The impact of viral infection during pregnancy on maternal immunity and fetal brain development

Neurodevelopmental disorders (NDDs), including autism spectrum disorder (ASD) and schizophrenia, are rising in prevalence, yet their etiology and underlying mechanisms remain largely elusive. Epidemiological studies implicate influenza A virus (IAV) infection during pregnancy as a risk factor for NDDs. To investigate this link, maternal immune activation (MIA) is often modeled using pathogen mimics, like poly I:C. While these models have provided invaluable mechanistic insights, poly I:C induces only a partial innate immune response, whereas replicating IAV elicits a complete innate and adaptive immune response. To address this gap, we tested two of the leading hypotheses in the MIA field using a biologically relevant strain of IAV: (1) maternal adaptive immune cells, T helper 17 (TH17) lymphocytes, and their effector cytokine, IL-17, drive inflammatory cascades that signal to the fetal brain and induce neocortical malformations, and (2) fetal brain-resident macrophages respond to maternal viral inflammation and are redirected from their normal neurotrophic support functions, leading to aberrant cortical development. We previously showed that a moderate dose of IAV during peak adaptive immunity spares the fetal brain. Here, we extend this work by characterizing the peak innate (2 days post inoculation, dpi) and adaptive (7 dpi) immune response at two viral titers to determine whether an infection severity threshold exists for the onset of fetal brain abnormalities. Respiratory IAV infection elicited a robust maternal inflammatory response in the lungs and blood in a dose- and time-dependent manner. Notably, circulating IL-6 and IFN-—but not IL-17—were elevated in both dams and fetuses. Although poly I:C models implicate maternal intestinal TH17 cells as drivers of IL-17-mediated fetal brain abnormalities, respiratory IAV infection in pregnant mice did not activate pre-existing TH17 cells or prime CD4+ T cells into pathogenic TH17 cells. Notably, this occurred despite signs of maternal gastrointestinal stress, as exhibited by colonic shortening and moderate changes to the colonic microbiome. Nevertheless, prenatal high-dose IAV exposure resulted in neocortical thinning and reduced expression of upper cortical marker, SATB2, concomitant with downregulation of fetal brain transcripts related to neuronal migration. Reduced SATB2 expression was not accompanied by a reduction in cellular density, suggesting an altered cellular identity rather than cell loss. Potential cellular mediators of these cortical abnormalities include brain-resident macrophages–microglia and border-associated macrophages (BAMs). Disruption of microglial-dependent processes has been observed in rodent models of poly I:C-initiated MIA, and several of these studies directly implicate microglia in MIA-mediated cortical pathologies. Less is known about BAMs, which do not infiltrate the brain parenchyma but rather reside in peripheral regions where they carry out constant immune surveillance. Therefore, BAMs could indirectly impair neocortical development through soluble molecule production. We found increased numbers of meningeal BAMs, but not microglia, in high-dose fetal brains. Functional assays revealed that prenatal IAV infection did not substantially alter fetal microglial immune response to a secondary immune challenge in vitro. In contrast, prenatal IAV infection altered fetal meningeal BAMs, leading to a blunted cytokine response to a secondary immune challenge, as well as elevated baseline production of chemokines, growth factors, matrix metalloproteinases, and osteopontin. Preliminary results indicate that culturing cortical neurons with microglia- or BAM-conditioned media from IAV-exposed fetal brains leads to a modest reduction in the number of NeuN+ and SATB2+ neurons. Collectively, these findings demonstrate that (1) a threshold of maternal infection is required to induce fetal brain abnormalities, (2) such abnormalities occur independently of enhanced maternal IL-17 signaling, underscoring differences across MIA models, (3) upper cortical layer SATB2 alteration represents a conserved feature of MIA, (4) fetal meningeal BAMs (and potentially microglia) are functionally altered by prenatal IAV infection, and (5) BAM-derived soluble factors may be leading to aberrant cortical development. Overall, this work provides evidence for the use of a biologically relevant model of MIA to identify biomarkers and therapeutic targets for the treatment and prevention of human NDDs.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Neuroscience

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Otero, Ashley

Contributors dc:contributor

• Antonson, Adrienne
• Steelman, Andrew
• Raetzman, Lori
• Loman, Brett

• Neuroimmunology
• Neurodevelopment
• Microglia
• Border-Associated Macrophages
• Influenza A Virus
• Pregnancy
• Neurodevelopmental Disorders
• Maternal Immune Activation

Statement dc:rights

• Copyright 2025 Ashley Otero

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132630

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132630