How Does Maternal Immune Activity Affect Fetal Survival and Brain Development? The Critical Roles of IL-17A and Microglia

Abstract

Maternal immune activation (MIA) during pregnancy has been associated with increased risk of fetal loss and neurodevelopmental disorders in offspring. This review summarizes recent findings on the effects of MIA on fetal survival and microglial phenotype. Studies using polyinosinic–polycytidylic acid [poly(I:C)-induced MIA mouse models have revealed the crucial role of interleukin-17A (IL-17A) in mediating these effects. Overexpression of RORγt, a key transcription factor for IL-17A production, enhances poly(I: C)-induced fetal loss, possibly due to increased placental vulnerability. Intraventricular administration of IL-17A in fetal brains activates microglia and alters their localization, particularly in periventricular regions and the medial cortex. These activated microglia may contribute to abnormal synaptic pruning and excessive phagocytosis of neural progenitor cells, potentially leading to long-term neurodevelopmental abnormalities. The insights gained from MIA research have important clinical implications, including the potential for early identification of high-risk pregnancies and the development of novel preventive and therapeutic strategies. Future research should focus on elucidating the roles of other cytokines, determining critical periods of MIA susceptibility, and translating findings to human populations, while carefully considering ethical implications and the need for appropriate risk communication.

1. Introduction

Maternal immune activation (MIA) during pregnancy has been associated with increased risk of fetal loss and neurodevelopmental disorders in offspring. Recent studies have identified interleukin-17A (IL-17A) and microglia as key mediators in these outcomes. This review focuses specifically on the IL-17A–microglia–placenta axis, which serves as a mechanistic bridge linking maternal inflammation to both placental dysfunction and fetal brain abnormalities. Background information on MIA is presented only to contextualize this central pathway. By emphasizing this axis, we aim to integrate evidence from molecular, cellular, and organismal levels to clarify how immune perturbations in the mother propagate through the placenta to affect fetal neurodevelopment (Figure 1).

Animal models have been instrumental in clarifying these pathways. Polyinosinic–polycytidylic acid [poly(I: C)], a synthetic double-stranded RNA analog that mimics viral infection, has been widely used to induce MIA in rodents and non-human primates. These models recapitulate Autism Spectrum Disorder (ASD)-like behaviors, cortical “patches,” and microglial alterations observed in human studies, thus providing construct and face validity [1,2,3]. Moreover, MIA intersects with other environmental risk factors, such as maternal stress, metabolic syndrome, and microbiome dysbiosis, highlighting the multifactorial nature of fetal programming [4,5]. Integration of these findings within the Developmental Origins of Health and Disease (DOHaD) framework underscores how prenatal inflammation can durably shape trajectories of brain and behavior [5,6].

At the mechanistic level, maternal cytokine surges, particularly interleukin-6 (IL-6) and interleukin-17A (IL-17A), have been identified as key mediators linking maternal immune status to fetal neurodevelopment [7,8,9]. Experimental blockade of these cytokines in animal models attenuates cortical malformations and abnormal behaviors, reinforcing their causal roles [10]. Microglia, the brain’s resident immune cells, emerge as pivotal effectors: they integrate maternal cytokine signals and sculpt synaptic architecture, thereby linking immune challenge to circuit-level abnormalities [11]. Dysregulated microglial activity may lead to excessive pruning, aberrant phagocytosis of neural progenitors, and impaired maturation of cortical networks—hallmarks shared by both ASD and schizophrenia.

MIA is recognized as an environmental factor that contributes to the pathogenesis of complex neurodevelopmental conditions through interactions with genetic susceptibility [12]. This “two-hit hypothesis” posits that the combination of genetic vulnerability and environmental insults initiates disease and provides a valuable framework for understanding ASD’s complex etiology. Beyond ASD, epidemiological and preclinical data indicate that MIA also increases susceptibility to schizophrenia, attention-deficit/hyperactivity disorder, and mood disorders, suggesting that prenatal inflammation confers broad and long-lasting consequences on mental health [13,14]. For instance, maternal influenza or other viral infections during mid-gestation have been associated with higher rates of schizophrenia in adulthood, providing historical evidence for the long-term effects of in utero immune perturbations [15].

Maternal immune activation (MIA) refers to a state in which the maternal immune system—critical for supporting fetal development—is activated during pregnancy by infections or other environmental triggers. Emerging evidence links MIA to an increased risk of miscarriage as well as neurodevelopmental disorders in offspring, particularly ASD [16,17,18]. According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), ASD is characterized by persistent deficits in social communication together with restricted, repetitive patterns of behavior. Surveillance by the U.S. Centers for Disease Control and Prevention (CDC) indicates that approximately 1 in 36 children in the United States is diagnosed with ASD [19,20]. The apparent prevalence has risen in recent years, underscoring the urgency of elucidating pathogenic mechanisms and establishing effective interventions. Epidemiological evidence further shows that maternal infection requiring hospitalization is associated with increased ASD risk [10,21].

Figure 1. Effects of maternal immune activation (MIA)-driven overproduction of IL-17A on the placenta and the fetal brain. Th17 cells residing in the intestinal lamina propria differentiate from naïve T cells under co-stimulation by IL-6 and TGF-β. Expression of the transcription factor retinoic acid receptor-related orphan receptor-γt (RORγt) is essential for Th17 differentiation. Excess IL-17A contributes to placental fragility; placental dysfunction can cause miscarriage and, in parallel, perturb fetal brain development. IL-17A may modulate neural circuits over the long term, either indirectly via microglia or directly by acting on neurons—figure created with BioRender.com [22].

This review is organized into four conceptual parts: (I) Placental Mechanisms, (II) Microglia and Brain Development, (III) Clinical Correlates and Biomarkers, and (IV) Translational Perspectives and Future Directions.

2. Placental IL-17A/IL-17RA Axis: A Fault Line in Pregnancy Immune Homeostasis

The establishment and maintenance of pregnancy rely on the barrier immunity of the placenta at the maternal–fetal interface. IL-17A, a Th17-derived cytokine, engages the IL-17RA/IL-17RC receptor complex to activate NF-κB, MAPK, and C/EBP pathways, inducing chemokines and antimicrobial programs. Although the placenta is not a classical immune organ, trophoblasts and other placental cells are responsive to IL-17 signals. When this axis is overdriven, it compromises nutrient transport and the integrity of adherens junctions, destabilizing placental homeostasis.

