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Event: 398

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

Activation, Dendritic 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, Dendritic 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
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
Cell term
dendritic cell

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
cell activation increased
MHC protein complex assembly increased

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
Skin Sensitisation AOP KeyEvent Agnes Aggy (send email) Open for citation & comment TFHA/WNT Endorsed
Covalent binding to proteins leads to Respiratory Sensitisation/Sensitization/Allergy KeyEvent Arthur Author (send email) Under Development: Contributions and Comments Welcome 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
mouse Mus musculus High NCBI
human 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

Immature epidermal dendritic cells, known as Langerhans cells, and dermal dendritic cells serve as antigen-presenting cells ([1];[2];[3];[4]). In this role, they recognize and internalize the hapten-protein complex formed during covalent binding leading to their activation. Subsequently, the dendritic cell loses its ability to seize new hapten-protein complexes and gains the potential to display the allergen-MHC-complex to naive T-cells; this process is often referred to as dendritic cell maturation. Simultaneously, under the influence of fibroblast- blood endothelial- and lymph endothelial chemokines (e.g. CCL19, CCL21) and epidermal cytokines (e.g. interleukin (IL), IL-1 α, IL-1β, IL-18, tumour necrosis factor alpha (TNF-α)) maturing dendritic cells migrate from the epidermis to the dermis of the skin and then to the proximal lymph nodes, where they can present the hapten-protein complex to T-cells via a major histocompatibility complex (MHC) molecule ([5];[6]). Dendritic cell activation, upon exposure to hapten-protein complexes also leads to functional changes in the cells. For example, there are changes in chemokine secretion, cytokine secretion and in the expression of chemokine receptors (see[3]). Additionally, during dendritic cell maturation MHC, co-stimulatory and intercellular adhesion molecules (e.g. CD40, CD86, and DC11 and CD54, respectively) are up-regulated (see[3];[4];[7]). Signal transduction cascades precede changes in expression of surface proteins markers and chemokine or cytokine secretion. In fact, there is evidence that during the response, hapten-protein complexes can react with cell surface proteins and activate mitogen-activated protein kinase signalling pathway. In particular, the biochemical pathway involving extracellulare signal-regulating kinases- the c-jun N-terminal kinases and the p38 kinases have been shown to be activated upon exposure to protein-binding chemicals[8]. These pathways are of particular importance in keratinocytes and dendritic cell response to protein-hapten complexes. Components of signal transduction pathways are kinases, which phosphorylate and dephosphorylate a variety of substrates in order to elicit a change in the expression or secretion of target molecules. As a result, components of the signal transduction cascade are thought to be biomarkers[9]. Investigations into the possible role of calcium influx as an early event in dendritic cell activation suggest that calcium influx is a second event following reactive oxygen species induction[10];[11].

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). ?

Omic studies

Genomic and proteomic studies also have the potential to reveal biomarkers in dendritic cell-based assays. Custom designed arrays or quantitative polymerase chain reaction (PCR) of selected genes have been used to highlight the reaction of dendritic cells (see[3]). VITOSENS, an assay that uses human CD34+ progenitor-derived dendritic cells (CD34-DC), is based on the differential expression of the cAMP-responsive element modulator (CREM) and monocyte chemotactic protein-1 receptor (CCR2)[12]. Genomic signatures have been also developed for the identification of human sensitising chemicals: a biomarker signature, the Genomic Allergen Rapid Detection test (GARD) based on the human myelomonocytic cell line MUTZ-3[13] and a genomic platform, SENSIS, which consists of measuring the over-expression of 3 sets of genes, that may allow the in vitro assessment of the sensitising potential of a compound[14].

