Parenteral Nutrition (PN) is a lifesaving strategy that provides intravenous nutrition in patients when enteral feeding is contraindicated, or access is insuffcient to prevent malnutrition. PN is used in low-birth-weight neonates whereprolonged use is associated with severe metabolic complications, including parenteral nutrition-associated liver disease (PNALD). PNALD is characterized by hepatitis, cholestasis, fibrosis, steatosis, and eventual organ failure. Elevated rates of PNALD in pediatric patients may be driven by liver immaturity, aberrant metabolic adaptation, and leaky gut barrier.To characterize the etiology of PNALD, we recently established a pediatric mouse model of PN. Using this model, we explored the intravenous use of bioactive milk components to augment hepatic immune response in pediatric mice without enteral milk intake. Extracellular vesicles (EVs) are involved in cell-to-cell communication, contain immune-augmenting microRNA, and are enriched in bovine milk. After isolating EVs from bovine milk and characterizing them, we explored EV use in vitro via M1 macrophage responses, showing TNF-alpha inhibition in the presence of LPS. Wethen hypothesized that EVs would protect the pediatric liver from hepatitis under PN feeding in vivo. Mouse pups were randomized to intravenous PN, PN + EV (1.39x109 particles/uL), or sham surgery control for 6 days. Flow cytometry showed PN elevated hepatic macrophages (CD11b+F4/80+), myeloid-derived suppressor cells (CD11b+GR1+) andreduced relative T cell populations compared with sham controls. PN+EV treatment restored hepatic immune profiles to patterns observed in sham controls. Spleen and liver cytokines also mirrored changes in hepatic flow results, where elevated proinflammatory IL-1 beta was induced with PN alone, but similar levels were found in sham and PN+EVanimals. MicroRNA sequencing showed the EV isolates contain 48% Let-7, a described myeloid suppressor microRNA. This data demonstrates that intravenous EV administration - or future synthetic microRNA - may provide a noveltherapeutic approach for patients requiring PN nutrition support, especially those with elevated risk of PNALD induced inflammation and organ dysfunction. Dairy Innovation Hub, UW-Madison. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.