| Summary: | <p>Abstract</p> <p>Background</p> <p>The mechanism(s) responsible for the reduced risk of allergic disease in breastfed infants are not fully understood. Using an established murine model of asthma, we demonstrated previously that resistance to allergic airway disease transmitted from allergic mothers to breastfed offspring requires maternal B cell-derived factors.</p> <p>Objective</p> <p>The aim of this study was to investigate the role of offspring neonatal Fc receptor for IgG uptake by intestinal epithelial cells (FcRn) in this breast milk transferred protection from allergy.</p> <p>Methods</p> <p>Allergic airway disease was induced during pregnancy in C57BL/6 female mice. These allergic mothers foster nursed naive FcRn<sup>+/- </sup>or FcRn<sup>-/- </sup>progeny born to FcRn<sup>+/- </sup>females that were mated to C57BL/6J-FcRn<sup>-/- </sup>male mice. In offspring deficient in FcRn, we expected reduced levels of systemic allergen-specific IgG<sub>1</sub>, a consequence of decreased absorption of maternal IgG from the lumen of the neonatal gastrointestinal tract. Using this model, we were able to investigate how breast milk IgG affected offspring responses to allergic sensitization.</p> <p>Results</p> <p>Levels of maternal antibodies absorbed from the breast milk of allergic foster mothers were determined in weanling FcRn-sufficient or -deficient mice. Maternal transmission of allergen-specific IgG<sub>1 </sub>to breastfed FcRn<sup>-/- </sup>offspring was at levels 10<sup>3</sup>-10<sup>4 </sup>lower than observed in FcRn<sup>+/- </sup>or FcRn<sup>+/+ </sup>mice. Five weeks after weaning, when offspring were 8 wk old, mice were sensitized and challenged to evaluate their susceptibility to develop allergic airway disease. Protection, indicated by reduced parameters of disease (allergen-specific IgE in serum, eosinophilic inflammation in the airways and lung) were evident in FcRn-sufficient mice nursed as neonates by allergic mothers. In contrast, FcRn-deficient mice breastfed by the same mothers acquired limited, if any, protection from development of allergen-specific IgE and associated pathology.</p> <p>Conclusions</p> <p>FcRn expression was a major factor in determining how breastfed offspring of allergic mothers acquired levels of systemic allergen-specific IgG<sub>1 </sub>sufficient to inhibit allergic sensitization in this model.</p>
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