Differential Roles of LTβR in Endothelial Cell Subsets for Lymph Node Organogenesis and Maturation

Cellular cross-talk mediated by lymphotoxin αβ-lymphotoxin β receptor (LTβR) signaling plays a critical role in lymph node (LN) development. Although the major role of LTβR signaling has long been considered to occur in mesenchymal lymphoid tissue organizer cells, a recent study using a VE-cadherin cre Ltbr fl/fl mouse model suggested that endothelial LTβR signaling contributes to the formation of LNs. However, the detailed roles of LTβR in different endothelial cells (ECs) in LN development remain unknown. Using various cre ransgenic mouse models ( Tek cre , a strain targeting ECs, and Lyve1 cre , mainly targeting lymphatic ECs), we observed that specific LTβR ablation in Tek cre+ or Lyve1 cre+ cells is not required for LN formation. Moreover, double- cre -mediated LTβR depletion does not interrupt LN formation. Nevertheless, Tek cre Ltbr fl/fl mice exhibit reduced lymphoid tissue inducer cell accumulation at the LN anlagen and impaired LN maturation. Interestingly, a subset of ECs ( VE-cadherin + Tek cre-low/neg ECs) was found to be enriched in transcripts related to hematopoietic cell recruitment and transendothelial migration, resembling LN high ECs in adult animals. Furthermore, endothelial Tek was observed to negatively regulate hematopoietic cell transmigration. Taken together, our data suggest that although Tek cre+ endothelial LTβR is required for the accumulation of hematopoietic cells and full LN maturation, LTβR in VE-cadherin + Tek cre-low/neg ECs in embryos might represent a critical portal-determining factor for LN formation.