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Relationship: 1702


A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

Interaction with the lung cell membrane leads to Increased proinflammatory mediators

Upstream event
The causing Key Event (KE) in a Key Event Relationship (KER). More help
Downstream event
The responding Key Event (KE) in a Key Event Relationship (KER). More help

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes.Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
Substance interaction with the pulmonary resident cell membrane components leading to pulmonary fibrosis adjacent Moderate Moderate Cataia Ives (send email) Under development: Not open for comment. Do not cite WPHA/WNT Endorsed
Interaction with lung resident cell membrane components leads to lung cancer adjacent Moderate Moderate Evgeniia Kazymova (send email) Under development: Not open for comment. Do not cite
Substance interaction with lung resident cell membrane components leading to atherosclerosis adjacent High Low Arthur Author (send email) Under development: Not open for comment. Do not cite Under Development

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 KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER.  More help

Sex Applicability

An indication of the the relevant sex for this KER. More help

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER.  More help

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

Innate immune response is the first line of defence in any organism against invading infectious pathogens and toxic substances. It involves tissue triggered startle response to cellular stress and is described by a complex set of interactions between the toxic stimuli, soluble macromolecules and cells (reviewed in Nathan, 2002). The process culminates in a functional change defined as inflammation, purpose of which is to resolve infection and promote healing. In lungs, the interaction of toxic substances with resident cells results in cellular stress, death or necrosis (Pouwels et al., 2016) leading to release of intracellular components such as alarmins (Damage associated molecular patterns [DAMPs], Interleukin (IL)-1α, High mobility group box 1 [HMGB1]). Released alarmins (danger sensors) bind cell surface receptors such as Interleukin 1 Receptor 1 (IL-1R1), Toll Like Receptors (TLRs) or others leading to activation of innate immune response signalling.

For example, binding of IL-1α to IL-1R1 can release Nuclear factor kappa B (NF-κB) resulting in its translocation to nucleus and transactivation of pro-inflammatory genes including cytokines, growth factors and acute phase genes. The signalling also stimulates secretion of a variety of pro-inflammatory mediators. Overexpression of IL-1α in cells induces increased secretion of pro-inflammatory mediators. Products of necrotic cells are shown to stimulate the immune system in an IL-1R1-dependent manner (Chen et al., 2007).

The secreted alarmins activate resident cells pre-stationed in the tissues such as mast cells or macrophages leading to propagation of the already initiated immune response by releasing more eicosanoids, cytokines, chemokines and other pro-inflammatory mediators. Thus, secreted mediators signal the recruitment of neutrophils, which are the first cell types to be recruited in acute inflammatory conditions. Neutrophil influx in sterile inflammation is driven mainly by IL-1α (Rider P, 2011). IL-1 mediated signalling regulates neutrophil influx in silica-induced acute lung inflammation (Hornung et al., 2008). IL-1 signalling also mediates neutrophil influx in other tissues and organs including liver and peritoneum. Other types of cells including macrophages, eosinophils, and lymphocytes are also recruited in a signal-specific manner. Recruitment of leukocytes induces critical cytokines associated with the T helper type 2 immune response, including Tumor necrosis factor alpha (TNF-α), IL-1β, and IL-13.

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings.  Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help
Biological Plausibility
Addresses the biological rationale for a connection between KEupstream and KEdownstream.  This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured.   More help

The biological plausibility of this relationship is high. There is a mechanistic relationship between the MIE (Event 1495) and KE1 (Event 1496) which has been evidenced in a number of both in vitro and in vivo model systems in response to stressors such as, asbestos, silica, bleomycin, carbon nanotubes, and metal oxide nanoparticles (NPs) (Behzadi et al., 2017; Denholm & Phan 1990; Dostert et al., 2008; Mossman & Churg 1998).

Increased expression of IL-1α or IL-1β following lung exposure to multi-walled carbon nanotubes (MWCNTs), bleomycin, micro silica particles, silica crystals, and polyhexamethylene guanidine phosphate has been shown to be associated with neutrophil influx in rodents (Gasse et al., 2007; Girtsman et al., 2014; Hornung et al., 2008; Nikota et al., 2017; Rabolli et al., 2014; Suwara et al., 2014). Inhibition of IL-1 function by knocking out the expression of IL-1R1 using IL-1R1 knockout mice or via treatment with IL-1α or IL-1β neutralising antibodies results in complete abrogation of lung neutrophilic influx following exposure to MWCNTs (Nikota et al, 2017), cigarette smoke (CS) (Halappanavar et al., 2013), silica crystals (Rabolli et al., 2014) and bleomycin (Gasse et al., 2007). IL1-R1, Myeloid differentiation primary response protein (Myd88) or the IL-33/St2 signaling are involved in pulmonary fibrosis induced by bleomycin (Gasse et al., 2007; Xu et al., 2016).

