TLR4 and inflammatory bowel disease: Human TLR4 proteins containing the D299G and the co-segregating D299G/T399I mutations in the extracellular domain have since been associated with increased susceptibility to many diseases, e.g., Gram negative sepsis (9), inflammatory bowel disease (IBD) (10), respiratory syncytial virus (RSV) (11, –, 14), and others (15, –, 21).