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Event: 1458

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. 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. More help
Pulmonary fibrosis
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Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. More help
Level of Biological Organization

Organ term

The location/biological environment in which the event takes place.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.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help
Organ term

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling).  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 signaling 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.  Further information on Event Components and Biological Context may be viewed on the attached pdf. 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 pulmonary cell membrane leading to pulmonary fibrosis AdverseOutcome Sabina Halappanavar (send email) Under development: Not open for comment. Do not cite WPHA/WNT Endorsed
TLR4 activation, PPAR gamma activation and Pulmonary fibrosis AdverseOutcome Seokjoo Yoon (send email) Under development: Not open for comment. Do not cite
AOPs of SiNPs: ROS-mediated oxidative stress increased respiratory toxicity. KeyEvent Hailin Xu (send email) Under development: Not open for comment. Do not cite

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.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

An indication of the the relevant life stage(s) for this KE. More help
Life stage Evidence
Adults High

Sex Applicability

An indication of the the relevant sex for this KE. 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. 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 and Sidhaye, 2017). Within this epithelium, basal cells are found which are stimulated to proliferate and differentiate in response to injury (Koval and 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 (AECs). Finally, in the terminal airspaces, the epithelium is made up entirely of type I and type II AECs. 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 (ACM), 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 ACM is occupied with collagen and cells.

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.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). Do not provide detailed protocols. More help

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. Real-time reverse transcription-polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assays (ELISA) measuring increased collagen, Transforming growth factor beta 1 (TGF-β1) 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

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided).  More help

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. More help


List of the literature that was cited for this KE description. More help

1. Ashcroft T, Simpson JM, Timbrell V. Simple method of estimating severity of pulmonary fibrosis on a numerical scale. J Clin Pathol. 1988 Apr;41(4):467-70. doi: 10.1136/jcp.41.4.467.

2. Gracey DR, Divertie MB, Brown AL Jr. Alveolar-capillary membrane in idiopathic interstitial pulmonary fibrosis. Electron microscopic study of 14 cases. Am Rev Respir Dis. 1968 Jul;98(1):16-21. doi: 10.1164/arrd.1968.98.1.16.

3. Hübner RH, Gitter W, El Mokhtari NE, Mathiak M, Both M, Bolte H, Freitag-Wolf S, Bewig B. Standardized quantification of pulmonary fibrosis in histological samples. Biotechniques. 2008 Apr;44(4):507-11, 514-7. doi: 10.2144/000112729. 

4. Koval M, Sidhaye VK. Introduction: The Lung Epithelium. In: Sidhaye VK, Koval M, editors. Lung Epithelial Biology in the Pathogenesis of Pulmonary Disease. Boston: Academic Press; 2017. p. 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. doi: 10.1186/s12989-017-0218-0.