Within the labyrinth layer, E-cadherin is a structural determinant of adherens junctions. Chronic skewing of the maternal IL-17A milieu can weaken E–cadherin–dependent adhesion, rendering the placental architecture vulnerable to secondary inflammatory hits. Our RORγt-Tg model exemplifies this principle and is detailed in the section on MIA and fetal-loss risk (see Section 7). A two-step mechanism is therefore plausible: (i) IL-17RA/RC-dependent signaling compromises cell–cell adhesion in the placenta; (ii) a viral-mimetic TLR3 activation [e.g., poly(I:C)] pushes the system past a critical threshold—particularly around E12.5—precipitating fetal loss.

Conceptually, the sequence is: maternal gut Th17 activation → placental IL-17RA/RC signaling → E-cadherin reduction with inflammatory reprogramming of the microenvironment → rarefaction of the labyrinth architecture → breakdown of the fetal-side circulation under inflammatory load. Figure 1 in this review provides a visual anchor for this placenta-to-brain cascade. Clinically, aberrant E-cadherin expression is recognized in placental pathology, and its attenuation aligns with impaired barrier integrity. Situating these observations within an IL-17A/IL-17RA framework clarifies how maternal immune tone can translate into placental fragility.

A recent advance is the PRIMA-17 model, in which maternal IL-17RA deficiency is combined with IL-17A overexpression. In this system, the mother cannot respond to IL-17A, but the fetus retains responsiveness to IL-17A. This elegant design demonstrated that maternal IL-17A crosses the placenta, accumulating in fetal membranes, placenta, and amniotic fluid [23]. This provides direct evidence that maternal IL-17A can bypass the placental barrier and act on the embryo, reinforcing the importance of the placental IL-17A/IL-17RA axis.

3. Critical Windows of Susceptibility

Experimental evidence suggests that the timing of maternal immune activation (MIA) plays a critical role in determining outcomes (Figure 2). In mice, induction of MIA at embryonic day (E) 12.5 reliably provokes cortical malformations and ASD-like behaviors, whereas exposures at later stages (E15.5 or E18.5) do not reproduce such robust phenotypes [24]. This temporal specificity aligns with developmental transitions: at E12.5, cortical progenitors are rapidly proliferating and radial migration has just commenced. Perturbations at this stage can disrupt laminar architecture and produce the “cortical patches” characteristic of MIA models.

Figure 2. Windows of Vulnerability to Maternal Immune Activation (MIA) Schematic alignment of mouse embryonic development with approximate human gestation. The mid-gestational period (E12.5–E14 in mice; approximately 10–18 weeks in humans) represents the peak window of susceptibility to maternal immune activation (MIA). During this phase, overlapping corticogenesis (E10–E16) and microglial colonization render the fetal brain highly sensitive to IL-17A signaling, which can alter neuronal migration and cortical patterning. Earlier stages correspond to implantation and placental development, whereas later stages (E16–P14) coincide with synaptogenesis and astrocyte maturation, influencing circuit refinement and gliogenesis.

In our RORγt-Tg studies, poly(I: C) exposure at E12.5—rather than at later stages—was sufficient to elicit a striking increase in fetal loss, consistent with a narrow critical window [25]. These observations imply that the gestational timing of infection or inflammation is as decisive as its intensity for both placental integrity and fetal brain development. These events are summarized in the gestational timeline, which highlights the E12.5 vulnerability.

4. Microglial Spatiotemporal Dynamics

Microglia exhibit profound developmental dynamics that render them sensitive to maternal inflammation. During early corticogenesis, microglia progressively acquire surveillant features and shape neuronal circuit assembly [26]. In MIA paradigms, IL-17A exposure alters both the activation state and the spatial distribution of fetal microglia. Direct intraventricular IL-17A administration at mid-gestation promotes clustering of amoeboid CD68-positive microglia in the periventricular zone and medial cortex [27], and activated aggregates may drive excessive engulfment of neural progenitors [28]. Complementarily, fetal brain responses to maternal inflammation require microglia, underscoring their causal role in transducing immune signals into developmental outcomes [9]. Such alterations in motility and transcriptional programs can persist long after the acute event, indicating durable reprogramming of microglial states [29].

In parallel, microglia were shown to be indispensable for MIA-induced fetal brain responses [9]. Using microglia-deficient mice, they showed that poly(I:C)-induced transcriptional changes in fetal cortical cells were abolished, highlighting that microglia are essential mediators of maternal immune signals to the fetal brain.

Recent work from our laboratory has highlighted the molecular basis of microglial polarization [30]. In this system, expression of psychiatric disorder-related kinesin superfamily proteins (KIFs)—notably Kif3a, Kif17, and Kif13a—was potentiated in alternatively activated microglia, while a truncating mutation in Kif17 disrupted their rod-shaped morphology. These findings suggest that microglial functional states are maintained not only by the cytokine milieu but also by the intracellular transport machinery, linking cytoskeletal dynamics and molecular motors to the pathophysiology of psychiatric disorders.

5. Complement Pathway and Synaptic Pruning

Synaptic refinement during development relies in part on microglial engulfment of weak or inactive synapses via the classical complement cascade. C1q and C3 decorate synapses, and microglial CR3 mediates their removal—mechanisms established by landmark studies [31,32]. MIA may intersect with this pathway by priming microglia toward a pro-inflammatory phenotype, which lowers the threshold for complement-dependent elimination. In the fetal brain, this could yield excessive pruning (hypoconnectivity) or aberrant selectivity, both of which are compatible with connectivity anomalies associated with ASD.

6. Overview of Maternal Immune Activation (MIA)

MIA is not a monolith; it varies with pathogen class (e.g., TLR3 versus TLR4 signals), dose–response, maternal physiological state (temperature, body weight, endocrine milieu), and genetic background. Preclinical paradigms commonly use polyinosinic–polycytidylic acid [poly(I:C)] to emulate viral dsRNA and lipopolysaccharide (LPS) for bacterial signals; however, the reagent lot/molecular weight, route, and timing critically shape the inflammatory waveform and downstream placental/fetal-brain outcomes [14]. Representative MIA models and their key features are summarized in Table 1. Mechanistically, a time-ordered cross-talk among IL-6, IL-1β, TNF-α, and IL-17A underlies MIA-induced perturbations, arguing for network-level interpretation rather than single-cytokine reductionism [15]. Significantly, the Treg/Th17 balance constrains pregnancy maintenance and likely tunes MIA susceptibility [33,34]. To enhance external validity, future studies should standardize stimulus parameters and maternal readouts and report them transparently (see Section 15 for a checklist). Historical data also include reports linking influenza epidemics during pregnancy to increased risk of schizophrenia in adulthood [35].

MIA induces a characteristic cytokine milieu dominated by interleukin-6 (IL-6), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and interleukin-17A (IL-17A) [15]. Each exerts discrete yet interacting effects on the developing brain: IL-6 governs neural progenitor proliferation and differentiation; IL-1β influences neuronal survival and synaptic plasticity; TNF-α modulates the balance between neuronal survival and death; and IL-17A, central to this review, drives microglial activation and can alter neural progenitor dynamics. These mediators operate within an integrated network rather than in isolation; understanding MIA therefore requires attention to the temporal dynamics and cross-talk of the cytokine network as a whole [36,37].

