Lymph node fibroblast phenotypes and immune crosstalk regulated by podoplanin activity.

Lymph nodes are uniquely organized niches for immune interactions. Fibroblastic reticular cells (FRCs) facilitate immune cell communication and regulate immune function by producing growth factors, chemokines, and inflammatory cues. Stromal expression of the glycoprotein podoplanin (PDPN) is required for lymph node development, but the requirement for PDPN signaling in FRCs in adult lymph nodes has not been directly tested. Using a conditional in vivo deletion model PDGFRαmGFPΔPDPN, single-cell RNA sequencing (scRNA-seq) reveals that PDPN deletion increases inflammatory signaling in lymph nodes and disrupts stromal-immune cell crosstalk in steady state and during adaptive immune responses. We confirm that PDPN/CLEC-2 signaling in FRCs switches transcriptional states and alters the expression of immune-related genes. We conclude that PDPN expression impacts the immunoregulatory properties of fibroblastic stroma in lymph nodes and is a key transcriptional regulator of fibroblast function in lymph nodes.