Aop: 315


Each AOP should be given a descriptive title that takes the form “MIE leading to AO”. For example, “Aromatase inhibition [MIE] leading to reproductive dysfunction [AO]” or “Thyroperoxidase inhibition [MIE] leading to decreased cognitive function [AO]”. In cases where the MIE is unknown or undefined, the earliest known KE in the chain (i.e., furthest upstream) should be used in lieu of the MIE and it should be made clear that the stated event is a KE and not the MIE. More help

Inhibition of JAK3 leading to impairment of T-Cell Dependent Antibody Response

Short name
A short name should also be provided that succinctly summarises the information from the title. This name should not exceed 90 characters. More help
Immune dysfunction induced by JAK3 inhibition

Graphical Representation

A graphical summary of the AOP listing all the KEs in sequence, including the MIE (if known) and AO, and the pair-wise relationships (links or KERs) between those KEs should be provided. This is easily achieved using the standard box and arrow AOP diagram (see this page for example). The graphical summary is prepared and uploaded by the user (templates are available) and is often included as part of the proposal when AOP development projects are submitted to the OECD AOP Development Workplan. The graphical representation or AOP diagram provides a useful and concise overview of the KEs that are included in the AOP, and the sequence in which they are linked together. This can aid both the process of development, as well as review and use of the AOP (for more information please see page 19 of the Users' Handbook).If you already have a graphical representation of your AOP in electronic format, simple save it in a standard image format (e.g. jpeg, png) then click ‘Choose File’ under the “Graphical Representation” heading, which is part of the Summary of the AOP section, to select the file that you have just edited. Files must be in jpeg, jpg, gif, png, or bmp format. Click ‘Upload’ to upload the file. You should see the AOP page with the image displayed under the “Graphical Representation” heading. To remove a graphical representation file, click 'Remove' and then click 'OK.'  Your graphic should no longer be displayed on the AOP page. If you do not have a graphical representation of your AOP in electronic format, a template is available to assist you.  Under “Summary of the AOP”, under the “Graphical Representation” heading click on the link “Click to download template for graphical representation.” A Powerpoint template file should download via the default download mechanism for your browser. Click to open this file; it contains a Powerpoint template for an AOP diagram and instructions for editing and saving the diagram. Be sure to save the diagram as jpeg, jpg, gif, png, or bmp format. Once the diagram is edited to its final state, upload the image file as described above. More help


List the name and affiliation information of the individual(s)/organisation(s) that created/developed the AOP. In the context of the OECD AOP Development Workplan, this would typically be the individuals and organisation that submitted an AOP development proposal to the EAGMST. Significant contributors to the AOP should also be listed. A corresponding author with contact information may be provided here. This author does not need an account on the AOP-KB and can be distinct from the point of contact below. The list of authors will be included in any snapshot made from an AOP. More help

Yasuhiro Yoshida (1) Takao Ashikaga (1) Tomoki Fukuyama (1) Ken Goto (1) Shinko Hata (1) Shigeru Hisada (1) Shiho Ito (1) Hiroyuki Komatsu (1) Sumie Konishi (1) Tadashi Kosaka (1) Kiyoshi Kushima (1) Shogo Matsumura (1) Takumi Ohishi (1) Yasuharu Otsubo (1) Junichiro Sugimoto (1)

(1) AOP Working Group, Testing Methodology Committee, The Japanese Society of Immunotoxicology

Corresponding author: Yasuhiro Yoshida (

Point of Contact

Indicate the point of contact for the AOP-KB entry itself. This person is responsible for managing the AOP entry in the AOP-KB and controls write access to the page by defining the contributors as described below. Clicking on the name will allow any wiki user to correspond with the point of contact via the email address associated with their user profile in the AOP-KB. This person can be the same as the corresponding author listed in the authors section but isn’t required to be. In cases where the individuals are different, the corresponding author would be the appropriate person to contact for scientific issues whereas the point of contact would be the appropriate person to contact about technical issues with the AOP-KB entry itself. Corresponding authors and the point of contact are encouraged to monitor comments on their AOPs and develop or coordinate responses as appropriate.  More help
Brendan Ferreri-Hanberry   (email point of contact)


