Elevated levels of inflammatory cytokines—such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6)—in IBD patients can cross the BBB to directly affect neurotransmitter synthesis, release, and metabolism, thereby disrupting emotional regulation (49, 50). This evidence concerns the gene IL6 and inflammatory bowel disease.