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Event: 1458

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

Pulmonary fibrosis

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
Pulmonary fibrosis

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
Organ term

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

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
Latent TGFbeta1 activation leads to pulmonary fibrosis AdverseOutcome Marvin Martens (send email) Under development: Not open for comment. Do not cite
Substance interaction with the lung cell membrane leading to lung fibrosis AdverseOutcome Sabina Halappanavar (send email) Under development: Not open for comment. Do not cite EAGMST Under Review
TLR4 activation, PPAR gamma activation and Pulmonary fibrosis AdverseOutcome Seokjoo Yoon (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
humans Homo sapiens High NCBI
mouse Mus musculus High NCBI
rat 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
Adults 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
Unspecific 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

Pulmonary fibrosis is broadly defined as the thickening or scarring of lung tissue, due to excessive deposition of extracellular matrix. In the normal human lung, the nasopharynx and the conducting airways are mainly covered by epithelium composed of ciliated, mucous secreting cells in direct contact with the basement membrane with submucosal glands containing goblet, duct, and serous cells also contributing to the fluid balance and mucous production (Koval & Sidhaye, 2017). Within this epithelium, basal cells are found which are stimulated to proliferate and differentiate in response to injury (Koval & Sidhaye, 2017). Further down the lung, in the terminal bronchiole region, the epithelium does not contain submucosal glands, but instead contains club cells which produce pulmonary surfactant and can differentiate into bronchiolar or alveolar epithelial cells. Finally, in the terminal airspaces, the epithelium is made up entirely of type I and type II alveolar epithelial cells. In between the two adjacent alveoli are two layers of alveolar epithelium resting on basement membrane, which consists of interstitial space, pulmonary capillaries, elastin and collagen fibres. Thus, the alveolar capillary membrane, where gas exchange takes place, is made up of the alveolar epithelium and alveolar endothelium (Gracey et al, 1968). In pulmonary fibrosis, damage to the pulmonary epithelium results in excessive deposition of collagen by constitutively activated myofibroblasts during the wound healing response. This causes a pronounced decrease in the number of capillaries within the alveolar septa with asymmetric deposition of collagen and cells between part of the surface of a capillary and the nearby alveolar lining. In areas where capillaries are not present, the alveolar capillary membrane is occupied with collagen and cells.

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, histopathological analysis is used for assessing fibrotic lung disease. Morphometric analysis of the diseased area versus total lung area is used to quantitatively stage the fibrotic disease. Although, some inconsistencies can be introduced during the analysis due to the experience of the individual scoring the disease, the histological stain, etc., a numerical scale with grades from 0 to 8, originally developed by Ashcroft et al., 1988 is assigned to indicate the amount of fibrotic tissue in histological samples. This scale is applied to diagnose lung fibrosis in both human and animal samples. Modifications to this scoring system were proposed (Hubner et al., 2008), which enables morphological distinctions thus enabling a better grading of the disease. Using the modified scoring system, bleomycin induced lung fibrosis in rats was scored as follows: Grade 0 – normal lung, Grade 1 – isolated alveolar septa with gentle fibrotic changes, Grade 2 – knot like formation in fibrotic areas in alveolar septa, Grade 3 – contiguous fibrotic walls of alveolar septa, Grade 4 – single fibrotic masses, Grade 5 – confluent fibrotic masses, Grade 6 – large contiguous fibrotic masses, Grade 7 – air bubbles and Grade 8 – fibrotic obliteration. Further morphometric analysis can be conducted to quantify the total disease area (Nikota et al., 2017).

Lungs are formalin fixed and paraffin embedded such that an entire cross section of lung can be presented on a slide. The entire cross section is captured in a series of images using wide field light microscope. Areas of alveolar epithelium thickening and consolidated air space are identified. ImageJ software (freely available) is used to trace the total area (green line) and the diseased area (red line) imaged and quantified. The diseased area is equal to disease area/total area (Nikota et al., 2017).

