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Event: 1497

Key Event Title

The KE title should describe a discrete biological change that can be measured. It should generally define the biological object or process being measured and whether it is increased, decreased, or otherwise definably altered relative to a control state. For example “enzyme activity, decreased”, “hormone concentration, increased”, or “growth rate, decreased”, where the specific enzyme or hormone being measured is defined. More help

Increased, recruitment of inflammatory cells

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. The short name should be less than 80 characters in length. More help
Recruitment of inflammatory cells

Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. Note, KEs should be defined within a particular level of biological organization. Only KERs should be used to transition from one level of organization to another. Selection of the level of biological organization defines which structured terms will be available to select when defining the Event Components (below). More help
Level of Biological Organization

Organ term

Further information on Event Components and Biological Context may be viewed on the attached pdf.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable. More help

Key Event Components

Further information on Event Components and Biological Context may be viewed on the attached pdf.Because one of the aims of the AOP-KB is to facilitate de facto construction of AOP networks through the use of shared KE and KER elements, authors are also asked to define their KEs using a set of structured ontology terms (Event Components). In the absence of structured terms, the same KE can readily be defined using a number of synonymous titles (read by a computer as character strings). In order to make these synonymous KEs more machine-readable, KEs should also be defined by one or more “event components” consisting of a biological process, object, and action with each term originating from one of 22 biological ontologies (Ives, et al., 2017; See List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signalling by that receptor).Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. More help
Process Object Action
inflammatory response inflammatory cell increased
macrophage activation macrophage increased
neutrophil activation neutrophil increased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE. Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
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
Dysregulated fibrinolysis/bradykinin leading to hyperinflammation KeyEvent Penny Nymark (send email) Under development: Not open for comment. Do not cite Under Development
Frustrated phagocytosis leads to malignant mesothelioma KeyEvent Penny Nymark (send email) Under development: Not open for comment. Do not cite
TLR9 activation leading to Multi Organ Failure and ARDS KeyEvent Gillina Bezemer (send email) Under development: Not open for comment. Do not cite
Interaction with lung cells leads to lung cancer KeyEvent Penny Nymark (send email) Under development: Not open for comment. Do not cite


This is a structured field used to identify specific agents (generally chemicals) that can trigger the KE. Stressors identified in this field will be linked to the KE in a machine-readable manner, such that, for example, a stressor search would identify this as an event the stressor can trigger. NOTE: intermediate or downstream KEs in one AOP may function as MIEs in other AOPs, meaning that stressor information may be added to the KE description, even if it is a downstream KE in the pathway currently under development.Information concerning the stressors that may trigger an MIE can be defined using a combination of structured and unstructured (free-text) fields. For example, structured fields may be used to indicate specific chemicals for which there is evidence of an interaction relevant to this MIE. By linking the KE description to a structured chemical name, it will be increasingly possible to link the MIE to other sources of chemical data and information, enhancing searchability and inter-operability among different data-sources and knowledgebases. The free-text section “Evidence for perturbation of this MIE by stressor” can be used both to identify the supporting evidence for specific stressors triggering the MIE as well as to define broad chemical categories or other properties that classify the stressors able to trigger the MIE for which specific structured terms may not exist. More help

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected from an ontology. In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help
Term Scientific Term Evidence Link
human Homo sapiens High NCBI
mouse Mus musculus High NCBI
rats Rattus norvegicus High NCBI

Life Stages

The structured ontology terms for life-stage are more comprehensive than those for taxa, but may still require further description/development and explanation in the free text section. More help
Life stage Evidence
All life stages High

Sex Applicability

The authors must select from one of the following: Male, female, mixed, asexual, third gender, hermaphrodite, or unspecific. More help
Term Evidence
Mixed High

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. For example, the biological state being measured could be the activity of an enzyme, the expression of a gene or abundance of an mRNA transcript, the concentration of a hormone or protein, neuronal activity, heart rate, etc. The biological compartment may be a particular cell type, tissue, organ, fluid (e.g., plasma, cerebrospinal fluid), etc. The role in the biology could describe the reaction that an enzyme catalyses and the role of that reaction within a given metabolic pathway; the protein that a gene or mRNA transcript codes for and the function of that protein; the function of a hormone in a given target tissue, physiological function of an organ, etc. Careful attention should be taken to avoid reference to other KEs, KERs or AOPs. Only describe this KE as a single isolated measurable event/state. This will ensure that the KE is modular and can be used by other AOPs, thereby facilitating construction of AOP networks. More help

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 et al., 2011). Sensing or recognition of pathogens and harmful substances results in the recruitment of monocytes to lungs (Shi and Pamer, 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, Event 1496 and Event 1497 act in a positive feedback loop mechanism and propagate the proinflammatory environment.

Literature evidence for its perturbation:

Macrophages accumulate in bronchoalveolar fluid (BALF) post-exposure to bleomycin (Phan et al., 1980; Smith et al., 1995). NM-induced inflammation is predominantly neutrophilic (Shvedova et al., 2005; Rahman L et al., 2016; Rahman et al., 2017; Poulsen et al., 2015). An increased number of neutrophils (Reynolds et al., 1977) is observed in the BALF of patients with idiopathic pulmonary fibrosis. 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 et al., 1977). MWCNTs induce increased eosinophil count in lungs (Købler C et al., 2015). MWCNTs act as allergens and induce lung infiltration of eosinophils and cause airway hypersensitivity (Beamer et al., 2013).