7. Comparative Roles of IL-17A, IL-6, and TNF-α in Maternal Immune Activation

Although IL-17A is central to the placenta–microglia axis emphasized in this review, other cytokines, particularly IL-6 and TNF-α, exert complementary and sometimes overlapping effects. IL-6 acts as an upstream regulator that primes the maternal immune milieu and promotes Th17 differentiation, thereby indirectly amplifying IL-17A responses [26,33]. It also influences neural progenitor proliferation and astrocyte differentiation in the fetal brain [3]. In contrast, TNF-α primarily modulates endothelial permeability, coagulation, and apoptosis, contributing to placental inflammation and vascular instability [14,25].

Unlike these systemic mediators, IL-17A functions at the maternal–fetal interface, directly affecting trophoblast adhesion and microglial activation through IL-17RA/RC signaling [9,16,25]. Comparative studies indicate that IL-6-driven effects are reversible in later gestation, whereas IL-17A perturbations during mid-gestation produce more persistent cortical abnormalities [23,33]. However, reports diverge regarding the relative contributions of each cytokine, reflecting differences in model design, cytokine dose, timing of exposure, and species-specific receptor distribution [36,37].

Unresolved questions remain concerning whether IL-6-initiated cascades are sufficient to explain neurodevelopmental outcomes or whether IL-17A acts as the final common effector downstream of multiple cytokine pathways. Moreover, the degree to which TNF-α interacts synergistically with IL-17A to exacerbate placental barrier breakdown has not been fully elucidated [38,39]. Addressing these discrepancies will require integrative experimental designs that combine cytokine profiling with temporal and spatial mapping of receptor expression across maternal and fetal tissues.

Table 1. Representative models of maternal immune activation (MIA) and their features—expanded.

Model	Trigger/Agent	Primary Receptor/Axis	Gestational Window (Rodent)	Dose/Route (Guideline)	Maternal Acute Readouts	Placental/Fetal Readouts	Core Offspring Phenotypes	Key Cytokines/Pathways	Strengths	Limitations	Standardization Notes	Key Refs
Poly(I:C)	dsRNA analog (viral mimic)	TLR3 → IL-6/IL-17A axis	E9.5–E13.5 (lab-dependent)	i.p.; strain/batch-dependent (see guideline)	Fever-like response, weight loss, serum cytokine surge	↑ Resorption rate (at higher doses), placental inflammation	↓ Social interaction, ↑ repetitive behaviors, sensorimotor gating changes	IL-6, IL-17A, chemokines	High reproducibility; rapid viral-mimic induction	Batch/dose/window-sensitive phenotypes	Report batch, dose, gestational window	[2,36]
LPS	Endotoxin (bacterial mimic)	TLR4 → IL-1β/TNF-α axis	E9.5–E13.5	i.p./s.c.; high dose near term increases fetal lethality	Fever, weight loss, inflammatory cytokines ↑	Preterm/abortion risk ↑, placental inflammation	Anxiety-/depression-like, learning/social changes	IL-1β, TNF-α	Bacterial infection mimic	Dose-dependent maternal toxicity; variability	Detail dose and route per guideline	[2,36]
Live influenza/infection	Influenza virus (example)	Multi-PRR, systemic inflammatory axis	Typically mid-gestation	Intranasal; BSL compliance	Fever, weight change, serum cytokines	Placental inflammation, fetal growth/viability impact	↓ Social attention, communication changes	IL-6, TNF-α, others	Highest clinical relevance	Pathogen/variant and site differences	Specify inoculum, timing, strain	[5,40]
Maternal IL-6 injection	Recombinant IL-6	IL-6R/gp130 → STAT3	E12.5 ±	i.p.; single/repeat per report	Acute cytokine rise; minimal maternal behavior change	Directly engages fetal neurodevelopmental pathways	Social/sensory phenotypes	IL-6	Pathogen-independent causality	Simplifies physiology; limits external validity	Clarify dose/timing rationale	[3,41]
Direct fetal IL-17A	Recombinant IL-17A (fetal intracerebral)	IL-17RA/RC → NF-κB/MAPK	E13 ± (corticogenesis)	Intraventricular (stereotaxic)	Minimal maternal load	Microglial activation/relocation; circuit disruption	Sensory/social phenotypes (study-dependent)	IL-17A	Direct fetal brain causality	Invasive; translational limits	Detail surgical conditions/operator skill	[7,16]
PRIMA-17	Maternal IL-17RA deficiency + IL-17A excess	Embryo-restricted IL-17A signaling	Mid-gestation (E12.5 ±)	Genetic × immunologic combination	Low dependence on maternal cytokine peaks	Placental adhesion ↓; fetal loss ↑; circuit defects	ASD-like (social ↓, repetitive ↑)	IL-17A/IL-17RA	Fetal-selective inference; reduces confounders	Complex to build; inter-site reproducibility	Protocol sharing/registration	[42]
NHP MIA	Poly(I:C) or live pathogen	Multi-PRR/IL-6–IL-17 axis	Mid-gestation (species-appropriate)	i.v./i.m./intranasal (site protocol)	Temp/weight/cytokines longitudinal	Placental function and brain growth imaging; behavior	↓ social attention/interactions	IL-6, IL-17A etc.	Closer to human behavior	High cost; small N; ethics	Protocol transparency; shared metrics	[43,44]
Clinical corollaries	Natural infection in pregnancy	Pathogen-dependent; systemic inflammatory axis	All trimesters (severity/pathogen-dependent)	EHR/lab/inpatient data	Fever; CRP/cytokines	Perinatal outcomes; placental pathology	Neurodevelopmental follow-up (e.g., ASD)	IL-6/IL-17A etc.	Max clinical validity	Confounding (comorbidity/access)	Rigorous epidemiologic adjustment	[5,45]
Human brain organoids	IL-6/IL-17A exposure; conditioned media	Cytokine receptors → downstream signaling	In vitro developmental model	Concentration/exposure optimization	—	Genotype-dependent cellular responses	Microcircuit/lineage phenotypes	IL-6/IL-17A	Test human-specific mechanisms	Does not recreate maternal–placental–fetal axis	Register dose/time/reproducibility	[46]

Note: ↑, increase; ↓, decrease. Follow MIA reporting guidelines for dose, route, batch, and gestational timing details (e.g., Reisinger 2015 [2]; Kentner 2019 [36]). This provides an overview of representative models of maternal immune activation (MIA) that have been used to investigate the causal links between maternal inflammation and offspring neurodevelopmental outcomes. Poly(I:C) and LPS models reproduce viral- and bacterial-like responses in rodents and remain the most widely used paradigms, whereas maternal IL-6 or IL-17A injection isolates the contribution of single cytokine pathways. The PRIMA-17 model uniquely demonstrates embryo-restricted IL-17A signaling without confounding cytokines. Non-human primate (NHP) MIA studies provide higher translational validity by capturing complex social behaviors, while clinical corollaries based on maternal infection history link epidemiological observations to experimental findings. Finally, human brain organoids exposed to inflammatory cues enable the mechanistic exploration of human-specific developmental processes. Each model has distinct strengths and limitations with respect to reproducibility, translational relevance, and mechanistic resolution. Standardization of dose, route, gestational timing, and reporting—guided by established MIA guidelines—remains essential for cross-study comparison and clinical translation.

