Igor R. Santos, University of Guelph

Igor R. Santos [1], Phuc H. Pham [1], Brandon Lillie [1], Jeff Caswell [1], Sarah K. Wootton [1], Leonardo Susta [1] 1 Department of Pathobiology, University of Guelph, Guelph, Canada

Fighting & Responding

Aquatic bird bornavirus 1 (ABBV-1) is a neurotropic virus associated with encephalitis in waterfowl. Despite inducing persistent infections and T-cell–predominant inflammation in the brain of avian models (chickens, ducks, turkeys), affected birds usually lack overt clinical disease, and host immune mechanisms driving disease progression remain understood. Here, we characterized the transcriptional profile of immune-related genes in brains of chickens experimentally infected with ABBV-1. Brains from 30 chickens, collected from 5 persistently infected and 5 control birds at 1, 8, and 12 weeks post-infection (wpi), were used to assess differential expression of 17 key genes (MX1, PKR, RSAD2, OASL, IFNα, IFNγ, IL-1B, IL-6, IL-8, IL-17, IL-4, IL-10, IL-13, CTLA4, LAG3, PD-1, PDL-1). Gene expression was quantified by RT-qPCR, normalized to housekeeping genes (GAPDH, ACTB), and referenced to 1 wpi values using the ΔΔCt method. Two-way ANOVA revealed significant time-infection interactions for 13 genes (P < 0.01). No major changes occurred at 1 wpi, except for early PKR activation. By 8 wpi, robust immune activation was observed, with peak expression of antiviral effectors (MX1, RSAD2, OASL), pro-inflammatory cytokines (IL-6, IL-8), and immune checkpoint inhibitors (CTLA4, PD-1, PDL-1). At 12 wpi, antiviral and chemotactic responses declined, whereas IFNγ, IL-1B, and LAG3 reached maximal expression. IL-10 remained elevated through 12 wpi, while IFNα, IL-4, IL-13, and IL-17 were not differentially regulated throughout the study (P > 0.05). Overall, this transcriptional profile suggests that induction of regulatory and checkpoint pathways may modulate the local immune response, favoring subclinical viral maintenance despite persistent neuroinflammation.