Uncertainties and Inconsistencies
Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

Attenuation or complete abrogation of KE1 (Event 1496) and KE2 (Event 1497) following inflammogenic stimuli is observed in rodents lacking functional IL-1R1 or other cell surface receptors that engage innate immune response upon stimulation. However, following exposure to MWCNTs, it has been shown that absence of IL-1R1 signalling is compensated for eventually and neutrophil influx is observed at a later post-exposure time point (Nikota et al., 2017). In another study, acute neutrophilic inflammation induced by MWCNTs was suppressed at 24 h in mice deficient in IL-1R1 signalling; however, these mice showed exacerbated neutrophilic influx and fibrotic response at 28 days post-exposure (Girtsman et al., 2014). The early defence mechanisms involving DAMPs is fundamental for survival, which may necessitate activation of compensatory signaling pathways. As a result, inhibition of a single biological pathway mediated by an individual cell surface receptor may not be sufficient to completely abrogate the lung inflammatory response. Forced suppression of pro-inflammatory and immune responses early after exposure to substances that cannot be effectively cleared from lungs, may enhance the injury and initiate other pathways leading to exacerbated response.

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references.  More help
Response-response Relationship
Provides sources of data that define the response-response relationships between the KEs.  More help

One study has demonstrated a response-response relationship for this KER.

Human intervertebral disc cells were treated with 0, 0.5, 1, or 2 mg/ml of recombinant HMGB1 for 24 h. Protein levels were determined in cell medium supernatant by enzyme-linked immunosorbent assay (ELISA). HMGB1 stimulates the expression of IL-6 and Matrix metalloproteinase 1 (MMP-1) in a response-response relationship. A strong correlation was observed by Spearman’s rank correlation coefficient between HMGB1 treatment and IL-6 or MMP-1 levels (Shah et al., 2019).

Other reports have studied both KEs, but they do not indicate if the response-response relationship was linear or not (coefficient or correlation is not shown) (Chakraborty et al., 2017; Fukuda et al. 2017; Kim et al., 2020, Piazza et al., 2013; Yang et al., 2012;).

Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help

Some studies have described how long after a change in the MIE (Event 1495; interaction substance and components), KE1 (Event 1496; pro-inflammatory mediators are secreted) is impacted (Table 2).

Table 2. Time-scale related studies relevant to the MIE (Event 1495) - KE1 (Event 1496) relationship.


In vitro/in vivo/population study


  MIE (Event 1495)

KE1 (Event 1496)



Xu et al., 2016

In vivo

40 Female Kunming strain mice

Bleomycin was intratracheally administered 5 mg/Kg.

Days post-exposure


3, 7 days

IL-4, IL-13

7, 14, and 28 days

Roy et al., 2014

In vitro

Primary mice macrophages exposed to 2.5 mg/ml ZnO for 24 hrs.

Increased TLR6 expression

0.5, 3, 6, 12, and 24 h

Increased IL-6, TNF-α 

24 h

Rabollli et al., 2014

In vivo

Female C57BL/6 mice

Exposed to silica 2.5 mg/mouse by instillation

Increased the release of IL-1α 

1, 3, and 6 h

Increased mRNA expression of pro-IL-1β 

6, 12, and 24 h

Known Feedforward/Feedback loops influencing this KER
Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Pancreatic cancer cells stimulated with S100 calcium-binding protein A8 (S100A8) and S100 calcium-binding protein A9 (S100A9) released pro-inflammatory cytokines IL-8, TNF-α, and Fibroblast growth factor (FGF). Cancer cell-derived conditioned media and the individual cytokines (TNF-α and Transforming growth factor beta [TGF-β]) induced the protein expression of S100A8 and S100A9 in HL-60 monocytic cell line and primary human monocytes (Nedjadi et al. 2018).

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help


List of the literature that was cited for this KER description. More help
  1. Behzadi S, Serpooshan V, Tao W, Hamaly MA, Alkawareek MY, Dreaden EC, Brown D, Alkilany AM, Farokhzad OC, Mahmoudi M. Cellular uptake of nanoparticles: journey inside the cell. Chem Soc Rev. 2017 Jul 17;46(14):4218-4244. doi: 10.1039/c6cs00636a. 

