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Event: 1710

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

Binding to estrogen receptor (ER)-α in immune 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
Binding to estrogen receptor (ER)-α

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
Organ term
immune system

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
Binding to ER-α leading to exacerbation of SLE MolecularInitiatingEvent Yasuharu Otsubo (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
Homo sapiens Homo sapiens High NCBI
Mus musculus Mus musculus 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
Life stage Evidence
All life stages High

Sex Applicability

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

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

ERα is expressed in all vertebrates (Eick GN. 2011).  ERα was discovered in the late 1960s and was cloned and characterized in 1985 (Melissa C. 2011).  ERα is expressed in a variety of immunocompetent cells, including thymocytes, CD4+ (Th1, Th2, Th17, and Tregs) and CD8+ cells and macrophages (Melissa C. 2011, Salem ML. 2004, Robinson DP. 2014).  One study examined ERα expression in resting and activated PBMC subsets and found that ERα was expressed at higher levels in thymocytes, CD4+ T cells than B cells (Melissa C. 2011).  ERα is a nuclear hormone transcription factor that classically binds with ligand (stressors), further stabilizing dimers that subsequently bind estrogen response elements (ERE) or non-ERE to transactivate or suppress specific target genes (Parker MG. 1993, Goldstein RA. 1993, Sasson S. 1991, Brandt ME. 1997, Carolyn MK. 2001).

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). ?

The binding affinities of E2 and BPA for ERα can be confirmed by radio receptor assay, and its dimer dissociation is measured using size exclusion chromatography (Brandt ME. 1997, Takayanagi S. 2006, OECD TG440 [in vivo] and TG455 [in vitro]).  While the binding affinities of PPT for ERα was determined by competitive radiometric binding assays by chemiluminescence (Kraichely DM. 2000, Carlson KE. 1997).

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

Since ERα expresses in the cells of a vast variety of (vertebrate) species (Maria B. 2015) and there is common functionality in the immune systems of at least humans and mice, this AOP might be applicable to many mammal species, including humans and rodents.  The estrogen receptors are composed of several domains important for hormone binding, DNA binding, dimer formation, and activation of transcription (Green S. 1986, Kumar V. 1986, Warnmark A. 2003).  Interspecies sequence identities for the entire ERα are 88.5% (human-mouse), 87.5% (human-rat), and 97.5% (mouse-rat). For the ligand binding domain (ERα-LBD) alone, the interspecies sequence identities are 95.5% (human-mouse), 95.1% (human-rat), and 99.2% (mouse-rat) (White R. 1987).

ERα is widely expressed in most tissue types including most immune cells in males and females (Couse JF. 1997, Chelsea C. 2017). The ERs’ expression patterns and functions vary in a receptor subtype, cell- and tissue-specific manner.  In the adult human, large-scale sequencing approaches show that ERα mRNA is detected in numerous human tissues, with the highest levels in the uterus, liver, ovary, muscle, mammary gland, pituitary gland, adrenal gland, spleen and heart, and at lower levels in the prostate, testis, adipose tissue, thyroid gland, lymph nodes and spleen (Fagerberg L. 2014, Sayers EW. 2012) (

Estrogen level is higher in women than men.  Ordinary estrogen levels in women are 20-30 pg/mL during diestrus, 100-200 pg/mL during estrus, and 5000-10000 pg/mL during pregnancy (Offner H. 2000).  Therefore, the influence of ligand binding to ERα in immune cells is expressed more strong in women than men, especially high estrogen level period.

Evidence for Perturbation by Stressor

Overview for Molecular Initiating Event

When a specific MIE can be defined (i.e., the molecular target and nature of interaction is known), in addition to describing the biological state associated with the MIE, how it can be measured, and its taxonomic, life stage, and sex applicability, it is useful to list stressors known to trigger the MIE and provide evidence supporting that initiation. This will often be a list of prototypical compounds demonstrated to interact with the target molecule in the manner detailed in the MIE description to initiate a given pathway (e.g., 2,3,7,8-TCDD as a prototypical AhR agonist; 17α-ethynyl estradiol as a prototypical ER agonist). Depending on the information available, this could also refer to chemical categories (i.e., groups of chemicals with defined structural features known to trigger the MIE). Known stressors should be included in the MIE description, but it is not expected to include a comprehensive list. Rather initially, stressors identified will be exemplary and the stressor list will be expanded over time. For more information on MIE, please see pages 32-33 in the User Handbook.

