Gram-negative species such as E. coli and Bacteroides/Prevotella species overgrow the inflamed ileal lumen during ileitis development [21], and the inflammatory scenario is further perpetuated by TLR-4-dependent signaling of lipopolysaccharide (LPS) derived from intestinal Gram-negative commensals [22], [23]. The gene discussed is TLR4; the disease is Crohn ileitis.