  2. Brown JM, Swindle EJ, Kushnir-Sukhov NM, Holian A, Metcalfe DD. Silica-directed mast cell activation is enhanced by scavenger receptors. Am J Respir Cell Mol Biol. 2007 Jan;36(1):43-52. doi: 10.1165/rcmb.2006-0197OC. 

  3. Chakraborty D, Zenker S, Rossaint J, Hölscher A, Pohlen M, Zarbock A, Roth J, Vogl T. Alarmin S100A8 Activates Alveolar Epithelial Cells in the Context of Acute Lung Injury in a TLR4-Dependent Manner. Front Immunol. 2017 Nov 13;8:1493. doi: 10.3389/fimmu.2017.01493.

  4. Chan JYW, Tsui JCC, Law PTW, So WKW, Leung DYP, Sham MMK, Tsui SKW, Chan CWH. Regulation of TLR4 in silica-induced inflammation: An underlying mechanism of silicosis. Int J Med Sci. 2018 Jun 14;15(10):986-991. doi: 10.7150/ijms.24715. 

  5. Chen CJ, Kono H, Golenbock D, Reed G, Akira S, Rock KL. Identification of a key pathway required for the sterile inflammatory response triggered by dying cells. Nat Med. 2007 Jul;13(7):851-6. doi: 10.1038/nm1603. 

  6. Denholm EM, Phan SH. Bleomycin binding sites on alveolar macrophages. J Leukoc Biol. 1990 Dec;48(6):519-23. doi: 10.1002/jlb.48.6.519.

  7. Dostert C, Pétrilli V, Van Bruggen R, Steele C, Mossman BT, Tschopp J. Innate immune activation through Nalp3 inflammasome sensing of asbestos and silica. Science. 2008 May 2;320(5876):674-7. doi: 10.1126/science.1156995. 

  8. Fukuda K, Ishida W, Miura Y, Kishimoto T, Fukushima A. Cytokine expression and barrier disruption in human corneal epithelial cells induced by alarmin released from necrotic cells. Jpn J Ophthalmol. 2017 Sep;61(5):415-422. doi: 10.1007/s10384-017-0528-7.

  9. Gasse P, Mary C, Guenon I, Noulin N, Charron S, Schnyder-Candrian S, Schnyder B, Akira S, Quesniaux VF, Lagente V, Ryffel B, Couillin I. IL-1R1/MyD88 signaling and the inflammasome are essential in pulmonary inflammation and fibrosis in mice. J Clin Invest. 2007 Dec;117(12):3786-99. doi: 10.1172/JCI32285. 

  10. Girtsman TA, Beamer CA, Wu N, Buford M, Holian A. IL-1R signalling is critical for regulation of multi-walled carbon nanotubes-induced acute lung inflammation in C57Bl/6 mice. Nanotoxicology. 2014 Feb;8(1):17-27. doi: 10.3109/17435390.2012.744110.

  11. Halappanavar S, Nikota J, Wu D, Williams A, Yauk CL, Stampfli M. IL-1 receptor regulates microRNA-135b expression in a negative feedback mechanism during cigarette smoke-induced inflammation. J Immunol. 2013 Apr 1;190(7):3679-86. doi: 10.4049/jimmunol.1202456.

  12. Heijink IH, Pouwels SD, Leijendekker C, de Bruin HG, Zijlstra GJ, van der Vaart H, ten Hacken NH, van Oosterhout AJ, Nawijn MC, van der Toorn M. Cigarette smoke-induced damage-associated molecular pattern release from necrotic neutrophils triggers proinflammatory mediator release. Am J Respir Cell Mol Biol. 2015 May;52(5):554-62. doi: 10.1165/rcmb.2013-0505OC. 

  13. Hornung V, Bauernfeind F, Halle A, Samstad EO, Kono H, Rock KL, Fitzgerald KA, Latz E. Silica crystals and aluminum salts activate the NALP3 inflammasome through phagosomal destabilization. Nat Immunol. 2008 Aug;9(8):847-56. doi: 10.1038/ni.1631.

  14. Kim DH, Gu A, Lee JS, Yang EJ, Kashif A, Hong MH, Kim G, Park BS, Lee SJ, Kim IS. Suppressive effects of S100A8 and S100A9 on neutrophil apoptosis by cytokine release of human bronchial epithelial cells in asthma. Int J Med Sci. 2020 Feb 4;17(4):498-509. doi: 10.7150/ijms.37833. 