E2 activates ERα and ERβ with the same affinity although they share only 56% similarity in their ligand binding domains (Monroe DG. 2005, Papoutsi Z. 2009).  Exposure E2 induced thymic atrophy, and changing T-cell phenotype (decreasing double positive (CD4+CD8+) T cell and increasing double negative (CD4-CD8-) T cell) in thymus (Okasha SA. 2001).

BPA binds to both ERα and ERβ, and ERα binding affinity of BPA is lower than that of ERβ (Takayanagi S. 2006).  While these bindings are less than 2000‑fold affinity compared to the binding of estradiol to estrogen receptors (Krishnan AV. 1993).

Propylpyrazoletriol (PPT) is an ERα-selective agonist, which shows 410-fold selectivity for ERα as compared with ERβ (Kraichely DM. 2000, Li J. 2006).  Li et al (2006) demonstrated that ovariectomized mice exposed PPT induced severe thymic atrophy, changing T-cell phenotype (CD4/CD8 phenotype profile) in thymus, and a reduction of mature B cell number in spleen.  Since these effects by PPT were equal to or greater than E2, ERα plays the predominant role in the upregulation of immune responses.


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. Eick GN, Thornton JW. Evolution of steroid receptors from an estrogen-sensitive ancestral receptor. Molecular and cellular endocrinology. 2011; 334: 31-38.
  2. Melissa, C. and Gary, G (2011). Estrogen Receptors in Immunity and Autoimmunity. Clinical Reviews in Allergy & Immunology 40:66-73.
  3. Salem ML. (2004). Estrogen, a double-edged sword: modulation of Th1- and Th2-mediated inflammations by differential regulation of Th1/Th2 cytokine production. Current Drug Targets - Inflammation & Allergy 3(1): 97-104.
  4. Robinson DP, Hall, O. J., Nilles, T. L., Bream, J.H. and Klein, S.L. (2014). 17β-estradiol protects females against influenza by recruiting neutrophils and increasing virus-specific CD8 T cell responses in the lungs. Journal of Virology 88 (9): 4711-4720.
  5. Parker MG, Arbuckle N, Dauvois S, Danielian P, White R. Structure and function of the estrogen receptor. Ann N Y Acad Sci. 1993. 684:119-26.
  6. Goldstein RA, Katzenellenbogen JA, Wolynes PG, et al. Three-dimensional model for the hormone binding domains of steroid receptors. Proc Natl Acad Sci. 1993;90 (21):9949-53.
  7. Sasson S. Equilibrium binding analysis of estrogen agonists and antagonists: relation to the activation of the estrogen receptor. Pathol Biol (Paris). 1991;39(1):59-69.
  8. Brandt ME, Vickery LE. Cooperativity and dimerization of recombinant human estrogen receptor hormone-binding domain. J Biol Chem. 1997;272(8):4843-9.
  9. Carolyn MK. Estrogen receptor interaction with estrogen response elements. Nucleic Acids Res. 2001 Jul 15; 29(14): 2905-2919.
  10. Takayanagi, S. Tokunaga, T., et al. (2006).  Endocrine disruptor bisphenol A strongly binds to human estrogen-related receptor γ (ERRγ) with high constitutive activity. Toxicology Letters, 167 (2):95-105.
  11. OECD Guideline for the Testing of Chemicals [Test No. 440: Uterotrophic Bioassay in Rodents]
  12. OECD Guideline for the Testing of Chemicals [Test No. 455: Performance-Based Test Guideline for Stably Transfected Transactivation In Vitro Assays to Detect Estrogen Receptor Agonists and Antagonists]
  13. Kraichely, DM. Sun, J. Katzenellenbogen, JA. Katzenellenbogen, BS. (2000). Conformational changes and coactivator recruitment by novel ligands for estrogen receptor-α and estrogen receptor-β: correlations with biological character and distinct differences among SRC coactivator family members. Endocrinology, 141 (10):3534–3545.