In Vitro Assays for Cell Surface Markers, Cytokines, and Chemokines

Alterations in intercellular adhesion molecules, cytokines, and chemokines are part of the immunology response which can serve as biomarkers. Since dendritic cell maturation upon exposure to hapten-protein complexes is accompanied by changes in surface marker expression, these surface markers are perceived as promising candidates as primary biomarkers of dendritic cell activation for the development of cell-based in vitro assays. While a variety of surface markers have been described to be up-regulated upon dendritic cell maturation, a review of the literature reveals that CD86 expression, followed by CD54 and CD40, are the most extensively studied intercellular adhesion and co-stimulator molecules to date. The human Cell Line Activation Test (h-CLAT) reported flow cytometry results for CD86 and CD54 expression in THP-1 cells[15];[16]. An OECD Test Guideline for the h-CLAT is currently under review. The h-CLAT protocol can be found in the EURL ECVAM Database Service on Alternative Methods to animal experimentation (DB-ALM): Protocol No158 for human Cell Line Activation Test (h-CLAT)[17]. Other studies with THP-1 cells include that of An et al. (2009). Another assay, the myeloid U937 skin sensitisation test (U-SENS), is based as well on the measurement of CD86 by flow cytometry[18];[19];[20]). In addition to that, a variety of cytokines have been studied in relationship to skin sensitizers[4]. IL-8 is a promising chemokine for distinguishing sensitisers from non-sensitisers. Quantification of IL-8 can be performed by Enzyme Linked Immunosorbent Assay, a technique that is far simpler and amenable to high throughput screening than the flow cytometry technique used to measure CD86 expression[3]. The expression of other cytokines linked to skin sensitisers include IL-1 α, IL-1β, IL-18, and TNF-α form the basis for other dendritic cell assays.

While some respiratory sensitizers have been assessed, it is unclear whether this event is distinct between skin and respiratory sensitizers. (dos Santos et al., 2009) The genomic allergen rapid detection (GARD) test is an MUTZ-3-based assay for assessing chemical sensitizers utilizing genomic biomarker prediction signatures to generate prediction calls of unknown chemicals such as skin sensitizers, respiratory sensitizers, or nonsensitizers, including irritants. (Johannsen et al., 2011) Preliminary data on the performance of the GARD for assessing chemical respiratory sensitizers using transcriptional readouts of a genomic biomarker signature indicated 80% accuracy. (Forreryd, et al., 2015)

There are several in vitro assays available to assess DC maturation; the most advanced is the h-CLAT, which determines changes in CD86 and CD54 levels on THP-1 cell.(Ashikaga, et al., 2006, Sakaguchi, et al., 2006) However, only limited data are available substantiating its performance on chemical respiratory sensitizers. (Basketter, et al. 2017) Several assays similar to the h-CLAT have emerged over time and are currently in the process of being validated (e.g., the MUSST measuring CD86 responses by U937 cells), but again no or minimal information is available to assess assay performance in detecting respiratory sensitizers. The MUTZ-3 cell line is also being investigated for the potential to assess the capacity of a chemical to induce LC migration. The discriminating feature of the assay is that irritant-induced migration is CCL5 dependent, while sensitizer-induced migration is CXCL12 dependent. The readout of the test is the ratio between migration toward CXCL12 or to CCL5. Despite its complexity, the assay seems to be relatively well transferable.(Rees et al., 2011)

Overview table: How it is measured or detected

Method(s) Reference URL Regulatory


Validated Non


h-CLAT draft TG under discussion at OECD [1]   X  
DB-ALM [2]
EURL ECVAM Recommendation [3]
Ashiga et al., 2015 [4]
Genomic Allergen Rapid Detection test (GARD) Johansson et al., 2013 [5]     X
VitroSens Hooyberghs et al., 2008 [6]     X

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

The main in vitro assays currently used and based on dendritic cells activation use human dendritic-cell-like cell lines (e.g. THP-1, U-937, MTZ-3)[3]. In addition to that some assays were performed on murine models[5].


