In order to assess the induction of host innate immune responses after infection (Figure 6), groups of C57BL/6 WT mice (n = 12) were infected i.n. with 105 (n = 6) or 106 (n = 6) PFU of PR8/ANS1, PR8/BNS1, PR8/CNS1, PR8/DNS1, and PR8/ΔNS1; sacrificed at days 2 (n = 3) and 4 (n = 3) p.i. and IFNβ (Figure 6A), chemokine CC motif ligand 2 (CCL2) (Figure 6B), and IFN-induced protein with tetratricopeptide repeats 2 (IFIT2) (Figure 6C) mRNA expression levels were measured in the lungs by reverse transcription-quantitative PCR (RT-qPCR). Here, IFNB1 is linked to infection.