Table 1. Representative models of maternal immune activation (MIA) and their features—expanded.

Model	Trigger/Agent	Primary Receptor/Axis	Gestational Window (Rodent)	Dose/Route (Guideline)	Maternal Acute Readouts	Placental/Fetal Readouts	Core Offspring Phenotypes	Key Cytokines/Pathways	Strengths	Limitations	Standardization Notes	Key Refs
Poly(I:C)	dsRNA analog (viral mimic)	TLR3 → IL-6/IL-17A axis	E9.5–E13.5 (lab-dependent)	i.p.; strain/batch-dependent (see guideline)	Fever-like response, weight loss, serum cytokine surge	↑ Resorption rate (at higher doses), placental inflammation	↓ Social interaction, ↑ repetitive behaviors, sensorimotor gating changes	IL-6, IL-17A, chemokines	High reproducibility; rapid viral-mimic induction	Batch/dose/window-sensitive phenotypes	Report batch, dose, gestational window	[2,36]
LPS	Endotoxin (bacterial mimic)	TLR4 → IL-1β/TNF-α axis	E9.5–E13.5	i.p./s.c.; high dose near term increases fetal lethality	Fever, weight loss, inflammatory cytokines ↑	Preterm/abortion risk ↑, placental inflammation	Anxiety-/depression-like, learning/social changes	IL-1β, TNF-α	Bacterial infection mimic	Dose-dependent maternal toxicity; variability	Detail dose and route per guideline	[2,36]
Live influenza/infection	Influenza virus (example)	Multi-PRR, systemic inflammatory axis	Typically mid-gestation	Intranasal; BSL compliance	Fever, weight change, serum cytokines	Placental inflammation, fetal growth/viability impact	↓ Social attention, communication changes	IL-6, TNF-α, others	Highest clinical relevance	Pathogen/variant and site differences	Specify inoculum, timing, strain	[5,40]
Maternal IL-6 injection	Recombinant IL-6	IL-6R/gp130 → STAT3	E12.5 ±	i.p.; single/repeat per report	Acute cytokine rise; minimal maternal behavior change	Directly engages fetal neurodevelopmental pathways	Social/sensory phenotypes	IL-6	Pathogen-independent causality	Simplifies physiology; limits external validity	Clarify dose/timing rationale	[3,41]
Direct fetal IL-17A	Recombinant IL-17A (fetal intracerebral)	IL-17RA/RC → NF-κB/MAPK	E13 ± (corticogenesis)	Intraventricular (stereotaxic)	Minimal maternal load	Microglial activation/relocation; circuit disruption	Sensory/social phenotypes (study-dependent)	IL-17A	Direct fetal brain causality	Invasive; translational limits	Detail surgical conditions/operator skill	[7,16]
PRIMA-17	Maternal IL-17RA deficiency + IL-17A excess	Embryo-restricted IL-17A signaling	Mid-gestation (E12.5 ±)	Genetic × immunologic combination	Low dependence on maternal cytokine peaks	Placental adhesion ↓; fetal loss ↑; circuit defects	ASD-like (social ↓, repetitive ↑)	IL-17A/IL-17RA	Fetal-selective inference; reduces confounders	Complex to build; inter-site reproducibility	Protocol sharing/registration	[42]
NHP MIA	Poly(I:C) or live pathogen	Multi-PRR/IL-6–IL-17 axis	Mid-gestation (species-appropriate)	i.v./i.m./intranasal (site protocol)	Temp/weight/cytokines longitudinal	Placental function and brain growth imaging; behavior	↓ social attention/interactions	IL-6, IL-17A etc.	Closer to human behavior	High cost; small N; ethics	Protocol transparency; shared metrics	[43,44]
Clinical corollaries	Natural infection in pregnancy	Pathogen-dependent; systemic inflammatory axis	All trimesters (severity/pathogen-dependent)	EHR/lab/inpatient data	Fever; CRP/cytokines	Perinatal outcomes; placental pathology	Neurodevelopmental follow-up (e.g., ASD)	IL-6/IL-17A etc.	Max clinical validity	Confounding (comorbidity/access)	Rigorous epidemiologic adjustment	[5,45]
Human brain organoids	IL-6/IL-17A exposure; conditioned media	Cytokine receptors → downstream signaling	In vitro developmental model	Concentration/exposure optimization	—	Genotype-dependent cellular responses	Microcircuit/lineage phenotypes	IL-6/IL-17A	Test human-specific mechanisms	Does not recreate maternal–placental–fetal axis	Register dose/time/reproducibility	[46]

Note: ↑, increase; ↓, decrease. Follow MIA reporting guidelines for dose, route, batch, and gestational timing details (e.g., Reisinger 2015 [2]; Kentner 2019 [36]). This provides an overview of representative models of maternal immune activation (MIA) that have been used to investigate the causal links between maternal inflammation and offspring neurodevelopmental outcomes. Poly(I:C) and LPS models reproduce viral- and bacterial-like responses in rodents and remain the most widely used paradigms, whereas maternal IL-6 or IL-17A injection isolates the contribution of single cytokine pathways. The PRIMA-17 model uniquely demonstrates embryo-restricted IL-17A signaling without confounding cytokines. Non-human primate (NHP) MIA studies provide higher translational validity by capturing complex social behaviors, while clinical corollaries based on maternal infection history link epidemiological observations to experimental findings. Finally, human brain organoids exposed to inflammatory cues enable the mechanistic exploration of human-specific developmental processes. Each model has distinct strengths and limitations with respect to reproducibility, translational relevance, and mechanistic resolution. Standardization of dose, route, gestational timing, and reporting—guided by established MIA guidelines—remains essential for cross-study comparison and clinical translation.