List user names of all  authors contributing to or revising pages in the AOP-KB that are linked to the AOP description. This information is mainly used to control write access to the AOP page and is controlled by the Point of Contact.  More help
  • Takumi Ohishi
  • Yasuhiro Yoshida
  • Brendan Ferreri-Hanberry


The status section is used to provide AOP-KB users with information concerning how actively the AOP page is being developed, what type of use or input the authors feel comfortable with given the current level of development, and whether it is part of the OECD AOP Development Workplan and has been reviewed and/or endorsed. “Author Status” is an author defined field that is designated by selecting one of several options from a drop-down menu (Table 3). The “Author Status” field should be changed by the point of contact, as appropriate, as AOP development proceeds. See page 22 of the User Handbook for definitions of selection options. More help
Author status OECD status OECD project SAAOP status
Under development: Not open for comment. Do not cite Under Development 1.74 Included in OECD Work Plan
This AOP was last modified on April 05, 2021 18:16
The date the AOP was last modified is automatically tracked by the AOP-KB. The date modified field can be used to evaluate how actively the page is under development and how recently the version within the AOP-Wiki has been updated compared to any snapshots that were generated. More help

Revision dates for related pages

Page Revision Date/Time
Inhibition of JAK3 February 15, 2021 06:25
Blockade of STAT5 phosphorylation February 15, 2021 06:27
Suppression of STAT5 binding to cytokine gene promoters February 24, 2021 06:52
Suppression of IL-4 production February 24, 2021 06:55
Impairment of T-cell dependent antibody response February 24, 2021 06:58
Inhibition of JAK3 leads to STAT5 inhibition February 15, 2021 06:35
STAT5 inhibition leads to Suppression of STAT5 binding to cytokine gene promoters February 24, 2021 07:02
Suppression of STAT5 binding to cytokine gene promoters leads to Suppression of IL-4 production March 30, 2021 11:07
Suppression of IL-4 production leads to Impairment, TDAR April 04, 2021 08:42
PF-06651600 (CAS No:1792180-81-4), September 15, 2020 05:38
RB1 September 15, 2020 05:38


In the abstract section, authors should provide a concise and informative summation of the AOP under development that can stand-alone from the AOP page. Abstracts should typically be 200-400 words in length (similar to an abstract for a journal article). Suggested content for the abstract includes the following: The background/purpose for initiation of the AOP’s development (if there was a specific intent) A brief description of the MIE, AO, and/or major KEs that define the pathway A short summation of the overall WoE supporting the AOP and identification of major knowledge gaps (if any) If a brief statement about how the AOP may be applied (optional). The aim is to capture the highlights of the AOP and its potential scientific and regulatory relevance More help

Signal transduction between immune-related cells depends in many cases on cytokines. The transduction involves cell surface cytokine receptors as well as direct cell-to-cell interaction. Cytokines influence the movement, proliferation, differentiation, and activation of lymphocytes and other leukocytes in a variety of ways. Some cytokine receptors require an activation step through a Janus-kinase (JAK)/signal transducer and activator of transcription (STAT) system. When cytokines bind to specific cytokine receptors, the receptors form dimers, which more closely resemble JAK molecules. JAK is activated and phosphorylates adjacent cytokine receptors. STATs bind to the phosphorylated receptor sites and are in turn phosphorylated by the activated JAK. The phosphorylated STAT is dimerized and translocated into the nucleus. There it binds to the promoter regions of cytokine genes, which initiates the transcription of these genes in the nucleus.

In mammals, four JAK families of enzymes (JAK1, JAK2, JAK3, and TYK2) and seven STATs (STAT1, STAT2, STAT3, STAT4, STAT5a, STAT5b, and STAT6) are utilized by more than 50 cytokines and growth factors to mediate intracellular signaling. In particular, pro-inflammatory cytokines such as interferon-γ (IFN-γ), interleukin-2 (IL-2), IL-4, IL-6, IL-13, IL-21, and IL-23 have been implicated in inflammatory diseases that utilize the JAK pathway. In addition, TH2 derived cytokines, including IL-31 and thymic stromal lymphopoietin (TSLP), are ligands for murine and human sensory nerves. These cytokines have critical roles in evoking itchiness. Because these cytokines also interact with JAK, several JAK inhibitors have received a lot of attention recently as therapeutic agents for major inflammatory diseases and pruritic diseases.

