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INTRODUCTION: Patients with Crohn's disease (CD) and ulcerative colitis (UC) may lose weight during periods of active disease and may gain weight when inflammation heals. Studies have hypothesized an association between antitumor necrosis factor-alpha (anti-TNF-α) and unintended weight gain during maintenance therapy, and this association has not been previously clarified. METHODS: In a nationwide observational study based on Danish national health registries, we included patients who initiated therapy with infliximab and followed changes in weight during induction therapy (0-90 days) and maintenance therapy (91-270 days). The association between the use of infliximab and weight gain was analyzed by a multilevel mixed-effects linear regression model. RESULTS: Among 851 patients with CD and UC who initiated infliximab therapy, long-term weight gain was not observed during maintenance therapy in most of the patients. Women with CD who were underweight at the initiation of therapy had an average weight gain of 7.5 kg. Men and women with CD and UC with normal or increased body mass index had an average weight gain of

Although anti-tumor necrosis factor (TNF) agents are highly effective in the treatment of psoriasis, 2–5% of treated patients develop psoriasis-like skin lesions called paradoxical psoriasis. The pathogenesis of this side effect and its distinction from classical psoriasis remain unknown. Here we show that skin lesions from patients with paradoxical psoriasis are characterized by a selective overexpression of type I interferons, dermal accumulation of plasmacytoid dendritic cells (pDC), and reduced T-cell numbers, when compared to classical psoriasis. Anti-TNF treatment prolongs type I interferon production by pDCs through inhibition of their maturation. The resulting type I interferon overexpression is responsible for the skin phenotype of paradoxical psoriasis, which, unlike classical psoriasis, is independent of T cells. These findings indicate that paradoxical psoriasis represents an ongoing overactive innate inflammatory process, driven by pDC-derived type I interferon that does not lead to T-cell autoimmunity., The pathogenesis of paradoxical psoriasis in patients receiving anti-TNF treatments for classical psoriasis is unclear. Here, the authors show that anti-TNF drugs enhance the production of type I interferon by plasmacytoid dendritic cells, causing skin lesions that, unlike classical psoriasis, lack T- cell autoimmunity.