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. Ryan CA, Gerberick GF, Gildea LA, Hulette BC, Bettis CJ, Cumberbatch M, Dearman RJ, Kimber I. 2005. Interactions of contact allergens with dendritic cells: opportunities and challenges for the development of novel approaches to hazard assessment. Toxicol. Sci. 88: 4-11.
  2. Ryan CA, Kimber I, Basketter, DA, Pallardy M, Gildea LA, Gerberick GF. 2007. Dendritic cells and skin sensitisation. Biological roles and uses in hazard identification. Toxicol. Appl. Pharmacol. 221: 384-394.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 dos Santos GG, Reinders J, Ouwhand K, Rustemeyer T, Scheper RJ, Gibbs S. 2009. Progress on the development of human in vitro dendritic cell based assays for assessment of skin sensitizing potential of compounds. Toxicol. Appl. Pharmacol. 236: 372-382.
  4. 4.0 4.1 4.2 Kimber I, Basketter DA, Gerberick GF, Ryan CA, Dearman, R.J. 2011. Chemical allergy: Translating biology into hazard characterization. Toxicol. Sci. 120(S1): S238-S268.
  5. 5.0 5.1 Antonopoulos C, Cumberbatch M, Mee JB, Dearman RJ, Wei XQ, Liew FY, Kimber I, Groves RW. 2008. IL-18 is a key proximal mediator of contact hypersensitivity and allergen induced Langerhans cell migration in murine epidermis. J. Leukoc. Biol. 83: 361-367.
  6. Ouwehand K, Santegoets SJAM, Bruynzeel DP, Scheper RJ, de Gruijl TD, Gibbs S. 2008. CXCL12 is essential for migration of activated Langerhans cells for epidermis to dermis. Eur. J. Immunol. 38: 3050-3059.
  7. Vandebriel RJ and van Loveren H. 2010. Non-animal sensitisation testing: State-of-the-art. Crit. Rev. Toxicol. 40: 389-404.
  8. Trompezinski S, Migdal C, Tailhardat M, Le Varlet B, Courtellemont P, Haftek M and Serres M. 2008. Charaterization of early events involved in human dendritic cell maturation induced by sensitizers: cross talk between MAPK signalling pathways. Toxicol. Appl. Pharmacol. 230: 397-406.
  9. Lambrechts N, Vanheel H, Hooyberghs J, De Boever P, Witters H, Van Den Heuval R, Van Tendeloom V, Nelissen I, Schoeters G. 2010. Gene markers in dendritic cells unravel pieces of the skin sensitisation puzzle. Toxicol. Letters 196: 95-103.
  10. Migdal C, Tailhardat M, Courtellemont P, Haftek M, Serres M. 2010. Responsiveness of human monocyte-derived dendritic cells to thimerosal and mercury derivatives. Toxicol. Appl. Pharmacol. 246: 66-73.
  11. Aeby P, Ashikaga T, Bessou-Touya S, Schapky A, Geberick F, Kern P, Marrec-Fairley M, Maxwell G, Ovigne JM, Sakaguchi H, Reisinger K, Tailhardat M, Martinozzi-Teisser S, Winkler P. 2010. Identifying and characterizing chemical skin sensitizers without animal testing; Colipa’s research and methods development program. Toxicol. In Vitro 24: 1465-1473.
  12. Hooyberghs J, Schoeters E, Lambrechts N, Nelissen I, Witters H, Schoeters G, Van Den Heuvel R. 2008. A cell-based in vitro alternative to identify skin sensitizers by gene expression. Toxicol. Appl. Pharmacol. 231: 103-111.
  13. Borrebaeck CA and Wingren C. 2009. Design of high-density antibody microarrays for disease proteomics: key technological issues. J. Proteomics 72: 928-935.
  14. Groux H and Sabatier JM. 2010. Polypeptides for the in vitro assessment of the sensitising potential of a test compound. International Application Patent No.: PCT/EP2010/055895.
  15. Sakaguchi H, Ashikaga T, Miyazawa M, Kosaka N, Ito Y, Yoneyama K, Sono S, Itagaki H, Toyoda H, Suzuki H. 2009. The relationship between CD86/CD54 expression and THP-1 cell viability in an in vitro skin sensitisation test-human cell line activation test (h-CLAT). Cell Biol. Toxicol. 25: 109-126.
  16. Ashikaga T, Sakaguchi H, Sono S, Kosaka N, Ishikawa M, Nukada Y, Miyazawa M, Ito Y, Nishiyama N, Itagaki H. 2010. A comparative evaluation of in vitro skin sensitisation tests: the human cell-line activation test (h-CLAT) versus the local lymph node assay (LLNA). Altern. Lab. Anim. 38:275-84.
  17. EURL ECVAM DB-ALM. Protocol No158: Human Cell Line Activation Test (h-CLAT) Available on:
  18. Ade N, Martinozzi-Teissier S, Pallaardy M, Rousset F. 2006. Activation of U937 cells by contact sensitizers: CD86 expression is independent of apoptosis. J. Immunotoxicol. 3: 189-197.
  19. Python F, Goebel C, Aeby P. 2007. Assessment of the U937 cell line for detection of contact allergens. Toxicol. Appl. Pharmacol. 220: 113-124.
  20. Ovigne JM, Martinozzi-Teissier S, Verda D, Abdou D, Piroird C, Ade N, Rousset F. 2008. The MUSST for in vitro skin sensitisation prediction: Applicability domains and complementary protocols to adapt to the physico-chemical diversity of chemicals. Toxicology Letters, 180: Supplement 1, 5, S216.

