A diverse fibroblastic stromal cell landscape in the spleen directs tissue homeostasis and immunity

The spleen is a compartmentalized organ that serves as a blood filter and safeguard of systemic immune surveil-lance. Labyrinthine networks of fibroblastic stromal cells construct complex niches within the white pulp and red pulp that are important for tissue homeostasis and immune activation. However, the identity and roles of the global splenic fibroblastic stromal cells in homeostasis and immune responses are poorly defined. Here, we per -formed a cellular and molecular dissection of the splenic reticular stromal cell landscape. We found that white pulp fibroblastic reticular cells (FRCs) responded robustly during acute viral infection, but this program of gene regula-tion was suppressed during persistent viral infection. Single-cell transcriptomic analyses in mice revealed diverse fibroblast cell niches and unexpected heterogeneity among podoplanin-expressing cells that include glial, meso-thelial, and adventitial cells in addition to FRCs. We found analogous fibroblastic stromal cell diversity in the human spleen. In addition, we identify the transcription factor SpiB as a critical regulator required to support white pulp FRC differentiation, homeostatic chemokine expression, and antiviral T cell responses. Together, our study pro-vides a comprehensive map of fibroblastic stromal cell types in the spleen and defines roles for red and white pulp fibroblasts for splenic function and orchestration of immune responses.