This proposed AOP consists of JAK3 inhibition as a MIE, blockade of STAT5 phosphorylation as the first key event (KE1), suppression of STAT5 binding to the promoter regions of cytokine genes as KE2, suppression of IL-4 production as KE3, and suppression of T cell dependent antibody response (TDAR) as an AO. This AOP especially focuses on the inhibition of JAK3, which is required for signal transduction by cytokines through the common γ chain of the receptors for IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. In the proposed AOP, JAK3 selective inhibitors that include PF-06651600 (CAS No: 1792180-81-4) and the 4-aminopiperidine-based compound RB1 are stressors. STAT5 that is phosphorylated by JAK3 forms a homo-dimer that translocate to the nucleus and induces expressions of genes, such as IL-4. Therefore, JAK3 inhibition leads to the suppressed binding of STAT5 to the promoter regions of cytokine genes and the subsequent suppression of IL-4 production. Thus, JAK/STAT regulation plays an important role in the TDAR. TDAR is frequently affected by immunosuppressive conditions and is a major endpoint in many preclinical immunotoxicity studies.

Background (optional)

This optional subsection should be used to provide background information for AOP reviewers and users that is considered helpful in understanding the biology underlying the AOP and the motivation for its development. The background should NOT provide an overview of the AOP, its KEs or KERs, which are captured in more detail below. Examples of potential uses of the optional background section are listed on pages 24-25 of the User Handbook. More help

Although many stressors inhibit JAK3 activity, this AOP is based on immunosuppression caused by the recently developed and highly selective JAK3 inhibitors PF-06651600 and RB1. A significant body of scientific literature has been published concerning these two inhibitors. We look forward to future amendments to this AOP with up-to-date information on other stressors, which will clarify the link between inhibition of JAK activity and impairment of TDAR.

Summary of the AOP

This section is for information that describes the overall AOP. The information described in section 1 is entered on the upper portion of an AOP page within the AOP-Wiki. This is where some background information may be provided, the structure of the AOP is described, and the KEs and KERs are listed. More help


Molecular Initiating Events (MIE)
An MIE is a specialised KE that represents the beginning (point of interaction between a stressor and the biological system) of an AOP. More help
Key Events (KE)
This table summarises all of the KEs of the AOP. This table is populated in the AOP-Wiki as KEs are added to the AOP. Each table entry acts as a link to the individual KE description page.  More help
Adverse Outcomes (AO)
An AO is a specialised KE that represents the end (an adverse outcome of regulatory significance) of an AOP.  More help
Sequence Type Event ID Title Short name
MIE 1715 Inhibition of JAK3 Inhibition of JAK3
KE 1716 Blockade of STAT5 phosphorylation STAT5 inhibition
KE 1717 Suppression of STAT5 binding to cytokine gene promoters Suppression of STAT5 binding to cytokine gene promoters
KE 1718 Suppression of IL-4 production Suppression of IL-4 production

Relationships Between Two Key Events (Including MIEs and AOs)

