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Event: 1857

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

Platelet-neutrophil interactions, Increased

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
Platelet-neutrophil interactions, Increased

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

Cell 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

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

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
TLR9 activation leading to Multi Organ Failure and ARDS KeyEvent Gillina Bezemer (send email) Under development: Not open for comment. Do not cite
Endothelial cell dysfunction leading to thromboinflammation KeyEvent Luigi Margiotta-Casaluci (send email) Under development: Not open for comment. Do not cite Under Development


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

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

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

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

Neutrophils represent 50–70% of all circulating leukocytes in humans and are the foot soldiers of the immune response, being the first immune cell on the scene of an infection or inflammation. They exert their functional roles via a combination of processes, including the generation of reactive oxygen species (ROS), degranulation, phagocytosis, and release of neutrophil extracellular traps (NETs).  On the other hand, approximately 750 billion platelets circulate in humans and these cells are traditionally known for their role in haemostasis and thrombosis and are first responders at sites of vascular damage. More recently investigations have shown that platelets play important roles in inflammatory and immune processes (Gu et al., 2019), including resolution (Senchenkova et al., 2019). Platelets have a range of different receptors including Toll-like receptors (TLRs), C-type lectin receptors, and nucleotide-binding and oligomerization domain–like receptors, which are known to recognise infection (Semple et al., 2011) and are effectors of injury in a variety of pulmonary disorders and syndromes, and facilitate tissue repair (Xu et al., 2016).

These two cell types modulate each other’s functions, and neutrophil-platelet interaction and platelet-platelet interactions are increased during inflammation (Lisman, 2018). Circulating platelet–neutrophil complexes have been observed in many different inflammatory conditions including bacterial infections (Gawaz et al. 1995) and pulmonary syndromes involving inflammation (Caudrillier et al. 2012). The physical interaction between neutrophils and platelets is mediated by multiple molecular mechanisms including platelet P-selectin binding to neutrophil P-selectin glycoprotein ligand-1 (PSGL-1) (Moore et al. 1995) and platelet glycoprotein Ibα binding to neutrophil MAC-1 (Simon et al. 2000).

A first important example of functional interaction between the two cell types is the ability of platelets to facilitate neutrophil adhesion to activated endothelial cells (i.e. at the site of inflammation or injury) and to promote their transmigration across the endothelium. Many studies have demonstrated that neutrophils patrol the vasculature for activated platelets to initiate inflammatory responses (Sreeramkumar et al. 2014), hence activated platelets are crucial in neutrophil-mediated inflammatory responses (Senchenkova et al., 2019). The depletion of platelets decreases neutrophil recruitment to the site of inflammation, and the depletion of neutrophils decreases platelet recruitment (Sreeramkumar et al. 2014). During activation, both neutrophils and platelets are capable of releasing microparticles, (MPs, also termed ectosomes) which carry markers of the parent cells outer membrane e.g. neutrophil MPs carry different cell adhesion molecules and proteases such as proteinase 3 or elastase (Ramirez et al., 2019).

Beyond recruitment and localization processes, activated platelets are able to modulate (i.e. both enhancing and inhibiting) neutrophil responses, including phagocytosis, production of ROS, and production of NETs. These effects can be mediated by direct cell-cell contact or by the release of soluble mediators such as CCL5 and platelet factor 4 (von Hundelshausen et al. 2005). On the other hand, neutrophils can also release soluble mediators (e.g. cathepsin G, elastase) that enhance or inhibit platelet responses (Mihara et al. 2013; Bonnefoy and Legrand 2000).

Platelets can stimulate the synthesis of various leukotrienes by neutrophils via transcellular transfer of the arachidonic acid metabolite 12-HETE, which is further processed by neutrophils into bioactive leukotrienes (Rossaint et al., 2018). Platelets also store preformed and immunomodulatory molecules that can affect neutrophils (e.g. affecting chemotaxis) and the immune response, including interleukin-1 and platelet-derived growth factor (Semple et al., 2011).

Over the past several years, the interactions between immune cells such as neutrophils and platelets have been given different names, including: thromboinflammatoin, immunothrombosis and immunohemostasis (Guo et al., 2019). These names have been introduced to try to capture the responses and mechanisms of both cell types (independently and collectively) in thrombosis and inflammation.

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). ?

Neutrophil-platelet complexes (sometimes called platelet-leukocyte aggregation, PLA) can be measured using the following techniques (see Finsterbusch et al. (2018) for a comprehensive review):

In vitro

  1. Microfluidic assays can allow to visualize neutrophil-platelet interactions in real time in vitro. This approach involves the use of isolated cells or whole blood that are perfused through a chamber coated with immobilized proteins or cells. Specific cells are visualized thanks to the use of specific antibodies. This technique allows a fine tuning of experimental conditions and the use of human cells.

In vivo

  1. Flow cytometry is the method of choice to measure circulating neutrophil-platelet complexes in both humans and animals. This technique is based on fluorescence-labelling of platelets and leukocytes in whole blood. Characteristic side scatter properties of leukocyte subtypes already permit basic discrimination of platelets binding to neutrophils, monocytes and lymphocytes. However, leukocyte subtype-specific antibodies generate more accurate data. The endpoint is quantified as the percentage of total leukocytes (i.e. neutrophils) that also stain for a platelet-specific marker. A limitation of standard flow cytometry is that potential platelet-derived macrovesicles fused to leukocytes could influence results.
  2. Flow cytometry coupled with fluorescence microscopy (imaging flow cytometry). This approach enables direct assessment of both number of bound platelets as well as involved interaction molecules and coincidental events.
  3. Histochemical and immunofluorescent imaging of frozen or paraffin-embedded tissue sections. This approach can provide valuable information about the location of platelet recruitment and neutrophil-platelet complexes within tissue microenvironments of most organs. These techniques can be coupled with confocal or electron microscopy to provide higher resolution visualization of platelet-neutrophil interactions. A major limitation of this approach is that it only provides a static assessment of the endpoint.
  4. Live cell imaging coupled with intravital microscopy (IVM) allows to track labeled cells in live animals over longer time periods in organs including liver, lung, and brain. This approach can be used to analyze the dynamic interactions between platelets and neutrophils (e.g., duration of interactions and behavioural changes in neutrophils and/or platelets upon contact).
  5. Intravenous administration of fluorochrome-conjugated monoclonal antibodies targeting specific protein markers on platelets.

