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Relationship: 3333

Title

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

Activation of gluten- and TG2-reactive B cells leads to Disruption of the intestinal barrier

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

Activation of gluten- and TG2-reactive B cells

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

Disruption of the intestinal barrier

Key Event Relationship Overview

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

AOPs Referencing Relationship

AOP Name	Adjacency	Weight of Evidence	Quantitative Understanding	Point of Contact	Author Status	OECD Status
Gluten-driven immune activation leading to celiac disease in genetically predisposed individuals	adjacent	Moderate		Antonio Fernandez Dumont (send email)	Under development: Not open for comment. Do not cite	Under Review

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. More help

Term	Scientific Term	Evidence	Link
human	Homo sapiens	High	NCBI

Sex Applicability

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

Sex	Evidence
Unspecific	Not Specified

Life Stage Applicability

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

Term	Evidence
All life stages	Not Specified

Key Event Relationship Description

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

The activation of adaptive T and B cell responses to gluten due to loss of mucosal tolerance results in inflammation in the lamina propria of the upper small intestine characterized by a highly significant increase in the presence of both innate and adaptive immune cells. This is accompanied by a highly significant upregulation of the expression of HLA-class II molecules, the production of immune stimulatory and pro-inflammatory cytokines, including IFN-γ, TNF-α, IL-2, IL-7, and IL-21, by the gluten-reactive CD4+ T cells (Santos et al., 2024;De Nitto et al., 2009; Garrote et al., 2008). In addition, there is a massive increase in the number and activation status of intraepithelial lymphocytes (IEL) in the intestinal epithelium, likely driven by a combination of the pro-inflammatory cytokines produced in the lamina propria and local production of IL-15 by the enterocytes (Abadie et al., 2020). Moreover, the expression of non-classical MHC molecules is upregulated in the epithelium. These activated IELs mediate epithelial cell destruction, contributing to the flattening of the intestinal villi and leading to loss of barrier function (Abadie et al., 2012).

Evidence Collection Strategy

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

Evidence was collected through a combination of literature searches and expert consultations. Experts contributed by reviewing drafted material asynchronously and participating in online discussions to refine the evidence base. Additionally, they provided key articles relevant to the topic, which served as a foundation for further literature searches in Scopus, PubMed, and Google Scholar. Keywords were tailored to each key event (KE) and key event relationship (KER) to ensure comprehensive coverage of relevant studies. The collected literature was systematically categorized in an Excel spreadsheet based on its relevance to specific KEs and KERs within the AOP. This approach facilitated the organization of data supporting different aspects of the pathway.

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Intestinal epithelial cells in active celiac disease express elevated levels of MHC class II molecules (HLA-DQ2/DQ8), enabling direct presentation of deamidated gluten peptides to CD4+ T cells. Organoid models expressing HLA-DQ2.5 demonstrate gluten-dependent activation of CD4+ T cells, leading to IL-2, IFN-γ, and IL-15 release (Rahmani et al., 2024).
IL-15 induces IEL survival, IFN-γ production, and epithelial killing in refractory celiac sprue (Mention et al., 2003)
There is a correlation between IEL activation, villous atrophy, and cytokine levels (IFN-γ, IL-15) in active celiac disease (Abadie et al., 2012)

Biological Plausibility

Addresses the biological rationale for a connection between KEupstream and KEdownstream. This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured. More help

While the disease underlying gluten-specific CD4+ T cell response is located in the lamina propria, celiac disease is also characterized by a pronounced increase in the presence of intraepithelial lymphocytes (IEL) that express Natural Killer-receptors in the epithelium (Setty et al., 2015). In addition, while IEL normally reside in the basal portion of the intestinal villi, in celiac disease they spread all over the epithelium, including the tip of the villi. These IEL are activated, express Natural Killer-receptors, and can mediate epithelial cell destruction, contributing to the flattening of the villi and loss of barrier function. IL-15 expression by epithelial cells is a key cytokine involved in the activation of the IEL (James et al., 2021). Also, the cytokines produced by the gluten-specific T cells in the lamina propria, including IFN-γ, TNF-α, IL-2, IL-7, and IL-21 create a proinflammatory environment that is likely crucial for the increased presence and sustained activation of the IEL compartment as intestinal morphology normalizes upon the introduction of a gluten-free diet and is accompanied by a reduction of the numbers of IEL. Thus, a cascade where activation of gluten-specific T cell leads to a pro-inflammatory environment, which eventually results in activation of IEL, epithelial cell destruction and a loss of barrier function, and absorptive capacity in the upper intestine.

