OBJECTIVES/SPECIFIC AIMS: We previously demonstrated that products released by cultured B cells from patients with Multiple Sclerosis (MS) are cytotoxic to neurons and oligodendrocytes, while minimal toxicity was observed in response to B cell secretory products from age- and sex-matched normal controls. The goal of this proposal is to identify the range of brain cells susceptible to MS B cell-mediated cytotoxicity, to define the cytotoxic factor(s) released by MS B cells, and to determine whether particular subset(s) of MS B cells harbor the greatest pathogenic potential. METHODS/STUDY POPULATION: The toxicity of B cell products will be demonstrated by incubating primary rat cultures of neurons, oligodendrocytes, and oligodendrocyte progenitor cells (OPCs) with B cell supernatants. B cells will be isolated from the peripheral circulation of untreated relapse-remitting MS (RRMS) patients and age- and sex-matched normal controls. The identification of specific toxic factor(s) in MS B cell supernatants will be achieved through a combination of exosome-depletion/enrichment of conditioned media, proteomics, next generation sequencing, and lipidomics. Determining pathogenic B cell subsets will be achieved by cell sorting into memory and naïve B cell subsets prior to collection of supernatants. RESULTS/ANTICIPATED RESULTS: We hypothesize that the toxicity of MS B cell products is mediated, at least in part, by extracellular vesicles, such as exosomes. We expect depletion of these exosomes from the B cell conditioned media or inhibition of their biogenesis will mitigate the observed toxicity. Furthermore, differences in B cell-derived exosomal content, such as proteins, (mi)RNAs, or lipids, likely explain the differences in observed toxicity. Lastly, we hypothesize that memory B cells, which are enriched in the CNS of MS patients and demonstrate a more pro-inflammatory profile than naïve B cells, are responsible for the toxicity observed in supernatants of total B cells. DISCUSSION/SIGNIFICANCE OF IMPACT: MS is the most prevalent chronic inflammatory disease of the CNS, affecting more than 2 million people worldwide. Although over a dozen disease-modifying therapies are approved for the treatment of RRMS, none are meaningfully effective at limiting disease progression. This proposal will provide new insight into immune-CNS interactions in progressive MS and provide much-needed novel targets for therapeutic intervention, either via blocking identified toxic molecule(s) or by selectively depleting pathogenic B cell subsets.