In vitro, there is no single assay that can measure the alveolar thickness. However, a combination of assays spanning various KEs described above provide a measure of the extent of fibrogenesis potential of tested substances. qRT-PCR and ELISA assays measuring increased collagen, TGFβ1 and various pro-inflammatory mediators are used as sensitive markers of potential of substances to induce the adverse outcome of lung fibrosis.

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

Evidence for Perturbation by Stressor


Bleomycin is a potent anti-tumour drug, routinely used for treating various types of human cancers (Umezawa H et al., 1967; Adamson IY, 1976). Lung injury and lung fibrosis are the major adverse effects of this drug in humans (Hay J et al., 1991). Bleomycin is shown to induce lung fibrosis in animals – such as dogs (Fleischman RW et al., 1971), mice (Adamson IY and Bowden DH, 1974), and hamsters (Snider GL et al., 1978) and is widely used as a model to study the mechanisms of fibrosis (reviewed in Moeller A et al., 2008; Gilhodes J-C et al., 2017).

  1. Umezawa H, Ishizuka M, Maeda K, Takeuchi T. Studies on bleomycin. Cancer. 1967 May;20(5):891-5.
  2. Adamson IY. Pulmonary toxicity of bleomycin. Environ Health Perspect. 1976 Aug;16:119-26.
  3. Hay J, Shahzeidi S, Laurent G  Mechanisms of bleomycin induced lung damage. 1991 Arch Toxicol 65:81–94.
  4. Fleischman RW, Baker JR, Thompson GR, et al. Bleomycin-induced interstitial pneumonia in dogs. Thorax. 1971;26(6):675-682.
  5. Adamson IYR, Bowden DH. The Pathogenesis of Bleomycin-Induced Pulmonary Fibrosis in Mice. The American Journal of Pathology. 1974;77(2):185-198.
  6. Snider GL, Celli BR, Goldstein RH, O'Brien JJ, Lucey EC. Chronic interstitial pulmonary fibrosis produced in hamsters by endotracheal bleomycin. Lung volumes, volume-pressure relations, carbon monoxide uptake, and arterial blood gas studied. Am Rev Respir Dis. 1978 Feb; 117(2):289-97.
  7. Moeller A, Ask K, Warburton D, Gauldie J, Kolb M. The bleomycin animal model: a useful tool to investigate treatment options for idiopathic pulmonary fibrosis? The international journal of biochemistry & cell biology. 2008;40(3):362-382.
  8. Gilhodes J-C, Julé Y, Kreuz S, Stierstorfer B, Stiller D, Wollin L (2017) Quantification of Pulmonary Fibrosis in a Bleomycin Mouse Model Using Automated Histological Image Analysis. PLoS ONE 12(1): e0170561.

Carbon nanotubes, Multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon nanofibres

Carbon nanotubes (CNTs) are allotropes of carbon, are made of rolled up sheet of graphene (single-walled carbon nanotubes) and are tubular in shape. A multi-walled carbon nanotube (MWCNT) is a multi-layered concentric cylinder of graphene sheets stacked one inside the other (N. Saifuddin et al., 2013). CNTs exhibit a combination of unique mechanical, thermal, and electronic properties and are highly desired commercially. They are light weight but their tensile strength is 50 times higher than that of steel, and they are stable chemically as well as in the environment. Consequently, they are produced in massive amounts and are increasingly incorporated in several industrial products.

CNTs are high aspect ratio materials and are shown to cause lung fibrosis in animals (Muller J et al., 2005; Porter DW et al., 2010; Dong and Ma 2016; Vietti, et al., 2016). In an intelligence bulletin published by NIOSH on ‘Occupational exposure to carbon nanotubes and nanofibers’, NIOSH reviewed 54 individual animal studies investigating the pulmonary toxicity induced by CNTs and reported that half of those studies consistently showed lung fibrosis (NIOSH bulletin, 2013). However, the evidence is inconsistent and the occurrence of fibrotic pathology is influenced by the specific physical-chemical properties of CNTs (i.e. length, rigidity), their dispersion in exposure vehicle, and the mode of exposure (Duke and Bonner 2018).

