Endothelial cell-specific lymphotoxin-β receptor signaling is critical for lymph node and high endothelial venule formation

The development of lymph nodes (LNs) and formation of LN stromal cell microenvironments is dependent on lymphotoxin-beta receptor (LT beta R) signaling. In particular, the LT beta R-dependent crosstalk between mesenchymal lymphoid tissue organizer and hematopoietic lymphoid tissue inducer cells has been regarded as critical for these processes. Here, we assessed whether endothelial cell (EC)-restricted LT beta R signaling impacts on LN development and the vascular LN microenvironment. Using EC-specific ablation of LT beta R in mice, we found that conditionally LT beta R-deficient animals failed to develop a significant proportion of their peripheral LNs. However, remnant LNs showed impaired formation of high endothelial venules (HEVs). Venules had lost their cuboidal shape, showed reduced segment length and branching points, and reduced adhesion molecule and constitutive chemokine expression. Due to the altered EC-lymphocyte interaction, homing of lymphocytes to peripheral LNs was significantly impaired. Thus, this study identifies ECs as an important LT beta R-dependent lymphoid tissue organizer cell population and indicates that continuous triggering of the LT beta R on LN ECs is critical for lymphocyte homeostasis.