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Despite our knowledge of the protective role of antibodies passed to infants through breast milk, our understanding of immunity transfer via maternal leukocytes is still limited. To emulate the immunological interface between the mother and her infant while breast-feeding, we used murine pups fostered after birth onto MHC-matched and MHC-mismatched dams. Overall, data revealed that: 1) Survival of breast milk leukocytes in suckling infants is possible, but not significant after the foster-nursing ceases; 2) Most breast milk lymphocytes establish themselves in specific areas of the intestine termed Peyer's patches (PPs); 3) While most leukocytes in the milk bolus were myeloid cells, the majority of breast milk leukocytes localized to PPs were T lymphocytes, and cytotoxic T cells (CTLs) in particular; 4) These CTLs exhibit high levels of the gut-homing molecules α4β7 and CCR9, but a reduced expression of the systemic homing marker CD62L; 5) Under the same activation conditions, transferred CD8 T cells through breast milk have a superior capacity to produce potent cytolytic and inflammatory mediators when compared to those generated by the breastfed infant. It is therefore possible that maternal CTLs found in breast milk are directed to the PPs to compensate for the immature adaptive immune system of the infant in order to protect it against constant oral infectious risks during the postnatal phase.

While the role of Transforming Growth Factor β (TGF-β) as an intrinsic pathway has been well established in driving de novo differentiation of Th17 cells, no study has directly assessed the capacity of TGF-β signaling initiated within dendritic cells (DCs) to regulate Th17 differentiation. The central finding of this study is the demonstration that Th17 cell fate during autoimmune inflammation is shaped by TGF-β extrinsic pathway via DCs. First, we provide evidence that TGF-β limits at the site of inflammation the differentiation of highly mature DCs as a means of restricting Th17 cell differentiation and controlling autoimmunity. Second, we demonstrate that TGF-β controls DC differentiation in the inflammatory site but not in the priming site. Third, we show that TGF-β controls DC numbers at a precursor level but not at a mature stage. While it is undisputable that TGF-β intrinsic pathway drives Th17 differentiation, our data provide the first evidence that TGF-β can restrict Th17 differentiation via DC suppression but such a control occurs in the site of inflammation, not at the site of priming. Such a demarcation of the role of TGF-β in DC lineage is unprecedented and holds serious implications vis-à-vis future DC-based therapeutic targets.

Constitutive expression of IL9 in the lungs of transgenic (Tg) mice resulted in an asthma-like phenotype consisting of lymphocytic and eosinophilic lung inflammation, mucus hypersecretion and mast cell hyperplasia. Several Th2 cytokines including IL4, IL5 and IL13 were expressed in the lung in response to Tg IL9. IL13 was absolutely necessary for the development of lung pathology. To understand how IL9 induces IL13-dependent lung inflammation and mucus production, we sought the IL13-producing cells. Surprisingly, we found that the absence of T cells and B cells in recombinase-activating gene 1 (RAG1)-deficient IL9 Tg mice enhanced lung inflammation and dramatically enhanced IL13 production. In addition, the lack of mast cells or eosinophils in IL9 Tg mice did not affect IL13 levels in the lung. In situ hybridization for IL13 on lung sections from RAG1−/− IL9 Tg mice revealed that airway epithelial cells were the major IL13-producing cell type. Our results implicate the lung epithelium as a potentially important source of inflammatory cytokines in asthma. [ABSTRACT FROM AUTHOR]