TNFSF15 genetic variants leading to increased TNFSF15 expression confer risk for IBD and TNFSF15 is being explored as a therapeutic target in IBD patients. While the focus for TNFSF15-mediated inflammatory outcomes has been predominantly on its action on T cells, TNFSF15 also promotes inflammatory outcomes in human macrophages. Given the critical role for macrophages in bacterial clearance, we hypothesized that TNFSF15 promotes antimicrobial pathways in human macrophages and that macrophages from TNFSF15 IBD risk-carriers with higher TNFSF15 expression have an advantage in these antimicrobial outcomes.
We analyzed protein expression, signaling, bacterial uptake and intracellular bacterial clearance in human monocyte-derived macrophages (MDMs) through flow cytometry, ELISA and gentamicin-protection.
Autocrine/paracrine TNFSF15 interactions with DR3 were required for optimal levels of pattern-recognition-receptor (PRR)-induced bacterial clearance in human macrophages. TNFSF15 induced PDK1-dependent bacterial uptake and promoted intracellular bacterial clearance through reactive oxygen species, NOS2 and autophagy upregulation. The TNFSF15-initiated TRAF2/RIP1/RIP3 pathway was required for MAPK and NFκB activation, and in turn, induction of each of the antimicrobial pathways; the TNFSF15-initiated FADD/MALT1/caspase-8 pathway played a less prominent role in antimicrobial functions, despite its key role in TNFSF15-induced cytokine secretion. Complementation of signaling pathways or antimicrobial pathways restored bacterial uptake and clearance in PRR-stimulated macrophages where TNFSF15:DR3 interactions were inhibited. MDMs from high TNFSF15-expressing rs6478108 T IBD-risk carriers in the TNFSF15 region demonstrated increased levels of the identified antimicrobial pathways.
We identify that autocrine/paracrine TNFSF15 is required for optimal PRR-enhanced antimicrobial pathways in macrophages, define mechanisms regulating TNFSF15-dependent bacterial clearance, and determine how the TNFSF15 IBD-risk genotype modulates these outcomes.

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