• Jeng-Chang Chen, Cheng-Chi Chan, Chia-Jen Wu, Liang-Shiou Ou, Hsiu-Yueh Yu, Hsueh-Ling Chang, Li-Yun Tseng, and Ming-Ling Kuo.
• 1 Department of Surgery.
• Am. J. Respir. Crit. Care Med. 2016 Oct 15; 194 (8): 934-947.

RationaleActively acquired tolerance occurs when foreign antigens come into contact with the immature fetal immune system.ObjectivesArmed with the knowledge of actively acquired tolerance, we attempted to prenatally abolish or diminish allergic responses.MethodsIn utero injection of adjuvant-free ovalbumin (OVA) was conducted in Gestational Day 14 FVB/N mouse fetuses. Postnatally, mice were evaluated for their resistance to intraperitoneal OVA sensitization and oral or aerosolized OVA challenge, and then they were examined for humoral and cellular immunological profiles, airway hyperresponsiveness to bronchospastic stimuli, and lung histology. Fluorescent conjugates of OVA were used for further studies of mechanisms.Measurements And Main ResultsThis presumed tolerogenic action turned out to be a sensitization process with the development of anaphylaxis or heightened recall, T-helper cell type 2-skewed responses to postnatal encounter with OVA. Further postnatal aerosolized OVA stress triggered allergic lungs with functional and structural alterations of airways. The unintended consequence resulted from macrophage-like fetal phagocytes that took up OVA and differentiated toward dendritic cells. These fetal dendritic cell progenitors attenuated proteolysis of endocytosed OVA for delayed presentation in postnatal life. This specialty of fetal phagocytes effectively retains the memory of antigens internalized early before full development of the immune system, leading to an event of in utero sensitization.ConclusionsOur results have mechanical implications for prenatal imprinting of atopy and shed light on the importance of fetal phagocytes in shaping the developing immune system and initiating allergic airway diseases.

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