design: Female C57BL/6 mice (68 weeks) were kept under SPF conditions and randomized in compliance with IACUC approvals. For this baseline control group, animals received vehicle (PBS, intraperitoneal; 500 L) on day 1, day 0, and days +1 and +3, and were mock-infected intranasally with sterile PBS (50 L). Mice were monitored for 5 days. On day 5, whole blood was collected into EDTA tubes for RNA purification. rRNA/globin-depleted RNA-seq libraries were prepared using NEBNext Ultra II with QIAGEN FastSelect HMR+Globin and sequenced on an Illumina NovaSeq (2150 bp, paired-end).