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Event: 1499

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, activation of T (T) helper (h) type 2 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
Activation of Th2 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

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

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


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

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

Sex Applicability

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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

How does this KE work

Naïve CD4+ T cells differentiate into four types of Th cells – Th1, Th2, Th17 and inducible regulatory T cells following exposure to infectious agents. The differentiation process begins when antigen presenting cells (APCs) come in contact with toxic substances and is mainly driven by cytokines that make up the microenvironment. For example, increased concentrations of IL-12 secreted by APCs in the environment may be biased towards Th1 type and increased IL-6 or IL-4 in the environment may commit to Th2 type differentiation. Th1 cytokines IFNg and IL-12 induce inflammation, aid in clearance of toxic substances, induce tissue damage and control the fibrotic responses. IFNg has suppressive effects on the production of extracellular matrix proteins including collagen and fibronectin. The Th2 response suppresses Th1 mediated response, which results in decreased Th1 cell-mediated tissue damage but at the same time contributing to the persistence of toxic substances leading to perpetuation of tissue damage, triggering uncontrolled healing response. The major sources of Th2 cytokines are Th2 cells themselves; however, mast cells, macrophages, epithelial cells and activated fibroblasts have shown to produce IL-4, IL-13 and IL-10 upon appropriate stimulation. Th2 cytokines IL-4 and IL-13 regulate wound healing.

KE4 associative event - Macrophage polarisation

Depending on the lung microenvironment (damaged cells, microbial products, activated lymphocytes), the precursor monocytes differentiate into distinct types of macrophages. Classically activated (M1) macrophages and alternatively activated (M2) macrophages are the important ones to consider in the context of this AOP. The M1 macrophages produce high levels of pro-inflammatory cytokines, mediate resistance to pathogens, induce generation of high levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS), and  T helper (Th) 1 type responses. M1 macrophages produce IL-1, IL-12, IL-23 and induce Th1 cell infiltration and activation. The M2 macrophages secrete anti-inflammatory mediators, by which they play a role in regulation of inflammation. The M2 polarisation is mediated by Th2 cytokines such as IL-4 and IL-13, which in turn, promotes M2 activation. M2 macrophages express immunosuppressive molecules such as IL-10, Arginase-1 and -2 (Arg-1, Arg-2), which suppress the induction of Th1 cells that produce the anti-fibrotic cytokine IFNg. The activity of M2 is associated with tissue remodelling, immune regulation, tumour promotion, tissue regeneration and effective phagocytic activity. During chronic inflammation, the phenotype of infiltrating macrophages is suggested to resemble that of M2, which is suggested to play a role in lung fibrosis.

Evidence for its perturbation

For fibroplasia or fibrosis, the type of CD4+ T cell response that develops is crucial. Studies conducted in mice that do not express Th2 cytokines IL-4, IL-5 and IL-13 show complete attenuation of fibrosis despite the highly active Th1 response. Th2 cytokines IL-4 and IL-13 are elevated in fibrotic lungs; IL-13 activates TGFb1 and initiates fibroblast proliferation and differentiation in lung fibrosis (Lee, 2001). Overexpression of IL-13 induces sub-epithelial airway fibrosis in mice in the absence of any other external pro-inflammatory or pro-fibrotic stimulus (Zhu, 1999). Both MWCNTs and SWCNTs induce elevated expression of IL-4 and IL-13 in BALF of mouse lungs (Park, 2011), and increased levels of IL-25 and IL-33 in BALF and mouse lungs exposed to MWCNTs (Dong, 2016). In a rare human study, increased levels IL-4 and IL-5 were observed in the sputum of humans exposed to MWCNTs at an occupational setting (Fatkhutdinova, 2016). Overexpression of IL-10 increases IL-4 and IL-13 production and lung fibrosis following exposure to silica (Barbarin, 2005). Alveolar macrophages from asbestosis patients (a form of lung fibrosis) exhibit M2 phenotype (Chao et al., 2013). Ex vivo culture of alveolar macrophages obtained from BALF of patients suffering from IPF with collagen type I showed enhanced levels of M2 macrophage markers CCL-18, CCL-2 and CD204 (Stahl, 2013). Th2 response associated expression of IL-33 cytokine enhances polarisation of M2 macrophages and inducing M2-mediated expression of IL-13 and TGFb1 in mice (Dong, 2014). Cigarette smoke induces expression of genes associated with M2 sub-phenotypes, which is further enhanced in smokers presenting with COPD (Shaykhiev, 2009).  

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). ?

Targeted enzyme-linked immunosorbent assays (ELISA) or real-time quantitative polymerase chain reaction (qRT-PCR) (routinely used and recommended)

The ELISA and qRT-PCR are routinely used to assess the levels of protein and mRNA of several Th1 and Th2 cytokines including IL-4, IL-5, IL-13, IL-10, IL-12, IFNg. In addition, the levels of Transforming growth factor b (TGFb) is also assessed, expression of which is increased following induction of IL-13 synthesis. The other genes of relevance to Th2 response and eventual pro-fibrotic response include Arg-1 and Arg-2. BALF supernatant collected from lungs of animals exposed to toxic substances or human patients is used. Tissue homogenates or cell pellets can also be used. Expression of these genes and proteins can be assessed in in vitro cell cultures exposed to pro-fibrotic stimulus.

