Fibroblastic reticular cells form reactive myeloid cell niches in human lymph nodes.

Lymph nodes play a key role in maintaining fluid balance in homeostatic and inflamed tissues and provide fibroblastic niche environments for optimal immune cell positioning and interaction. Here, we used single-cell and spatial transcriptomic analyses in combination with high-resolution imaging to molecularly define and functionally characterize niche-forming cells that control inflammation-driven remodeling in human lymph nodes. Fibroblastic reticular cells responded to inflammatory perturbation with activation and expansion of poised niche environments. Inflammation-induced adaptation of lymph node infrastructure and topography included the expansion of peptidase inhibitor 16 (PI16)-expressing reticular cell (PI16+ RC) networks that enwrap the perivenular conduit system. Interactome analyses indicated that macrophage-derived oncostatin M directs PI16+ RC activation in inflamed lymph nodes and thereby promotes immune cell aggregation in the perivenular space. In conclusion, these data demonstrate that the inflammatory remodeling of human lymph nodes results in the formation of reactive myeloid cell niches by PI16+ RCs.