Samples from individuals homozygous for the IBD protective allele that is associated with increased monocyte TNFSF15 exhibited significantly increased CD25 expression and proliferation of CD4+ T cells compared to individuals homozygous for the IBD risk allele (p 9.32 x 10−3, p 0.0289, respectively, Fig 5B and 5C). This evidence concerns the gene TNFSF15 and inflammatory bowel disease.