8. MIA and the Risk of Fetal Loss

Epidemiology links maternal infections, including influenza and COVID-19, to increased risks of miscarriage and stillbirth [12,19,20]. Mechanistically, MIA can disrupt maternal–fetal immune tolerance and degrade placental barrier function, with secondary impacts on coagulation and fetal development. In our RORγt-Tg model, chronic IL-17A elevation reduces E-cadherin in the labyrinth. It increases fetal-loss rates after poly(I: C), indicating that baseline placental fragility can determine outcomes independently of an acute IL-17A surge [25]. Consistent with the poly(I: C) literature on viral-mimetic signaling [14], a two-step mechanism—pre-existing adhesion weakness plus an acute innate trigger—offers a parsimonious account. Clinically, aberrant E-cadherin expression has long been recognized in placental pathology, aligning with impaired barrier integrity and altered trophoblast turnover, which provides a practical histopathologic anchor for risk assessment [43,47].

Among candidate mediators, interleukin-17A (IL-17A) is of particular interest given its role in Th17 biology and its elevation in recurrent pregnancy loss. To probe causality, we used a T-cell-specific RORγt-overexpressing mouse (RORγtTg). Under a poly(I: C) based MIA paradigm, RORγtTg dams exhibited a significantly higher abortion rate than wildtype dams and showed reduced placental E-cadherin in the labyrinth layer. Notably, pregnant RORγtTg mice failed to mount an acute IL17A surge after poly (I: C), suggesting that constitutive Th17/IL17A skewing predisposes to loss via mechanisms beyond transient cytokine peaks. Detailed data (rates, histology, and time course) are provided here, whereas the mechanistic interpretation of the placental IL17A/IL17RA axis is elaborated in the dedicated section (“Placental IL-17A/IL-17RA Axis”).

Together, these findings support a model in which baseline IL17A-driven placental fragility interacts with acute virally mimetic inflammation to cross a threshold for fetal loss. Readers are referred to Figure 1 for the integrated placenta–brain schematic.

9. Relationship Between Miscarriage and Neurodevelopmental Disorders

Shared etiologic substrates at the placenta–brain axis—vascular dysregulation, hypoxia, nutrient insufficiency, and endocrine–immune reprogramming—may help explain associations between miscarriage history and later neurodevelopmental risk in offspring [2]. Prospective cohort designs integrating maternal inflammatory biomarkers (e.g., IL-6, IL-17A), placental histopathology, and infant neurodevelopmental readouts are needed to establish temporal precedence and clarify mediation pathways [2,8,9].

Several studies suggest an association between miscarriage and subsequent neurodevelopmental disorders in offspring [2]. Reports indicate that women who experience recurrent miscarriages may have an increased likelihood that later-born children will develop neurodevelopmental conditions; however, the mechanisms underlying this association remain incompletely understood. Common etiologic substrates may contribute to both outcomes. The placenta, far from being a mere conduit for nutrients, is an active endocrine and immunologic organ that produces hormones and growth factors influencing fetal brain development. Placental dysfunction can precipitate miscarriage and, at the same time, adversely affect neurodevelopment—for example, by inducing fetal hypoxia and nutrient insufficiency. Moreover, specific placental histopathological features have been linked to increased risk of ASD in offspring. Collectively, these observations raise the possibility that placental health forms a mechanistic bridge between miscarriage and neurodevelopmental outcomes, although this field remains in progress and many questions persist.

10. Effects of MIA on Fetal Brain Development

MIA reconfigures microglial transcriptional states, spatial distribution, and motility, with durable effects on synaptic pruning and network assembly [26,27,28,29,37,48]. IL-17A engages IL-17RA on CNS glia to amplify inflammatory programs [2,11], while the classical complement pathway (C1q/C3 → CR3) provides a tag-and-engulf framework that may sensitize MIA, lowering thresholds for elimination or distorting target selectivity [2,11]. In parallel, blood-brain barrier (BBB) destabilization—exacerbated by astrocyte-derived mediators such as VEGF-A—can enhance cytokine ingress and immune–neuronal cross-talk [38]. Together, these elements point to a temporally staged cascade from maternal immune tone to fetal circuit topology (see Figure 1).

Recent studies implicate T helper 17 (Th17) cells and interleukin-17A (IL-17A) in the pathogenesis of ASD. Elevated serum IL-17A has been observed in individuals with ASD, and higher IL-17A levels have been reported to correlate with greater symptom severity [33,34]. In mouse models of maternal immune activation (MIA), maternal production of IL-17A is induced by viral-mimetic immune challenges; notably, ASD-like cortical abnormalities and behavioral phenotypes are ameliorated by administration of anti-IL-17A antibodies, by genetic blockade of Th17 differentiation via RORγt deficiency, and by depletion of gut microbiota that drive Th17 responses [45].

IL-17A appears to play a central role in the induction of ASD-like behaviors and cortical structural anomalies (so-called cortical “patches”) under MIA. MIA-induced maternal IL-17A production, the rescue of ASD-like behaviors by anti-IL-17A treatment, the suppression of these behaviors in RORγt-knockout mice, and the reproduction of ASD-like behaviors and cortical patches by direct fetal intraventricular IL-17A delivery were demonstrated [24]. Mechanistically, IL-17A may act directly on neural progenitors or indirectly via microglia; additional proposed mechanisms include increased blood–brain barrier permeability, altered neuronal gene expression, and astrocyte activation. In combination, these actions can yield ASD-like structural and behavioral outcomes [7,12,22,48].

Microglia—the resident immune cells of the central nervous system—are pivotal to neurodevelopment [48]. MIA alters microglial activation profiles in the fetal brain and can perturb circuit formation [37]. Reported effects include changes in microglial transcriptional programs, activation states, cytokine production, synaptic pruning, and motility, any of which may disrupt normal brain development and produce long-lasting neurodevelopmental abnormalities [29].

Microglia express the IL-17A receptor IL-17RA, and in models of neuroinflammation (e.g., experimental autoimmune encephalomyelitis and Parkinsonian paradigms), IL-17A drives overexpression of pro-inflammatory mediators in glia and exacerbates pathology [31,32]. Complementary in vitro studies likewise show that IL-17A stimulation increases microglial expression of inflammatory cytokines and chemokines.

In our laboratory, direct intraventricular administration of recombinant IL-17A to fetal mouse brains revealed robust effects on microglia: cells accumulated predominantly in periventricular zones and in medial cortical regions (including cingulate cortex), and those at the ventricular surface adopted amoeboid morphologies and CD68-positive activated phenotypes [26,27]. These findings indicate that IL-17A reconfigures both the activation state and spatial distribution of microglia. Periventricular aggregation of activated microglia could promote excessive phagocytosis of neural progenitors [28], whereas medial cortical accumulation may influence the formation of long-range commissural connections such as the corpus callosum.