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

The formation of HLA-DQ2/8-gluten complexes drives gluten-specific CD4+ T-cell activation by presenting deamidated peptides with high affinity, particularly in HLA-DQ2.5 homozygous individuals who exhibit stronger T-cell responses due to broader peptide presentation (Okura et al., 2023). Gluten-reactive T-cell receptor generation enables clonal expansion of T cells with focused repertoires, licensing B-cell help via CD40L and IL-21 (Zou et al., 2022). Gluten/TG2-reactive B-cell receptor allow B cells to internalize TG2-gluten complexes, process gluten peptides, and present them to T cells, facilitating epitope spreading and autoantibody production (Zou et al., 2022). T-cell/APC co-localization ensures direct collaboration, with TG2-specific B cells acting as APCs to amplify T-cell help. Innate immune activation via protease-resistant gluten fragments enhances APC maturation and antigen presentation (Voisine et al., 2021), while CD4+ T-cell activation provides critical cytokines (e.g., IL-21) that drive B-cell differentiation into plasma cells. Together, these upstream KEs create a feedforward loop where HLA-DQ2.5-mediated antigen presentation, T-B cell collaboration, and cytokine signaling converge to activate gluten- and TG2-reactive B cells, producing pathogenic autoantibodies (Zou et al., 2022).

Uncertainties and Inconsistencies

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

While the evidence supporting the role of the gluten-specific T and B cell response in disease pathogenesis is very strong, it is less clear what drives the upregulation of IL-15 and non-classical MHC-molecules in the epithelium. It has been suggested that gluten itself has the capacity to induce innate immune activation and could be responsible for the upregulation of IL-15 (Abadie et Jabri, 2014; Abadie et al., 2020). However, it is entirely unclear why this innate effect of gluten would only manifest itself in certain individuals, nor is there clarity about the molecular mechanism involved. Alternatively, viral and bacterial infections play a role in this as these can induce the expression of type I interferons (McNab et al., 2015; Mancuso et al., 2007).

Known modulating factors

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

Modulating Factor (MF)	MF Specification	Effect(s) on the KER	Reference(s)
Gender	Female	Females have a higher chance (2:1) of developing celiac disease	Jansson-Knodell et al., 2017
Composition of the intestinal microbiota and metabolites of food derived compounds	For example, the vegetable-derived phytochemical indole-3-carbinol, a ligand for the aryl hydrocarbon receptor (AhR)	Higher chance of developing celiac disease	Abadie et al., 2012
IgA deficiency		It increases the risk of development of celiac disease	Leonard et al., 2017

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

B cell activation is closely linked to changes in the intestinal barrier in celiac disease. Patients with active celiac disease produce autoantibodies, predominantly targeting transglutaminase 2 (TG2). Recent studies have visualized plasma cells producing TG2-specific antibodies within celiac disease lesions, achieved through the use of labeled TG2 antigens. On average, approximately 10% of the plasma cells in a disease lesion are TG2-specific, with the majority producing immunoglobulin A (IgA). These TG2-specific plasma cells diminish once patients adopt a gluten-free diet (Di Niro et al., 2012; Sollid et Jabri, 2013).

The strict association of TG2-specific antibodies with individuals carrying specific HLA types, combined with the observation that antibody avidity decreases when reverted to their presumed germline configuration, suggests that these antibodies undergo affinity maturation. This process indicates that their development is T cell-dependent (Sollid et Jabri, 2013; Björck et al., 2010).

The levels of FABP2 (fatty acid binding protein), a marker of intestinal epithelial cell damage, are significantly elevated in celiac disease patients, correlating with the levels of IgA antibodies to TG2 (Uhde et al., 2016).

Time-scale

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

The exact time-scale of the development of celiac disease is unknown as patients are usually only identified when disease symptoms are manifest. However, based on the knowledge about the development of innate and adaptive immune responses one may assume the gluten-specific T cell response could develop within a period of weeks to months. It is also noteworthy that long-term exposure to gluten contributes to cumulative barrier disruption, suggesting a progressive timeline of damage rather than a specific time point (Schumann et al., 2012).

Strict compliance with a gluten free diet in most CD patients leads to the disappearance or significant decrease of antibodies within 12 months (18–24 months if the antibody titer is very high) together with regrowth of the intestinal villi (Caio et al., 2019).

