Abstract The hygiene hypothesis, first postulated in 1989, suggests that exposure to bacterial-derived products like endotoxin early in life, contribute towards protection against type 2 pulmonary inflammation, particularly asthma. The epidemiological and experimental studies spurred by the hygiene hypothesis underscore that the early postnatal period offers a critical window for the establishment of mucosal protection. Maternal milk represents a novel transgenerational mechanism by which offspring may acquire early-life immunity. The objective of this grant is to understand immune protective mechanisms by which maternal milk from mothers to neonates confers immunity to allergic diseases. In work in progress we have novel and promising data from a new model of maternal transference of immune protection. In this model, exposure to endotoxin in murine dams postpartum, resulted in pups obtaining protection against type 2 inflammation to a common indoor allergen, house dust mite and to a clinical strain of Respiratory Syncytial Virus (RSV). The overall downregulation of type 2 immune responses to an allergen and a virus indicated that the mechanism of protection was common for different antigens. Metabololipidomics analysis of murine milk from endotoxin-exposed dams revealed elevated levels of the specialized pro-resolving mediator (SPM), Resolvin D4(RvD4) derived from the essential fatty acid, Docosahexaenoic acid. Pups from endotoxin-exposed dams had overall lower type 2 immune response, altered pulmonary dendritic cell (DC) subsets and lower levels of alarmin cytokine IL-33 in the lungs. Based on published and preliminary findings, we form our central hypothesis: Maternal airway exposure to select microbial products influences the generation of specific SPM in milk. These SPM confer protective pulmonary immune responses in infants by promoting regulatory function in airway DCs and maintaining mucosal homeostasis. We test this hypothesis through three specific aims. Aim 1: Determine the generation and role of SPMs present in maternal milk in type 2 pulmonary inflammation. Aim 2: Investigate the impact of SPMs in CD103+ DC subset in type 2 pulmonary inflammation and resolution. Aim 3: Establish SPM-mediated mechanisms for the modulation of IL-33 expression in epithelial cells. The findings from these aims will be significant since they will establish that critical immune pathways targeted by SPMs generated in maternal milk, which confer protection against allergic diseases. The proposal is innovative since we propose to show that maternal milk provides a novel transgenerational immunological conduit of protection in a heretofore-unexamined process. The findings from this study will be vital to our understanding of how indirect early-life microbial exposure modulates the development of childhood allergic diseases.