This study reveals that glucocorticoids indirectly regulate the expression of TSC22D3 via the DBI/ACBP–GABAAR signaling axis, thereby suppressing dendritic cell antigen presentation function, providing a novel therapeutic target for overcoming immunosuppression associated with immunotherapy.
Literature Overview
The article titled 'The autophagy-inhibitory tissue hormone DBI/ACBP is essential for glucocorticoid-induced immunosuppression,' published in the journal Autophagy, systematically investigates a non-canonical signaling pathway through which glucocorticoids (GCs) mediate immunosuppression. The study finds that GCs do not directly act on the glucocorticoid receptor in dendritic cells (DCs), but instead induce multiple cell types to secrete the tissue hormone DBI/ACBP, which subsequently activates the GABAAR receptor, upregulates the transcription factor TSC22D3, and ultimately inhibits the antigen-presenting capacity of DCs. This mechanism has been validated in both mouse and human cells, and neutralizing DBI/ACBP reverses the suppressive effects of GCs on immune responses.Background Knowledge
Currently, glucocorticoids are widely used to control excessive inflammatory responses, but their long-term use leads to significant immunosuppression, increasing the risks of infection and tumor progression. Although the traditional view holds that their effects are directly mediated by the glucocorticoid receptor, recent studies suggest the existence of indirect mechanisms. Notably, DBI/ACBP, an evolutionarily conserved peptide hormone, has been shown to participate in stress responses, autophagy regulation, and tissue repair. In patients with Cushing's syndrome, circulating DBI/ACBP levels are elevated, and neutralizing this hormone can reverse various metabolic and behavioral phenotypes, indicating its systemic role. However, its function in immune regulation remains unclear. This study focuses on whether DBI/ACBP is involved in GC-induced immunosuppression, filling this mechanistic gap and revealing a novel pathway through which GABAAR regulates TSC22D3, providing a theoretical basis for developing selective immune modulation strategies.
Research Methods and Experiments
The authors employed multiple animal models to validate the inhibitory effects of GCs on tumor immune surveillance, including orthotopically transplanted EO771 breast cancer, MCA205 fibrosarcoma, and TC1 non-small cell lung cancer models. In these models, GCs accelerated tumor growth, whereas neutralizing anti-DBI/ACBP antibodies, dbi gene knockout, or the Gabrg2F77I mutation (blocking DBI/ACBP binding to GABAAR) partially reversed this effect. Furthermore, restoring GABAAR signaling with the benzodiazepine drug diazepam abolished the protective effect of DBI/ACBP neutralization, confirming pathway specificity.
In vitro experiments utilized a co-culture system of bone marrow-derived dendritic cells (BMDCs) and B3Z hybridoma to assess antigen presentation function. The results showed that GCs inhibit the ability of BMDCs to present the ovalbumin-derived peptide SIINFEKL, reducing IL-2 production, and this function could be partially restored by anti-DBI/ACBP antibodies. In human mixed lymphocyte reactions (MLR), GCs suppressed T cell secretion of IFNG and proliferation, effects that were also blocked by anti-DBI/ACBP antibodies.Key Conclusions and Perspectives
Research Significance and Prospects
This study overturns the traditional view that GCs act directly on immune cells, establishing DBI/ACBP as a key mediator in glucocorticoid-induced immunosuppression. This provides a theoretical foundation for developing novel adjuvant therapies to preserve antitumor immunity in cancer patients receiving GCs. For example, in patients undergoing PD-1 blockade who require GCs to manage irAEs, targeting DBI/ACBP may reduce immunosuppression without compromising GC-mediated control of inflammation.
Moreover, this mechanism involves autophagy regulation and GABAAR signaling, highlighting deep crosstalk within the metabolic-neural-immune network. Future research could explore the role of DBI/ACBP in other immune cell subsets and its dynamic changes in chronic inflammation or autoimmune diseases. From a drug development perspective, anti-DBI/ACBP antibodies or small-molecule antagonists could serve as 'safety companions' for GC therapy, expanding the therapeutic window.
Conclusion
This study establishes the essential role of DBI/ACBP in glucocorticoid-mediated immunosuppression, revealing an indirect signaling pathway from the GC receptor to GABAAR and then to TSC22D3. This discovery not only deepens our understanding of the pharmacological mechanisms of GCs but also offers new strategies for clinically managing their side effects. Particularly in the context of cancer immunotherapy, when patients require GCs due to immune-related adverse events (irAEs), targeting DBI/ACBP may become an effective means to preserve antitumor immunity. Leveraging existing animal model resources, conditional knockout models of dbi or Tsc22d3 in immune cells can be further developed to validate their roles in different tumor microenvironments. The discovery of this pathway marks a shift from 'non-specific suppression' to 'precise regulation,' potentially driving the development of next-generation immune-modulating adjuvant therapies and optimizing comprehensive care systems for cancer patients.