TESTINGThis table summarises all of the KERs of the AOP and is populated in the AOP-Wiki as KERs are added to the AOP. Each table entry acts as a link to the individual KER description page.To add a key event relationship click on either Add relationship: events adjacent in sequence or Add relationship: events non-adjacent in sequence.For example, if the intended sequence of KEs for the AOP is [KE1 > KE2 > KE3 > KE4]; relationships between KE1 and KE2; KE2 and KE3; and KE3 and KE4 would be defined using the add relationship: events adjacent in sequence button.  Relationships between KE1 and KE3; KE2 and KE4; or KE1 and KE4, for example, should be created using the add relationship: events non-adjacent button. This helps to both organize the table with regard to which KERs define the main sequence of KEs and those that provide additional supporting evidence and aids computational analysis of AOP networks, where non-adjacent KERs can result in artifacts (see Villeneuve et al. 2018; DOI: 10.1002/etc.4124).After clicking either option, the user will be brought to a new page entitled ‘Add Relationship to AOP.’ To create a new relationship, select an upstream event and a downstream event from the drop down menus. The KER will automatically be designated as either adjacent or non-adjacent depending on the button selected. The fields “Evidence” and “Quantitative understanding” can be selected from the drop-down options at the time of creation of the relationship, or can be added later. See the Users Handbook, page 52 (Assess Evidence Supporting All KERs for guiding questions, etc.).  Click ‘Create [adjacent/non-adjacent] relationship.’  The new relationship should be listed on the AOP page under the heading “Relationships Between Two Key Events (Including MIEs and AOs)”. To edit a key event relationship, click ‘Edit’ next to the name of the relationship you wish to edit. The user will be directed to an Editing Relationship page where they can edit the Evidence, and Quantitative Understanding fields using the drop down menus. Once finished editing, click ‘Update [adjacent/non-adjacent] relationship’ to update these fields and return to the AOP page.To remove a key event relationship to an AOP page, under Summary of the AOP, next to “Relationships Between Two Key Events (Including MIEs and AOs)” click ‘Remove’ The relationship should no longer be listed on the AOP page under the heading “Relationships Between Two Key Events (Including MIEs and AOs)”. More help

Network View

The AOP-Wiki automatically generates a network view of the AOP. This network graphic is based on the information provided in the MIE, KEs, AO, KERs and WoE summary tables. The width of the edges representing the KERs is determined by its WoE confidence level, with thicker lines representing higher degrees of confidence. This network view also shows which KEs are shared with other AOPs. More help


The stressor field is a structured data field that can be used to annotate an AOP with standardised terms identifying stressors known to trigger the MIE/AOP. Most often these are chemical names selected from established chemical ontologies. However, 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). It can also include non-chemical stressors such as genetic or environmental factors. Although AOPs themselves are not chemical or stressor-specific, linking to stressor terms known to be relevant to different AOPs can aid users in searching for AOPs that may be relevant to a given stressor. More help
Name Evidence Term
PF-06651600 (CAS No:1792180-81-4), High
RB1 High

Life Stage Applicability

Identify the life stage for which the KE is known to be applicable. More help
Life stage Evidence
All life stages High

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected. 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

Sex Applicability

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

Overall Assessment of the AOP

This section addresses the relevant biological domain of applicability (i.e., in terms of taxa, sex, life stage, etc.) and WoE for the overall AOP as a basis to consider appropriate regulatory application (e.g., priority setting, testing strategies or risk assessment). The goal of the overall assessment is to provide a high level synthesis and overview of the relative confidence in the AOP and where the significant gaps or weaknesses are (if they exist). Users or readers can drill down into the finer details captured in the KE and KER descriptions, and/or associated summary tables, as appropriate to their needs.Assessment of the AOP is organised into a number of steps. Guidance on pages 59-62 of the User Handbook is available to facilitate assignment of categories of high, moderate, or low confidence for each consideration. While it is not necessary to repeat lengthy text that appears elsewhere in the AOP description (or related KE and KER descriptions), a brief explanation or rationale for the selection of high, moderate, or low confidence should be made. More help
Attached file: Ovewall

JAKs are a family of nonreceptor tyrosine kinases and consist of four members: JAK1, JAK2, JAK3, and Tyk2 (Johnston, et al. 1994). All four mediate signals initiated by cytokines through interactions with receptors for IL-2, IL-5, IL-7, IL-9, and IL-15 via the common γ chain (Witthuhn, et al. 1994). Different studies have shown that JAK3 is widely expressed in different organs (Witthuhn, et al. 1994). Previous studies with IL-2Rγ-null mice showed that JAK3 is related to the development of spontaneous inflammatory bowel disease symptoms (Miyazaki, et al. 1994). Moreover, abnormal activation of JAK3 was associated with human hematology (Ihle, et al. 1997), indicating that a tight balance of its activity is essential for normal hematopoietic development.