It is important to note that the stressor-induced Event 1495, Event 1496, and Event 1497 are part of the functional changes that we collectively consider as inflammation, and together, they mark the initiation of acute inflammatory phase. Event 1495 and Event 1496 occur at the cellular level. Event 1497 occurs at the tissue level.

How It Is Measured or Detected

One of the primary considerations in evaluating AOPs is the relevance and reliability of the methods with which the KEs can be measured. The aim of this section of the KE description is not to provide detailed protocols, but rather to capture, in a sentence or two, per method, the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements. Methods that can be used to detect or measure the biological state represented in the KE should be briefly described and/or cited. These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA).Key considerations regarding scientific confidence in the measurement approach include whether the assay is fit for purpose, whether it provides a direct or indirect measure of the biological state in question, whether it is repeatable and reproducible, and the extent to which it is accepted in the scientific and/or regulatory community. Information can be obtained from the OECD Test Guidelines website and the EURL ECVAM Database Service on Alternative Methods to Animal Experimentation (DB-ALM). ?

In vivo, recruitment of pro-inflammatory cells is measured using BALF cellularity assay. The fluid lining the lung epithelium is lavaged (BALF) 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. Alternatively, the use of precision cut lung slices can allow for limited assessment of recruitment of tissue resident inflammatory cells, based on the repertoire of cells remaining in the specific slice following harvesting. This method was used to show that there is a histological increase in inflammatory foci following treatment with bleomycin and MWCNTs (Rahman et al., 2020). Finally, more complicated microfluidic lung-on-a-chip devices can be used to assess the migration of select immune cells and fibroblasts toward a simulated epithelium following treatment with a pro-fibrotic compound (He et al., 2017). However, this method is limited to two cell types, and it lacks the reservoirs of immune cells present in the body in vivo.

Domain of Applicability

This free text section should be used to elaborate on the scientific basis for the indicated domains of applicability and the WoE calls (if provided). While structured terms may be selected to define the taxonomic, life stage and sex applicability (see structured applicability terms, above) of the KE, the structured terms may not adequately reflect or capture the overall biological applicability domain (particularly with regard to taxa). Likewise, the structured terms do not provide an explanation or rationale for the selection. The free-text section on evidence for taxonomic, life stage, and sex applicability can be used to elaborate on why the specific structured terms were selected, and provide supporting references and background information.  More help

Human, mouse, rat


List of the literature that was cited for this KE description. Ideally, the list of references, should conform, to the extent possible, with the OECD Style Guide ( (OECD, 2015). More help

1. Beamer, C., Girtsman, T., Seaver, B., Finsaas, K., Migliaccio, C., Perry, V., Rottman, J., Smith, D. and Holian, A. (2013). IL-33 mediates multi-walled carbon nanotube (MWCNT)-induced airway hyper-reactivity via the mobilization of innate helper cells in the lung. Nanotoxicology, 7(6), pp.1070-1081

2. 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.

3. He, J.; Chen, W.; Deng, S.; Xie, L.Modeling alveolar injury using microfluidic co-cultures for monitoring bleomycin-induced epithelial/fibroblastic cross-talk disorder. RSC Adv. 2017, 7, 42738– 42749.

4. 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.

5. 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.

6. Kolaczkowska, E. and Kubes, P. (2013). Neutrophil recruitment and function in health and inflammation. Nature Reviews Immunology, 13(3), pp.159-175.

7. 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.

8. 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.

9. 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.

10. Rahman, L., Williams, A., Gelda, K., Nikota, J., Wu, D., Vogel, U., & Halappanavar, S. (2020). 21st Century Tools for Nanotoxicology: Transcriptomic Biomarker Panel and Precision-Cut Lung Slice Organ Mimic System for the Assessment of Nanomaterial-Induced Lung Fibrosis. Small, 16(36), e2000272.

11. Rahman, L., Jacobsen, N., Aziz, S., Wu, D., Williams, A., Yauk, C., White, P., Wallin, H., Vogel, U. and Halappanavar, S. (2017). Multiwalled 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.

12. 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

13. 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.

14. Shi, C., & Pamer, E. G. (2011). Monocyte recruitment during infection and inflammation. Nature reviews. Immunology11(11), 762–774.

15. Shvedova, A. A., Kisin, E. R., Mercer, R., Murray, A. R., Johnson, V. J., Potapovich, A. I., Tyurina, Y. Y., Gorelik, O., Arepalli, S., Schwegler-Berry, D., Hubbs, A. F., Antonini, J., Evans, D. E., Ku, B. K., Ramsey, D., Maynard, A., Kagan, V. E., Castranova, V., & 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 33-5), 698–708. 

16. Smith, R. E., Strieter, R. M., Zhang, K., Phan, S. H., Standiford, T. J., Lukas, N. W., & Kunkel, S. L. (1995). A role for C-C chemokines in fibrotic lung disease. Journal of Leukocyte Biology, 57(5), 782–787.