Known Feedforward/Feedback loops influencing this KER

Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

There have been observations on the transient presence of TG2-specific antibodies in children predisposed to celiac disease development, suggesting that emerging gluten-specific adaptive immune responses may be controlled to maintain mucosal tolerance to gluten (Tosco et al., 2011).

In addition, cytokine release (e.g., IL-15) may promote further activation of B cells and perpetuate barrier dysfunction (Abadie et Jabri, 2014).

Domain of Applicability

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

Human beings

References

List of the literature that was cited for this KER description. More help

Abadie V, Discepolo V, Jabri B. Intraepithelial lymphocytes in celiac disease immunopathology. Semin Immunopathol. 2012;34:551-566.
Abadie V, Jabri B. IL-15: a central regulator of celiac disease immunopathology. Immunol Rev. 2014 Jul;260(1):221-34.
Abadie V, Kim SM, Lejeune T, Palanski BA, Ernest JD, Tastet O, Voisine J, Discepolo V, Marietta EV, Hawash MBF, Ciszewski C, Bouziat R, Panigrahi K, Horwath I, Zurenski MA, Lawrence I, Dumaine A, Yotova V, Grenier JC, Murray JA, Khosla C, Barreiro LB, Jabri B. IL-15, gluten, and HLA-DQ8 drive tissue destruction in celiac disease. Nature. 2020 Feb;578(7796):600-604.
Björck S, Brundin C, Lörinc E, Lynch KF, Agardh D. Screening detects a high proportion of celiac disease in young HLA-genotyped children. J Pediatr Gastroenterol Nutr. 2010 Jan;50(1):49-53.
Caio G, Volta U, Sapone A, Leffler DA, De Giorgio R, Catassi C, Fasano A. Celiac disease: a comprehensive current review. BMC Med. 2019 Jul 23;17(1):142.
De Nitto D, Monteleone I, Franzè E, Pallone F, Monteleone G. Involvement of interleukin-15 and interleukin-21, two γ-chain-related cytokines, in celiac disease. World J Gastroenterol. 2009; 7;15(37):4609-4614.
Di Niro R, Mesin L, Zheng NY, Stamnaes J, Morrissey M, Lee JH, Huang M, Iversen R, du Pré MF, Qiao SW, Lundin KEA, Wilson PC, Sollid LM. High abundance of plasma cells secreting transglutaminase 2-specific IgA autoantibodies with limited somatic hypermutation in celiac disease intestinal lesions. Nat Med. 2012 Feb 26;18(3):441-5.
Garrote JA, Gómez-González E, Bernardo D, Arranz E, Chirdo F. Celiac disease pathogenesis: the proinflammatory cytokine network. J Pediatr Gastroenterol Nutr. 2008;47 Suppl 1:S27-32.
James OJ, Vandereyken M, Marchingo JM, Singh F, Bray SE, Wilson J, Love AG, Swamy M. IL-15 and PIM kinases direct the metabolic programming of intestinal intraepithelial lymphocytes. Nat Commun. 2021 Jul 13;12(1):4290.
Jansson-Knodell CL, King KS, Larson JJ, Van Dyke CT, Murray JA, Rubio-Tapia A. Gender-Based Differences in a Population-Based Cohort with Celiac Disease: More Alike than Unalike. Dig Dis Sci. 2017 Nov 10;63(1):184-192.
Leonard MM, Sapone A, Catassi C, Fasano A. Celiac disease and nonceliac gluten sensitivity: A review. JAMA. 2017 Aug 15;318(7):647-656.
Mancuso G, Midiri A, Biondo C, Beninati C, Zummo S, Galbo R, Tomasello F, Gambuzza M, Macrì G, Ruggeri A, Leanderson T, Teti G. Type I IFN signaling is crucial for host resistance against different species of pathogenic bacteria. J Immunol. 2007 Mar 1;178(5):3126-33.
McNab F, Mayer-Barber K, Sher A, Wack A, O'Garra A. Type I interferons in infectious disease. Nat Rev Immunol. 2015 Feb;15(2):87-103.
