PROJECT SUMMARY/ABSTRACT The brain must maintain immunological homeostasis to prevent dysregulation and disease. Coordination of immunity in most tissues involves the drainage of antigens or antigen-presenting cells within conventional lymphatic vessels to the draining lymph nodes. In the lymph node, antigen presented to T cells, typically by dendritic cells (DCs), can initiate an immune response. Control of immune response is unique in the central nervous system as the brain parenchyma lacks conventional infiltrating lymphatic vessels and instead utilizes a combination of intra-tissue glial-dependent clearance pathways and meningeal lymphatics surrounding the brain to drain waste, antigens, fluid, and cells. Recently there has been mounting evidence implicating meningeal lymphatic vessels as passive conductors of drainage in the progression, and resolution of various neuropathologies. We previously discovered that neuroinflammation induces lymphangiogenesis of the meningeal lymphatic vessels at the cribriform plate (cp) (Hsu et al. Nat Comm. 2019). We found that in situ meningeal lymphangiogenesis was driven by VEGF-C producing DCs, and this is unique to the cp, highlighting potentially different roles for dural lymphatics in neuroinflammation depending on their precise location. Here we show single-cell RNA sequencing data revealing that neuroinflammation induces cribriform plate lymphatic endothelial cell (cpLECs) gene expression related to antigen presentation, leukocyte adhesion, and immunoregulation. This indicates that cpLECs are not just passive conductors of drainage, but active contributors to the formation of a neuroimmune regulatory niche. We hypothesize that during neuroinflammation, the cribriform lymphatics represent an immunoregulatory niche in which migratory DCs drained from the brain are retained and communicate with cpLECs to regulate downstream immune response and homeostasis of the central nervous system. The pathways of DCs traffic through the brain to the cribriform lymphatics, the mechanism of their interaction with cpLECs, and the functional consequence of these interactions on both cell types and on the formation of a neuroimmune niche are not known. The long-term objective of this project is to define the pathways and dynamics of interactions between dendritic cells and the cribriform plate lymphatics to understand the regulation of brain homeostasis and disease. The specific objectives of this proposal are to map the timeline, origin, and mechanism of dendritic cell - cribriform lymphatic endothelial cells interaction (DC-cpLEC) in the meningeal lymphatic vessels at the cribriform plate (Aim 1); to define expressional consequences of the interaction between DCs and cpLECs (Aim 2), and to examine the impact of DC-cpLEC interactions on lymphatic functionality and immunity (Aim 3). Pharmacological manipulation of the cross-talk between dendritic cells and cribriform lymphatic endothelial cells in CNS diseases may have po...