Single-cell Transcriptomics of the 13-lined Ground Squirrel Spleen Reveals a Shift to Energy-Conserved Immune Stasis During Torpor 2336515

Abstract Introduction Hibernating mammals undergo profound metabolic depression during torpor, severely constraining immune energetics. Although reversible leukopenia is well documented, how immune organization within secondary lymphoid organs adapts to this extreme state remains unclear. Methods We combined quantitative splenic histology with single-cell RNA sequencing to profile architectural and transcriptional remodeling in the spleen of 13-lined ground squirrels during torpor. Results Torpor induced selective architectural remodeling of the spleen, marked by contraction of white pulp regions without changes in overall organ size or mass. This was accompanied by an ∼52.4% reduction in the relative abundance of B cells and a proportional enrichment of innate immune populations, including macrophages and dendritic cells, indicating a shift in splenic immune composition during metabolic quiescence. Notably, these changes did not reflect passive immunosuppression. Instead, immune cells across lineages adopted transcriptional programs consistent with active regulation, including coordinated suppression of anabolic signaling, glycolysis, cell-cycle progression, antigen presentation, and effector pathways, alongside induction of stress-adaptive maintenance programs. Adaptive immune lineages responded divergently: B cells entered a restrained state linked to genomic integrity and long-term maintenance, whereas T cells remained numerically stable but shifted into a deeply quiescent, energy-minimal state. In contrast, innate immune cells–including macrophages, dendritic cells, and neutrophils–were retained in a subdued configuration compatible with tissue surveillance and rapid reactivation upon arousal. Conclusion Together, these findings show that torpor establishes a reversible, lineage-specific program of regulated immunological stasis within the spleen, redefining it from an activation hub into a preservation reservoir poised for rapid immune reactivation. Funding Source n/a Topic Categories Veterinary and Comparative Immunology (VET)