Microglial activation in response to MIA is unlikely to be purely transient. Potential longer-term consequences include altered synapse density, chronic neuroinflammation, shifts in neurotransmitter balance, and dysregulated production of neurotrophic factors. We posit that the convergence of these durable changes contributes to the pathogenesis of neurodevelopmental disorders, and we are continuing to dissect how IL-17A shapes cortical morphogenesis over time.

Single-cell transcriptomic analyses have confirmed the indispensability of microglia in MIA cascades. In microglia-deficient mice, fetal cortical responses to MIA were absent, underscoring that the fetal brain cannot mount an inflammatory response without microglia. These results emphasize microglia as central effectors of MIA and highlight them as promising therapeutic targets.

The PRIMA-17 model further revealed that fetal-specific IL-17A responses alone are sufficient to drive selective behavioral abnormalities. Offspring displayed reduced social ultrasonic vocalizations, increased anxiety-like behavior in the open field, and reduced marble burying, while three-chamber social and social novelty tests were routine. Thus, fetal IL-17A imprinting resulted in a selective behavioral phenotype that was independent of maternal systemic responses [23]. These results highlight the embryo-restricted IL-17A response as a direct programming mechanism for neurodevelopmental disorders.

11. DOHaD and MIA

Within the DOHaD framework, prenatal inflammatory milieus can be ‘remembered’ through persistent epigenomic and immune–metabolic reprogramming. Microglial priming is one plausible substrate linking MIA to later-life neuroinflammatory propensity and neurodegenerative risk. We anticipate that combined exposures (infection, nutritional stress, psychosocial adversity) interact nonlinearly with genetic susceptibility; modeling these interactions is essential for prevention strategies grounded in DOHaD principles [43,47].

The Developmental Origins of Health and Disease (DOHaD) framework posits that the prenatal and early postnatal environment shapes lifelong health and disease risk [43,47]. Within this framework, maternal immune activation (MIA) constitutes a salient prenatal environmental exposure. As reviewed above, MIA is associated with increased risk of fetal loss and with neurodevelopmental outcomes—particularly ASD—aligning with the DOHaD concept that the fetal immune milieu programs later health trajectories.

The roles of interleukin-17A (IL-17A) and microglia highlighted in this review offer concrete mechanistic inroads for DOHaD. Their influence on fetal cortical development relates not only to phenotypes evident at birth or in early childhood but also to vulnerability to psychiatric conditions across adulthood [30]. MIA-driven reconfiguration of microglial activation can persist, predisposing the brain to chronic neuroinflammation and potentially increasing the risk of neurodegenerative disease [21]. More broadly, MIA provides a tractable model for interrogating gene–environment interactions—a core DOHaD tenet—thereby refining the “two-hit” view in which genetic susceptibility and environmental challenges jointly determine developmental trajectories.

Positioned at the nexus of neuroimmunology and developmental neuroscience, MIA research is accelerating our understanding of immune–neural interactions during gestation. It is informing pathophysiology and therapeutic discovery for neurodevelopmental disorders. Ultimately, the significance of this work extends beyond disease-specific mechanisms to the broader DOHaD context of how fetal environments sculpt lifelong health. From a public-health perspective, advancing this knowledge base should catalyze prevention strategies and precision medicine grounded in DOHaD principles.

12. Clinical Implications and Future Directions

Integrating the evidence reviewed above, the IL-17A–microglia–placenta axis emerges as a pivotal target for preventive and therapeutic strategies against MIA-induced disorders. From a translational standpoint, infection control during pregnancy remains the primary strategy for reducing MIA risk [8,9]. For risk stratification, multiplexed biomarker panels combining maternal cytokines (including IL-17A) with placental functional indices (e.g., circulating placental miRNAs) merit evaluation. Translationally relevant biomarker candidates are summarized in Table 2. Intervention windows span: (i) preconception–early gestation infection prevention; (ii) mid-gestation modulation of inflammatory polarity with attention to the Treg/Th17 axis [33,34]; and (iii) neonatal surveillance of neurodevelopmental trajectories. Standardized MIA reporting and cross-species translational benchmarks (see Section 13 and Section 15) will accelerate clinical utility.

Table 2. Translationally relevant biomarkers associated with maternal immune activation (MIA)—expanded.

Sample Source	Biomarker/Panel	Mechanistic Link (Summary)	Evidence Tier	Primary Translational Use Case	Key Refs
Maternal blood	IL-6 (±IL-1β, TNF-α), IL-17A	Core MIA cytokines; placental IL-6 signaling shapes fetal brain; IL-17A linked to cortical malformations	Strong	Prenatal inflammation risk stratification; trial eligibility; longitudinal monitoring	[3,7,41]
Maternal blood	Treg/Th17 balance markers (e.g., IL-10, TGF-β ↔ IL-17A)	Tolerance vs. inflammation; tunes pregnancy maintenance and MIA susceptibility	Supportive	Resilience stratification; immunophenotyping for interventions	[26,28]
Maternal blood	VEGF-A	With IL-17A, disrupts endothelial tight junctions; impacts barrier integrity	Supportive	Surrogate for barrier fragility; vascular response monitoring	[25,39,49]
Placenta (pathology/molecular)	E-cadherin (trophoblast adhesion), VEGF-A	Loss weakens labyrinth architecture; vascular factors reshape microenvironment	Strong/Supportive	Histopathologic anchor; evaluation of prior inflammation	[25,38]
Placenta (single-cell)	Immune/trophoblast ligand–receptor interactions (incl. IL-17A/IL-17RA)	Maps immune–epithelial/vascular crosstalk at the human maternal–fetal interface	Strong	Cross-species triangulation; pathway nomination	[37]
Cord blood/Neonatal serum	IL-6, IL-17A	Reflects in utero inflammatory exposure; early-life immune programming	Supportive	Early-life stratification; baseline for follow-up	[3,7]
Maternal clinical context	Infection requiring hospitalization	Pregnancy infections requiring hospitalization associate with increased ASD risk	Strong	Risk stratification; covariate control in analyses	[45]
Neonatal/infant functional	EEG, eye-tracking, social gaze metrics	Downstream functional readouts of circuit impact	Supportive/Emerging	Pre-intervention screening; predictive marker development	[36]
Mechanistic bridge (preclinical → clinical)	NVU/BBB dysfunction signals (IL-17A-, VEGF-A-mediated)	IL-17A induces tight junction breakdown; VEGF-A increases permeability	Strong/Supportive	Target selection; biomarker prioritization	[39,49]
Model-to-human triangulation	PRIMA-17, NHP, human organoids	Conserved IL-17A axis and convergent circuit phenotypes across models	Strong/Supportive	External validation; bridge from discovery to validation	[42,44,46]