Although JAK1, JAK2, and Tyk2 are widely expressed, JAK3 is predominantly expressed in hematopoietic cells and is associated only with the common γ chain of the IL-2, IL-4, IL-7, IL-9, and IL-15 receptors (Nosaka, et al. 1995). IL-4 is a very well-known cytokine that is crucial in the polarization of naïve T cells to type 2 helper T cells. IL-4 plays a major role in the growth and proliferation of many immune cells, such as natural killer (NK) cells and T cells (Dhupkar and Gordon 2017). Homozygous mutant mice harboring a disrupted JAK3 gene display profound reductions in thymocytes and severe B cell and T cell lymphopenia, similar to severe combined immunodeficiency disease (SCID), and functionally deficient residual T cells and B cells. Thus, JAK3 plays a critical role in γ chain signaling and lymphoid development.

Domain of Applicability

The relevant biological domain(s) of applicability in terms of sex, life-stage, taxa, and other aspects of biological context are defined in this section. Biological domain of applicability is informed by the “Description” and “Biological Domain of Applicability” sections of each KE and KER description (see sections 2G and 3E for details). In essence the taxa/life-stage/sex applicability is defined based on the groups of organisms for which the measurements represented by the KEs can feasibly be measured and the functional and regulatory relationships represented by the KERs are operative.The relevant biological domain of applicability of the AOP as a whole will nearly always be defined based on the most narrowly restricted of its KEs and KERs. For example, if most of the KEs apply to either sex, but one is relevant to females only, the biological domain of applicability of the AOP as a whole would be limited to females. While much of the detail defining the domain of applicability may be found in the individual KE and KER descriptions, the rationale for defining the relevant biological domain of applicability of the overall AOP should be briefly summarised on the AOP page. More help

The proposed AOP involves inhibition of JAK activity, which leads to suppression of TDAR independent of life stage, sex, or age. Since JAK3 inhibitors (PF-06651600, RB1) are currently under phase 2 clinical evaluation for the treatment of rheumatoid arthritis, the AOP appears to be applicable to all life stages. JAK3 inhibitor-induced outcomes in humans are mimicked by similar responses in a variety of animal models, including non-human primates and rodents. Thus, immunosuppression induced by inhibition of JAK3 activity is considered to occur across a variety of mammalian species. For example, PF-06651600 was reported to reduce paw swelling with an unbound EC50 of 169 nM in rat adjuvant-induced arthritis. Similarly, PF-06651600 significantly reduced disease severity in an experimental autoimmune encephalomyelitis mouse model at 30 or 100 mg/kg or prophylactically at 20 and 60 mg/kg. PF-06651600 will be evaluated in clinical trials (Telliez, et al. 2016).

Essentiality of the Key Events

An important aspect of assessing an AOP is evaluating the essentiality of its KEs. The essentiality of KEs can only be assessed relative to the impact of manipulation of a given KE (e.g., experimentally blocking or exacerbating the event) on the downstream sequence of KEs defined for the AOP. Consequently evidence supporting essentiality is assembled on the AOP page, rather than on the independent KE pages that are meant to stand-alone as modular units without reference to other KEs in the sequence.The nature of experimental evidence that is relevant to assessing essentiality relates to the impact on downstream KEs and the AO if upstream KEs are prevented or modified. This includes: Direct evidence: directly measured experimental support that blocking or preventing a KE prevents or impacts downstream KEs in the pathway in the expected fashion. Indirect evidence: evidence that modulation or attenuation in the magnitude of impact on a specific KE (increased effect or decreased effect) is associated with corresponding changes (increases or decreases) in the magnitude or frequency of one or more downstream KEs.When assembling the support for essentiality of the KEs, authors should organise relevant data in a tabular format. The objective is to summarise briefly the nature and numbers of investigations in which the essentiality of KEs has been experimentally explored either directly or indirectly. See pages 50-51 in the User Handbook for further definitions and clarifications.  More help