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

Bonnefoy, A., Legrand, C., 2000. Proteolysis of Subendothelial Adhesive Glycoproteins (Fibronectin, Thrombospondin, and von Willebrand Factor) by Plasmin, Leukocyte Cathepsin G, and Elastase. Thrombosis Research 98, 323-332.

Caudrillier, A., Kessenbrock, K., Gilliss, B.M., Nguyen, J.X., Marques, M.B., Monestier, M., Toy, P., Werb, Z., Looney, M.R., 2012. Platelets induce neutrophil extracellular traps in transfusion-related acute lung injury. J Clin Invest 122, 2661-2671.

Finsterbusch, M., Schrottmaier, W.C., Kral-Pointner, J.B., Salzmann, M., Assinger, A., 2018. Measuring and interpreting platelet-leukocyte aggregates. Platelets 29, 677-685.

Gawaz, M., Fateh‐Moghadam, S., Pilz, G., Gurland, H.-., Werdan, K., 1995. Platelet activation and interaction with leucocytes in patients with sepsis or multiple organ failure. European Journal of Clinical Investigation 25, 843-851.

Guo, L., Rondina, M.T., 2019. The Era of Thromboinflammation: Platelets Are Dynamic Sensors and Effector Cells During Infectious Diseases. Front Immunol 10.

Lisman, T., 2018. Platelet–neutrophil interactions as drivers of inflammatory and thrombotic disease. Cell Tissue Res 371, 567-576.

Mihara, K., Ramachandran, R., Renaux, B., Saifeddine, M., Hollenberg, M.D., 2013. Neutrophil Elastase and Proteinase-3 Trigger G Protein-biased Signaling through Proteinase-activated Receptor-1 (PAR1). J Biol Chem 288, 32979-32990.

Moore, K.L., Patel, K.D., Bruehl, R.E., Li, F., Johnson, D.A., Lichenstein, H.S., Cummings, R.D., Bainton, D.F., McEver, R.P., 1995. P-selectin glycoprotein ligand-1 mediates rolling of human neutrophils on P-selectin. Journal of Cell Biology 128, 661-671.

Ramirez, G.A., Manfredi, A.A., Maugeri, N., 2019. Misunderstandings Between Platelets and Neutrophils Build in Chronic Inflammation. Front Immunol 10.

Rossaint, J., Margraf, A., Zarbock, A., 2018. Role of Platelets in Leukocyte Recruitment and Resolution of Inflammation. Front Immunol 9.

Semple, J.W., Italiano, J.E., Freedman, J., 2011. Platelets and the immune continuum. Nature Reviews Immunology 11, 264-274.

Senchenkova, E.Y., Ansari, J., Becker, F., Vital, S.A., Al-Yafeai, Z., Sparkenbaugh, E.M., Pawlinski, R., Stokes, K.Y., Carroll, J.L., Dragoi, A., Qin, C.X., Ritchie, R.H., Sun, H., Cuellar-Saenz, H.H., Rubinstein, M.R., Han, Y.W., Orr, A.W., Perretti, M., Granger, D.N., Gavins, F.N.E., 2019. Novel Role for the AnxA1-Fpr2/ALX Signaling Axis as a Key Regulator of Platelet Function to Promote Resolution of Inflammation. Circulation 140, 319-335.

Simon, D.I., Chen, Z., Xu, H., Li, C.Q., Dong, J., McIntire, L.V., Ballantyne, C.M., Zhang, L., Furman, M.I., Berndt, M.C., López, J.A., 2000. Platelet Glycoprotein Ibα Is a Counterreceptor for the Leukocyte Integrin Mac-1 (Cd11b/Cd18). J Exp Med 192, 193-204.

Sreeramkumar, V., Adrover, J.M., Ballesteros, I., Cuartero, M.I., Rossaint, J., Bilbao, I., Nácher, M., Pitaval, C., Radovanovic, I., Fukui, Y., McEver, R.P., Filippi, M., Lizasoain, I., Ruiz-Cabello, J., Zarbock, A., Moro, M.A., Hidalgo, A., 2014. Neutrophils scan for activated platelets to initiate inflammation. Science 346, 1234-1238.

von Hundelshausen, P., Koenen, R.R., Sack, M., Mause, S.F., Adriaens, W., Proudfoot, A.E.I., Hackeng, T.M., Weber, C., 2005. Heterophilic interactions of platelet factor 4 and RANTES promote monocyte arrest on endothelium. Blood 105, 924-930.

Xu, X.R., Zhang, D., Oswald, B.E., Carrim, N., Wang, X., Hou, Y., Zhang, Q., Lavalle, C., McKeown, T., Marshall, A.H., Ni, H., 2016. Platelets are versatile cells: New discoveries in hemostasis, thrombosis, immune responses, tumor metastasis and beyond. Critical Reviews in Clinical Laboratory Sciences 53, 409-430.