Inflammatory monocyte-derived S1P in the lymph node regulates immune response

Sphingosine 1-phosphate (S1P), a lipid chemoattractant, guides immune cells from the low-S1P environment of tissues into the high-S1P environment of circulatory fluids. Most notably, S1P directs T cell exit from lymph nodes (LN), where T cells are initially activated to fight pathogens, into lymph, from which T cells flow into blood and ultimately reach inflamed tissues. T cells follow these gradients primarily using S1P receptor 1 (S1PR1). The drugs Gilenya and Siponimod, both FDA-approved for the autoimmune disease multiple sclerosis, target S1PR1. They blind self-reactive T cells to S1P gradients, block them from exiting LN, and thus prevent them from infiltrating the central nervous system. While recent work has revealed key aspects of how S1P gradients are established at steady-state, very little is known about S1P distribution in disease, and in turn how changing S1P gradients may affect the immune response. Here, we find that LN S1P increases during an immune response, which prolongs the time T cells spend in the LN before exiting into lymph. Inflammatory monocytes, which had not previously been implicated in shaping S1P gradients, are an important source of this S1P. Inflammatory monocytes must express the early activation marker CD69 to supply S1P to T cells; CD69 represses transcription of S1P receptor 5 (S1pr5), enabling monocytes to infiltrate the LN T zone and efficiently release S1P. Here we compared RNA sequencing of inflammatory monocytes WT or CD69-KO infiltrating the draining lymph node.$ Overall design: 12 hours after Poly (I:C) immunization, WT and CD69 KO inflammatory monocytes (CD11b, Ly6C high), sorted from lymph node of mixed BM chimeras (1:1 WT:CD69-KO BM) were analyzed by RNA-seq