We propose to decipher the mechanisms of action of neuroendothelial N-methyl-D-aspartate receptors (NMDAR). In addition to neurons, where they drive glutamatergic neurotransmission, NMDAR are expressed in a variety of cell types. In particular, brain endothelial cells express NMDAR, which could be involved in blood-brain barrier maintenance and alteration. In a recent paper, we identified an unexpected population of NMDAR in endothelial cells, expressed at the luminal side of microvessels and located at the vicinity of blood/spinal cord barrier-forming tight junctions. We developed a monoclonal antibody (Glunomab®), directed against a specific site of NMDAR (aminoacids 176-180), which blocked the entry of leukocytes to the inflamed spinal cord, thus providing therapeutic effects in experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis (MS). Nevertheless, the downstream targets which link endothelial NMDAR function to leukocyte migration across the blood/brain and blood/spinal cord barriers are not fully understood yet. Interestingly, our current studies show that these receptors have an unconventional composition, including the presence of the rare GluN3 subunit, which provides response to glycine (in addition to glutamate) and metabotropic signaling (in addition to ionotropic function). Interestingly, naturally occurring circulating auto-antibodies against NMDAR are present in ~10% of human subjects and are overexpressed in neuropsychiatric and neurological diseases. Beyond these quantitative data, qualitative information are needed concerning the regions of NMDAR recognized by these antibodies. In fact, circulating autoantibodies against NMDAR could provide either beneficial or deleterious effects, depending on the region that they target. In line with this, we postulate that identifying the regions targeted by NMDAR auto-antibodies could have prognosis value in neurological diseases. Given our recent work concerning NMDAR in animal models of MS, we believe that investigating circulating antibodies would be particularly relevant for prognosis of MS. Thus the goals of this project are i) To characterize the signaling pathways and downstream targets triggered by NMDAR activation in endothelial cells, in relation to leukocyte penetration towards the spinal cord, ii) To identify the repertoire of NMDAR antibodies in MS patients (based on their target regions on NMDAR) and to determine whether different clusters of antibodies are associated with different outcomes, iii) To investigate the effects of these different clusters on the function of endothelial NMDAR and in animal models of MS, and iv) To bridge experimental data and clinical observations.