Note: Evidence tier indicates overall strength of translational support (Strong = human or strong human + preclinical convergence; Supportive = primarily mechanistic/preclinical; Emerging = exploratory). Abbreviations: NVU, neurovascular unit; BBB, blood–brain barrier. This table summarizes translationally relevant biomarkers that bridge maternal immune activation (MIA) research from animal models to clinical contexts. The listed biomarkers include maternal cytokines such as IL-6 and IL-17A, Treg/Th17 balance indicators, and placental structural or molecular readouts like E-cadherin and VEGF-A, all of which reflect pregnancy-specific immune tolerance and barrier integrity. Neonatal and infant biomarkers, including cord blood cytokines, EEG, and social gaze metrics, provide early indicators of altered neurodevelopmental trajectories. Mechanistic markers such as BBB dysfunction signals (IL-17A/VEGF-A mediated) and cross-species triangulation with NHP or organoid models highlight conserved pathways underlying ASD-like outcomes. Evidence tiers (Strong, Supportive, Emerging) indicate the level of validation across preclinical and clinical studies, while the “Key refs” column aligns with citations in the text.

The translational limitations discussed above have also been recognized in several key studies addressing interspecies differences, dose scaling, and gestational timing. Reisinger et al. [17] and Kentner et al. [36] outlined how variability in stimulus type, gestational window, and maternal physiology critically influence the outcomes of MIA paradigms and limit direct extrapolation to human pregnancy. Vento-Tormo et al. [37] demonstrated human-specific patterns of immune–trophoblast interactions at the maternal–fetal interface, underscoring placental differences across species. Non-human primate MIA studies by Bauman et al. [44] provide valuable intermediate models bridging rodent and human data, although ethical and logistical constraints remain. In addition, Argaw et al. [38] showed that cytokine-mediated vascular changes, including IL-17A/VEGF-A-driven barrier disruption, differ in magnitude between species, while Paşca et al. [46] proposed human brain organoid systems as translationally relevant models to validate cytokine-driven neurodevelopmental mechanisms.

Collectively, these studies [17,27,37,38,44,46] reinforce the necessity of integrating rodent, primate, and human cellular models to refine translational inference and establish clinically meaningful intervention windows.

Interventions aimed at modulating IL-17A signaling during pregnancy raise critical safety and ethical concerns. IL-17A is essential for mucosal and vascular immunity; its suppression could increase maternal susceptibility to infection or impair vaccine responses [38,45]. Conversely, excessive inhibition may disturb placental immune tolerance and trophoblast function, disrupting the maternal–fetal immune equilibrium [37].

Furthermore, fetal development represents a period of heightened immune and neural plasticity. Depending on dose and timing, IL-17A blockade might influence fetal immune maturation or long-term neurodevelopmental trajectories, as suggested by the PRIMA-17 paradigm showing that fetal IL-17A responsiveness alone can reshape cortical circuits [23]. Therefore, clinical translation must adhere to rigorous eligibility criteria, including precise risk stratification, gestational-stage restrictions, stepwise dosing, and comprehensive biomarker monitoring of maternal cytokines and placental function [17,27].

Ethical oversight should involve independent review boards, transparent informed consent clearly describing uncertain risks, real-time adverse-event surveillance, and participation in pregnancy registries. Until robust safety data are available, preventive measures—such as infection control, vaccination, and supportive care—should remain the primary strategy, while continued preclinical validation using humanized models and placental organoids will help define safe and effective intervention windows [37,38,45].

Progress in MIA research carries broad clinical implications, including early identification of high-risk pregnancies, development of novel therapeutics, improved infection control during pregnancy, design of early-life intervention programs, and applications to precision medicine. For example, profiling serum IL-17A together with microglial activation markers is a candidate strategy for stratifying neurodevelopmental risk during pregnancy. Therapeutically, IL-17A-neutralizing antibodies and agents that modulate microglial activation represent promising foundations for preventive and disease-modifying approaches. To advance the field, key priorities include:

• Cytokines beyond IL-17A. Define how IL-6, TNF-α, and other inflammatory mediators contribute to MIA-driven alterations in fetal brain development [22,35].
• Durable circuit effects of microglial activation. Determine how MIA—particularly IL-17A–driven microglial activation—shapes synaptogenesis, circuit remodeling, and network function across development [40,41].
• Critical windows of susceptibility. Pinpoint gestational stages at most significant risk to guide targeted prevention and timing of interventions [23].
• Gene–environment interplay. Identify genetic backgrounds that confer heightened vulnerability to MIA and leverage these insights for individualized prevention and treatment [44].
• Therapeutic mitigation. Develop and test strategies to blunt MIA sequelae, including IL-17A blockade and microglia-modulating drugs [42,50]. Together, these findings suggest that interventions targeting IL-17A signaling in the fetus may represent a promising strategy for preventing neurodevelopmental abnormalities. The PRIMA-17 paradigm underscores that IL-17A alone, without confounding cytokines such as IL-6, is sufficient to reprogram neurodevelopment [23].
• Translation to humans. Rigorously evaluate the extent to which animal-model findings generalize to human pregnancy and neurodevelopment [51].
• Longitudinal follow-up. Conduct long-term cohort studies of MIA-exposed offspring to define trajectories of risk, prognosis, and windows for intervention [39,46].
• Co-exposures and context. Map interactions between MIA and other environmental factors—nutrition, psychosocial stress, and chemical exposures—to capture real-world complexity [49].

As science advances, ethical and societal questions require parallel attention: clear risk-communication strategies for pregnant individuals and the public, careful evaluation of the ethical acceptability of prenatal immunomodulation, and measures to mitigate anxiety among expectant mothers. Addressing these dimensions will facilitate responsible translation. In tandem with human validation, deeper mechanistic work, and therapeutic development, the field should prioritize returning insights to clinical practice to strengthen prenatal care and support healthy fetal development.

13. Sex-Differential Vulnerability to MIA

Epidemiological patterns and preclinical studies converge on a male-biased vulnerability to neurodevelopmental outcomes following prenatal inflammation. Sex differences in microglial ontogeny and immune responsivity are plausible substrates: microglia have stage-specific roles in circuit assembly, and perturbations during critical windows may disproportionately affect male trajectories [26]. Hormonal milieu and sex chromosome effects likely intersect with immune–metabolic reprogramming, producing sex-specific thresholds for circuit injury and repair. Prospective studies should pre-specify sex stratification in both animal models and human cohorts to enable precision prevention [42,44].

Epidemiological studies show that ASD prevalence is approximately fourfold higher in males than in females, suggesting sex-specific vulnerability to MIA-related mechanisms. Preclinical rodent models replicate this bias, with male offspring displaying more pronounced social deficits following MIA. Mechanistically, sex hormones such as testosterone, sex-chromosome immune genes, and differential DNA methylation profiles may converge to produce male-biased risk. Microglial developmental trajectories also differ: male microglia show higher density and enhanced inflammatory responsivity during early postnatal periods, amplifying the consequences of maternal cytokines such as IL-17A. Together, these findings underscore the importance of considering sex as a biological variable in both preclinical and clinical studies of MIA.

