TNFSF9 and inflammatory bowel disease: TNFSF9 is a co-stimulatory molecule expressed on T cells and natural killer cells upon activation [35,36,37], LCN2 expression is reportedly upregulated in IBD patients [38,39], and the regulatory dynamics of fecal LCN2 have been harnessed as a sensitive biomarker of gut inflammation, both in animal models and in patients with IBD [40,41,42].