensitivity pneumonitis. Journal of Clinical Investigation, 59(1), pp.165-175.
- Shi, C. and Pamer, E. (2011). Monocyte recruitment during infection and inflammation. Nature Reviews Immunology, 11(11), pp.762-774.
- Shvedova, A., Kisin, E., Mercer, R., Murray, A., Johnson, V., Potapovich, A., Tyurina, Y., Gorelik, O., Arepalli, S., Schwegler-Berry, D., Hubbs, A., Antonini, J., Evans, D., Ku, B., Ramsey, D., Maynard, A., Kagan, V., Castranova, V. and Baron, P. (2005). Unusual inflammatory and fibrogenic pulmonary responses to single-walled carbon nanotubes in mice. American Journal of Physiology-Lung Cellular and Molecular Physiology, 289(5), pp.L698-L708.
- Smith, R., Stricter, R., Zhang, K., Phan, S., Standiford, T., Lukacs, N. and Kunkel, S. (1995). A role for C-C chemokines in fibrotic lung disease. Journal of Leukocyte Biology, 57(5), pp.782-787.