Quercetin attenuates maternal respiratory virus-induced fetal neuroimmune dysregulation

Maternal respiratory viral infections during pregnancy are epidemiologically linked to increased risk of neurodevelopmental disorders in offspring, yet the causal immunological mechanisms that disrupt fetal neuroimmune homeostasis remain unclear. A murine pregnancy influenza model was established by intranasal inoculation of a sublethal dose of H1N1 (PR8) at embryonic day 9.5. Maternal immune modulation was performed using natural killer (NK) cell depletion and genetic deletion of granzyme B ( Gzmb ) in maternal NK cells, as well as quercetin administration during defined gestational windows. Fetal neuroimmune outcomes were assessed by immunostaining and quantitative analysis of macrophage activation in fetal brain barrier regions, complemented by single-cell RNA sequencing of fetal brain CD11b⁺ myeloid populations. Offspring behavioral phenotypes were evaluated in adulthood, and decidual transcriptomic profiling was performed to characterize changes at the maternal-fetal interface. In parallel, human decidual NK cells were stimulated in vitro with interferon-β with or without quercetin to examine conserved immunoregulatory effects. Maternal H1N1 infection induced robust maternal lung inflammation and was accompanied by fetal neuroimmune dysregulation characterized by increased Iba1⁺CD68⁺ macrophage accumulation in the fetal choroid plexus and meninges. Depletion of maternal NK cells significantly ameliorated these fetal neuroimmune abnormalities, implicating maternal NK cells as key mediators. Quercetin treatment mitigated fetal neuroinflammation and improved autism-like behaviors in offspring. Single-cell transcriptomic analysis showed that quercetin reversed interferon-stimulated gene programs and attenuated infection-induced expansion of proinflammatory fetal macrophage subsets. Mechanistically, quercetin reduced NK-derived granzyme B while enhancing decidual Serpina3n and broader pregnancy-supportive molecular programs, and alleviated infection-associated fetal growth restriction. These findings identify maternal NK cell-derived granzyme B as a central driver of respiratory virus-induced fetal neuroimmune disturbance and support quercetin as a dual-action immunomodulatory candidate capable of mitigating maternal immune dysregulation and fetal neuroinflammation.