MIE and later events: JAK3-knockout (KO) mice

JAK3 was initially identified (Johnston, et al. 1994, Witthuhn, et al. 1994) in studies designed to identify the JAK family member involved in the signaling of a group of cytokines with shared utilization of the γ chain first identified in the IL-2 receptor complex. It was subsequently demonstrated that JAK3 physically associates with the γ chain and is activated in a receptor complex that also contains JAK1, which associates with the ligand-specific α or β chain of the receptors (Miyazaki, et al. 1994). JAK3 is somewhat unique within the JAK family in that it is predominantly expressed in hematopoietic cells and is only activated in response to cytokines that use the γ chain (Ihle, et al. 1997). The phenotype of the JAK3 deletion mice is striking, with a range of deficiencies that collectively constitute SCID (Nosaka, et al. 1995, Thomis, et al. 1995). At the same time, two groups identified individuals that lacked JAK3 and exhibited somatically acquired SCID (Macchi, et al. 1995, Russell, et al. 1995). One of the most striking components of the phenotype are the dramatic reductions in both the T and B-cell lineages. Comparable reductions are seen in mice that lack IL-7 (von Freeden-Jeffry, et al. 1995), the IL-7 receptor α chain (Peschon, et al. 1994), or the γ chain. Despite the reduced numbers, the cells that do develop are phenotypically normal. These results are consistent with the hypothesis that activation of JAK3 is critical in the expansion, but not differentiation, of early lymphoid lineage-committed cells. In addition to the reduced numbers, the differentiated lymphoid cells that are generated fail to respond to the spectrum of cytokines that utilize the γ chain and activate JAK3 normally.

B6.Cg-Nr1d1tm1Ven/LazJ mouse

Primary immunodeficiencies (PIDs) are inborn errors that cause developmental and/or functional defects in the immune system (Picard, et al. 2015). PIDs are usually rare and monogenic. They present clinically with a broad array of phenotypes, including increased susceptibility to infection. One of the most deadly categories of PID is SCID. SCID is invariably caused by severe developmental and/or functional defects of T lymphocytes. However, SCID may also present with variable defects of B and/or NK cells. The B6.Cg-Nr1d1tm1Ven/LazJ mouse line harbors a spontaneous mutation in JAK3, which generates the SCID phenotype (Robinette, et al. 2018).

KE1: STAT5-KO mice

STAT5 plays a major role in regulating vital cellular functions, such as proliferation, differentiation, and apoptosis of hematopoietic and immune cells (Rani and Murphy 2016, Wittig and Groner 2005). STAT5 is activated by phosphorylation of a single constituent tyrosine residue (Y694) and is negatively regulated by dephosphorylation. A wide variety of growth factors and cytokines can activate STAT5 through the JAK-STAT pathway. The activation of STAT5 is transient and tightly regulated in normal cells (Quezada Urban, et al. 2018).

Phenotypes observed in STAT5-KO mice

The transcription factor STAT5 is expressed in all lymphocytes and plays a key role in multiple aspects of lymphocyte development and function (Owen and Farrar 2017). STAT5 was initially identified as a transcription factor activated by prolactin in mammary gland epithelial cells (Schmitt-Ney, et al. 1992, Wakao, et al. 1992). Subsequent studies identified STAT5 binding activity in T cells (Beadling, et al. 1994). Other authors described that the expression of STAT5 in multiple cell types and its’ activation by a number of cytokines, including the common γ-chain-dependent cytokines IL-2, IL-4, IL-7, IL-13, and IL-15 (Lin, et al. 1995).