  14. Carlson, KE. Choli, I. Gee, A. Katzenellenbogen, BS. Katzenellenbogen, JA. (1997) Altered Ligand Binding Properties and Enhanced Stability of a Constitutively Active Estrogen Receptor:  Evidence That an Open Pocket Conformation Is Required for Ligand Interaction. Biochemistry, 36:14897-14905.
  15. Maria, B., Ruixin, H., Chin-Yo, L., Cecilia, W., Jan-Ake, G. (2015). Estrogen receptor signaling during vertebrate development. Biochim Biophys Acta 1849: 142-151.
  16. Green S, Walter P, Chambon P, et al. Human oestrogen receptor cDNA: sequence, expression and homology to v-erb-A. Nature. 1986; 320:134-139.
  17. Kumar V, Green S, Chambon P, et al. Localisation of the oestradiol-binding and putative DNA-binding domains of the human oestrogen receptor. The EMBO journal. 1986; 5: 2231-2236.
  18. Warnmark A, Treuter E, Gustafsson JA, et al. Activation functions 1 and 2 of nuclear receptors: molecular strategies for transcriptional activation. Molecular endocrinology (Baltimore, Md). 2003; 17:1901-1909.
  19. White, R., Lees, JA., Needham, M., Ham, J. and Parker, M. (1987). Structural Organization and Expression of the Mouse Estrogen Receptor. Molecular Endocrinology 1 (10): 735-744.
  20. Couse JF, Lindzey J, Grandien K, Gustafsson JA, Korach KS. (1997) Tissue distribution and quantitative analysis of estrogen receptor-alpha (ERalpha) and estrogen receptor-beta (ERbeta) messenger ribonucleic acid in the wild-type and ERalphaknockout mouse. Endocrinology 138(11):4613-4621.
  21. Fagerberg L, Hallstrom BM, Edlund K, et al. Analysis of the human tissue- specific expression by genome-wide integration of transcriptomics and antibody-based proteomics. Molecular & cellular proteomics. 2014; 13:397-406.
  22. Sayers EW, Barrett T, Federhen S, et al. Database resources of the National Center for Biotechnology Information. Nucleic acids research. 2012; 40: D13-25.
  23. Offner H, Adlard K, Zamora A, Vandenbark AA. Estrogen potentiates treatment with T-cell receptor protein of female mice with experimental encephalomyelitis. J Clin Invest. 2000;105(10):1465-72.
  24. Monroe DG, Secreto FJ, Subramaniam M, Getz BJ, Khosla S, Spelsberg TC. Estrogen receptor alpha and beta heterodimers exert unique effects on estrogen- and tamoxifen-dependent gene expression in human U2OS osteosarcoma cells. Molecular endocrinology (Baltimore, Md). 2005; 19:1555–1568.
  25. Papoutsi Z, Zhao C, Putnik M, Gustafsson JA, Dahlman-Wright K. Binding of estrogen receptor alpha/beta heterodimers to chromatin in MCF-7 cells. J Mol Endocrinol. 2009; 43:65-72.
  26. Okasha SA, Ryu S, Do Y, McKallip RJ, Nagarkatti M, Nagarkatti PS. Evidence for estradiol-induced apoptosis and dysregulated T cell maturation in the thymus. Toxicology. 2001, 163 (1):49-62.
  27. Takayanagi S, Tokunaga T, Liu X, Okada H, Matsushima A, Shimohigashi Y.  Endocrine disruptor bisphenol A strongly binds to human estrogen-related receptor γ (ERRγ) with high constitutive activity. Toxicology Letters, 2006, 167 (2):95-105.
  28. Krishnan, AV., Stathis, P., Permuth, S. F., Tokes, L. and Feldman, D. (1993). Bisphenol-A: an estrogenic substance is released from polycarbonate flasks during autoclaving. Endocrinology 132; 2279-2286.
  29. Li, J., McMurray, RW. (2006). Effects of estrogen receptor subtype-selective agonists on immune functions in ovariectomized mice. International Immunopharmacology, 6 (9):1413-1423.