Necrotizing enterocolitis (NEC) is one of the most common gastrointestinal emergency in the neonatal period. It is characterized by severe intestinal inflammation that can rapidly result in intestinal necrosis, sepsis, and potentially death. Despite advances in medical care, mortality and morbidity caused by NEC has not changed. This is largely due to the poor understanding of the complex pathogenesis, the limitations of the current animal models, and the lack of specific therapeutic or preventative therapies. Although the etiology is unclear, evidence suggests that prematurity, formula feeding, altered intestinal microbiome, and hypoxia-ischemia play major roles in NEC. Preterm infants have impaired intestinal permeability, and exhibit prominent intestinal epithelial TLR4 expression; all of which render the bowel at risk of bacterial translocation, an exaggerated inflammatory response, and NEC development. Therefore, identifying strategies or interventions that promote maturation of intestinal defenses, epithelial integrity, and modulate inflammation is critical in preventing this deadly disease. We have promising preliminary data demonstrating that oral hyaluronan at a molecular weight of ~ 35 kDa (HA 35kDa) reduces mortality, severity of intestinal injury, and systemic inflammation in a murine model of NEC. HA is a glycosaminoglycan found in almost all tissues including extracellular matrix. Studies showed that HA isolated from breast milk or commercially available HA 35kDA, protects against bacteria-induced colitis by increasing the expression of antimicrobial ?-defensins, and tight junction protein ZO-1 in colonic epithelium in vivo and in vitro. Based on our preliminary data and the previously reported biological effects of HA in the large intestine, we propose to directly investigate the effect of HA 35kDa on the (1) immature intestinal defenses, specifically antimicrobial peptides produced by enterocytes and Paneth cells, (2) intestinal barrier including mucous lining and TJ formation, and (3) on the development of the intestinal microbiome in healthy pups and pups with NEC (Aim 1).To facilitate translation of our results to human studies, we propose to evaluate the effect of HA 35kDa on a novel premature non-human primate model (NHP) of NEC (Aim 2). The ultimate goal of this project to initiate a new research direction in a disease that has shown little clinical progress over the past 50 years. Results from our study would enhance our understanding of NEC and lead to identification of new preventative strategies that will improve patient outcomes.