STAT5 in T cell development

The observation that STAT5 is activated by multiple cytokines in T cells suggests that it might play a critical role in the development and/or function of these cells. Disruption of the Stat5a gene or Stat5b gene reportedly resulted in relatively modest phenotypes. For example, Stat5a-/- mice displayed defects in mammary gland development and lactation, while Stat5b-/- mice displayed defects in response to growth hormone in male mice and NK cell proliferation (Imada, et al. 1998, Liu, et al. 1997). To determine whether combined deletion of Stat5a and Stat5b might result in more profound immunodeficiencies, subsequent studies deleted the first coding exons of both Stat5a and Stat5b. This intervention resulted in the production of truncated forms of STAT5a and STAT5b, which acted as functional hypomorphs. These mice had surprisingly mild defects in lymphocyte development, although T cells were grossly dysfunctional as they could no longer proliferate in response to IL-2 (Moriggl, et al. 1999, Teglund, et al. 1998). Finally, complete deletion of Stat5a and Stat5b using Cre-LoxP approaches demonstrated that STAT5a and STAT5b are absolutely required for lymphocyte development, as Stat5a/b-/- mice had profound blocks in lymphocyte development, which mimicked that observed in Il7r-/- mice (Cui, et al. 2004, Yao, et al. 2006). These studies definitively demonstrated the retention of appreciable STAT5 function in STAT5 hypomorph mice.

Evidence Assessment

The biological plausibility, empirical support, and quantitative understanding from each KER in an AOP are assessed together.  Biological plausibility of each of the KERs in the AOP is the most influential consideration in assessing WoE or degree of confidence in an overall hypothesised AOP for potential regulatory application (Meek et al., 2014; 2014a). Empirical support entails consideration of experimental data in terms of the associations between KEs – namely dose-response concordance and temporal relationships between and across multiple KEs. It is examined most often in studies of dose-response/incidence and temporal relationships for stressors that impact the pathway. While less influential than biological plausibility of the KERs and essentiality of the KEs, empirical support can increase confidence in the relationships included in an AOP. For clarification on how to rate the given empirical support for a KER, as well as examples, see pages 53- 55 of the User Handbook.  More help

T cell development is mainly regulated by the JAK-STAT system. JAK3 deficiency in T cells induces multiple types of immunosuppression, including TDAR.

JAK3-deficient mice reportedly displayed profound reductions in thymocytes and severe B cell and T cell lymphopenia, similar to SCID disease. The residual T cells and B cells were functionally deficient (Peschon, et al. 1994).

Mice lacking JAK3 also showed a severe block in B cell development at the pre-B stage in the bone marrow. In contrast, although the thymuses of these mice were small, T cell maturation progressed relatively normally. In response to mitogenic signals, peripheral T cells in JAK3-deficient mice did not proliferate and secreted small amounts of IL-4. These data demonstrate that JAK3 is critical for the progression of B cell development in the bone marrow and for the functional competence of mature T cells (Nosaka, et al. 1995).

Furthermore, the abnormal architecture of lymphoid organs suggested the involvement of JAK3 in epithelial cells. T cells that developed in the mutant mice did not respond to IL-2, IL-4, or IL-7 (Ito, et al. 2017).

PF-06651600 and RB1 specifically inhibit JAK3 with over 100-fold preference over JAK2, JAK1, and TYK2 in kinase assays. Reduced inflammation and associated pathology have been described in collagen-induced arthritis mice. Importantly, the administration of PF-06651600 or RB1 results in decreased pro-inflammatory cytokines and JAK3 and STAT phosphorylation in mice. The findings suggest that the inhibition of JAK3/STAT signaling is closely correlated with the induction of multiple types of immunosuppression, including TDAR.

Quantitative Understanding

Some proof of concept examples to address the WoE considerations for AOPs quantitatively have recently been developed, based on the rank ordering of the relevant Bradford Hill considerations (i.e., biological plausibility, essentiality and empirical support) (Becker et al., 2017; Becker et al, 2015; Collier et al., 2016). Suggested quantitation of the various elements is expert derived, without collective consideration currently of appropriate reporting templates or formal expert engagement. Though not essential, developers may wish to assign comparative quantitative values to the extent of the supporting data based on the three critical Bradford Hill considerations for AOPs, as a basis to contribute to collective experience.Specific attention is also given to how precisely and accurately one can potentially predict an impact on KEdownstream based on some measurement of KEupstream. This is captured in the form of quantitative understanding calls for each KER. See pages 55-56 of the User Handbook for a review of quantitative understanding for KER's. More help

KER1 (MIE => KE1)