14. Cross-Species Translation: NHP and Human Multi-Omics at the Maternal–Fetal Interface

Bridging rodent insights to humans requires mechanistic continuity across species. Non-human primate (NHP) MIA paradigms report abnormalities in social attention and fronto-striatal circuitry, consistent with human phenotypes, which reinforces external validity [41]. On the human side, single-cell atlases of the maternal–fetal interface have resolved trophoblast and immune cell states, and mapped ligand–receptor circuits that regulate tolerance and vascular remodeling [26]. We propose a triangulation strategy—rodent causal assays → NHP circuit/behavior → human single-cell and spatial—to identify conserved axes and derive clinically tractable biomarkers.

Cross-species translation is essential for validating MIA mechanisms. In rhesus monkeys, maternal immune activation leads to reduced social gaze and altered prefrontal connectivity, providing strong face validity for ASD-related phenotypes. The PRIMA-17 mouse model further highlights conserved IL-17A pathways across species. Human placental single-cell transcriptomic maps reveal ligand–receptor interactions, including IL-17A/IL-17RA signaling circuits, that align with findings in animal models. Moreover, human brain organoids exposed to IL-17A display disrupted synaptogenesis and altered network maturation, directly paralleling rodent and primate data. These triangulated approaches—rodent causality, NHP behavior and circuits, and human omics—provide a robust framework for translation and biomarker discovery.

15. Neurovascular Unit and the BBB in MIA

The neurovascular unit (NVU)—endothelium, pericytes, astrocytes, and microglia—governs blood–brain barrier (BBB) integrity. MIA perturbs the NVU through endothelial junctional changes and astrocyte-derived mediators; VEGF-A can drive BBB disruption and facilitate leukocyte trafficking under inflammatory conditions [38]. IL-17A–responsive glia (IL-17RA in CNS glia) can amplify NVU inflammation via Act1-dependent signaling, further destabilizing barrier function [31,32]. We posit that placental IL-17A and maternal cytokines converge on the NVU to create a transiently permeable microenvironment enabling cytokine ingress and microglial reprogramming during critical windows.

The developing blood–brain barrier (BBB) is particularly vulnerable during mid-gestation, coinciding with peak susceptibility to MIA. IL-17A signaling disrupts endothelial tight junctions and synergizes with astrocyte-derived VEGF-A, increasing permeability and permitting maternal cytokines to access the fetal brain. Human studies suggest that maternal infection is associated with elevated placental and fetal vascular inflammation, supporting the relevance of BBB compromise in clinical contexts. Transient barrier leakage provides a conduit for immune factors to engage fetal microglia and reshape circuit assembly. Stabilizing the neurovascular unit may thus represent a therapeutic strategy for mitigating the neurodevelopmental impact of MIA.

16. Reporting Standards for MIA (Checklist)

To enhance rigor, reproducibility, and translation, we recommend adopting a minimum reporting checklist derived from field guidelines: (1) animal species/strain/sex and pregnancy confirmation; (2) stimulus identity (poly(I:C)/LPS), manufacturer/lot/molecular weight; (3) dose, route, and precise timing (embryonic day); (4) maternal physiology (temperature, body weight, behavior); (5) cytokine validation (time-courses of IL-6/IL-17A); (6) placental sampling layout (layer-specific analyses); (7) fetal-brain sampling and analytics; (8) blinding and randomization; (9) exclusion criteria/missingness; (10) data and code sharing. We provide a tabular checklist (Table 3) to facilitate adoption.

Table 3. Minimum reporting checklist for MIA studies (after Kentner et al., 2019 [36]).

Domain	Items to Report	Rationale
Animal information	Species, strain, substrain; supplier; sex; age; housing (light/dark cycle, enrichment, cage density); microbiological status (SPF, gnotobiotic, conventional)	Baseline characteristics influence immune response and neurodevelopmental outcomes.
Breeding and pregnancy	Mating scheme (timed mating, plug check, IVF/ET use); parity of dams; gestational staging method; number of dams per group	Accurate pregnancy staging is critical for reproducibility.
MIA induction	Inducing agent (poly(I:C), LPS, influenza, recombinant cytokines, genetic model); source, lot, purity; dose and concentration; administration route (i.p., i.v., s.c., intranasal, intraventricular); timing (gestational day); injection schedule (single vs. repeated)	Variability in agent and timing strongly affects outcomes.
Maternal readouts	Acute sickness behaviors (weight loss, hypothermia, mobility); maternal cytokine levels (IL-6, IL-17A, TNF-α); clinical chemistry (CRP, glucose); mortality	Confirms effective immune activation and safety margins.
Pregnancy outcomes	Implantation number, resorption rate, stillbirths; litter size; sex ratio; placental weight; fetal weight; E-cadherin or VEGF-A expression; histopathology (labyrinthine structure)	Links maternal immune state with placental/fetal health.
Fetal and neonatal measures	Fetal brain cytokines; microglial morphology/motility; apoptosis markers; neonatal survival; growth curves; developmental milestones (eye opening, reflexes)	Establishes early-life impact of MIA.
Offspring phenotypes	Behavioral domains (social, repetitive, anxiety-like, cognition, sensory gating); neuroanatomy (cortical layering, interneuron markers); electrophysiology (EEG, evoked potentials)	Provides translational readouts relevant to ASD/SCZ.
Randomization and blinding	Random assignment of dams; blinding of experimenters for behavioral testing and histology	Minimizes bias.
Statistical considerations	Litter effects accounted for; power analysis; number of dams vs. pups reported separately; attrition documented	Ensures appropriate inference and reproducibility.
Ethical and reporting standards	ARRIVE guideline adherence; approval numbers from ethics committees; compliance with MIA reporting guideline [36]	Transparency, reproducibility, and comparability.

Table 3 outlines a reporting checklist designed to improve the rigor, reproducibility, and transparency of maternal immune activation (MIA) studies. The checklist emphasizes detailed reporting of animal strain, sex, and age, as well as MIA-inducing agents, routes, doses, and gestational timing. It also highlights the importance of specifying control conditions, maternal health indices, and pregnancy outcomes, including implantation, fetal number, and resorption rate. Standardized reporting of placental and fetal measures, randomization and blinding procedures, and compliance with ARRIVE or MIA-specific guidelines are recommended. By adopting these reporting standards, researchers can reduce variability between laboratories, facilitate comparison across models, and strengthen the translational value of MIA research.