Preprint Club
A cross-institutional Journal Club Initiative

Keywords

● Sex-differences

● ILC2

● Helicobacter pylori

● Gastritis

Main Findings

In this preprint, the authors investigate the role of androgens in gastric inflammation and disease severity during Helicobacter infection. Chronic inflammation from Helicobacter infection is a critical risk factor in gastric carcinogenesis. Gastric cancer (GC) is a male-dominated disease, having a >2-fold higher incidence in men than women. Interestingly, this difference only emerges until after 50 years of age, a period marked by declining androgen levels in men. However, sex differences in Helicobacter-driven inflammation and metaplasia are poorly characterized. Using a Helicobacter felis (HF) infection model, a natural mouse pathogen, the authors compared gastric inflammatory responses and pathology in male and female mice under chronic conditions. Their flow cytometry and immunofluorescence data reveal striking disparities in immune infiltration and gastric atrophy between sexes. HF-infected males had lower inflammation, reduced epithelial cell atrophy and protection from metaplastic lesions, suggesting a potential role for androgens as a protective factor. By comparing castrated to intact males, they determined that androgen depletion enhances inflammation, atrophy and metaplasia in males. Conversely, dihydrotestosterone (DHT) treatment reduced atrophy while normalizing inflammation and metaplasia in females. Confirming that androgens are protective in chronic Helicobacter infection, the authors then identified type 2 innate lymphoid cells (ILC2) as a highly Androgen Receptor (AR)-expressing population from their single cell RNAseq dataset. By mapping ligand-receptor communication networks in their dataset of females, intact males and castrated males, CellChat predicted that ILC2—Dendritic cell and ILC2—macrophage interactions were suppressed by androgens. To test the hypothesis that ILC2 drives inflammation in HF infection, the authors use a genetic approach to deplete ILC2, demonstrating that gastric macrophage and T cell infiltration is normalized without ILC2. Moreover, epithelial atrophy is improved, and metaplastic markers are decreased upon ILC2 depletion. Based on these findings Duncan et al., conclude that androgens suppress Helicobacter-induced disease progression by negatively regulating ILC2-mediated inflammation in the stomach.

Limitations

• While the authors perform some immunophenotyping in this preprint, the observed characterization would greatly benefit from a more indepth analysis. Their proposed rationale that ILC2-DC interactions are drivers of adaptation in the immune system remains unaddressed. A more detailed assessment of effector function could be supportive in bridging the reported observations.

• The authors clearly demonstrate that androgens protect the host against parietal/chief cell atrophy. How are other gastric epithelial cells impacted by androgens—are Tuft cell (IF staining with Dclk1) numbers increased when androgens are absent? Considering that their model aims at investigating gastric cancer, are there androgen receptor-expressing gastric epithelial stem cells? While their observations suggest that androgens act on ILC2s to regulate their effector function, the authors should aim at investigating a direct impact on gastric epithelium by androgens, and/or IL5 and IL13. If they express receptors for these factors, does their expression change during chronic H. felis infection?

• H. pylori infections are increased in human males compared to females. Does H. felis virulence impact sexes differently in mice? Are there differences in H. felis infection density in stomach of males vs females during chronic inflammation? It would be interesting if there is a link between androgens, inflammation and pathogen clearance.

• H. felis-infected females mounted greater inflammatory responses, developing more severe atrophy and metaplasia. This suggests that carcinogenesis would be increased in females compared to males. However, in humans, women have a greater inflammatory response to infection, but a lower rate of gastric cancer. Does chronic H. felis infection lead to carcinoma over a longer period of time (>12months)? Testing the role of androgens in subsequent tumorigenesis by extending timepoints until cancer development would be a powerful addition to the preprint.

• ILC2 depletion delayed development of preneoplastic lesions but did not prevent their formation. A prior study showed that ILC2-derived IL13 is required for metaplasia in a model of autoimmune gastritis. An alternate approach could be to use H. felis-infected Rag2-/- mice to determine if ILC2 are sufficient to mediate gastric inflammation. The authors speculate that other IL13-producing cells contribute to metaplasia development at the 2 month read-out. Is IL13 required to drive Helicobacter-induced atrophic gastritis? Neutralization of IL13 by in vivo antibody depletion could prove useful. Additionally, by assessing response in Rag2-/-Il2rg-/- mice, they could determine if IL13 is sufficient to drive metaplasia. Lastly, identifying other IL13-producing cells would be important. It is possible that eosinophils, shown to be increased in female gastric inflammation in Suppl Fig2, are a source of IL13 in the gastric gland. Do gastric eosinophils remain increased when IL5-producing ILC2 are depleted?

• This worked showed that genetic depletion of T cells in TCRβδ-/- mice decreased overall immune cell infiltration, yet macrophage numbers remained elevated. This suggests that T cells do not initiate macrophage recruitment during H. felis infection. However, does T cell depletion impact atrophy and metaplasia? Furthermore, establishing a link between ILC2, macrophages and atrophic gastritis would be important —i.e. does macrophage depletion improve atrophy? This could be addressed using inducible genetic depletion models like Cx3cr1-Cre; R26iDTR or perhaps by anti-F4/80 in vivo depletion. Determining the mechanism downstream of ILC2 by which macrophages and/or T cells induce atrophy and metaplasia would be beneficial.

Significance/Novelty

This study highlights the importance of investigating the impact of sex in Helicobacter-induced pathology. The authors uncover a novel finding explaining sex disparities in inflammatory response to Helicobacter infection. Their experimental design demonstrates that androgens regulate gastric inflammation and metaplasia during Helicobacter infection by mediating ILC2 activity. Although a prior study found that ILC2 drive gastric disease progression via IL-13 production, this work showing the critical link between androgen signalling in ILC2-driven inflammation is novel in this field. Further work using this model could uncover sex differences in tumorigenesis. Additionally, investigating the impact of oestrogens in Helicobacter inflammation and metaplasia would shed light on the puzzling association between increased gastric inflammation in females, but lower gastric cancer incidence.

General Immunology Impact

This study contributes to the general finding that androgens negatively regulate ILC2 function. Previously, a link between androgen signalling in ILC2 was demonstrated in the lungs where androgens suppress ILC2-mediated airway inflammation (Cephus et al., Cell Reports, 2017). More recently, another group demonstrated that androgens inhibit ILC2-mediated regulation of dendritic cells in the skin, reducing tissue immunity (Chi et al., Science, 2024). Therefore, future studies regarding ILC2 biology in tissue homeostasis and disease should strongly consider sex differences in their experimental design and/or analysis.

Translational Impact

This work clearly demonstrates that androgens are protective in Helicobacter-induced inflammation, atrophic gastritis and development of metaplasia. Male bias in gastric cancer incidence only occurs from middle age, coinciding with decreasing androgen levels. By showing that loss of androgens promotes disease progression in H. felis-infected male mice, measuring androgen levels could serve as a potential biomarker for cancer-risk in male gastritis patients. (Although this work also demonstrates that ILC2 mediate disease progression in Helicobacter infection, the association between ILC2 and worse survival in gastric cancer patients has been previously established).

Credit

Reviewed by Miki Gams (University of Toronto, Department of Immunology) as part of a cross-institutional journal club between the Icahn School of Medicine at Mount Sinai, the University of Oxford, the Karolinska Institute and the University of Toronto.

The author declares no conflict of interests in relation to their involvement in the review.