Single cell RNAseq analysis of fibroblastic reticular cells from murine brachial lymph nodes during inflamed and resting states

The lymph node is home to resident macrophage populations that are essential for healthy immune function and homeostasis. They are involved in multiple processes including the initiation of the local response to pathogens, halting viral and bacterial spread, and clearance of apoptotic cells, but the macrophage niche and factors that create it are largely undefined. Here we analyse fibroblastic reticular cells (FRCs) as an essential component of the lymph node macrophage niche using single-cell RNA-sequencing. Our analysis revealed that most reticular cell subsets within lymph nodes expressed master macrophage regulator CSF1. We further show that signalling through CSF1R was sufficient to support macrophage development, while in the presence of LPS, FRCs underwent a mechanistic switch and maintained support through CSF1R-independent mechanisms. Our data reveal a critically important role for FRCs in the creation of the parenchymal macrophage niche within LNs.