VALIDATION OF THE POLY(I:C) MOUSE MODEL FOR NEURODEVELOPMENTAL DISORDERS IN A SOPF ANIMAL FACILITY

Introduction
Maternal immune activation (MIA) during pregnancy is a known risk factor for neurodevelopmental disorders such as autism spectrum disorder and schizophrenia. In mice, poly(I:C) induces MIA by activating toll-like receptor 3 and elevating maternal IL17a, a cytokine implicated in offspring neurodevelopmental abnormalities. MIA outcomes vary depending on poly(I:C) fragment composition, dose, timing, and the maternal microbiome. Segmented Filamentous Bacteria (SFB) have been identified as a key determinant of IL17a responses and MIA severity. This study investigates MIA induction after administration of poly(I:C) with different fragment compositions and the influence of SFB levels under ultra-strict specific opportunistic pathogen free (SOPF) conditions.

Methods
Pregnant C57BL/6N mice were injected intraperitoneally on gestational day 12.5 with saline or poly(I:C) (HMW, LMW, or Sigma; 20 mg/kg). Rectal temperature was monitored for 3 hours, and plasma was collected at 3 and 48 hours for cytokine measurements. Adult offspring underwent behavioral testing. Stool was collected weekly for microbiome analysis. Additional experiments tested the effects of diet, water and cage type. SFB levels were quantified by qPCR.

Results
Poly(I:C) failed to induce hypothermia or increase IL17a in pregnant dams, and offspring showed no MIA-associated behavioural phenotype across the different types of poly(I:C). Although mice initially contained SFB, levels declined sharply within one week of arrival at our facility, unaffected by diet, water, or cage type.

Conclusion
The absence of MIA responses may be due to a rapid drop in SFB levels. Our findings highlight microbiome instability as a major source of poor reproducibility in poly(I:C)-based MIA models.