Trigeminal ganglion interferon-γ signaling drives orofacial neuropathic pain in rats

Background Chronic neuropathic pain, particularly in the orofacial region, markedly reduces quality of life. Peripheral trigeminal nerve injury activates satellite glial cells (SGCs) in the trigeminal ganglion (TG), which contributes to orofacial neuropathic pain. However, the upstream signal responsible for SGC activation remains unclear. This study investigated the role and cellular sources of interferon gamma (IFN-γ) signaling in the TG following infraorbital nerve injury (IONI) in rats. Methods Mechanical sensitivity of the whisker pad skin was assessed after IONI. Changes in IFN-γ levels, IFN-γ receptor expression, and glial fibrillary acidic protein (GFAP; a marker of SGC activation) were examined in the TG by immunohistochemistry. The effects of intra-TG administration of IFN-γ, an IFN-γ receptor antagonist, and isolated CD8⁺ T cells on mechanical hypersensitivity were evaluated. GFAP expression after intra-TG administration of IFN-γ or the receptor antagonist was also quantified. Flow cytometry and immunohistochemistry were used to identify IFN-γ–producing cells. In primary SGC cultures, IFN-γ–induced interleukin-1β (IL-1β) release was measured, and the impact of IL-1 receptor antagonism on mechanical hypersensitivity was tested. IL-1 receptor localization and expression in TG neurons were further evaluated after IONI. Results IONI induced persistent mechanical hypersensitivity and upregulated IFN-γ, IFN-γ receptor, and GFAP expression in the TG. CD8⁺ T cells were the primary source of IFN-γ after IONI, and intra-TG transfer of isolated CD8⁺ T cells transiently induced mechanical hypersensitivity. IFN-γ receptors were localized to SGCs, with expression levels increasing after IONI. Intra-TG IFN-γ administration triggered mechanical hypersensitivity and SGC activation, whereas receptor antagonism attenuated IONI-induced hypersensitivity. IFN-γ stimulation of cultured SGCs enhanced IL-1β release. Co-administration of an IL-1 receptor antagonist prevented IFN-γ–induced mechanical hypersensitivity. IL-1β receptors were localized on TG neurons and were upregulated following IONI. Conclusions CD8⁺ T cell–derived IFN-γ activates SGCs in the TG, leading to IL-1β release that promotes neuronal hyperactivity and orofacial neuropathic pain following IONI. Targeting the IFN-γ–SGC–IL-1β signaling axis may represent a novel therapeutic strategy for orofacial neuropathic pain.