PROJECT SUMMARY Multiple sclerosis (MS) is a chronic, immune-mediated demyelinating and neurodegenerative disease of the central nervous system (CNS). The immune pathophysiology of MS is still incompletely understood. This gap in understanding can be partially attributed to the relative inaccessibility of several immune compartments implicated in MS immune pathophysiology, namely, the CNS, deep cervical lymph nodes, gut, and other lymphoid tissues. In humans, the immune compartments of these tissues drain, at least partially, into the human deep efferent lymphatics, which coalesce ultimately in the thoracic duct (TD). To this end, our laboratory has established a research protocol by which to obtain TD lymph from patients with MS and healthy donors without MS, as a means by which to better understand the immune processes associated with MS in these upstream compartments. With this resource, alongside an existing cerebrospinal fluid (CSF)/peripheral blood (PB) single cell gene expression database from patients with and without MS, I hypothesize that I will be able to identify novel, tissue-specific immune signatures of MS present within the TD. In this proposal, I will employ a high throughput proteo-genomic single-cell approach that recovers joint gene expression and surface marker profiles from single cells in order to determine immune signatures detected in the TD of patients with MS. Immune signatures will be assessed using both compositional and gene-expression analyses in parallel. Furthermore, the findings will be integrated with our laboratory’s existing CSF/PB single cell gene expression database to better determine the tissue-specificity of the detected TD immune signatures. Overall, this proposal will provide insight into a still unexplored immune compartment in MS (the TD) and will help guide future studies to further the field’s understanding of MS immune pathophysiology.