1. Dong, J., & Ma, Q. (2016). Myofibroblasts and lung fibrosis induced by carbon nanotube exposure. Particle and fibre toxicology, 13(1), 60.

2. Duke, K. S., & Bonner, J. C. (2018). Mechanisms of carbon nanotube-induced pulmonary fibrosis: a physicochemical characteristic perspective. Wiley interdisciplinary reviews. Nanomedicine and nanobiotechnology, 10(3), e1498.

3. Muller, J., Huaux, F., Moreau, N., Misson, P., Heilier, J. F., Delos, M., Arras, M., Fonseca, A., Nagy, J. B., & Lison, D. (2005). Respiratory toxicity of multi-wall carbon nanotubes. Toxicology and applied pharmacology, 207(3), 221–231.

4. NIOSH: Occupational exposure to carbon nanotubes and nanofibers: current intelligence bulletin 65. 2013.

5. Porter, D. W., Hubbs, A. F., Mercer, R. R., Wu, N., Wolfarth, M. G., Sriram, K., Leonard, S., Battelli, L., Schwegler-Berry, D., Friend, S., Andrew, M., Chen, B. T., Tsuruoka, S., Endo, M., & Castranova, V. (2010). Mouse pulmonary dose- and time course-responses induced by exposure to multi-walled carbon nanotubes. Toxicology, 269(2-3), 136–147.

6. N. Saifuddin, A. Z. Raziah, and A. R. Junizah. Carbon Nanotubes: A Review on Structure and Their Interaction with Proteins. Journal of Chemistry, vol. 2013, Article ID 676815, 18 pages, 2013.

7. Vietti, G., Lison, D., & van den Brule, S. (2016). Mechanisms of lung fibrosis induced by carbon nanotubes: towards an Adverse Outcome Pathway (AOP). Particle and fibre toxicology, 13, 11.

Regulatory Significance of the Adverse Outcome

An AO is a specialised KE that represents the end (an adverse outcome of regulatory significance) of an AOP. For KEs that are designated as an AO, one additional field of information (regulatory significance of the AO) should be completed, to the extent feasible. If the KE is being described is not an AO, simply indicate “not an AO” in this section.A key criterion for defining an AO is its relevance for regulatory decision-making (i.e., it corresponds to an accepted protection goal or common apical endpoint in an established regulatory guideline study). For example, in humans this may constitute increased risk of disease-related pathology in a particular organ or organ system in an individual or in either the entire or a specified subset of the population. In wildlife, this will most often be an outcome of demographic significance that has meaning in terms of estimates of population sustainability. Given this consideration, in addition to describing the biological state associated with the AO, how it can be measured, and its taxonomic, life stage, and sex applicability, it is useful to describe regulatory examples using this AO. More help


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. Ashcroft, T., J.M. Simpson, and V. Timbrell. 1988. Simple method of estimating severity of pulmonary fibrosis on a numerical scale. J. Clin. Pathol. 41:467-470.

2. Gracey DR, Divertie MB and Brown Jr. AL. Alveolar-Capillary Membrane in Idiopathic Interstitial Pulmonary Fibrosis. 1968. American Review of Respiratory Disease, 98(1), pp. 16–21.

3. Hübner, R. H., Gitter, W., El Mokhtari, N. E., Mathiak, M., Both, M., Bolte, H., Freitag-Wolf, S., & Bewig, B. (2008). Standardized quantification of pulmonary fibrosis in histological samples. BioTechniques, 44(4), 507–517.

4. Koval, M., & Sidhaye, V. (2017). Introduction: The Lung Epithelium. In Lung Epithelial Biology in the Pathogenesis of Pulmonary Disease (pp. xiii-xviii). Elsevier.

5. Nikota J, Banville A, Goodwin LR, Wu D, Williams A, Yauk CL, Wallin H, Vogel U, Halappanavar S. Stat-6 signaling pathway and not Interleukin-1 mediates multi-walled carbon nanotube-induced lung fibrosis in mice: insights from an adverse outcome pathway framework. Part Fibre Toxicol. 2017 Sep 13;14(1):37.