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The aim was to explore factors associated with intestinal tissue levels of anti-TNF alpha (anti-TNF), anti-TNF antibodies, and cytokines in pediatric patients with Crohn Disease (CD). In a prospective exploratory study of CD patients undergoing ileocecal resection or colonoscopy between 6/2020 and 1/2023, we analysed tissue levels of anti-TNF, anti-TNF antibodies, and cytokines (TNF-α, IL-17, IL-1β, IFN-γ) from intestinal biopsies. Mixed-effects regression models, adjusted for potential confounders, were used. Data from 27 CD patients (18 females, 66.7%) were analysed. Fourteen (52%) received adalimumab (ADA) and thirteen received infliximab (IFX), with a median therapy duration of 17 (IQR 4.5-41.5) months. Higher levels of free anti-TNF were found in macroscopically inflamed tissue compared to non-inflamed tissue (β = 3.42, 95% CI 1.05-6.10). No significant association was found between serum and tissue anti-TNF levels (β= -0.06, 95% CI - 0.70-0.58). Patients treated longer with anti-TNF had increased IL-17 levels (β = 0.19, 95% CI 0.05-0.33), independent of disease duration and age. IFN-γ levels were linked with both follow-up duration and anti-TNF length. Our study shows significantly higher free drug levels in inflamed tissue. Long-term anti-TNF treatment has been linked to increased IL-17 levels, suggesting a possible impact on the cytokine response pathway. We did not observe a relationship between serum and tissue anti-TNF levels., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)