Apart from assaying single protein or gene at a time, cytokine bead arrays or cytokine PCR arrays can be used to detect a whole panel of Th1 and/or Th2 cytokines using a multiplex method. This method is quantitative and especially advantageous when the sample amount available for testing is scarce.

The details of ELISA and qRT-PCR are described under MIE. The details of BALF sample collection is described under KE2.

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


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. Barbarin, V., Xing, Z., Delos, M., Lison, D. and Huaux, F. (2005). Pulmonary overexpression of IL-10 augments lung fibrosis and Th2 responses induced by silica particles. American Journal of Physiology-Lung Cellular and Molecular Physiology, 288(5), pp.L841-L848.
  2. Dong, J. and Ma, Q. (2016). In vivo activation of a T helper 2-driven innate immune response in lung fibrosis induced by multi-walled carbon nanotubes. Archives of Toxicology, 90(9), pp.2231-2248.
  3. Fatkhutdinova, L., Khaliullin, T., Vasil'yeva, O., Zalyalov, R., Mustafin, I., Kisin, E., Birch, M., Yanamala, N. and Shvedova, A. (2016). Fibrosis biomarkers in workers exposed to MWCNTs. Toxicology and Applied Pharmacology, 299, pp.125-131.
  4. He, C., Ryan, A., Murthy, S. and Carter, A. (2013). Accelerated Development of Pulmonary Fibrosis via Cu,Zn-superoxide Dismutase-induced Alternative Activation of Macrophages. Journal of Biological Chemistry, 288(28), pp.20745-20757.
  5. Huaux, F., Liu, T., McGarry, B., Ullenbruch, M., Xing, Z. and Phan, S. (2003). Eosinophils and T Lymphocytes Possess Distinct Roles in Bleomycin-Induced Lung Injury and Fibrosis. The Journal of Immunology, 171(10), pp.5470-5481.
  6. Lee, C., Homer, R., Zhu, Z., Lanone, S., Wang, X., Koteliansky, V., Shipley, J., Gotwals, P., Noble, P., Chen, Q., Senior, R. and Elias, J. (2001). Interleukin-13 Induces Tissue Fibrosis by Selectively Stimulating and Activating Transforming Growth Factor β1. The Journal of Experimental Medicine, 194(6), pp.809-822.
  7. Li, D., Guabiraba, R., Besnard, A., Komai-Koma, M., Jabir, M., Zhang, L., Graham, G., Kurowska-Stolarska, M., Liew, F., McSharry, C. and Xu, D. (2014). IL-33 promotes ST2-dependent lung fibrosis by the induction of alternatively activated macrophages and innate lymphoid cells in mice. Journal of Allergy and Clinical Immunology, 134(6), pp.1422-1432.e11.
  8. Park, E., Roh, J., Kim, S., Kang, M., Han, Y., Kim, Y., Hong, J. and Choi, K. (2011). A single intratracheal instillation of single-walled carbon nanotubes induced early lung fibrosis and subchronic tissue damage in mice. Archives of Toxicology, 85(9), pp.1121-1131.
  9. Shaykhiev, R., Krause, A., Salit, J., Strulovici-Barel, Y., Harvey, B., O'Connor, T. and Crystal, R. (2009). Smoking-Dependent Reprogramming of Alveolar Macrophage Polarization: Implication for Pathogenesis of Chronic Obstructive Pulmonary Disease. The Journal of Immunology, 183(4), pp.2867-2883.
  10. Stahl, M., Schupp, J., Jäger, B., Schmid, M., Zissel, G., Müller-Quernheim, J. and Prasse, A. (2013). Lung Collagens Perpetuate Pulmonary Fibrosis via CD204 and M2 Macrophage Activation. PLoS ONE, 8(11), p.e81382.
  11. Tao, B., Jin, W., Xu, J., Liang, Z., Yao, J., Zhang, Y., Wang, K., Cheng, H., Zhang, X. and Ke, Y. (2014). Myeloid-Specific Disruption of Tyrosine Phosphatase Shp2 Promotes Alternative Activation of Macrophages and Predisposes Mice to Pulmonary Fibrosis. The Journal of Immunology, 193(6), pp.2801-2811.
  12. Zhu, Z., Homer, R., Wang, Z., Chen, Q., Geba, G., Wang, J., Zhang, Y. and Elias, J. (1999). Pulmonary expression of interleukin-13 causes inflammation, mucus hypersecretion, subepithelial fibrosis, physiologic abnormalities, and eotaxin production. Journal of Clinical Investigation, 103(6), pp.779-788.