Treatment with the highly selective JAK3 inhibitor PF-06651600 or RB1 suppresses the complex formation of STAT5 in the nucleus. IL-2 stimulates STAT5 and induces tyrosine phosphorylation of STAT5 (Wakao, et al. 1995). RB1 inhibits the phosphorylation of STAT5 elicited by IL-2, as evidenced by an IC50 value of 31 nM in the peripheral blood mononuclear cells (PBMCs) of humans. PBMCs isolated from the buffy coats of healthy volunteers by density gradient centrifugation on Lymphoprep were cultured in complete RPMI 1640 medium (containing 10% fetal bovine serum, 100 μg/mL streptomycin and 100 U/mL penicillin) plus 10 μg/mL lectin phytohemagglutinin (PHA) for 3 days. The cells were then treated with recombinant human IL-6 (400 ng/mL), recombinant human IL-2 (100 ng/mL), or recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF; 50 ng/mL) at 37°C for 20 min. To terminate the stimulation, the cells were fixed with Lyse/Fix Buffer and then incubated with 100% methanol for 30 min. The cells were incubated with anti-pSTAT3 and anti-CD4 antibodies, or anti-pSTAT5 and anti-CD4 antibodies at 4°C overnight, washed twice with PBS, and analyzed with by flow cytometry (Ju, et al. 2011).

The fluorescence intensity of phospho-STAT5 in CD3-positive lymphocytes was observed to increase upon incubation of peripheral blood with IL-2. Peficitinib inhibited STAT5 phosphorylation in a concentration-dependent manner with a mean IC50 of 124 nM (101 and 147 nM for two rats). Additionally, the effect of peficitinib on IL-2 stimulated STAT5 phosphorylation in human peripheral T cells was evaluated. Parallel with the results in rats, the fluorescence intensity of phospho-STAT5 in CD3-positive lymphocytes increased in human peripheral blood after adding IL-2. Peficitinib inhibited STAT5 phosphorylation in a concentration-dependent manner with a mean IC50 of 127 nM in human lymphocytes (Ito, et al. 2017).

KER2 (KE1 => KE2)

STAT5 can be activated and phosphorylated by cytokines, such as IL-2 and IL-15. Tyrosine phosphorylation of STAT5 is important for the dimerization of STAT5 (Wakao, et al. 1995). The STAT5 dimer has an identical DNA binding specificity and immunoreactivity.

KER3 (KE2 => KE3)

STAT5 is phosphorylated by JAK kinases, allowing its dimerization and translocation into the nucleus where it can bind to its specific DNA binding sites. Electrophoretic mobility shift assay (EMSA) data revealed that IL-2 activation induced STAT5 dimerization and DNA binding to the gamma interferon activated site (GAS) motif in the IL-4 receptor alpha promoter region (John, et al. 1999). Other EMSA data showed that dexamethasone (10-6 M) inhibited STAT5 DNA binding in mononuclear cells in a dose-dependent fashion at dexamethasone concentrations of 10-8 to 10-7 M (Bianchi, et al. 2000)Dexamethasone could inhibit tyrosine phosphorylation, and nuclear translocation of STAT5 in primary T cells. The mechanism of inhibition involved suppression of IL-2 receptor and JAK3 expression.

KER4 (KE3 => AO)

Binding of IL-4 to the T cell receptor induces proliferation and differentiation into Th2 cells. Th2 cells assist B cells and promote class switching from IgM to IgG1 and IgE. Therefore, the suppression of IL-4 production leads to impairment of TDAR.

In co-cultured human T and B cells stimulated with anti-CD3 monoclonal antibody, the calcineurin inhibitors (CNIs) FK506 and cyclosporin A (CsA) lowered the levels of T cell cytokines, including IL-2 and IL-4, and inhibited IgM and IgG production in a dose-dependent manner (Heidt, et al. 2010).

The collective results demonstrate the quantitative relationships between the inhibition of IL-4 by specific antibodies or CNI and suppression of antibody production.

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List the bibliographic references to original papers, books or other documents used to support the AOP. More help

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