CXCL8 and irritable bowel syndrome: Patients with IBS are known to have no visible sign of intestinal inflammation, but researchers have reported that those with IBS have higher levels of cytokines, including interleukin 1 (IL)-1β, tumor necrosis factor, IL-6 and IL-8, resulting in an increased production of serotonin and histamine, which are associated with inflammation [43].