  15. Martin-Murphy BV, Holt MP, Ju C. The role of damage associated molecular pattern molecules in acetaminophen-induced liver injury in mice. Toxicol Lett. 2010 Feb 15;192(3):387-94. doi: 10.1016/j.toxlet.2009.11.016.

  16. Mossman BT, Churg A. Mechanisms in the pathogenesis of asbestosis and silicosis. Am J Respir Crit Care Med. 1998 May;157(5 Pt 1):1666-80. doi: 10.1164/ajrccm.157.5.9707141.

  17. Nathan C. Points of control in inflammation. Nature. 2002 Dec 19-26;420(6917):846-52. doi: 10.1038/nature01320. 

  18. Nedjadi T, Evans A, Sheikh A, Barerra L, Al-Ghamdi S, Oldfield L, Greenhalf W, Neoptolemos JP, Costello E. S100A8 and S100A9 proteins form part of a paracrine feedback loop between pancreatic cancer cells and monocytes. BMC Cancer. 2018 Dec 17;18(1):1255. doi: 10.1186/s12885-018-5161-4. 

  19. 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.

  20. Piazza O, Leggiero E, De Benedictis G, Pastore L, Salvatore F, Tufano R, De Robertis E. S100B induces the release of pro-inflammatory cytokines in alveolar type I-like cells. Int J Immunopathol Pharmacol. 2013 Apr-Jun;26(2):383-91. doi: 10.1177/039463201302600211.

  21. Pouwels SD, Zijlstra GJ, van der Toorn M, Hesse L, Gras R, Ten Hacken NH, Krysko DV, Vandenabeele P, de Vries M, van Oosterhout AJ, Heijink IH, Nawijn MC. Cigarette smoke-induced necroptosis and DAMP release trigger neutrophilic airway inflammation in mice. Am J Physiol Lung Cell Mol Physiol. 2016 Feb 15;310(4):L377-86. doi: 10.1152/ajplung.00174.2015. 

  22. Rabolli V, Badissi AA, Devosse R, Uwambayinema F, Yakoub Y, Palmai-Pallag M, Lebrun A, De Gussem V, Couillin I, Ryffel B, Marbaix E, Lison D, Huaux F. The alarmin IL-1α is a master cytokine in acute lung inflammation induced by silica micro- and nanoparticles. Part Fibre Toxicol. 2014 Dec 13;11:69. doi: 10.1186/s12989-014-0069-x.

  23. Rider P, Carmi Y, Guttman O, Braiman A, Cohen I, Voronov E, White MR, Dinarello CA, Apte RN. IL-1α and IL-1β recruit different myeloid cells and promote different stages of sterile inflammation. J Immunol. 2011 Nov 1;187(9):4835-43. doi: 10.4049/jimmunol.1102048. 

  24. Roy R, Singh SK, Das M, Tripathi A, Dwivedi PD. Toll-like receptor 6 mediated inflammatory and functional responses of zinc oxide nanoparticles primed macrophages. Immunology. 2014 Jul;142(3):453-64. doi: 10.1111/imm.12276.

  25. Shah BS, Burt KG, Jacobsen T, Fernandes TD, Alipui DO, Weber KT, Levine M, Chavan SS, Yang H, Tracey KJ, Chahine NO. High mobility group box-1 induces pro-inflammatory signaling in human nucleus pulposus cells via toll-like receptor 4-dependent pathway. J Orthop Res. 2019 Jan;37(1):220-231. doi: 10.1002/jor.24154. 

  26. Suwara MI, Green NJ, Borthwick LA, Mann J, Mayer-Barber KD, Barron L, Corris PA, Farrow SN, Wynn TA, Fisher AJ, Mann DA. IL-1α released from damaged epithelial cells is sufficient and essential to trigger inflammatory responses in human lung fibroblasts. Mucosal Immunol. 2014 May;7(3):684-93. doi: 10.1038/mi.2013.87.

  27. Xu J, Zheng J, Song P, Zhou Y, Guan S. IL‑33/ST2 pathway in a bleomycin‑induced pulmonary fibrosis model. Mol Med Rep. 2016 Aug;14(2):1704-8. doi: 10.3892/mmr.2016.5446.

  28. Yang D, Postnikov YV, Li Y, Tewary P, de la Rosa G, Wei F, Klinman D, Gioannini T, Weiss JP, Furusawa T, Bustin M, Oppenheim JJ. High-mobility group nucleosome-binding protein 1 acts as an alarmin and is critical for lipopolysaccharide-induced immune responses. J Exp Med. 2012 Jan 16;209(1):157-71. doi: 10.1084/jem.20101354.