Mention JJ, Ben Ahmed M, Bègue B, Barbe U, Verkarre V, Asnafi V, Colombel JF, Cugnenc PH, Ruemmele FM, McIntyre E, Brousse N, Cellier C, Cerf-Bensussan N. Interleukin 15: a key to disrupted intraepithelial lymphocyte homeostasis and lymphomagenesis in celiac disease. Gastroenterology. 2003 Sep;125(3):730-745.
Meresse B, Chen Z, Ciszewski C, Tretiakova M, Bhagat G, Krausz TN, Raulet DH, Lanier LL, Groh V, Spies T, Ebert EC, Green PH, Jabri B. Coordinated induction by IL-15 of a TCR-independent NKG2D signaling pathway converts CTL into lymphokine-activated killer cells in celiac disease. Immunity. 2004 Sep;21(3):357-66.
Okura Y, Ikawa-Teranishi Y, Mizoroki A, Takahashi N, Tsushima T, Irie M, Harfuddin Z, Miura-Okuda M, Ito S, Nakamura G, Takesue H, Ozono Y, Nishihara M, Yamada K, Gan SW, Hayasaka A, Ishii S, Wakabayashi T, Muraoka M, Nagaya N, Hino H, Nemoto T, Kuramochi T, Torizawa T, Shimada H, Kitazawa T, Okazaki M, Nezu J, Sollid LM. Characterizations of a neutralizing antibody broadly reactive to multiple gluten peptide:HLA-DQ2.5 complexes in the context of celiac disease. Nat Commun. 2023 Dec 22;14:8846.
Rahmani S, Galipeau HJ, Clarizio AV, Wang X, Hann A, Rueda GH, Kirtikar UN, Constante M, Wulczynski M, Su HM, Burchett R, Bramson JL, Pinto-Sanchez MI, Stefanolo JP, Niveloni S, Surette MG, Murray JA, Anderson RP, Bercik P, Caminero A, Chirdo FG, Didar TF, Verdu EF. Gluten-dependent activation of CD4⁺ T cells by MHC class II–expressing epithelium. Gastroenterology. 2024 Nov;167(6):1113-1128.
Santos AJM, van Unen V, Lin Z, Chirieleison SM, Ha N, Batish A, Chan JE, Cedano J, Zhang ET, Mu Q, Guh-Siesel A, Tomaske M, Colburg D, Varma S, Choi SS, Christophersen A, Baghdasaryan A, Yost KE, Karlsson K, Ha A, Li J, Dai H, Sellers ZM, Chang HY, Dunn JCY, Zhang BM, Mellins ED, Sollid LM, Fernandez-Becker NQ, Davis MM, Kuo CJ. A human autoimmune organoid model reveals IL-7 function in coeliac disease. Nature. 2024; 632:401–410.
Schumann M, Kamel S, Pahlitzsch M, Lebenheim L, May C, Krauss M, Hummel M, Daum S, Fromm M, Schulzke JD. Defective tight junctions in refractory celiac disease. Ann N Y Acad Sci. 2012 Jul;1258:43-51.
Setty M, Discepolo V, Abadie V, Kamhawi S, Mayassi T, Kent A, Ciszewski C, Maglio M, Kistner E, Bhagat G, Semrad C, Kupfer SS, Green PH, Guandalini S, Troncone R, Murray JA, Turner JR, Jabri B. Distinct and synergistic contributions of epithelial stress and adaptive immunity to functions of intraepithelial killer cells and active celiac disease. Gastroenterology. 2015 Sep;149(3):681-91.e10.
Sollid LM, Jabri B. Triggers and drivers of autoimmunity: lessons from coeliac disease. Nat Rev Immunol. 2013 Apr;13(4):294-302.
Tosco A, Salvati VM, Auricchio R, Maglio M, Borrelli M, Coruzzo A, Paparo F, Boffardi M, Esposito A, D'Adamo G, Malamisura B, Greco L, Troncone R. Natural history of potential celiac disease in children. Clin Gastroenterol Hepatol. 2011 Apr;9(4):320-5; quiz e36.
Uhde M, Ajamian M, Caio G, De Giorgio R, Indart A, Green PH, Verna EC, Volta U, Alaedini A. Intestinal cell damage and systemic immune activation in individuals reporting sensitivity to wheat in the absence of coeliac disease. Gut. 2016 Dec;65(12):1930-1937.
Voisine J, Abadie V. Interplay between gluten, HLA, innate and adaptive immunity orchestrates the development of coeliac disease. Front Immunol. 2021 Jun 2;12:674313.
Zhou C, Østerbye T, Dahal-Koirala S, Steinsbø Ø, Jahnsen J, Lundin KEA, Buus S, Sollid LM, Iversen R. Antibodies to native gluten arise from cross-reactive B cells with implications for epitope spreading in celiac disease. bioRxiv. 2022 Jan 29.