Project SummaryFood allergy is a growing public health concern. Regulatory T (Treg) cells play a pivotal role in tolerance tofood allergens, however, the effects of maternal immune responses on the induction of Treg cell-mediatedtolerance in offspring are poorly understood. We have recently found that maternal sensitization with allergen(ovalbumin; OVA or peanut) prevented food allergic responses in murine offspring, as indicated by a decreasein levels of food anaphylaxis, allergen-specific immunoglobulin (Ig) E, serum mouse mast cell proteinase 1,and intestinal mast cell expansion in response to epicutaneous sensitization and oral challenge with the sameallergen. This protection was associated with an increase in levels of IgG and food allergen immune complexes(IgG-IC) and transforming growth factor (TGF) ? in breast milk. Neonatal Fc receptor (FcRn)-dependenttransfer of maternal IgG-IC via breast milk and IgG-IC presentation by neonatal CD11c+ dendritic cells (DCs)promoted the differentiation of allergen-specific Treg cells in offspring. Breastfeeding by OVA-sensitizedmothers or maternal supplementation with IgG-IC induced neonatal tolerance. Consistently, human breast milkcollected from non-atopic mothers contained IgG-IC and induced tolerance in humanized FcRn mice. Theseresults suggest that maternal IgG-IC in breast milk and offspring CD11c+ DCs are critical for the induction ofTreg cell responses and control food-specific tolerance in neonates and that TGF? may facilitate this effect. Q576R mice, a genetic murine model of atopy, carry the naturally-occurring interleukin (IL)-4 receptor(IL-4R) ? chain Q576R polymorphism associated with asthma and atopic dermatitis in humans. Offspring ofOVA-sensitized Q576R mothers showed a decrease in the frequencies of allergen-specific Treg cells andsuboptimal levels of tolerance against food allergy as compared to wild-type controls. This partial protectionwas associated with lower levels of TGF? in breast milk and dysregulation of intestinal CD11c+ DCs inoffspring. These results suggest that genetic predisposition of mothers and offspring to atopy may hinderoptimal induction of neonatal tolerance via modulation of maternal TGF? and offspring DCs. The goals of this proposal are to decipher the time frame and the mechanistic interactions ofmaternal factors and offspring immune responses critical to establish effective food-specific tolerancein neonates, and how they are modulated by genetic susceptibilities to atopy. We hypothesize thatexposure of neonatal DCs to sufficient levels of TGF? in breast milk during a specific time window in theperinatal period is critical to generate functional Treg cells specific to maternally transferred allergen IgG-IC inbreast milk. We also hypothesize that excessive IL-4R signaling, a key signaling in the pro-allergic Th2responses, modifies maternal TGF? levels and offspring DC phenotype, and induces the reprograming of Tregcells in offspring that hampers optimal induction of neonatal tolerance. These studies have the potential toidentify interventional strategies to induce tolerance in early life to prevent food allergy in children.