The association between transforming growth factor beta (TGF-β) isotypes and thymic stromal lymphopoietin (TSLP) in breast milk and infant gut permeability in term infants: ProPACT study Background: There is little known about the role of breast milk cytokines on the influence of allergy disease development through modifying gut permeability. We aimed to analyze the association between two cytokines in breast milk: TGF-β isotypes and TSLP, and term infant gut permeability plasma markers: LBP and FABP-2. Methods: Samples were collected during a randomized-controlled trial cohort within the context of maternal probiotic supplementation's effect on childhood atopic dermatitis and other allergy diseases (the ProPACT Study), consisting of 415 mother-infant pairs. In this sub-study, we analyzed breast milk cytokines from 255 mothers and infant gut permeability plasma samples from 115 children. The association between TGF-β isotypes and TSLP in breast milk and term-infant gut permeability plasma LBP and FABP-2 markers were investigated using multivariate analyses at two breastfeeding timepoints, 10 days and 3 months. Results: Both at 10 days and at 3 months, TGF-β1 had the greatest number of varied concentrations, TGF-β2 had the highest concentration and TGF-β3 had the lowest concentration. Most of the detectable breast milk TSLP (55.4%, n = 238) at 10 days were in low concentration (32.3%). The median concentration of term infant plasma LBP at 10 days and 3 months were low (1 and 1.4 μg/mL), while term infant plasma FABP-2 concentrations were lower than 2 000 pg/mL (2 ng/mL) at both timepoints and still within the normal range of the assay. There was no statistically significant association between breast milk TGF-β isotypes and TSLP and term infant plasma LBP and FABP-2, although there was an inverse tendency between the concentration of breast milk TSLP and infant plasma LBP at 10 days. Conclusions: Breast milk TGF-β isotypes and TSLP do not appear to be associated with the term infant gut permeability markers, plasma LBP and FABP-2 both at 10 days and 3 months after birth in a Norwegian population. Further studies are required to investigate and confirm whether increased gut permeability in term infants has a role in the development of childhood allergy diseases. Keywords: breast milk, TGF-beta isotypes, TSLP, LBP, FABP-2, term infant gut permeability