TNF and irritable bowel syndrome: In past studies, cytokines that have appeared at higher levels in IBS patients include (IL)-1, IL-3, IL-4, IL-5, IL-6, IL-8, IL-12, IL-13, IL-16, IL-17, IL-18, tumor necrosis factor-alpha (TNF-α), and interferon-γ (IFN-γ) [32,54,122,125,126].