Pathogenic Th17 cells orchestrate mucosal inflammation and drive secondary loss of response to infliximab in inflammatory bowel disease: clinical and mechanistic evidence.

Infliximab (IFX) has revolutionized inflammatory bowel disease (IBD) treatment, yet secondary loss of response (LOR) remains a prevalent and mechanistically unresolved challenge. This study elucidates the pivotal role of pathogenic Th17 (pTh17) cells in this process. We conducted a retrospective longitudinal analysis of 62 IFX-treated IBD patients with a minimum follow-up of three years, supplemented by an independent cross-sectional immune profiling cohort including healthy controls, IFX responders, and secondary LOR patients. Peripheral blood and colonic mucosal tissues were collected and analyzed using a multi-platform approach encompassing flow cytometry for immune cell subsetting, multiplex immuno fluorescence for spatial phenotyping, immunohistochemistry for protein localization, and Western blotting for signaling pathway assessment. Our results demonstrated that patients with secondary LOR exhibited a distinct immunological signature: significantly elevated serum levels of IL-17A and IFN-γ, alongside a marked expansion of IL-17A+IFN-γ+CD4+ T cells in both peripheral blood and the inflamed intestinal mucosa. The frequency of these circulating pTh17 cells correlated strongly with intestinal inflammation (fecal calprotectin, r = 0.730) and systemic inflammatory activity (ESR, r = 0.606). Within the mucosa, the pTh17 cell defining transcription factor RORγT was strikingly overexpressed in LOR patients. This mucosal RORγT expression not only correlated closely with clinical disease activity scores (Mayo and CDAI) but also served as a powerful discriminator of secondary LOR from sustained response, with an area under the curve (AUC) of 0.83. Critically, high RORγT expression emerged as an independent predictor of clinical relapse (adjusted HR = 4.900). Mechanistically, we identified hyperactivation of the JNK pathway in mucosal lymphocytes from LOR patients as a key driver, with in vitro JNK inhibition effectively curtailing pTh17 cell differentiation. In conclusion, our work proposes that pTh17 cell-driven mucosal inflammation, potentially sustained via JNK signaling, contributes to secondary IFX resistance. These findings support the potential of mucosal RORγT as a candidate predictive biomarker and highlight the JNK pathway for further investigation as a potential therapeutic target for overcoming treatment failure in IBD.