{'fraction_non_alphanumeric': 0.015255530129672006, 'fraction_numerical': 0.0, 'mean_word_length': 5.939153439153439, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
A diverse fibroblastic stromal cell landscape in the spleen directs tissue homeostasis and immunity

Description A diverse fibroblastic stromal cell landscape in the spleen directs tissue homeostasis and immunity. Surveying spleen stromal cells The spleen is organized into distinct anatomical niches that support dedicated functions in blood filtration and initiation of immune responses against blood-borne pathogens. Using single-cell transcriptomics and confocal microscopy, Alexandre et al. mapped the fibroblastic stromal cell network within the mouse spleen during homeostasis and acute or chronic systemic viral infection. Although white pulp fibroblastic reticular cells (FRCs) were largely conserved with those in lymph nodes, they also displayed tissue-specific transcriptional programs. Compared with red pulp fibroblasts, FRCs specifically expressed the transcription factor SpiB, which controlled their differentiation into specialized FRC subsets and supported virus-specific T cell responses. Human splenic stromal cells were similarly diverse, highlighting the importance of the spleen microenvironment in shaping fibroblastic stromal cell heterogeneity and function. The spleen is a compartmentalized organ that serves as a blood filter and safeguard of systemic immune surveillance. 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 performed 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 regulation 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, mesothelial, 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 provides 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.