ASHIKAGA T, YOSHIDA Y, HIROTA M, YONEYAMA K, ITAGAKI H, SAKAGUCHI H, MIYAZAWA M, ITO Y, SUZUKI H, TOYODA H. 2006. Development of an in vitro skin sensitization test using human cell lines: the human Cell Line Activation Test (h-CLAT). I. Optimization of the h-CLAT protocol. Toxicol In Vitro. 20(5), 767-73. 

BASKETTER, D., POOLE, A., KIMBER, I., 2017. Behaviour of chemical respiratory allergens in novel predictive methods for skin sensitisation, Reg Tox and Pharmacol. 86,101-106,

DOS SANTOS, G. G., REINDERS, J., OUWEHAND, K., RUSTEMEYER, T., SCHEPER, R. J. & GIBBS, S. 2009. Progress on the development of human in vitro dendritic cell based assays for assessment of the sensitizing potential of a compound. Toxicol Appl Pharmacol, 236, 372-82.

FORRERYD A, JOHANSSON H, ALBREKT AS, BORREBAECK CA, LINDSTEDT M. 2015. Prediction of chemical respiratory sensitizers using GARD, a novel in vitro assay based on a genomic biomarker signature. PLoS One.11;10(3):e0118808.

JOHANSSON H, LINDSTEDT M, ALBREKT AS, BORREBAECK CA. 2011. A genomic biomarker signature can predict skin sensitizers using a cell-based in vitro alternative to animal tests. BMC Genomics. 8;12:399. 

REES B, SPIEKSTRA SW, CARFI M, OUWEHAND K, WILLIAMS CA, CORSINI E, MCLEOD J.D., GIBBS S. 2011. Inter-laboratory study of the in vitro dendritic cell migration assay for identification of contact allergens. Toxicol In Vitro. 25(8), 2124-34.

SAKAGUCHI H, ASHIKAGA T, MIYAZAWA M, YOSHIDA Y, ITO Y, YONEYAMA K, HIROTA M, ITAGAKI H, TOYODA H, SUZUKI H. 2006. Development of an in vitro skin sensitization test using human cell lines; human Cell Line Activation Test (h-CLAT). II. An inter-laboratory study of the h-CLAT. Toxicol In Vitro. 20(5), 774-84.