Role of Zinc Insufficiency in Fetal Alveolar Macrophage Dysfunction and RSV Exacerbation Associated with Fetal Ethanol Exposure

Background: We previously reported that maternal alcohol use significantly increases the risk of sepsis in premature and term newborns. In the mouse, fetal ethanol exposure results in an immunosuppressed phenotype for the alveolar macrophage (AM) and decreases bacterial phagocytosis. In pregnant mice, ethanol decreased AM zinc homeostasis, which contributed to immunosuppression and impaired AM phagocytosis. In this study, we explored whether ethanol-induced zinc insufficiency extended to the pup AMs and contributed to immunosuppression and exacerbated viral lung infections.

Methods: C57BL/6 female mice were fed a liquid diet with 25% ethanol-derived calories or pair-fed a control diet with 25% of calories as maltose-dextrin. Some pup AMs were treated in vitro with zinc acetate before measuring zinc pools or transporter expression and bacteria phagocytosis. Some dams were fed additional zinc supplements in the ethanol or control diets, and then we assessed pup AM zinc pools, zinc transporters, and the immunosuppressant TGFβ1. On postnatal day 10, some pups were given intranasal saline or respiratory syncytial virus (RSV), and then AM RSV phagocytosis and the RSV burden in the airway lining fluid were assessed.

Results: Fetal ethanol exposure decreased pup AM zinc pools, zinc transporter expression, and bacterial clearance, but in vitro zinc treatments reversed these alterations. In addition, the expected ethanol-induced increase in TGFβ1 and immunosuppression were associated with decreased RSV phagocytosis and exacerbated RSV infections. However, additional maternal zinc supplements blocked the ethanol-induced perturbations in the pup AM zinc homeostasis and TGFβ1 immunosuppression, thereby improving RSV phagocytosis and attenuating the RSV burden in the lung.

Conclusion: These studies suggest that, despite normal maternal dietary zinc intake, in utero alcohol exposure results in zinc insufficiency, which contributes to compromised neonatal AM immune functions, thereby increasing the risk of bacterial and viral infections.